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                                  SECTION 2

                                CONCLUSIONS
      Porous pavements can be an effective means of reducing the increase in runoff
rates and volumes, and  water  quality degradation, resulting  from urbanization
and/or other land use changes. The design of porous pavements has to be undertaken
with  extreme  care,  particularly in  areas where the natural  soils  do not  have
sufficient permeability to naturally drain the stored runoff within a reasonable time.

      The use of porous pavements is presently limited to  parking lots only.  Ideally,
these parking lots should be located on soils which have very low runoff potential or
which have a high percolation rate.   Because all runoff from  the  site as well as
adjacent  areas are effectively retained, it may  be assumed that the entire area
contributing to the porous pavement has been removed from the surface hydrologic
regime.  Consequently, the increase in runoff rates and volumes by urbanization is
offset by a reduction in drainage area.

      The net downstream effect of porous pavements can range anywhere from a
reduction of runoff rates and volumes to below  natural  levels, or  to the  total
elimination  of  runoff from  the  immediate  area.   In  either case,  the  effect
downstream  can be quite substantial; in  the  case of  storm  sewers,  the  sewer
requirements may be reduced or eliminated,  thereby  providing substantial cost
reductions;  and in  the case of combined sewers, the  number of overflows will  be
reduced or eliminated, thereby providing direct benefits to the  receiving water.  In
both cases, the cost of additional drainage  facilities is reduced; and, consequently,
the incremental additional cost of porous pavement systems may be recovered.

      The water quality of urban runoff has been  shown to be severely  polluted in
some instances, but in all  instances the runoff is at least partly  contaminated. It is
obvious that just the infiltration and velocity  reductions in porous  pavements will
result in some suspended particulate removal  and some  chemical pollutant  reduc-
tion.  Preliminary data at The Woodlands site also indicate that nutrients can be
reduced to  safely disposable  forms and concentrations of  some heavy metals can
also be reduced.  In any case,  the removal of water from  the surface runoff regime
prevents  the introduction  of pollutants  into  the  receiving  water and  creating
problems in downstream areas.        ,

      If  it is known, or the possibility exists, that water infiltrating  into the ground
could reach  a water  supply  aquifer,  adequate precautions should be  taken  to
determine  that the surface runoff is not still  contaminated when  it reaches the
aquifer.   If there is  a possibility of  adversely affecting the aquifer, the porous
pavement area should  be designed to  be sealed off from the aquifer recharge zone.
                                       10

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If, on the other hand, the surface runoff Is designed to be cleaned before it reaches
the aquifer,  then  the infiltration of runoff into the porous paving and  into  the
natural ground should be encouraged in order to enhance the water supply from that
aquifer.

     Another cost reduction can be realized in the elimination of curbs and gutters
around the parking lot. Porous pavements will operate more efficiently and there is
less chance of debris accumulation on the parking  lot if curbs are eliminated. The
removal of curbs is also aesthetically desirable.

     The removal of surface water from porous pavement surfaces proves to be a
distinct advantage under  wet road conditions when it has been  found  that porous
pavements are approximately  15 percent  more resistant to skids.  This  expected
result was evaluated by testing at The Woodlands, Texas site (4).

     A review of the size gradations recommended by various highway  authorities
and the Franklin Institute Research Laboratories for composition of the aggregate in
porous pavements  indicates that a minimum of two percent passing the Number 200
sieve  was  required  to  provide  stabilization  of  the coarse  aggregate  fraction.
Consequently, the following size  gradation  is  recommended for the open  graded
asphalt mix.
                      Sieve
                      Size

                          fe"
                        3/8"
                      #    4
                      #    8
                      #   16
                      #  200
  Gradation
Recommended

      100
   90-100
    35-50
    15-32
     2-15
      0-3
     The total asphalt cement content for the mix is suggested to be between 5.5
and 6.0 percent.  However, the actual percentage is a function of the source and
type of aggregate.   The  exact percentage  must  be determined  in the  field,
particularly if  the  characteristics of the  aggregate are not known from previous
experience.  Also,  dry aggregate should be used to avoid vapor release after the
aggregate  is coated.  Insulated covers must be used on all loads during  haul  to
prevent the asphalt from crusting on the surface  of the load.  Also, medium to light
weight  vibratory rollers  are somewhat better  for compaction of the open graded
asphalt mix.  A set of sample specifications is included in Appendix A to this report.

     The design of porous pavement goes contrary to the classical requirements  of
high density and low air voids in the surface course and base course of conventional
asphalt paving.  Also, the idea of exclusion of water from  the base course as  in
classical design has to be reevaluated in the case of porous pavement.
                                       11

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      A two-inch (5.08 cm) top gravel  course was found  to be desirable to stabilize
 the top of the gravel reservoir underlying the open graded asphalt mix.  The gravel
 reservoir is designed to control the total volume of runoff computed for the area
 based on a preselected design storm and a hydrologic analysis of the area.  Because
 the length and width of the base reservoir are generally limited by the dimensions of
 the parking lot, the only variable dimension can  be  the  depth.  If  sufficient depth
 cannot be obtained due to physical  limits, additional relief drainage structures such
 as  french drains and pipe drains may be  installed.  In this case, the  cost of such
 structures can be quite expensive, and  consequently, conventional drainage schemes
 may become cost-competitive and viable alternatives.  If the subbase does not drain
 at  a sufficient rate, relief drainage structures may be  incorporated  or additional
 excavation  or replacement with material having  more desirable drainage charac-
 teristics may be contemplated.

     ^ The  total  thickness  of  the  base  reservoir  should  be  the largest  depth
 requirement for  the  bearing strength  of  the wet subbase,  the hydrologic storage
 requirements, or the frost depth for the site.  In  most cases, the hydrologic depth
 requirement and the bearing  strength of the  soil  are  dependent upon the area
 contributing to the porous pavement site; consequently, the frost depth may be the
 governing or limiting factor (except in the case of very  weak supporting soils).   A
 deep base may also be required to support heavy traffic loads.

      The initial costs of porous asphalt can go as high as 35 to 50 percent above the
 cost of conventional  paving.  However, the  major reason for this difference is the
 new ^ technology  involved in porous pavement  production,  primarily  in  gradation
 requirements  and the narrow limit  on asphalt  cement content in the  hot mix.   If
 curbs, gutters or storm  sewers are not required,  the total cost of the parking lot can
 be  comparable  to  or cheaper  than a conventional  parking lot, especially if  the
 aggregate source for the asphalt mix as well as  for  the base  reservoir  are  easily
 available.   Therefore,  it is anticipated  that  with the construction  of  additional
 porous pavement areas, technology  transfer  should be facilitated.  Also, construc-
 tion crews will become more familiar with the process, and contractors will be able
 to bid lower on porous pavement jobs.

     The hydrologic design for porous pavements has been adopted onto a computer
 program, PORPAV, which is available as  a stand-alone program or  as  a  subroutine
 within the USEPA  Storm Water  Management Model.  Both versions can be used to
 determine  the storage requirements  for  a given area, size, design storm, and
 permeability and void ratios of the component parts and existing soil.

     For  most efficient  operation  of  porous pavements it  is desirable that  the
subbase not be compacted or be only  minimally compacted.   This v/ill  retain  the
original  permeability  of  the   soil   which  can  be  substantially  reduced  after
compaction.
                                      12

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                                 SECTION 3

                            RECOMMENDATIONS
     The design of  porous pavement  parking  lots  is  just  emerging  from  the
experimental phase.  Most porous pavement users and designers would  agree that
further  research and test demonstration . pavement areas must be installed.  Al-
though existing  porous pavements have performed more than adequately and have
required minimal maintenance, some questions stjll  remain.  These include quanti-
fication of runoff and water quality  changes, the long-term effects of  continuous
saturation  of the  subgrade, maintenance  and  potential  for  plugging,  aggregate
gradation and asphalt content in  the  hot mix, construction material types, and the
economic efficiency of using this type of pavement under existing regulations. Also,
the  operation  of porous  pavements under snow  and ice  conditions  should  be
evaluated in detail.

     Instrumented  porous pavement  systems would be desirable.  This  instrumen-
tation  should provide information on rainfall, drainage,  soil moisture,  and  water
quality  effects; the data  provided should be continuous during the progress of a
storm,  thereby  allowing an evaluation  of  dynamic changes in runoff  and  water
quality.  Toward this end, a detailed analysis is being  undertaken in Phase II of this
study.   Phase II includes the evaluation of porous pavement  and comparison to
various other pavement types.   The data to be collected should  prove helpful in
identifying  the drainage  and  water quality  benefits  to be  derived  by  porous
pavements for a variety of rainfall events.  Also, presently unpredictable problems
may be uncovered.

     The following paragraphs discuss specific recommendations in regard to future
analyses that may be conducted for porous pavement systems:

           I)    A detailed evaluation of runoff and water quality with respect to
porous  pavement must be conducted.   It would  be desirable  to  determine these
characteristics  under various rainfall intensities and climates.   At  present, the only
site thus observed is at The Woodlands, Texas. It would be interesting to determine
if  pavement infiltration rates  can  be  exceeded by  naturally occurring rainfall
intensities because pavement environmental  factors may affect  the pavement
infiltration rate.  Also, factual  data is required for all climates in order to prove
porous pavement is truly effective world-wide. Particular attention must be paid to
winter  conditions - the  effects  of  freezing, de-icing  materials, and maintenance
(snow  removal, etc.).  The Naval  Civil  Engineering Laboratory has surveyed  five
porous  friction courses  in Great Britain and West  Germany.   Although the  evalu-
ations were  favorable in  regard  to service life in cold climates, similar efforts for
comparison purposes should be undertaken in the United States, particularly in  the
mid-western and mountainous parts of the nation.
                                        13

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           2)    Another  aspect of  porous  pavement evaluation is the duration of
base saturation and its effect on pavement life and load bearing capacity. Because
existing conventional pavements may have saturated bases for extended periods as a
result  of  infiltration through pavement  surface  cracks,  it seems that base and
subbase saturation should not be a problem, particularly since pavement strength is
based on saturated conditions.  Although conventional roadway base material has a
critical water content limit, in large graded  base material, where load transfer is
basically independent of water content, the load-bearing capacity of the base may
not be substantially  affected.  However, the subbase may  lose some strength.  This
loss  in strength may be  related  to  the  proportion  of granular  materials  in the
subbase.  It would be desirable to investigate this  loss of strength characteristic for
various subbase materials. Only site condition evaluation can determine the design
adequacy under a non-uniform dynamic traffic loading situation.  Also, if the gravel
tends to become embedded in the saturated subbase during pavement  loading, the
efficacy of a more stable but permeable membrane (filter  cloth) or sand layer  must
be investigated.

           3)    A third  and conjunctive area of interest is the change in water
quality as runoff moves through the surface course into the base course and finally
into the subbase. These changes may also depend  on the detention time in the  base.
If any correlation between detention  time, base and subbase chemical composition,
and water  quality can  be determined, the  design of porous pavement systems for
water  quality would be vastly  improved.  As a result of rapid introduction of
polluted runoff into the subbase, the effects on soil chemistry and biology as well as
ground water must be considered.  Anaerobic bacteria culture in the base may allow
biological  water treatment  processes  to  be  introduced  into porous  pavement
systems.  One major problem  will be the assurance of bacteria medium survival
during dry periods  between storms,   If  this  approach proves successful, the
efficiency of porous  pavement systems with regard to water quality control will be
greatly increased.

           4)    The question of porous pavement  surface clogging by urban dirt and
sand is of  concern to most  users.  The feasibility of pavement  clogging and the
efficiency  of currently  available equipment to  restore  premeability  should  be
investigated  in  order  to  provide maximum  life expectancy  of the  pavement.
Existing data  indicate that the surface of porous pavement is not easily clogged
under general  use, but accidental  spills of cloggable  material do result in reduced
pavement permeabilities  which  can be restored  with vacuum cleaning  and hosing
with a water jet.  In extreme cases, additional drain holes  may be required to be
drilled in the pavement surface course.

           5)    Loss of cementitious properties  in the asphalt  or polishing of base
gravel  by certain pollutants in runoff, e.g.,  acidic rain or  spilled gasoline, must be
investigated.  The results of this effort will  provide  means of identifying critical
localities or undesirable pollutants for which adequate precautions must be taken.  If
a certain pollutant is found to be undesirable,  porous pavement systems designed for

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this  area  should be  located away from runoff carrying these pollutants.  Another
phase of this investigation should address the feasibility of using an impermeable
liner between the base and subbase.  This results in storage of runoff for future
treatment  or  disposal and  consequently  the  effects  of  long-term contact  with
polluted runoff must be evaluated.

           6)    A standard set of construction specifications should be developed
for open  graded porous pavement  mix design and  construction.   However,  the
specifications should be flexible enough to allow certain design  changes if needed.
Also, the design procedure and guide specifications for porous pavement as supplied
in this report should be investigated and utilized whenever possible.

           7)    The aggregate gradation and asphalt content for the porous pave^
ment and porous friction course mixes should be standardized  so  as to provide
greater acceptability by the design engineer and contractor.  Standardization should
be on a regional or local basis because of material availability and  construction
methods.  This approach will allow a more standard pavement structural design and
will  obviate the  need to  conduct a Jorge  series of tests  for  each  project.
Furthermore, as engineers and contractors gain experience in this type  of pavement
construction, and as research on the  design of mixes provides  for an optimum design,
the cost of designing and  installing  porous pavement  lots will probably be reduced.
The  development of asphalt additives, e.g., neoprene,  or other  binding agents to
improve porous pavement service life  and  performance must be  evaluated.  As the
acceptability of porous  pavements increases, these new materials may  become
evident by exposure to different paving materials.

           8)    Asphalt hot mix plants should be reorganized to provide uniform
stockpiles and desirable aggregate cold feed in order to assure that the aggregate
will have the desired properties identified in the specifications.

           9)    The economy of porous pavement usage relative to conventional
paving must be  evaluated because  this aspect will be of major concern  to most
owners and developers of porous pavement  systems.  In particular, if all aspects of
porous pavement need not be considered, e.g., areas  where urban runoff water
quality is not of concern, then the cost comparison to conventional paving may not
be as complete or as valid, especially at present when construction experience leans
heavily toward conventional  paving.

           10)   Public awareness of the  porous  pavement approach to runoff  and
water quality control  must be  encouraged because most  people do not generally
recognize any difference between porous and conventional asphalt pavements which
are similar in appearance.  Increased public acceptance of proven porous pavement
systems will result in rapid responses to public demand by local government officials
and planning and designing communities.
                                       15

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                                  SECTION 4

                                BACKGROUND
      The Federal Water Pollution Control Act Amendments of 1972 (PL 92-500) set
 forth the requirements to insure "fishable and swimmable water"  throughout  the
 nation by 1983 and to eliminate  any polluting discharge into these waters by 1985.
 Section 208 of this Act provides for areawide water quality management planning
 which has subsequently been authorized under various sections of the Federal Clean
 Water Act of 1977 (PL 95-217).

      The accumulation  and analysis  of  water quality  data from urban  areas by
 various investigators (5, 6, 7) has indicated that storm water runoff is a major non-
 point source of pollution. Structural measures to alleviate this problem have often
 been the solution; however,  former USEPA Administrator Russel  E.  Train (8) and
 other proponents of non-structural  measures,  specifically land use controls, have
 been recognized and appreciated  in recent years.  The primary objective of land use
 controls is not exclusion of  specific uses, but rather inclusion of land use practices
 which do not degrade the  receiving  water quality.   The installation of porous
 pavements in urban areas is one  significant land  use practice which can be used to
 meet the water quality objectives of PL 92-500.

      A second set of  Federal  legislation which affects  land uses in urban areas is
 Section 1302 of the National  Flood : Insurance  Act Amendments  of  1968,  which
 encourages state and  local governments to "make appropriate land use adjustments
 to restrict the development of land,  which is exposed  to flood damage..."  This
 objective was enforced by the Flood Disaster Protection  Act of 1973 (PL 93-234) by
 requiring states  and local governments, as a condition for future Federal financial
 assistance, to participate in the flood insurance program and to adopt adequate
 flood plain ordinances with effective enforcement provisions.

     The enforcement of these  ordinances is contingent  upon a stable hydrologic
 regime; however,  Brater (9), Espey, Morgan and  Masch(IO), McPherson (11),  and
 others have  indicated increased runoff rates and peak discharges after urbanization
which  result in  downstream land which  originally experienced no flood hazard
becoming flood-prone.  Therefore, upstream land use practices  impact upon down-
stream areas, and, in recognition of this fact, numerous municipalities have enacted
 legislation  to prevent increases in runoff  rates, and  sometimes volumes, from
development  sites.

     The  use of porous asphalt pavement  for runoff  control  and water quality
enhancement is a relatively recent development. Open graded (large size aggregate
                                      16

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only and  therefore  porous)  asphaltic mix  was initially develope'd and  tested  for
safety applications as friction courses on conventional paving.

     Porous friction  courses 3/4  to  1 inch  (1.91-2.54 cm)  thick  are  used  on
conventionally paved and impermeable surfaces with the objective being to remove
surface water from the pavement and  still maintain a  dry base strong enough to
sustain design traffic loads.

     Porous friction courses allow  drainage through  the voids in  the  mix,  and if
adequate transverse grades are provided, out to the shoulders.  The rapid removal of
surface water results in minimum pressure  build-up under moving vehicle tires and
consequently, increased wet  skid resistance and  elimination  of  hydroplaning, as
previously described.

     The elimination  of hydroplaning  and the improved wet  skid  resistance by
application  of open graded asphaltic mix  to  conventional  paving  encouraged  the
highway departments of California,  Nevada, New Mexico,  Utah, and Louisiana to
incorporate open graded friction courses in their highway design.  The aforemen-
tioned safety features also instigated the use of porous friction courses for airport
runways; initially at Farnborough, England  in 1967, by the British Royal Air  Force,
and by the United States Air Force at two military air fields in Europe.  In 1971,  the
United  States Naval Facilities Engineering Command  installed a porous friction
course on the main runway at Hensley Airfield at the Naval Air Station in Dallas,
Texas.  Concurrently, the United States Air Force Weapons  Laboratory  constructed
test strips  of 8  different porous friction  courses  at  Kirtland Air Force Base in
Albuquerque, New Mexico (12). Subsequent applications of porous  friction courses
include Peace Air Force Base, New Hampshire; airports at Salt Lake City, Denver,
Greensboro (North Carolina); and several more  state highway departments, including
Colorado, Kentucky, and Pennsylvania.

      In all  of these early  investigations, emphasis was  placed on removing surface
water laterally through the asphalt bound open graded matrix.  Although the rate of
runoff was also affected, this aspect was not investigated. The total design for this
system  also required a permanently  sealed and prepared base and, therefore,  the
runoff volume  of the  paved area was  unchanged by addition of  the open  graded
overlay.

      On  the other hand,  the  use  of an open  graded  base course  was first
incorporated into highway design in  1947 on United States Highway 99, near Red
Bluff,  California.   7.1 miles  (11.4 km) of  this highway were constructed  with  a
3/4-inch  (1.91 cm)  conventional  asphalt concrete wearing course over  an open
graded  asphaltic concrete binder course, 2.4 inches (6.10 cm) thick, underlain by  a
6-inch  (15.24cm) cement treated base and a  gravel subbase.  After  10 years of
service under heavy truck traffic, this road was still in  very good condition and  has
required minimum maintenance (13).
                                        17

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     Since  1966, the  United States  Forest  Service has  been using permeable
materials to repave forest roads in the Pacific  Northwestern states.  This pavement
consists of 4 to  10 inches (10.2-25.4 cm) of crushed rock, held together with asphalt
binder and a thin chip seal wearing course.  Most of these roads carry large  numbers
of heavy logging trucks rather  successfully  because the  water drains  into the
pavement and, because of the generally steep  grades, water drains away from the
roadway very quickly (14).

     This concept of using an open graded gravel base between an existing prepared
subbase and a conventional asphalt concrete or concrete wearing course has been
developed and applied to several areas in California. The theory behind this concept
is to rapidly remove any water that percolated into  the open graded base.  This
removal is achieved  by means of drain pipe collectors which discharge into adjacent
roadside ditches.  This approach  is based on  the  idea  that the best  solution for
pavement drainage is to install an artificial  drain system under  the wearing course
to prevent saturation of the underlying subbase layers of  soil.  Water  filtering
through the cracks in  the pavement  is rapidly discharged horizontally through the
gravel base so it does not stand on the subgrade long enough to saturate and weaken
it.  A total pavement thickness of 8 to 10  inches (20.3-25.4 cm) was found to be
sufficient for highway design.   A  typical  cross-section of an installation near
Redwood City, California is shown in Fig. I  (14).  This installation was constructed
in 1970.

     During  1970 and 1971, the Franklin Institute Research Laboratories in  Phila-
delphia, Pennsylvania, under contract with the USEPA, attempted to combine the
porous friction course and the porous base concepts and  thereby control runoff and
enhance  water quality.  They investigated the use of an open graded asphalt mix
underlain by a gravel base course and a minimally compacted subbase as a potential
solution (1). The successful  test results suggested a unique approach to meeting the
requirements of the  Federal Water Pollution Control and Flood Disaster Protection
Acts.   Several  applications of this  technology,  generally  referred  to  as porous
asphalt, are now in operation mainly on  the eastern coast and Gulf of Mexico regions
of the United States, as listed in Table I.
                                       18

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                                 SECTION 5

              DESCRIPTION OF POROUS ASPHALT PAVEMENTS


     In general, porous pavement is composed of four layers:

           1.   Minimally compacted subbase  consisting  of undisturbed  existing'
               soil or,  in  the case of  unsuitable base  soils,  an imported  and
               prepared base  course.    Auxiliary drainage  structures  (French
               drains, pipe drains, etc.) may also be required.

           2.   Reservoir base course consisting of I to 2 inches (2.54-5.08 cm)
               diameter crushed stone aggregate.  The thickness of  this layer  is
               determined from runoff  storage  needs and frost  depth consider-
               ations as described later in this report.

           3.   Two  inches (5.08 cm) of fe-inch (1.27 cm)  crushed  stone aggregate
               to stabilize the reservoir base course surface.

           4.   Porous asphalt concrete surface course whose thickness is based on
               bearing  strength and pavement  design  requirements.    In  most
               applications, 2fe inches (6.35 cm) has been found to be sufficient.
     A typical porous asphalt pavement cross-section is presented in Fig. 2.
following descriptions are adapted from Thelen and Howe (15).

     The Subbase
The
     AH soils  under roads  may  become  wet, but they  must drain in order to
maintain their bearing strength. Because soils under porous pavement will get wet,
they must be permeable to water; they must not heave due to freezing or thawing,
and they must not swell or substantially lose their strength when wet.  Most soils
can meet these requirements if proper drainage is available.  In current practice it
is very important that the subbase under conventional pavement remain dry and that
pavements often may be wet due to cracks in the pavement, percolation through the
shoulders, and capillarity from ground water.  However, base strength is essentially
retained because free  water  can drain away, leaving the soil particle structure
intact.  Soil strengths, as defined by the California Bearing Ratio, are measured on
wet soils because soil wetness is anticipated.

     The contaminants on  a road  surface  can  range  from random spills and
pesticides to engine  fuel residues.  In  a storm sewer or  street system, they are
typically collected  in the initial runoff and discharged at one point in a receiving
                                      20

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stream; in the porous pavement system they are delivered to the soil over the entire
area of the pavement.

      It Is expected that contaminated water will  tend  to  be purified  as it passes
through the soil, as a result of absorption of contaminants by soil particles, bacterial
action, and dilution.  On the other hand, water passing  through soil may leach out
minerals and  pick up bacteria.

      At the  Franklin Institute Research Laboratories, preliminary tests  indicated
that aerobic bacteria can live in the soil under porous pavement; these could act like
sewage treatment plants to digest organic contaminants. At The Woodlands, Texas
site (4), aerobic digestion was discovered, with ammonia in the runoff being con-
verted to nitrites  and nitrates.  Further reduction was not  possible due  to
faulty drainage of the subbase.   However,  the nitrogen in the runoff from
the control  pavement was  mostly nitrates.   Both total organic carbon and
chemical  oxygen demand were much lower  in  the porous  pavement percolate than
in the runoff, because of bacterial action  in the base and subbase.  The
limestone base material also raised the conductivity  of the  percolate which
then  neutralized the carbonic  acid in the  rain and runoff.

      Even though initial runoff had high  lead concentrations, the percolate at The
Woodlands site  showed practically  no  lead, because  of  faulty  drainage of  the
subbase,  so that the percolate was diluted by storage, and  because lead accumula-
tions  were not significant.

      The Reservoir Base Course

      In conventional pavement, the base consists of stones, sand, and dust particles
packed into  a  dense mass  and designed to transmit mechanical  loads from  the
hardtop to the soil below.

      In porous pavement, the base consists  of large-sized and graded stones, lightly
rolled into an  open,  interlocking structure which not only transmits  mechanical
loads, but also  stores runoff water which the  soil  cannot immediately absorb.  This
water is held in the reservoir formed by  voids  in the  rock matrix until  it can
percolate into the soil. For size gradations recommended  in this report, the voids
will be as high as  forty percent of  the total volume.  Of course, if the soil has  a
higher permeability rate than the rate of  rainfall, a reservoir  is not  needed.
However, this is unlikely because maximum  rainfall intensities of design storms are
generally much higher than the infiltration rates of most soils.

      The aim of having a  reservoir is  to store runoff water for several hours to
allow it to percolate into the soil.  On sloping pavements, base areas at the higher
end of the site are not credited with storage capability even  though water enters the
base  in these  areas, because they drain laterally and do not contribute to the
percolation system at the higher end of the site.
                                      22

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      Because the base reservoir serves a purpose similar to retention basins, runoff
from roofs or other impervious and pervious surfaces could be drained into it; but
the base must be designed to have the required capacity.

      The aggregate used  in the  base must be  hard  and durable.   Generally it is
angular and not round.  Crushed  stone is the most desirable material  because the
aggregate interlocks very well.  Rounded gravel must be avoided for all  areas where
heavy traffic  is anticipated.   The  crushed stone should  come from one of the
following rock groups:

                (a)   Granite

                (b)   Basalt

                (c)   Gabbro

                (d)   Porphyry

                (e)   Blast furnace slag

Limestones which are susceptible  to polishing by water should be used in only special
situations where design loads are within the loading limits for this type of material.

      The Reservoir Top Stabilizing Course

      To assist in final grading of the reservoir base course to stabilize  the surface,
a two-inch (5.08cm) layer of  fe-inch (1.91 cm)  crushed stone aggregate  is recom-
mended.   Based  on previous  construction experience,  this stabilizer  course is
necessary because construction vehicles hauling the asphalt hot  mix across the
reservoir course would create ruts which consequently require constant regrading to
finished grade immediately prior to application of the hot mix.

      Open Graded Asphalt Concrete Surface Course

      Porous asphalt consists of a wearing  course of  open graded  asphalt concrete
laid  over a base course of uniformly sized  aggregate.  It differs from conventional
asphalt concrete chiefly in that it contains  very  little dust or sand; its void volume
typically is around  16 percent, as compared  with  the  two to  three percent void
volume of conventional asphalt concrete.

      Asphalts  used in  asphalt  concrete  range  from  50 to  100 penetration grade,
depending upon the ambient temperatures and viscosity characteristics desired.  In
general,  the grades used in a given locality for conventional asphalt concretes will
suffice for porous asphalt as well.  However, the porous product is  more subject to
scuffing, such  as occurs  when the  front  wheels of stationary cars  with power
                                       23

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steering are  turned.   It is  therefore suggested  by Franklin Institute Research
Laboratories that for porous asphalt, 50 to 60 penetration grade be used in the South
(Texas, Florida, etc.), 65  to 80 in the mid-Atlantic states, and 85 to 100 penetration
grade in the northern states.

     The percent of asphalt should be specified between 5.5 and 6, based on the
total weight  of the pavement. The  lower  limit is to assure adequately thick  layers
of asphalt around the stones and the upper limit is to prevent the mix from  draining
asphalt during transport,  particularly if it  is accidentally shipped  at a  temperature
of over 300°  Fahrenheit (149° C).

     To avoid damage due to photo-oxidative degradation of the  asphalt (since air
and sunlight can penetrate further), the asphalt coatings on the aggregate surfaces
should be thicker than usual.  In this case, the asphalt can form skins or otherwise be
mildly degraded without significant loss of cementitiousness.

     The open graded asphalt concrete is similar  in Marshall properties (strength
and flow) to  conventional asphalt concrete.  Hence, the usual  thickness  of base
course and paving should  satisfy load requirements.  The base course thickness may
have to be increased to  provide  greater reservoir  capacity where runoff  volumes
and/or soil percolation require it.

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                                 SECTION 6

                  ADVANTAGES AND DISADVANTAGES OF
                    POROUS ASPHALT PAVEMENT USAGE
     The primary design objective of porous asphalt pavements is to control runoff
rate and volume increases and water quality degradation resulting from developed
and  impervious areas  in deference  to  the requirements of the Water Pollution
Control and the Flood Disaster Protection Acts.  However, numerous other primary
and secondary benefits are also realized with  porous asphalt pavements.  Each of
these benefits is identified and discussed in this section but the  intensity of each
benefit is a site- and region-specific function and therefore a relative evaluation
was not attempted.

     The  advantages  and/or  benefits  one may "reasonably expect  from  porous
asphalt pavements are as follows:

           I)    Runoff rate and volume control in areas where pervious ground is
replaced with impervious cover.  The main impact is  a substantial  reduction of
runoff rate and volume from impervious areas.  If the pavement and reservoir base
are designed  adequately, all of the runoff may be detained  and released at a rate
adequate to prevent increases in flood flows.  Concurrently, the stored water may
be allowed to infiltrate into the natural ground.

           2)    Erosion control on unprotected overland flow and channel areas.
Because impervious areas generate higher rates  of runoff than pervious areas, the
erosive capacity of the flow is also increased  by means of increased depth of flow
and  increased velocities.  Consequently, overland  flow and channel areas down-
stream from impervious areas  would experience additional erosion and sediment
removal.  However, the use of  porous asphalt pavement systems would reduce or
entirely remove the excess  runoff problem and therefore considerable benefits may
be derived from bank and soil protection and sediment reduction.

           3)   Water  quality  enhancement  will  be evident  in areas where the
runoff generated from impervious areas has the potential for becoming contamin-
ated, as in the case of industrial and commercial land use areas.  If the pollution is
not toxic and depending upon its characteristics, detention in the reservoir layer and
percolation through the  subbase m'ay  be sufficient to reduce the  pollution  to
acceptable levels.

      If the stormwater requires treatment for toxic or non-filterable substances, it
may be stored  in porous pavement systems isolated from the natural  ground by an
impermeable membrane until treatment plant capacity becomes available.  Thus,
                                       25

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treatment plant capacity does not need to be expanded. Also, detention of highly
polluted  initial  runoff by  the porous  pavement,  and dilution  by  less polluted
subsequent runoff can result in acceptable pollution concentrations throughout the'
storm duration.

          4)    The need for curbs and storm sewer installation  or expansion may
be avoided.  In already urbanized areas,  such-as established areas of most cities as
well as existing  shopping centers, where the storm sewer network was designed and
Installed prior to excessive impervious cover  development (parking lot expansion,
etc.), the storm  sewers may become overloaded, and if parking lot or roof storage is
not a design criterion, the disposal of excess runoff becomes a problem that porous
pavements could solve.  This benefit is enhanced in areas with combined  sewerage
because  the probability of  sewer overloading  and the  resultant  discharge of  raw
sewage into the receiving water is reduced.

      In areas of slight topography or with minimal soil depths, the cost of installing
storm sewers is very high because both sewer size and excavation  volumes are high.
The use of porous pavements in these areas reduces both sewer size and excavation
depth, thus resulting in a net savings in drainage costs.

          5)    Natural drainage boundaries and patterns  can  be  maintained.
Consequently, elaborate drainage schemes to collect and deliver runoff to a safe
conveyance will not be necessary.   Instead, drainage boundaries existing prior to
development may be retained without sacrificing the finished grade of the paving.

          6)    The   nuisance  factor  to pedestrian and   motorist  arising from
standing  puddles in parking lots, streets,  and detention basins will  not be a problem.
Also, disease vector control (mosquitoes, etc.) may be accomplished through the use
of porous pavement systems.

          7)    Natural vegetation and drainage  patterns can be retained by the
use of porous pavements.  Consequently, the clearing of trees  from large  areas for
parking lots is unnecessary and secondary  aesthetic benefits are also derived.  This
also applies to roadside vegetation in highly developed areas where, under conven-
tional paving, the soil moisture is severely deficient.

          8)    Groundwater recharge may be possible  with porous asphalt paving.
In water deficient areas,  impermeable  paving may prevent  recharge to a local
aquifer and  thereby  reduce  its  safe  yield.   Porous  paving  would correct  this
condition.
                                                          •"• '•••"VI1 "'-
           9)    The  full  range of  safety  improvements resulting  from  porous
pavements has been evaluated only at The Woodlands, Texas,  site (4).  However, as
previously discussed, the improvements to wet pavement skid resistance have been
used successfully on'road surfaces in numerous  states and  airport pavements in
England, New Mexico and  New Hampshire.  The results of sliding friction  tests
                                       26

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 conducted by Hollinger (4) at The Woodlands site and the United States Air Force
 Weapons Laboratory at the Dallas site (12) are presented in Table 4.  As expected,
 the friction coefficients for wet porous paving are significantly greater than for wet
 conventional paving.  Also during these tests a singular,  and as  yet unresolved,
 anomaly was discovered at The Woodlands site - porous pavement  surfaces have a
 higher friction  coefficient when  wet than when they are dry.   Hollinger  also
 determined that:

           a)    Porous asphalt pavements generate  slightly less traffic noise than
                conventional asphalt pavements.

           b)    There is no real  difference in light  intensity reflected from white
                and yellow markings  on either  type of pavement.  However, the
                effects  of glare  from oncoming vehicle lights, which obscure the
                reflected light  from paint on a wet conventional asphalt pavement,
                were not evaluated.

           c)    Porous asphalt pavements tend to deflect for a longer time than
                conventional asphalt pavements, but the magnitude of deflection is
                approximately equal.

      On the negative side of  porous pavement usage, the most often expressed
concern is the susceptibility of the pavement to clogging.  With proper care and
maintenance,  this  problem  should not occur  and  past experience  supports the
veracity of this statement.

      Clogging  of the pavement  pores generally  occurs  due  to  operational  and
construction scheduling problems.   For example, spills of construction materials on
finished pavements, or hillside erosion and sedimentation on finished pavements may
clog the pavement or reduce  its  permeability.  Obviously,  the  solution  to  con-
struction-related problems with  porous pavements is to finish all ground preparation
and earth work prior to installation of porous pavements.   After construction, the
haulage of clogable materials  across porous pavements must  be conducted  with
extreme care to prevent spills.

      If a spill should occur, immediate vacuuming and washing with  a water jet will
restore pavement permeability  almost to pre-spill rates - tests conducted at  The
Woodlands site indicate a permeability recovery in excess of 95 percent.  However,
if the pores are clogged and the  dirt is compacted or ground in by traffic to a depth
greater than 0.5 inches (1.27 cm), full permeability cannot be restored.  In this case,
holes  may be drilled through the  clogged area to provide  the necessary drainage.
The areal  distribution of holes required would be a function of pavement slope and
degree of clogging.

     Porous pavement surfaces  can also be ineffective during the melting  of snow
which has accumulated on the surface;  or if rain occurs on a frozen surface.
                                       27

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                                   TABLE  4

             FRICTION COEFFICIENTS  FOR POROUS PAVEMENT SURFACES
TEST
DATE
PAVEMENT
  TYPE
   DRY
CONDITION
   WET
CONDITION
                             Dallas, Texas  (12)
11/71
 12/75
 2/76
 V76
Porous asphalt
Conventional asphalt
Grooved concrete
   0.76
   0.7^
   0.76
                            Woodlands, Texas  (k)
Porous Asphalt old
Porous asphalt new
Conventiona1 aspha1t

Porous asphalt old
Porous asphalt new
Conventional asphalt

Porous asphalt old
Porous- asphalt new
Conventional asphalt
   0.61
   0.66
   0.73

   0.82
   0.83
   0.99

   0. Ik
   0.80
   0.78
   0.70
   0.16
   0.71
   0.85
   0.74
   0.59

   0.95
   0.90
   0.81

   0.84
   0.84
   0.71
                                       28

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     A second disadvantage in the use of porous pavement results from  the  fact
that some existing building codes and regulations are not intended for this new  type
of technology.  Specifically, if conventional  drainage structures  (curbs, gutters,
inlets,  etc.) are arbitrarily required in all parking areas, then the construction costs
of porous pavement installation become economically excessive.

     A temporary drawback arises out of a lack of data to indicate the capabilities
of porous pavement to filter and purify all contaminants in runoff.  Initial results at
The  Woodlands  site  indicate a reduction of  most  pollutants,  but  the  data  is
insufficient for  generalization.   Also, it  is obvious that severely polluted  runoff
should  be excluded from a porous pavement because of its susceptibility to clogging.

     Spillage  of gasoline from  leaking tanks of automobiles parked on  the  porous
pavement  lot will break down the  asphalt  binder to  greater  depths  than on
conventional pavements, primarily because the pores on the open graded mix permit
excursion of the gasoline into a  larger spatial volume.  The solution to this problem
may be the use of tar binders rather than asphalt.

     The  negative aspects of porous  pavements as discussed above are not insur-
mountable  in most instances.  Also, the advantages  far outweigh the disadvantages.
Consequently, the potential for porous pavement usage is expected to increase as
the problems outlined in this section are resolved.
                                       29

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                                  SECTION 7
                          DESIGN CONSIDERATIONS

      The  design  of a  porous pavement  parking  area requires the  same  basic
procedures as for a conventional parking area.  However, the drainage  aspects and
the corresponding changes in load-bearing capacity of the pavement require detailed
attention.  In general, the design procedure will follow 3 basic functions:
           I.    Determination of existing soil properties
           2.    Load-bearing design of pavement and subgrade
           3.    Hydrologic design of pavement and subgrade
 In addition to  these 3 basic functions, corresponding operational  and maintenance
 factors during  and after construction must also be considered.  Each of the functions
 is described in  the following discussion:
      Determination of Existing Soil Properties
      At most building  sites,  the  location  of  the parking  area is governed  by
 numerous factors, including;
           a.    Building aspects
           b.    Aesthetics
           c.    Convenience
           d.    Surface slope
 During the pre-design phase,  factors  affecting porous pavement installation must
 also be considered.
      Initially, a site inspection is  imperative. Environmentally critical, unique, and
 undevelopable areas must be identified and adequate precautions taken to prevent
 damage to these  areas during and after  construction.  The ideal location for porous
 pavement is a  well-drained soil on a relatively flat slope. Desirable trees and  shrubs
 which will not significantly affect traffic patterns and yet provide shade and beauty
 to the area must  also be identified and demarcated for preservation.  Predominantly
 clay soils  must be avoided or, if this is not possible, relief measures must be adopted
' in the design.
                                        30

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      All  available soil data for the site should be acquired and  inspected.  The
United  States Department of Agriculture Soil Conservation Service has  developed
soil  maps for most counties in  the  United States;  but in  some areas even more
detailed soil information  may be available.  The Soil  Conservation  Service  has
classified most soils into 4 hydrologic  soil  groups, defined as follows:

           (A)   Soils having high infiltration rates, when thoroughly saturated and
                 consisting chiefly of deep and well-drained sand or gravel.  These
                 soils  have a  high  rate  of water  transmission and low  runoff
                 potential.

           (B)    Soils, having moderate infiltration rates, when thoroughly saturated
                 and consisting chief ly of generally deep and well-drained soils with
                 moderately fine to moderately coarse texture.  These soils have a
                 moderate rate of water transmission.

           (C)    Soils having slow infiltration rates when thoroughly saturated and
                 consisting chiefly of soils  with  a  layer that  impedes  downward
                 movement of water,  or .soils with moderately fine or fine texture.
                 These soils have a low rate of water transmission.

           (D)    Soils having a very slow infiltration rate when thoroughly saturated
                 and consisting chiefly of clay soils with a high swelling  potential,
                 soils  with a permanent  high water table, soils  with a clay pan or
                 clay  layer  at  or near the surface,  and shallow soils  over nearly
                 impervious materials.  These soils have a very  slow rate of water
                 transmission and a very high runoff potential.

      In the above definitions, infiltration rate is the  rate at which water enters the
soil at the surface, which is controlled by surface conditions (percolation  rate), and
the  transmission rate  is  the rate at which the  water moves  in  the soil  and is
controlled by the soil horizons or layers.

      Appendix B presents a list  of more than 4,000 soils in the United States and
Puerto Rico compiled by the Soil Conservation Service with hydrologic soil group
classifications for each soil.  These classifications are based  partly  on the use  of
rainfall runoff data from  small  watersheds  or  infiltrometer plots.   However, the
majority of the classifications are based on the judgement of soil scientists who use
physical properties of  the soil in making their decisions. Each  soil was classified in
a particular hydrologic group by  comparing its profile with profiles of soils already
classified. It was assumed that the soil surfaces were bare, maximum swelling had
taken place, and rainfall rates exceeded  surface  detention and  infiltration. Thus,
most of the classifications are based on  the premise that similar soils (similar  in
depth, organic matter content, structure, and degree of swelling when saturated)
                                        31

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will respond in  an essentially similar manner during a rainstorm having sufficient
intensities to generate runoff.

      If the site  inspection or other information  indicates that the original  soil
classification  may not be correct, additional  testing may be required to properly
identify the hydrologic soil  group for that particular soil.  Hydrologic soil groups (A)
and (B) are ideal for porous paving sites.  However, potential areas in soil groups (C)
and (D) require  more  attention.  In certain areas (low design runoff volumes),  soil
groups (C) and (D) may be  acceptable.  However, in the  general  case, appropriate
external drainage measures, e.g., greater excavation and replacement with porous or
drainable  fill, may be justified.

      After the  site  is tentatively located  for  the best available location  and
drainage conditions, core samples must be taken of the soils which will lie under the
proposed  parking  area.    Core  depth  should  go  down to the water  table or
impermeable layer of rock or  clay.  If this is impractical,  borings should  extend to a
depth sufficient to indicate no barriers to vertical seepage of water. In  most cases,
a maximum depth of  20 feet (6.1 m), should be adequate, or if the  water  table  is
intersected prior to this,  down  to the  water  table.   The soil borings must be
inspected  for any soil  layers of  reduced permeability.   If bedding  planes  are
horizontal,  the  permeability  in the  least permeable soil must  be used as the soil
design permeability.

      If the soil structure  shown  by adjacent soil borings  is not  similar,  steeply
sloping or vertical, bedding plants, or previously disturbed soil (compacted fill, etc.)
may be indicated.  In this case, an intensive soil boring program may be necessary to
assure no impermeable  lenses or  layers.  In  general, two cores  may be all that  is
required  on small parking areas no  greater  than fe-acre  (0.2 hectare) in  extent.
On larger areas,  the cores may be taken 100 to  150 feet (30.5 to 45.7m) apart.
However, prior  experience  and knowledge of the site (from foundation core analysis,
etc.) may dictate a less extensive program.

      The core  samples are used  to  determine  soil  structures  and subsurface
characteristics  including permeability  and barriers to  the movement of ground
water.   If surface sealing,  from  silt  accumulation or  compaction by traffic,  is
suspected,  percolation tests  may  be required.   These tests essentially define the
surface absorption capacity and permeability of  the top  layer of soil. However^as
mentioned previously, the  least permeable layer of soil must be used to determine
the design permeability of the soil mass.

      Soil core  samples must also be tested for bearing and shear  strength.  All
strength  and drainage  tests must be  conducted  for  dry  (general)  and  saturated
(critical) conditions.  Also, susceptibility to frost  heave and loss of strength under
saturated conditions must also be determined.
                                        32

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      Load Bearing Design of Pavement and Subgrade

      Final design of a porous pavement system requires the  determination of the
total thickness of the porous pavement  from top of pavement to subbase soil. This
thickness is influenced by the bearing strength, water storage required, and frost
depth.  The greatest thickness determined by each of these conditions will be the
design thickness.

      Bearing  strength  properties of different  soils  have been  thoroughly investi-
gated  by Franklin  Institute Research Laboratories.   Using the  California Bearing
Ratio  (CBR) test,  all soils can be classified into  four soil  strength categories, as
listed  in Table 5.  The design traffic intensity may be divided into 3 groups, defined
by  the average  daily Equivalent Axle Load (EAL) and the  minimum thickness for
each strength category and  traffic intensity  group  defined.   These  results are
presented in Table 6.

      As  described  previously, the  total  thickness  of   the  paving system  is  a
combination of the open graded base course and the  surface layer of open graded
asphalt mix.

     Recent studies by the Federal Highway Administration (FHWA) indicated that
variations in asphalt content have little effect on Marshall and Hveem stabilities or
flow values.   However, the importance of having  at  least some fine aggregate to
provide a "chocking" action for the stabilization of the  porous  aggregate fraction
must be recognized.  Also, a minimum  of  2 percent passing the Number 200  sieve
must be required to control the asphalt  drainage characteristics of the mixture by
effectively increasing the viscosity of asphalt cement.

     The Franklin Institute Research  Laboratory  and  the FHWA recommended
gradation limits  for aggregate mix as well as gradation limits developed by the U.S.
Army  Corps of  Engineers' Waterways Experiment Station (WES) and  U.S.   Naval
Facilities Engineering Command (NAVFAC) and others are  listed  in Table 7 along
with the slightly modified gradation limits  proposed in this report.  It can  be seen
from the comparison of gradations in Table 7 that the Franklin  Institute Research
Laboratories gradation allows slightly  larger aggregate and  more fines passing the
Number 8 sieve.   However,  it does  not  require any mineral  filler passing the
Number 200 sieve or fines passing  the  Number 16 sieve.  The gradation recom-
mendation herein  is essentially  similar  to that recommended by  the  Franklin
Institute Research Laboratories, except that a minimum of two percent passing the
Number 200 sieve has been included.

     The reasons for favoring the Franklin Institute Research Laboratories grada-
tions are as follows:

           I.    The experience with existing porous  asphalt parking  lots has been
                generally good.
                                      33

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-------
                                TABLE 7




          AGGREGATE GRADATION LIMITS FOR POROUS ASPHALT MIXES

Sieve
Size
1/2"
3/8"
#*»
#8
#16
#200



1/2"
3/8"
#^
#8
#16
#200


13.2 mm
9.5 mm
6.7 mm
A. 75 mm
2.36 mm
1.18 mm
0.6 mm
0.3 mm
0.15 mm
0.075 mm

Gradation
Recommended
100
90-100
35 - 50
15 - 32
2-15
2-15
Newark,
Delaware

100
90 - 100
35 - 50
15 - 32
0-15
0-3
Perth
Austral ia
100
96
66
38
22
15
13
13
5
3
Percent Passing
Frank! in
. FHWA Institute
100
100 90-100
30 - 50 35 - 50
5-15 15-32
0-15
2-5 0-3
Chester Co., Greensboro, Dallas,
Pennsylvania N. Carolina Texas
100
100 100 90 _ 100
95 - 100 97 30-55
35 38 0-22
15 ]5.7 0-12
10 6.1 0-5
2 2.0












Note:
1 inch - 2.54 cm
-------
            2.    The FHWS, WES, and NAVFAC mixes are aimed at a thin overlay
                 over existing pavements, whereas the Franklin Institute Research
                 Laboratories mix  has been  placed  in  a thicker  layer
                 graded base material.
over open
            3.    The primary objective of the FHWA open graded asphalt friction
                 course is removal of water from the surface of the pavement.  The
                 objective  of the Franklin Institute Research Laboratories porous
                 asphalt pavement,  however,  is  to provide  a  porous  and stable
                 surface over base material  that essentially  functions  as  a water
                 storage basin.

            4.    The traffic  levels experienced  by  existing pavements using  each
                 type of  gradation  have  been  different,  although  the Franklin
                 Institute  gradation  originated   from  California  experience  on
                 highways.

      The approach to mix  design taken from FHWA is aimed at testing the porous
aggregate to arrive  at  the surface  coverage  capacity,  which includes  absorption,
superficial  area, and surface roughness.  All of these properties affect the asphalt
cement requirement. A simple linear relationship obtained from  field  experience is
then applied to arrive at the  percent asphalt that should both provide the necessary
cementation between particles and leave sufficient voids (the average FHWA goal is
a  minimum of  15 percent  voids as  compared  to  Franklin  Institute  Research
Laboratories goal of  16 percent) while not creating excess asphalt that will drain or
cause flushing.

      The relatively open spaces within a porous asphalt  mix require that additional
resistance  to  oxidation, raveling,  and  retention  of cementitious  properties is
required of the asphalt  binder. Consequently, the aggregate particle must be coated
with asphalt films in the  range of  3 to  4  times  those  of  conventional  asphalt
concrete.   The asphalt content used in porous friction courses has  generally been
approximately  6.5 percent  by  weight.    Initially, this  content  was selected  to
minimize the probability of excess drainage asphalt.  Also, the mixing temperature
was selected to  be relatively higher than the  temperature used for  conventional
asphalt mixes.  Table 8 lists the asphalt content recommended and used by various
agencies.

     The Franklin  Institute Research Laboratories mix  design goals are similar to
those for a  porous friction asphalt course, but the approach  has been one of simply
applying a  narrow  band of asphalt content of 5.5 to 6 percent  which has proven
effective for the aggregates tested.

     In  a  recent  innovation by  Husky  Oil   Company, the  tenacity,  ductility,
toughness,  and low and high  temperature performance  of asphalt  has been  sig-
nificantly enhanced by  the addition  of neoprene.  This  modified asphalt contains
                                      37
-------
                              '   TABLE 8

                     RECOMMENDED ASPHALT CONTENT FOR
                          POROUS ASPHALT MIXES
Thickness
Location Inches
Newark, Delaware
New Castle Co., Delaware
Chester Co., Pennsylvania
Newtown, Pennsylvania
Perth, Austral ia
Woodlands, Texas
Greensboro, N. Carolina
Dallas, Texas
2.5!
2-5
2.5
4.0
2.0
2.5
0.75
0.63
Asphalt
Content
%
5.5
6.0
5.0
5.0
5.0
6.0
6.5
6.5
Temperature
°F
275 -
275
240 -

212 -
300
280
240
•i ' 	 "
300

280

257


M«,^«— —•— ^^£*~"
Notet  1 inch ^ 2.54 cm
                          32
                               38
-------
 1.5 percent neoprene synthetic rubber which was specially formulated by the DuPont
 Company for asphalt applications, and was used as a binder for the porous  friction
 courses at the Salt Lake City, Utah International Airport and Stapleton International
 Airport  in  Denver, Colorado.  It has been shown that neoprene  has good  aging
 characteristics with high resistance to deterioration from ozone, sunlight, heat, and
 weathering (16).

      This product was  tested  at varying  temperatures and  asphalt content in a
 porous friction course  mix for the Greenboro-High Point-Winston-Salem Regional
 Airport.  The variations investigated and the resulting asphalt mix performance are
 indicated in Table 9.  Based on these results, the optimum asphalt binder content
 was selected to be 6.5 percent and a mixing temperature  of  300° F (I49°C) at a
 viscosity of 275 centistokes (16).

      When design  construction  actually proceeds on  a  specific porous  asphalt
 pavement, it is suggested that asphalt  drainage tests such as those described by
 FHWA be conducted on  the recommended mix to establish  the sufficiency of 5.5 to
 6 percent asphalt  content for  the specific aggregate characteristics  that  will  be
 proposed  for use.   This  approach  will be much more direct than implementing the
 detailed  tests  recommended by the FHWA  for  their open graded  asphalt friction
 course. ^ It will also provide a more positive approach than the general assumption
 that a single asphalt cement content is sufficient for all aggregates.

      Some other  considerations  in  the preparation of the  open graded  asphalt
 concrete mix are as follows:

           I.   Relatively dry aggregates should be used to avoid vapor  release
                after the aggregate is coated.

           2.   Problems of crusting on the surface of the truck load during haul
                may be experienced; consequently, the use  of  insulated covers over
                the load to avoid  heat loss is recommended.

           3.    Most types of compaction equipment have been used successfully,
                but medium to light weight vibratory rollers are somewhat  better.
                Also, the pavement has to be sufficiently  cooled  before rolling in
                order to retain its shape.

           4.    The vibrating  screed  on laydown equipment is probably better for
                this application than the tamping screed.

           5.    Damage from freeze thaw on this kind of pavement is minimal.

     At present, this type of  pavement system is  almost  completely outside the
experience of  most pavement  engineers and pavement  contractors.  Because the
classical  need for  high density and low  air voids in conventional pavement is the
                                      39
-------
                  TABLE 9

EFFECTS OF VARYING ASPHALT CONTENT AND MIXING
 TEMPERATURES ON POROUS PAVEMENT MIXES (16)
Asphalt
Content
%
6.5
6.5
\S 9 ,S
6.5

6.5
6.75
7.0



Note: °F « J..8(°c;
Mixing ;
Temperature
Deg. F
280
300
320

300
300
300



) -J- 32


Comments
Satisfactory
Smoother laydown
Bleeding in laydown
machine hopper
Satisfactory
Satisfactory
Loss of mix consistency,
individual aggregate
could be separated from
mix

-------
 direct  opposite  of the construction  goal  for  porous pavement systems, previous
 experience of both design and construction personnel is to some extent obviated.

      The  porous asphalt cement layer is recommended to be 2'/2 inches (6.35 cm) in
 depth and  the mix is to consist of the gradation previously recommended with 5.5 to
 6.0 percent asphalt content initially.  In order  to obtain this close limit on asphalt
 content, it is  proposed to  specify 5.75 percent and to  establish a  tolerance  of
 0.25 percent on asphalt.  Because the usual tolerance is approximately 0.5 percent,
 it is not certain that this low tolerance can be obtained; however, it is believed that
 it will  be more  nearly accepted  if  this type of tolerance  is  exercised  in  the
 specifications.

      Compaction with light equipment must be applied on a closely observed basis
 to avoid over-compaction and  collapsing of pores during construction.  This should
 be carefully organized at the time of construction.  Sample specifications presented
 in Appendix A  have been developed by combining  features  of tentative specifica-
 tions developed by Franklin Institute Research Laboratories and the Texas Trans-
 portation Institute.

      Hydro logic Design of Pavement and Subgrade

      The thickness for porous  pavement systems required for  the  storage of water
 may be determined from a dynamic mass balance of inflow to and outflow from the
 R^oSA,P?^ment  sXstem-    As  described  in  Sections,  a  computer  model,
 PORPAV(I7),  has  been developed by  the USEPA  to perform  these calculations.
 However, manual calculations  are also feasible  but very  tedious.  An  oversimpli-
 fication, in general use, substitutes a steady-state operation for the dynamic process
 of inflow,  storage, and outflow from the  porous pavement  system.   Furthermore,
 some of the earlier designs ignored soil  permeability and determined  the  total
 thickness of the porous pavement system to store all runoff from the design storm.
 This last approach is too conservative, and not recommended for use at this time.

      A very important consideration is the relative  permeability of the  base to the
 subbase under the porous pavement.   If the initial undisturbed permeability of the
 subbase can be maintained  during construction, then  this permeability  may  be
 expected to be available during operation of the porous pavement system. However,
 if the subbase is compacted in any way, by design or  inadvertently, a substantial loss
 in permeability may be expected.  Some studies have indicated that even sand can
 be compacted  to  where  its  permeability  is  comparable  to  that  of clay (14).
 Consequently, potential porous pavement areas must be treated with due care prior
 to and during construction to minimize subbase  compaction at the site.  Traffic or
 material storage activities on the site should also be excluded.

     The design for frost depth must consider both  loss of strength due to freeze
thaw cycling and frost penetration, particularly in soils where  more than 3 percent
of the particles are smaller than 0.02 mm  in diameter.  Table  10 lists the Franklin
-------


















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-------
 Institute Research Laboratories recommendations for frost depth design  thickness
 for the 3 traffic groups previously described.  The local frost penetration depth at
 the proposed site must also be considered.  This information is generally available in
 the building codes of most municipalities and used primarily in foundation design.

      The  design  storm, contributing  areas, and  soil permeability selected for a
 given  porous pavement design  will determine  the storage volume required in the
 base.  The  selection  of the design storm is in most cases dictated by local drainage
 regulations, but more frequent (less  intense)  design storms may be selected if
 adequate handling of runoff from storms in excess of the design storm is considered.
 If the design storm is  not specified  by local regulation, a prudent choice must  be
 made  after evaluating the consequences of flooding induced or exacerbated by the
 proposed development.  Areally large  developments tend to create major flooding
 problems ^during infrequent storms, but small developments do not generally  impact
 the existing drainage systems and more frequent storms may be selected for these
 f-t*»f~\j-t ft
areas.
      The contributing area to a porous pavement system may be dictated by the
design storm and local hydrologic conditions.  In areas of long duration and intense
rainfall, the contributing area will be minimum. However, in more arid areas, where
rainfall is of short duration, the contributing area  can be quite extensive.  Another
factor to be  considered is the nature  of the contributing area,  because pervious
and/or grassed uphill areas will not contribute as much runoff as impervious areas.
In practice, most contributing areas are rooftops, driveways, and other impervious
ground  cover.   Therefore,  the design  storm magnitude is  generally  the  most
important criterion for hydrologic determination of porous pavement depth.

      If the design storm and contributing area are pre-defined for a given drainage
area, and if the base storage capacity is physically  or economically limited, drainage
relief measures may be incorporated into the system.  These relief  measures can
range  from  french drains and perforated  pipe  drains to  underground  cisterns.
However, the  drain discharge must be properly disposed of, to the most convenient
drainageway,  if only peak reduction of runoff is desired, or  to a retention pond if
both peak and volume reduction are desired.

      When the subbase  permeability is relatively  low (hydrologic soil group (C)  or
(D)), a  very thick base may be required to store the water, and  residence time  in
the base may  be sufficiently long to develop undesirable side  effects, like freezing
or anaerobic or septic water conditions.  One solution would be to provide a relief
drain as described above, or, as in the case of The Woodlands, Texas site, a portion
of the subbase may  be replaced with sand and drains located  in the sand.  On the
other hand, if  a drainage channel is available nearby, a buried  trench filled with the
same type base material as the porous pavement  may be  installed from  the base
reservoir side  to the channel, thereby providing an  underground connection  and flow
conduit.
-------
     When the site is level, the rdin falling at a given spot stays  in the reservoir
until it can percolate into the ground. However, when the site is sloped, the water
in the  reservoir tends to flow to  the lower areas, leaving  the  upper parts of the
reservoir empty and useless.  Thus,; the  low  parts of the base should be thicker, to
hold more water, and the  higher  parts not  thicker than necessary to handle the
mechanical loads.

     The proposed slope df the pprous pavement  should  be reduced as much _ as
possible in order to utilize the base  storage volume more efficiently.  On any sloping
porous pavement or on a horizontal porous pavement with an artificially induced
hydraulic head at one end, e.g., inflow at one end only, a substantial flow may be
expected  through  the relatively open  base course, and  in the case of  certain
pavements water may drain out of the pavement at the low end  because lateral
movement is  much faster  than  infiltration.  This condition could be avoided by
reducing the  slope, increasing the depth of the base  course  in the downstream
direction, and installing relief drains as previously described, or terracing the area
using cut-off walls under the pavement and concrete curbs on top of it.  The latter
option  is particularly effective on  very  steep slopes or very  large areas where site
leveling would not be practical or economical.

     Porous  pavement,  layed  out on  an  existing low  or moderate slope with
adequate base storage capacity,  is  the  most ideal,  aesthetic, and  economical
solution because grading a site to be level can be very expensive. Also, the exposed
slopes  draining onto the porous pavement  must be stabilized  to  prevent eroded
materials from washing onto the pavement and clogging the pores.

     Operation and Maintenance During and After Construction Activities

     In general, operation and maintenance during and after construction of porous
pavements  is minimal  and most  existing  sites  remain functional  as  designed.
However, one loss of porosity failure has been experienced at Bryn Mawr Hospital
near Philadelphia,  Pennsylvania.   The reason  for this  failure is discussed below.
Other failures could result from poor construction supervision, or lack of experience
with this product.

     Experience with porous friction courses has indicated several other potential
problem areas.  These include "cool down" time to allow the asphalt binder to set
prior to the regular operations on new construction. This problem was recognized at
the North Carolina Airport (16).   Another problem  can be the use  of these porous
friction  courses  on steep (by Interstate Highway  standards) grades, where heavy
trucks are required to brake.  In this instance, the pores collapse and  the gravel
aggregate may even come apart,  resulting in a loss of pavement.

     The porous asphalt will lose its porosity as a result of several factors, the most
important of which are listed below:
-------
           I.    Eroded soil and detritus being washed onto the pavement.
                                                                      k
           2.    Construction materials being deposited or tracked in by construc-
                tion equipment.

           3.    Washing  of construction equipment, especially concrete  trucks,
                onto the pavement.

           4.    Finishing of concrete structures on, or adjacent to, the pavement.

           5.    Collapsed pores due to constant vehicle  braking at the same spot
                (entrance, exit, curves, etc.).

           6.    Collapsed pores  resulting from  rolling  of hot  open_ graded  mix
                before it  is  sufficiently  cooled  to resist  the  roller.   Also, the
                temperature of the hot mix  at the site should not be so high that
                the asphalt will  drain away,  thereby  causing  a loss  of cemen-
                tiousness.

      It is obvious that with careful attention to construction scheduling, and close
supervision of site operations, as well as a regular maintenance program, all of these
problem  areas can be  avoided.  Also, if a spill  should occur, immediate corrective
measures should be taken.  Vacuuming  and jet spray washing will generally restore
the original pavement permeability.

      Also, the  use of curbs should be avoided  because these can prevent wind
removal of site-generated or  airborne influx materials (trash and  leaves) common to
most  parking lots.  This factor is the major reason for the failure of the Bryn Mawr
lot.

      Furthermore, Franklin  Institute Research  Laboratories have determined that
at some  locations interficial  surface tension of water on  asphalt will cause the
pavement to temporarily become unable to absorb  water.  However, after the
pavement is thoroughly wet, full permeability will be restored.

      In order to prevent any loss of permeability during the life cycle of the parking
lot, a regular maintenance program which includes vacuuming and jet spray washing
should be  implemented.    If  substantial amounts  of  wind-borne  materials  are
expected to accumulate on  the pavement  surface and be washed into the base by
runoff, additional  storage should  be provided within the base for these materials.
The  volume  required  for  this  type of  storage  must  be  determined from site
conditions and expected environmental conditions.

      The greatest hazard to loss of porosity  in porous pavement occurs during the
construction  phase.  During  that time,  an  extensive portion  of the area  is not
protected from  erosion and/or  construction  equipment.  Therefore, special pre-
-------
cautions must be  taken to prevent  construction  equipment  from depositing or
tracking dirt onto the pavement, and to prevent sediment from  adjacent  hillsides
being washed onto the pavement.  If this should occur, immediate vacuuming and jet
spray washing should be conducted.

      To prevent sediment  from being deposited on the pavement, sediment trap
fences  or  diversion ditches may be. installed around the  pavement  area.   The
sediment  fence could  be filter  material or  fabric  anchored in the ground  and
supported by vertical  stakes adequately spaced behind the fabric to  support the
water pressure. A diversion ditch should be designed to have sufficient capacity to
remove all of the  expected runoff and be able to maintain its grade below  that of
the pavement.  Also, the design velocity should not exceed the non-erodible velocity
for the channel lining material.

      If at all possible, the installation of the porous pavement lot should be delayed
to be the last  construction activity on the site.  This approach  would necessarily
involve  additional soil  erosion  areas; during construction  and these would  require
further  controls.  However, the integrity of the porous pavement would be retained
at a much less diligent effort.  Also, some protection may be necessary  immediately
after construction.  Once vegetation  is  established and most areas are stabilized,
the runoff should be devoid of excess sediment material.
-------
                                 SECTION 8

               COMPUTER MODEL FOR HYDROLOGIC DESIGN
     The model developed In this project provides a comprehensive analysis of flow
and storage in porous pavements.  Although the model  is not very complex, limited
tests indicate that it can adequately quantify the hydrologic responses of a porous
pavement.  Also,  the effects of different  pavement characteristics  can be evalu-
ated.   This  allows  for the investigation of various  porous pavement  systems  to
determine the optimum system, particularly during planning phases of  a project.

     The hydrologic responses of a porous pavement may be simulated by a system
of hydraulically connected control volumes  for which the inflows and outflows are
mathematically defined.  The porous pavement, the base and the natural ground (or
the drain system) are considered to be sequential  but internally independent storage
reservoirs.

     The basic equation  of continuity of conservation of mass is applied to  each
reservoir:
where
          0
          ds
          dt
                                    - I _ o
                                 dt~ '   u
        inflow into the reservoir

        outflow from the reservoir
-TT   =  change in storage volume
     Inflows to the Porous Pavement System

     As shown in Fig. 3, the porous pavement area would serve to control runoff
from contributing impervious areas.  Therefore,  inflow  to  the porous  pavement
system, RUNOFF, is defined ass
where:
                           RUNOFF = PAY + HYD
          PAV  =  direct rainfall onto the porous pavement
-------
                 LEGEND
                                                RUNOFF FROM CONTRIBUTING
                                                SUiAREAS, INFLOW
S$jV>«   PREPARED EARTH  (IF REQUIRED)
                                                                                                    — EVAPORATION, OEVAP
                                                                                                           STORAGE ON SURFACE, SURDEP

                                                                                                           SURFACE RUNOFF, OSURF
                                                                                                           HORIZONTAL OUTFLOW
                                                                                                           THROUGH PAVEMENT, OHORP
                                                                                                          HORIZONTAL OUTFLOW
                                                                                                          THROUGH BASE, OHORS
                                                                                                         ,—LOCATION OF OPTIONAL
                                                                                                          IMPERMIABLE MEMBRANE,
                                                                                                                 ISEAL
                                                                                                           WATER TABLE OR DRAIN
                                                                                                    WTER TABLE OR DRAIN
           FIGURE  3     HYDROLOGIC  MODEL  PARAMETERS FOR  POROUS  PAVEMENTS
-------
           HYD =  surface runoff hydrograph from contributing areas

Contributing areas to the porous pavement will generally be developed and  imper-
vious In  nature.   Consequently, the surface runoff  hydrograph from contributing
areas is determined by use of the method developed by Izzard (18).  This method,
selected  for  its programming ease, utilizes a dimensionless hydrograph from paved
areas as  shown  in  Fig. 4.  The key parameters in this method are  time  to
equilibrium, t ; equilibrium flow, q ; equilibrium surface detention volume, VG; the
intensity of rainfall, i; and the length of overland flow, L.   The following equations
define these parameters:
                                       wiL
                                  %-43200
where:
           L

           w
=  equilibrium flow, cfs

=  rainfall intensity, inches per hour

=  length of overland flow, feet

=  width of overland flow, feet.
               V  =
                e
                                     Ll.33 jO.33
                                        35J
where:
           V    =  equilibrium surface detention volume, cu. ft.

           k    =  an empirically derived,  lumped coefficient for the effects of
                   slope and flow retardance of the pavement

                                        V.
                                  fe=  30 a
           t    =  time to equilibrium, minutes
            6

      Using t/t  values based on the computation Interval and Fig. 4, the q/q  values
and the corresponding q values are determined for the rising limb of the hydrograph.

      The 3 factor, defined as
-------
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-------
                                      60
                                   3 =
                                         V
 where

           tQ    =  time after rainfall has ceased, minutes

           VQ    =  equivalent to VG without  the  rainfall intensity component, cu.
                   TT»

 is used to determine  the q/q  and corresponding q values for the recession limb of
 the hydrograph.            c

      If.the duration of rainfall is  greater than the time required to reach flow
 equilibrium, (te 
-------
where:                             :

           K    =  permeability of flow element, ft/sec

           a    =  cross-sectional area of surface water, sq ft

           A    =  cross-sectional area of flow element, sq ft

           L    =  thickness of flow element, ft

           h I    =  depth of surface water at time 11, ft

           h?    =  depth of surface water at time \<^ - 11 + A t, f t

     These parameters are graphically depicted in Fig. 3.

In a porous pavement system,  the cross-sectional areas of surface water and flow
elements are always equal, and  so the equation is reduced to:
                                = 2.3
                                      At
This equation may be rearranged to solve for r^ as follows:

                                   .     hl
where
                                   E =
                                        IOE
    KAt
    2.3L
Then, vertical seepage is equal to the change in water depth during At or,

                               OVERT = h, - h2


OHOR  is the lateral outflow to a drain or into the natural ground as a result of
water storage in the base and  pavement.   This  condition  is analogous to bank
recharge from a rising stream.  In most porous pavement systems, lateral outflow
will be negligible because OVERT »:OHOR. However if this condition is not met as
in Class C or D soils, then OHOR may be a significant factor.  For a homogenous
isotropic aquifer of  finite  width, the influence of each increment of rise in  the
stream is determined by the following set of equations (20):
                                 d2h
                                 dx
     S  dh
2 =  T  dt
                                      52
-------
                               h(0,t) = 0 for t < 0
                              h(0,t)= AH. fort>0
                                  dh(L,t)
                                    dx
                         =  0
 where
           h

           x

           S

           T
                   h(x,0) = 0



=  hydraulic head or water depth, ft

=  distance from boundary, ft

=  coefficient of storage of aquifer

=  aquifer transmissivity, cfs/ft
         AH.    =  change in water depth at boundary, ft

           L    +  distance to impermeable boundary or discharge point, ft.

      AH. is the increase in stored water depth as a result of vertical drainage from
an upper storage volume (previous OVERT).   If AH. is negative (after inflow has
ceased) water will drain back into the storage  volume from the surrounding natural
ground. If  AH. is 0 then OHOR = 0.

      Integrate the first equation and apply boundary conditions to get:
                                dh
                                dx
                      S   dh
                      T   dt
The Darcy flow equation can be extended,by continuity to define net flow rate as
follows:
                                  V = K
                                         dx
                                      53
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 Q
                         dh
                                                dh
where:
           V
           K
           dh
           dx
           Q
           A
           h
           w
           q
           T
=  velocity of flow^ ft/sec
=  permeability of flow element, ft/sec
=  change in hydraulic grade, ft/ft
=  total mass  flow rate, cfs
=  total flow area, sq. ft.
=  depth of flow, ft.
=  width of flow, ft.
=  flow rate per unit width, cfs/ft
=  transmissivity of flow element, cfs/ft
Then by substitution:
define:
                                   S  dh
          dh
          dt
h!-h;
   At
                                          forx- 1.0ft
and S  is the storage coefficient of the natural ground.  At a distance  x from the
porous pavement boundary, the discharge per unit width is def ined\as:
                               q =  S  (-
                                      h, - h.
                                         At
 Because the volume of flow remaining is the only item of interest, the value of x
 was arbitrarily set equal to 1.0. Then, lateral outflow,

                      OHOR  =  q P At = S ( ' At 2)  P  At
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where:
                =  pavement perimeter, ft.
Figure 3 shows how these parameters apply to porous pavement areas.  OSURF is
the surface runoff resulting from ponding on top of the porous lavement, which
occurs  either because  the  inflow  rate  is  greater than  the porous pavement
permeability or  the  total  storage  capacity  in  the porous pavement system  is
exceeded.  The model requires a depth-storage relationship to determine when the
storage is exceeded.  On  a horizontal  pavement, the model determines the depth-
storage relationship by use of input pavement and base depths and porosities; on a
sloping  pavement, this relationship has to be independently computed and input to
the model.

     The surface runoff  from  a horizontal  pavement  is  defined  by the weir
equation:

                             OSURF =  CLH1'5
where?
           C

           L

           H

           h
            0
=  input weir coefficient

=  input weir length, ft.

=  h - hQ, ft.

=  depth of dead surface storage on the porous pavement, ft.

=  depth of flow on the porous pavement, ft.
On a sloping porous pavement, Manning's Equation is used to determine the surface
runoffs
where:
                        OSURF  =
                           y!.33 S0.5
          y     =  computed depth of flow, ft.

          t     =  width of flow, ft,,

          n     =  input roughness coefficient

          s     =  input energy slope, ft/ft
                                      55
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OEVAP is the volume of water lost to evaporation.  This water  loss is computed
during and after a storm  if water  remains on the surface i.e.  the  pavement  is
flooded.  Although the loss during a storm may be negligible, ponded surface water
loss after a storm may be significant particularly in arid climates.

      Either monthly, weekly or daily evaporation rates may be input to the model;
the monthly  and weekly  rates  are divided into average  daily rates.  The  daily
evaporation rate may be increased by an input ratio to allow for heat absorption by
the dark asphalt. The model only allows for evaporation from 6 a.m. to 8 p.m., with
the maximum  rate  at 2 p.m.   As shown in  Fig. 5,  a triangular  distribution of
evaporation is developed by the model by use of the equation:
where:
                                   EP  = T
                   peak evaporation rate, in/hr

                   total daily evaporation, in
                for 0 < t  < 6,    E = 0
                                        t-«
                for 14 < t  < 20,
V   6
                 for 20 < t  < 24,  E = 0
                         C ""

 where:

           t     =  clock time, hours
            C
           E    =  instantaneous evaporation rate

      Model Operation

      The  paths  of-water flow through the porous pavement system are shown in
 Fig. 3.   For each  computational  time  interval,  all  inflows  and  outflows  are
 accounted for.   The total  runoff  hydrograph,  in  inches per computational  time
 interval, is either input  to the  model  or may be computed as  the sum of runoff
 hydrographs from contributory areas  and  direct  rainfall  onto the pavement as
 described previously.
                                        56
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                                     o
                                     CL


                                     §
                                     LU

                                     U_

                                     O
                               10    r:
o


<
                               UJ
                               o:

                               15
X

i
a.
a.
                                    £T
57
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The following sequential computational steps are -ihen performed:

      I.   Evaporation  losses in inches per computational time interval are
          computed and subtracted from  the sum of the runoff  depth and
          previous surface storage, if any.

     2.   The volume of runoff after allowing for evaporation is compared to
          the  permeability in  inches per time interval of the porous pave-
          ment. In general, the permeability is much greater than the inflow
          runoff rate  and  all of the water moves into the pavement  control
          volume.   In those cases where the permeability has been severely
          reduced  and is  less; than  the runoff   rate,  the  inflow into the
          pavement and the excess is stored on the surface of the pavement
          for later computation of surface runoff from the pavement.

     3.   The  inflow   into the pavement  control volume  is added  to the
          storage volume  in  the  pavement  and  then compared to the per-
          meability, in inches per computational time  interval, of the  base.
          If the  base permeability  is greater   than  the  inflow into the
          pavement, then  all of the flow is transferred into  the base  control
          volume.  This is true for most porous pavement systems operating
          according  to design.   In  those  instances where the  base per-
          meability is less than the inflow volume, the inflow into  the base is
          computed as the vertical  seepage  into the  base.  The  lateral
          outflow  from the pavement is also  computed  if  an  impermeable
          membrane is not installed along the  pavement perimeter.   The
          difference between the inflow into the  pavement and  the outflows
          (vertical and lateral) from the pavement is stored in the pavement.

      4.   The  inflow  into  the base control volume  is  added to the  storage
          volume in the base and then compared to the permeability in inches
          per  computational time interval, of the natural  ground.   If the
          bottom is sealed with  an impermeable membrane, then the per-
          meability is set  equal to zero,  and no flow  is lost to the  natural
          ground.   The flow  volume  remaining   in the base after vertical
          seepage into the natural ground is compared  to the drain capacity,
          in inches per computational time interval.  If the natural ground
          permeability and/or drain capacity are inadequate to remove  all of
          the flow  in the  base, the vertical seepage into the natural ground
          and drains, as well as the lateral outflow, if any, is computed. The
          difference between the inflow  into the  base and the outflows
          (vertical and lateral) from the base is stored in the base.

      5.   All  stored volumes are compared to available volumes.   If  storage
          volume  in  the  base is exceeded,  the excess is stored  in the
          pavement;  if storage volume in the  pavement  is exceeded, the
-------
                excess Is  added to the surface storage on the pavement, if  any
                exists.  Surface runoff is then computed either as  broad channel
                flow or weir flow from the pavement to an adjacent drainageway.

     This computational procedure  is repeated for every time interval in the inflow
hydrograph.  The surface and drain outflows are stored in retrievable arrays.  The
primary output objective is the  surface runoff, if any.  However, the other output
variables  allow  for a thorough  examination of  the  hydraulic operational charac-
teristics of the porous pavement system, including the analysis of the  desirability or
adequacy of the  drains and the discharge rate from the drains.
                                      59
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                               REFERENCES
I.      Thelen, E., et al., "Investigations  of Porous Pavements for Urban Runoff
       Control,"  EPA  11034 DUY 03/72,  U.S.  Environmental  Protection Agency,
       Cincinnati, Ohio,  1972, 141 pp.

2.      "When It Rains, It Pours Through the Pavement," Engineering News Record,
       Oct. II, 1973, 38pp.

3.      Diniz, E. V., and W. H. Espey, Jr., "Maximum Utilization of Water Resources
       in a Planned Community  -  Application of the Storm  Water Management
       Model," EPA - 600/2-79-050C, U.S. Environmental Protection Agency, Cin-
       cinnati, Ohio, 1979.

4.      HoIIinger, R. H., "Maximum Utilization of Water Resources in a Planned
       Community- Field Evaluation  of  Porous Paving," EPA-  600/2-79-050E,
       U.S. Environmental Protection Agency,  Cincinnati, Ohio, (pending publica-
       tion).                                                V

5.      Diniz, E.  V., "Water Quality Prediction  for Urban Runoff - An  Alternative.
       Approach,"  Proceedings  of the  SWMM  User's  Group  Meeting,   EPA
       600/9-79-026, U.S.   Environmental  Protection Agency, Washington,  D.C.
       1979.                      :

6.      Sartor, J. D., and G. B. Boy;d, "Water Pollution Aspects of Street Surface
       Contaminants," EPA-R2-72-08I, U.S. Environmental  Protection Agency,
       Cincinnati, Ohio,  1972.

7.      Colston, N. V., Jr., and A.  N. Tafuri, "Characterization and  Treatment of
       Urban Land Runoff," EPA - 620/2-74-096, U.S.  Environmental Protection
       Agency, Cincinnati, Ohio,  1974.

8.      "Train Cites Need  to Control  Non Point Sources  by  Land Management,"
       Clean Water Report, 1975, p. 212.

9.      Brater, E. F.,  "Rainfall - Runoff  Relations on  Urban and Rural Areas,"
       EPA - 670/2-75-046, U.S.  Environmental  Protection  Agency,  Cincinnati,
       Ohio,  I975i

10.    Espey, W. H., Jr., et al., "A  Study of Some Effects of Urbanization on Storm
       Runoff from a Small Watershed,"  Technical Report HYD 07-6501, Center
       for Research in Water Resources, University of Texas at Austin,  1965.
                                      60
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11.    McPherson, M. B., "Urban Runoff," Technical Memoir No.  18, ASCE Urban
       Water Resources Research Program, 1972.

12.    Jones, M.  P., "Friction Overlay  Improves  Runway Skid  Resistance," Civil
       Engineering - ASCE, 1973, pp. 45-48.

13.    Asphalt Institute Quarterly, October, 1957.

14.    Cedergren, H. R., and K.  A.  Godfrey, Jr., "Water: Key Cause of Pavement
       Failure?," Civil Engineering - ASCE, September, 1974, pp. 78-82.

15.    Thelen, E., and L.  F.  Howe,  "Porous  Pavement,"  The  Franklin  Institute
       Press, Philadelphia, Pennsylvania, 1978, 98 pp.

16.    Johnson, E. A., and  T. D. White, "Porous Friction  Course Solves Airport
       Hydroplaning Problem," Civil  Engineering -  ASCE, April, 1976, pp. 90-92.

17.    Diniz, E.  V., "Quantifying  the  Effects of  Porous Pavements on  Urban
       Runoff," Proceedings  of  the  National  Symposium  on  Urban Hydrology,
       Hydraulics, and  Sediment Control,  University  of  Kentucky, Lexington,
       Kentucky,  1976.

18.    Izzard, C.F.  "Hydraulics  of Runoff from Developed Surfaces," Proceedings
       Highway Research Board, Vol. 26, pp. 129-150, 1946.

19.    Taylor, D.W. "Permeability," Chapter 6 in Fundamentals  of Soil Mechanics,
       John Wiley & Sons, 1965.

20.    Pinder,  G.F.,  J.D* Bredehoeft, and H.H. Cooper, Jr.  "Determination of
       Aquifer Diffusivity from Aquifer  Response  to Fluctuations in River Stage,"
       Water Resources Research, Vol. 5, No. 4, August 1969.
                                     61
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                                APPENDIX A

        SAMPLE SPECIFICATIONS FOR POROUS ASPHALT PAVEMENT
     The following sample specifications are presented in this report to assist the
specification writer for whom  porous  pavement  construction is a new area  of
practice.  These specifications will have to be tailored to individual area needs, but
sufficient detail is  provided so  that;only minimal changes will have to be made.
Consequently, these specifications may have  to  be reduced  in some cases,  but
precautions must be taken to assure  that a contractor understands the  exact scope
of work, particularly if this is the first attempt at porous pavement construction.

ITEM A:  SUBGRADE PREPARATION FOR POROUS PAVEMENT

A.I  DESCRIPTION

     The work covered by this item consists of scarifying, Hading, and rolling the
subgrade to obtain a uniform texture and provide as nearly as practicable a uniform
density for the top six inches of the subgrade.

A.2  CONSTRUCTION METHODS

     The subgrade shall be shaped in conformity with the typical sections shown on
the plans  and to the lines and grades: established by the Engineer by the removal of
existing material or addition of approved material.  All unsuitable or otherwise
objectionable material  shall  be removed  from the subgrade and replaced with
approved  material.  All  holes,  ruts  and depressions shall be filled with approved
material.   The  surface of the subgrade  shall be finished to the lines and grades as
established, and be in conformity with the typical sections shown on the plans.  Any
deviation  in excess  of  one-half  (fe) inch (1.27cm)  cross-section and in a length of
sixteen (16) feet (4.9m) measured  longitudinally shall be corrected by loosening,
adding, or removing material, reshaping and compacting by sprinkling and rolling if
required to attain but  not exceed the density of the natural subgrade.  Sufficient
subgrade  shall  be prepared in  advance to ensure satisfactory prosecution  of  the
work.  The contractor will be required to set blue tops for the subgrade on center-
line, at quarter points and curb lines  at  intervals  not  exceeding fifty (50)  feet
(15.2m).

     Material removed may be utilized  in the addition of material to the subgrade
if approved by the Engineer.  All other material required  for the completion  of  the
subgrade shall also be subject to approval by the Engineer.

     The  type  of equipment used in subgrade preparation  construction shall  not
cause  undue subgrade compaction.   Traffic over  subgrade  shall be  kept at a
                                      62
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minimum.  Where fill is required, it shall be compacted to a density equal to the
undisturbed subgrade, and inherent soft spots corrected.

A.3  MEASUREMENT

     All acceptable subgrade preparation will be measured by the  square yard as
the area for  the  entire  width of  the roadway plus twelve inches (30.5 cm) behind
each curb for the  entire  length.

A.4  PAYMENT

     This item shall be paid for at the  contract  unit price bid  for "Subgrade
Preparation for Porous Pavement," which price shall be  full compensation for  all
work herein specified, including the furnishing of all materials, equipment, tools,
and labor and incidentals necessary to complete the work.
     Payment shall be made under:
          Pay Item No. 240:
          Square Yard (m2).
Subgrade Preparation for Porous Pavement - Per
ITEM B:  STONE BASE COURSE FOR STORMWATER STORAGE

B.I   DESCRIPTION

     "Stone Base  Course for Stormwater  Storage" shall  consist of a foundation
course  for surfacing, pavement or other base courses; shall be composed of crushed
stone or gravel, and shall be constructed as herein  specified in two courses in
conformity with the typical sections shown on the plans and to the lines and grades
as established by the  Engineer.

B.2   MATERIAL

     The material shall be crushed as necessary to meet the requirements herein-
after specified, and shall consist of durable stone or gravel, crushed and/or screened
to the required particle size. The material shall be from approved sources.

     Testing of flexible base materials shall be  in accordance  with the following
Texas Highway Department standard laboratory test procedures:

           I)   Preparation for Soil Constants and Sieve Analysis       TEX-IOI-E
           2)   Sieve Analysis                                       TEX-110-E
           3)   Wet Bail Mill                                        TEX-M6-E
                                     63
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Unless otherwise specified  on  the  plops, all base material will be stockpiled  after
crushed; tested by  the testing  agency designated by the City  of 	 and
approved by the City of	prior !to being hauled to the project site.

      The material, when properly tested, shall  meet the following requirements:
      Course
      Stone Base Course

      Stone Top Course
Sieve Size
    Ife"
   5/8"
   3/8"
Retained on Sieve, Percent

            0
          100

            0
          100
               Max. Wet Ball Mill
                 50
Unless otherwise shown on plans, the maximum increase  in material passing the
Number 40 sieve resulting from the Wet Ball Mill  Test shall not exceed 20.

B.3  CONSTRUCTION METHODS

     (I)   Preparation of Subgrade

           The street shall be prepared and  shaped in conformity with Item 240,
           "Subgrade Preparation for Porous Pavement" and the  typical sections
           shown  on plans and  to  the  lines and grades as  established by  the
           Engineer.  The surface of the subgrade shall be finished to line and grade
           as established and in conformity with  the typical section shown on plans,
           and any deviation in excess ;of In inch (0.6 cm) in cross-section and in a
           length^ of  10 feet (3.0m) measured longitudinally shall  be corrected by
           loosening, adding or removing material and reshaping.   Sufficient sub-
           grade  shall be prepared in advance to ensure satisfactory prosecution of
           the work.  Material excavated in the preparation of the subgrade shall be
           utilized  in the  construction  of  slopes or  otherwise  disposed   of  as
           directed, and any  additional material required  for  the  completion  of
           slopes shall be secured from sources indicated on plans  or designated by
           the Engineer.  Blue tops shqll be set by the contractor  for subgrade on
           centerline, quarter points and  curb  lines  at  intervals  not  exceeding
           50 feet (15.2m).

     (2)    Stone Base Course

           Immediately before placing the stone base material, the subgrade shall
           be checked as to conformity with grade and section.

           The material  shall be delivered  in  approved  vehicles  of  a uniform
           capacity and it shall be the charge of the Contractor that the required
-------
           amount of specified material shall be delivered in each 100-foot (30.5 m)
           station.

           Stone base course shall be laid over a dry subgrade to the depth shown in
           drawings, in lifts to lay naturally compacted.  The stone base course is
           not to be rolled or compacted and is to be kept clean from debris, clay,
           and eroding soil.

     (3)   Stone Top Course

           This course is to be two inches in depth. Construction methods shall be
           the same as prescribed for the stone base course. Blue tops shall  be  set
           by the contractor for finished base grade on center-line and intermediate
           points not exceeding 11 feet (3.4 m) between points at 50-foot (15.2 m)
           intervals.

B.4  MEASUREMENT

     "Stone Base Course" including the "Stone Top Course" will be measured by the
square yard (m  ) at depths specified in the proposal for the area of  Parking  Lot as
shown on the typical sections of the plans or otherwise provided for  in the contract
documents, complete irx place;  by the cubic yard (m ),  loose vehicle measurement;
or by the cubic yard (m ), complete in place, as indicated in the proposal.

B.5  PAYMENT

     This item  will be paid for  at the  contract  unit price bid for "Stone Base
Course," which  price  shall  be full  compensation  for  all  work herein  specified,
including the furnishing, hauling, and placing of all materials, for all  water required
and for all equipment, tools, labor and incidentals necessary to complete the work.

     Payment will be made under:

           Pay  Item No. 250-A^  Stone  Base  Course  (complete  in  place) -  Per
                Square Yard (m ), or
           Per  Item No. 250-B: Stone Base  Course (loose vehicle measurement)-
                Per Cubic Yard (m ), or
           Pay Item No. 250-C: Stone Base Course (complete in place) - Per Cubic
                Yard (mJ).

     *  This item must be verified for local requirements and site conditions.
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ITEM C:  HOT MIX POROUS ASPHALT PAVEMENT '

C.I   DESCRIPTION

      This item shall consist of a surface course as shown on the plans, composed of
a lightly compacted mixture of mineral aggregate and asphaltic material.

      The  pavement shall be constructed on the previously completed and approved
subgrade and  stone base course  as  herein specified  and in accordance with  the
details shown on the plans.

C.2   MATERIALS

      (I)  Coarse Aggregate

          The mineral  aggregate shall be composed of a coarse aggregate, a fine
          aggregate, and if required, a mineral filler.  Samples of coarse aggregate
          and mineral  filler shall  be submitted for  testing as directed by  the
          Engineer and approval  of.both material and of the source of  supply must
          be obtained from the Engineer prior to delivery.

          (a)    Coarse Aggregate

                Coarse aggregate shall be that part of the aggregate retained on
                the No. 8 sieve; shall consist of clean, tough, durable fragments of
                crushed  stone,  or  crushed  gravel,  as hereinafter  specified of
                uniform quality throughout.

                When  the  coarse aggregate  is  tested  in  accordance with Test
                Method Tex-217-F*  (Part I,  Separation of  Deleterious Material),
                the amount of  organic  matter,  clay, loam  or  particles coated
                therewith  or other  undesirable  materials  shall  not  exceed  two
                percent and when remaining part  of the sample is further tested in
                accordance with Test Method Tex-127-F*  (Part II, Decantation),
                the amount of  material  removed shall  not be more than  two
                percent.

                The coarse aggregate shall have an abrasion of not more than forty
                percent loss by weight when subjected  to the Los Angeles Abrasion
                Test, Test  Method Tex-410-A*.

                Unless specified otherwise, gravel shall be so crushed that seventy-
                five percent of the particles  retained on the No. 4 sieve shall have
                more than one crushed face when tested in accordance with Test
                Method Tex-413-A* (Particle Count).
                                     66
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(b)   Fine Aggregate

      The fine aggregates shall be that part of the aggregate passing the
      No. 8  sieve and  shall consist of  sand, screenings, or combination
      thereof as hereinafter specified of uniform quality throughout.

      Fine aggregate shall consist of durable particles, free from injur-
      ious foreign matter.  Screenings  shall  be of the same or similar
      materials as specified for coarse aggregate.  The plasticity index
      of  that part of the fine aggregate posing the No. 40 sieve shall be
      not more  than 6  when tested  in accordance with Test Method
      Tex-106-E*.   Fine aggregate from  each source shall meet plas-
      ticity  requirements.

      Where stone screenings  are specified for use, the stone screenings
      shall meet the  following grading requirements  unless otherwise
      shown on plans:
           Passing the fe" Sieve
           Passing the No. 200 Sieve
Percent by Weight
       100
      10-30
     When  authorized by  the Engineer,  stone screenings containing
     particles  larger than fe" may be used  but  only that portion of the
     material passing the 3/8" sieve shall be considered as fulfilling the
     requirements for  screenings when  a minimum  percentage  of
     screenings is specified for a particular mixture.

(c)   Mineral Filler

     Mineral filler shall consist of thoroughly dry stone dust, slate dust,
     Portland cement, fly ash or  other  mineral dust  approved by  the
     Engineer.  The  mineral filler shall be free from foreign and other
     injurious matter.

     When tested by Test Method Tex-200-F*  (Dry Sieve Analysis), it
     shall meet the following grading requirements:
           Passing a No. 30 Sieve
           Passing a No. 80 Sieve, not less than
           Passing a No. 200 Sieve, not less  than
Percent by Weight

     95 to  100
           75
           55
                             67
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(2)   Asphaltic Material for Porous Asphalt Paving Mixture

     Asphalt for the paving mixture shall be asphalt cement, viscosity grade
     AC-20* and shall meet the requirements of the Item, "Asphalts, Oil and
     Emulsions." The Contractor shall notify the Engineer of the source  of
     his asphaltic material pri6r to  production of the asphaltic mixture and
     this source shall not be changed during the course of the project  except
     on written permission of the Engineer.

     The paving mixture  shall consist  of  a  uniform  mixture  of  coarse
     aggregate,  fine  aggregate,  asphaltic  material  and  mineral  filler,  if
     required.

     The grading of each constituent of the mineral aggregate shall be such as
     to produce,  when properly proportioned, a mixture which, when tested in
     accordance  with Test Method Tex-200-F*  (Dry  Sieve Analysis), will
     conform to the limitations for master grading given below:
           Passing fe" Sieve
           Passing 3/8" Sieve, Retained on No. 4 Sieve
           Passing No. 4 Sieve, Retained on No. 8 Sieve
           Passing No. 8 Sieve, Retained on No. 16 Sieve
           Passing No. 16 Sieve^ Retained on No. 200 Sieve
           Passing No. 200 Siev^
Percent by Weight

         100
       40-65
        3-35
        1-20
        0-10
         2-5
     The asphaltic material shall form from 5.5 to 6.0 percent of the mixture
     by weight unless specified Otherwise on the plans.

     The Engineer  will designate the  exact grading of the aggregate  and
     asphalt content, within the above limits, to be used in the mixture.  The
     paving mixture produced should not vary from the designated grading and
     asphalt content by more 'than the tolerances allowed herein;  however,
     the mixture produced shall conform to the limitations for master grading
     specified above.
           Passing fe" Sieve, Retained on 3/8" Sieve
           Passing 3/8" Sieve, Retained on No. 4 Sieve
           Passing No. 4 Sieve,'Retained on No. 8 Sieve
           Total Retained on No. 8 Sieve
           Passing No. 8 Sieve, Retained on No. 16 Sieve
           Passing No.  16 Sieve, Retained on No. 200 Sieve
           Passing No. 200 Sieve
           Asphalt Material
         Percent
        by Weight

          ±5
          + 5
          + 5
          ±5
          + 3
          + 3
          ±3
          + 0.25
                                 68
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           Should the paving mixture produced vary from  the  designated grading
           and asphalt content by more than the above tolerances, proper changes
           are to be made until it is within these tolerances.

           Samples of the mixture  when tested  in accordance  with Test Method
           Tex-210-F* shall  not  vary from the grading proportions of the aggregate
           and the asphalt content  designated  by the Engineer by more than the
           respective  tolerances specified above and  shall be within the  limits
           specified for master grading.
C.3  EQUIPMENT

     (I)   Mixing Plants
           Mixing plants that will not continuously meet all the requirements of this
           specification shall be condemned.

           Mixing plants may be either the weight-batching type or the continuous
           mixing type.  Both  types of plants shall be equipped with  satisfactory
           conveyors, power units, aggregate handling equipment, aggregate screens
           and bins and shall consist of the following essential pieces of  equipment:

           (a)   Weight-Batching Type

                Cold Aggregate Bin and Proportioning Device.  The cold aggregate
                bins or aggregate stockpiles shall be of sufficient number and size
                to supply the  amount of  aggregate required to keep  the plant in
                continuous operation.  The proportioning device shall be such as
                will provide a uniform  and continuous flow of aggregate  in  the
                desired proportion to the plant.

                Dryer.  The  dryer shall be of the type that continually  agitates the
                aggregate during heating and in  which the temperature will be so
                controlled  that aggregate will  not be  injured in the necessary
                drying and heating operations required to obtain a mixture of  the
                specified temperature.

                The burner, or combination of burners, and type of fuel used shall
                be such that  in the process of heating the aggregate to the desired
                or specified temperatures, no residue from the fuel shall adhere to
                the heated aggregate.

                A recording thermometer  shall  be  provided which will record the
                temperature of the aggregate when  it leaves the dryer.  The dryer
                shall be of sufficient size to keep the plant in continuous operation.
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Screenings and Proportioning.  The screening capacity and size of
the bins shall  be  sufficient  to screen and  store the  amount  of
aggregate required to properly operate the plant and keep the plant
in continuous operation at full  capacity.  Proper proportions shall
be made to enable inspection forces to have easy and safe access
to the proper  location on the mixing plant  where accurate repre-
sentative samples of aggregate  may  be  taken from the bins for
testing.   Separation  of hot bin into compartments will not  be
required providing uniform grading and asphalt content are  con-
sistently produced in the completed mix.

Aggregate Weigh  Box and Batching Scales.  The aggregate weigh
box and batching scales shall be of sufficient capacity to hold and
weigh a complete batch of aggregate. The weigh  box  and scales
shall  conform  to the requirements  of the Item,  "Weighing  and
Measuring Equipment."

Asphaltic  Material  Bucket  and Scales.   The  asphaltic material
bucket and scales shall be of sufficient capacity to hold and weigh
the necessary  asphaltic material for  one  batch.  If  the material is
measured  by weight, the  bucket and scales shall conform to the
requirements of the jtem, "Weighing and Measuring Equipment.

If a  pressure  type flow  meter is  used to measure the asphaltic
material,  the  requirements of the Item,  "Weighing and Measuring
Equipment" shall apply.

Mixer.  The mixer shall  be  of the pug mill type and shall have a
Capacity of not less than  20 cubic feet (0.57 rrO unless otherwise
shown on the plans. The number of blades and the position of same
shall be such as to give a uniform  and complete circulation of  the
 batch in the mixer.  The mixer shall be equipped with an approved
 spray bar that will I distribute the asphaltic material  quickly and
 uniformly throughout the  mixer. Any mixer that has a tendency to
 segregate the mineral  aggregate or fails to secure  a thorough and
 uniform mixing with the asphaltic  material shall not be used.  This
 shall be determined by mixing the standard batch for the required
 time, then  dumping  the mixture and  taking samples from  its
 different parts.  This will  be tested by the extraction test and must
 show that the batch  is uniform throughout.  All mixers shall  be
 provided with an automatic time lock that will lock the discharge
 doors of the  mixer -jfor the required mixing period.  The dump door
 or doors and the shaft seals of the mixer shall be tight enough to
 prevent spilling of aggregate or mixture from the pug mill.
                        70
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(b)   Continuous Mixing Type

     Cold  Aggregate Bin  and  Proportioning Device.  Same  as for
     weight-batching type of plant.

     Dryer.  Same as for weight-batching type of plant.

     Screening and Proportioning.  Same as for weight-batching type of
     plant.

     Aggregate Proportioning Device.  The hot aggregate proportioning
     device shall be so designed that when properly operated a uniform
     and continuous  flow of  aggregate into the mixer  will be  main-
     tained.

     Asphaltic Material  Spray Bar.  The asphaltic material spray bar
     shall be  designed such that the asphalt will  spray  uniformly and
     continuously into the mixer.

     Asphaltic Material  Meter.  An accurage asphaltic material re-
     cording meter shall be placed in  the  asphalt  line  leading  to the
     spray  bar so that the cumulative amount of asphalt used can be
     accurately determined.  Provisions of a permanent nature shall be
     made  for checking the accuracy of the meter output.  The asphalt
     meter and line to the meter shall be protected with a jacket of hot
     oil or other approved  means to maintain  the  temperature  of the
     line and  meter near the temperature  specified for  the asphaltic
     material.

     If a pressure  type  flow  meter  is used to measure the asphaltic
     material, the requirements of the Item "Weighing and Measuring
     Equipment" shall apply.

     Mixer.  The mixer  shall  be of the pug mill continuous type  and
     shall have a capacity of not  less than 40 tons (36.3 Mg  metric ton)
     of mixture per hour.  Any mixer that has a tendency to segregate
     the aggregate or fails to  secure a thorough and uniform mixing of
     the aggregate  with  the asphaltic material shall not  be  used.  The
     dam gate at the discharge end of the pug mixer and/or pitch  of the
     mixing paddles  shall  be so adjusted  as  to  maintain   a  level of
     mixture in the pug mixer between the paddle shaft and  the paddle
     tips (except at the discharge end).

     Truck  Scales.  A set of standard platform  truck scales,  conforming
     to the Item, "Weighing and Measuring Equipment," shall be placed
     at a location approved by  the Engineer.
                           71
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(2)   Asphaltic Material Heating Equipment

     Asphaltic material  heating  equipment  shall be  adequate to  heat  the
     amount  of  asphaltic  material required  to the  desired  temperature.
     Asphaltic material  may  be heated  by  steam  coils  which  shall  be
     absolutely tight.   Direct fire heating  of  asphaltic  material will  be
     permitted, provided the heater used is manufactured by a  reputable
     concern and there is positive circulation of the  asphalt throughout the
     heater.  Agitation with steam or air will not be permitted.  The heating
     apparatus shall  be equipoped  with a  recording thermometer with^ a
     24-hour chart that will record the temperature of the asphaltic material
     at the highest temperature.

(3)  Spreading and Finishing Machine

     The spreading and finishing machine shall be of  a type approved by the
     Engineer, shall be capable  of producing  a  surface  that  will  meet the
     requirements  of  the  typical cross-section and a  surface  test, when
     required, and  when the  mixture is  dumped directly  into the finishing
     machine shall  have adequate power to  propel the delivery vehicles m a
     satisfactory manner.   The  finishing machine shall  be equipped with a
     flexible  spring  and/or  hydraulic  type  hitch sufficient  m  design and
      capacity to maintain contact between the rear wheels  of  the  hauling
      equipment  and the pusher  rollers of  the  finishing machine  while the
      mixture is being unloaded.

      The use of any vehicle which requires dumping directly into the finishing
      machine and which the finishing machine cannot  push or propel in such a
      manner as to obtain  the desired  lines and grades  without  resorting to
      hand finishing will not be allowed.

      Automatic screed controls,  if required, shall meet the requirements of
      the Item, "Automatic Screed Controls for Asphaltic Concrete Spreading
      and Finishing Machines."

 (4)   Pneumatic Tire Rollers

      The rollers shall be acceptable light pneumatic tire  rollers conforming to
      the requirements of the  Item, "Rolling (Pneumatic Tire)," unless other-
      wise specified on plans.

      The tire pressure of each tire shall  be  adjusted as  directed  by the
      Engineer' and this pressure shall not  vary by  more  than 5 pounds per
      square inch (34.5 kP2, kilo pascal).
                                   72
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      (5)   Two Axle Tandem Roller

           This roller  shall be an acceptable power driven tandem roller weighing
           not less than 6 tons (5.4 Mg), or more than 10 tons (9.1  Mg).

      (6)   Three Wheel Roller

           This roller  shall  be  an acceptable  power driven three  wheel roller
           weighing not more  than 10 tons (9.1 Mg).

      (7)   All  Equipment shall be maintained  in good repair and operating condition
           and shall be approved by the Engineer.

      (8)   Alternate Equipment

           When  permitted by the Engineer, in writing, equipment other than  that
           specified, which will consistently produce satisfactory  results,  may be
           used.

C.4   STOCKPILING, STORAGE, PROPORTIONING AND MIXING

      (I)   Aggregate Storage

           If the  mineral aggregates are stored or stockpiled, they  shall  be handled
           in  such a manner  as  to  prevent  segregation,  mixing  of the  various
           materials  or sizes, and contamination  with  foreign materials.   The
           grading of  aggregates proposed for  use and as  supplied to the mixing
           plant shall  be uniform.  Suitable equipment of acceptable  size shall be
           furnished  by the Contractor to work the stockpiles and prevent segre-
           gation of the aggregates.

      (2)   Storage and Heating of Asphaltic Materials

           The asphaltic material storage shall be ample to meet the requirements
           of the plant.  Asphalt shall not be heated to a temperature in excess of
           that specified in the Item, "Asphalts, Oils and Emulsions." All  equipment
           used in the storage and handling of asphaltic material shall be kept  in a
           clean condition at all times and shall be operated in such a  manner that
           there will be no contamination with foreign matter.

      (3)   Feeding and Drying of Aggregates

           The feeding of various  sizes of aggregate to the.dryer shall  be done
           through the cold aggregate bin and proportioning device in such a manner
           that a  uniform and  constant flow of materials in the required proportions
           will be maintained.  When specified on the plans,  the cold aggregate bins
                                      73
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     shall  be charged by  use of a clamshell,  dragline, shovel  or  front end
     loader.  The aggregate  shall be dried and heated to the temperature
     necessary to produce a mixture having the specified temperature.

(4)   Proportioning

     The proportioning of the various materials entering the asphaltic mixture
     shall  be as directed by the Engineer  and in accordance with  these
     specifications.  Aggregate  shall  be proportioned by weight  using  the
     weigh box and batching scales herein specified when the  weight-batch
     type of plant is used and by volume using the hot aggregate proportioning
     device when the continuous mixer type  of plant is used.  The asphaltic
     material shall  be proportioned by weight or by volume  based  on weight
     using the specified equipment.

(5)   Mixing

     (a)   Batch Type Mixer

           In the charging of the weigh box and in  the charging of the mixer
           from the weigh box, such methods or devices shall be used as are
           necessary to secure a uniform  asphaltic mixture.  In introducing
           the batch into the  mixer, the mineral aggregate shall  be  introduced
           first; shall be mixed;thoroughly for a period of 5 to 20 seconds, as
           directed, to uniformly distribute the various sizes throughout the
           batch before the asphaltic material is added; the asphaltic material
           shall then be added and the mixing continued for a total  mixing
           period of not less than 30 seconds.  This mixing period may be
           increased if, in the ppinion of  the Engineer,  the mixture  is not
           uniform.

      (b)   Continuous Type Mixer

           The amount of  aggregate and asphaltic material entering the mixer
           and the rate of travel through  the  mixer shall be so coordinated
           that a uniform  mixture of the specified grading and asphalt content
           will  be  produced.   Checks on asphalt used shall be made at least
           twice daily by comparing the asphalt  used in  ten loads of com-
            pleted mix as shown on the asphalt recording meter and the  design
            amount for these ten loads.  The acceptable percent of variation
            between the asphalt used and the design amount  will be as shown
            on the plans or as  determined by the Engineer.

      (c)    The Mixture produced from each type of mixer shall not vary from
            the specified mixture by more than the tolerances herein specified.
-------
           (d)   The Surface  Mixture from each  type of mixer will not exceed a
                temperature  of 260  F  (127° C)  and shall  be specified  by  the
                Engineer. The temperature of the mixture will not be lower than
                180° F (82° C) when placed on the road.

C.5  CONSTRUCTION METHODS

     (I)   The surfacing  mixture shall not be placed when the air temperature is
           below 50  F (10 C)  and is falling, but it may be placed when the air
           temperature is above 40° F (4° C)  and  rising.  The air temperature shall
           be taken in the shade away from artificial heat.  It is further provided
           that  the surfacing mixture shall  be placed  only  when  the humidity,
           general weather conditions and temperature and moisture condition of
           the pavement surface, in the opinion of the Engineer, are suitable.

     (2)   Transporting the Surface Mixture

        ,   The mixture, prepared as specified above, shall be hauled to the work in
           tight vehicles with smooth dump beds that have been previously  cleaned
           of all foreign material.  The dispatching of vehicles shall be arranged so
           that  all material  delivered may  be placed, and  all rolling shall be
           completed during daylight hours.   In  cool  weather or for  long hauls,
           canvas  covers  and insulating of the truck bodies may be required.  The
           inside of the truck body shall  be  sprayed with a non-petroleum relase
           agent satisfactory to the Engineer, if necessary, to  prevent the mixture
           from adhering to the body.

     (3)   Placing

           The asphaltic  mixture  shall  be  dumped  directly  into  the specified
           spreading and  finishing  machine and spread on the approved prepared
           surface in such a manner that, when properly compacted, the finished
           surface  will be  smooth and  of  uniform  texture  and  density.   The
           spreading and finishing machine shall be operated at a speed satisfactory
           to the Engineer.  During application of asphaltic material, care shall be
           taken to prevent splattering of adjacent pavement,  curb and  gutter and
           structures.

     (4)   Compacting

           (a)   As directed  by the Engineer, the surface mixture shall be  com-
                pressed lightly  and uniformly  with the specified  rollers and/or
                other approved rollers.

           (b)   Compaction of the surface course shall be done while the surface is
                cool enough  to  resist the roller used.  One or two passes by the
                                      75
-------
                roller  Is  all that  is required,  as excess  rolling  could cause  a
                reduction in surface course porosity.

           (c)   The motion of the rollers shall be slow enough at all times to avoid
                displacement of the mixture.  If any  displacement  occurs, it shall
                be corrected at  once by the use  of  rakes and of fresh mixture
                where  required.  To prevent adhesion of the surfacing mixture to
                the roller, the  wheels shall be  kept  thoroughly moistened  with a
                soap-water  solution.   Necessary  precautions  shall  be  taken  to
                prevent  the  dropping of gasoline, oil, grease  or other foreign
                matter on the pavement, either when the rollers are in operation or
                when standing.

     (5)   Surface Tests
                                  i
           The surface  of the pavement, after compaction, shall be smooth and true
           to the established line, grade and cross-section, and  when tested  with a
           10-foot (3.0 m) straight-edge, the maximum deviation shall  not exceed
           & inch  (6mm)  in  10 feet  (3.0m),  and  any point  in the  surface  not
           meeting this requirement shall be corrected as directed by the Engineer.
           The completed surface shall meet the approval of the Engineer for riding
           surface finish and appearance.

     (6)   After final rolling, no vehicular traffic of any kind shall be permitted on
           the  porous  pavement  until cooling  or  hardening has taken place,  as
           directed by the Engineer, but in no case less than six hours.

C.6  MEASUREMENT

     (1)   The  surfacing  mixture ;will  be  measured separately  by  the ton  of
           2,000 pounds (907 kilograms, Kg) of "Asphalt" and by the cubic yard of
           dry,  loose "aggregate" o'f the type actually  used in the completed  and
           accepted work  in accordance with the plans and specifications for  the
           project.  The  volume  of  aggregate in the  compacted mix  shall  be
           calculated from the measured weights of  the surfacing mixture  by use of
           the following formula:
                                 V =
                      (W-A)
                       (27)K
     V
     W
     A
     K
Cubic Yards of aggregate, dry, loose
Total weight of surfacing mixture in pounds (Kg)
Weight of Asphalt in pounds (Kg)                       o
Unit Weight of Aggregate in pounds per cubic foot (Kg/m )
                                       76
-------
           The value "K" shall be the average of two or more tests determined by
           the Engineer in the following manner:

           At  the beginning of plant operations,  a specified weight of dried mineral
           aggregate shall be placed in an acceptable container that will contain a
           minimum volume of three cubic yards (2.3 mj).  The aggregate shall be
           leveled or "struck-off" and  measured, to determine the volume of the
           mineral aggregate, in cubic feet (mj).   The unit weight of the mineral
           aggregate shall  be obtained by dividing  the  specified weight of  dried
           aggregate in pounds (Kg) by the measured volume in cubic feet  (m ).
           The value "K" is an average of two or  more of the above-described tests.

           The value  "K"  shall be .checked  a minimum of  one  time for  each
           3,000 cubic yards (2,294 m ) of mineral  aggregate.  If, in the opinion of
           the Engineer or the Contractor's representative, the value  of  "K" has
           changed, a check  test shall  be made.   A new value for "K" shall  be
           determined  if the checked  value of  "K"  varies more than two percent
           (plus or minus) from the value being used.

           The  weight,  "W," if mixing  is  done by a  continuous  mixer,  will  be
           determined by truck scales.  The weight,  if batched, will be determined
           on batch scales and records  of the number of batches, batch designs and
           weight of "Asphalt" and "Aggregate" shall be kept.

C.7  PAYMENT

     (I)   The work performed and materials furnished as prescribed by this  item
           and measured as provided under "Measurement," will be paid for at the
           unit prices bid for "Asphalt"  and "Aggregate," of the types specified,
           which prices shall each be full compensation for quarrying, furnishing all
           materials and freight involved; for all heating, mixing, hauling, cleaning
           the  existing  pavement,  placing  asphalt-aggregate  surfacing mixture,
           rolling and  finishing; and  for all  manipulations, labor, tools, equipment
           and incidentals necessary to complete  the work.

     (2)   All  templates, straight-edges, scales  and  other weighing and measuring
           devices necessary for the proper construction, measuring and checking of
           the  work shall be furnished,  operated and maintained by the Contractor
           at his  expense.

* This item must be verified for local requirements and site conditions.
                                       77
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                                    TECHNICAL REPORT DATA
                             (Please read Instructions on the reverse before completing)
 1. REPORT NO.

  EPA-600/2-80-155
                                                           3. RECIPIENT'S ACCESSION NO.
 4. TITLE AND SUBTITLE
  Porous Pavement; Phase I
  Design and Operational Criteria
                                                           5. REPORT DATE
                                                              August 1980
  (Issuing Date)
                                                           6. PERFORMING ORGANIZATION CODE
 7. AUTHOR(S)
  Elvidio V. Diniz
                                                           8. PERFORMING ORGANIZATION REPORT NO
9. PERFORMING ORGANIZATION NAME AND ADDRESS
                                                             10. PROGRAM ELEMENT NO.
  City of Austin
  P.O. Box 1088
  Austin, Texas 78767
                                                             35 BIG,  Task No. 415225
                                                           11. CONTRACT/GRANT NO.

                                                             R806338
 I 2. SPONSORING AGENCY NAME AND ADDRESS
Municipal Environmental Research Laboratory— c in.
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati. Ohio 45268 __
                                                       Oh
                                                            13. TYPE OF REPORT AND PERIOD COVERED
                                                               Final. 2/1/79 - 8/1/79
                                                            14. SPONSORING AGENCY CODE
                                                               EPA/600/14
15. SUPPLEMENTARY NOTES
  Project Officer: Hugh Masters (201)321-6678, FTS 340-6678
 1C. ABSTRACT
  Design and operational criteria,  utilization concepts, benefits and disadvantages,  as
  well as other characteristics  of porous pavements are presented in this report.  Par-
  ticular emphasis is placed on  porous asphalt pavements, but the criteria and design
  approach are applicable to all other porous pavement types.

The_design considerations presented in this report include siting problems, load bearing
design,  and hydrologic design.   A brief history of porous  pavement development and pre-
vious  experience with porous pavement by several designers,  contractors, and operators
are described.

A computer model for hydrologic performance evaluation of  existing or proposed porous
pavement systems is also described in this report.  Load bearing design criteria are
based on previous work conducted for porous asphalt pavements.

Appendices to this report include a sample set of specifications for porous asphalt
construction and a list of  soils and their permeability classes  as prepared by the U.S.
Soil  Conservation Service.
17.
                                KEY WORDS AND DOCUMENT ANALYSIS
                  DESCRIPTORS
                                             b.lDENTIFIERS/OPEN ENDED TERMS  C.  COSATI Field/Group
Pavements,  Pavement bases, Porous materials,
Asphalt pavements,  Urban land use, Urban
planning, Design criteria
                                              Porous pavements,
                                              Urban runoff control,
                                              Asphalt concrete
  13B
18. DISTRIBUTION STATEMENT

Release to Public
                                             19. SECURITY CLASS (ThisReport)
                                              Unclassified
21. NO. OF PAGES

  99
                                              20. SECURITY CLASS (Thispage)
                                               .Unclassified
                                                                          22. PRICE
EPA Form 2220-1 (Rev. 4-77)
                                             87
                                                                   * U.S. GOVERNMENT PRINTING OFFICE: 1980-657-165/014Z
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