United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park, NC 27711
Research and Development
EPA7600/SR-93/091 July 1993
? EPA Project Summary
Recommended Foundation
Barrier Construction
Standard of the Florida Radon
Research Program
R. Eggink, E. Gazetas, D. Steuernagel, and A. Scott
The report gives results of a study to
determine the causes of cracking in
slab-on-grade construction, particularly
for single-family residential structures
in Florida, and to recommend a foun-
dation barrier construction standard to
minimize such cracking.
This Project Summary was developed
by EPA's Air and Energy Research
Laboratory, Research Triangle Park, NC,
to announce key findings of the re-
search project that is fully documented
in a separate report of the same title
(see Project Report ordering informa-
tion at back),
Almost all of the radon that moves from
the ground into buildings is carried along
as part of a flow of soil gas that enters at
every opening in the foundation that con-
tacts or corr municates to the soil. Soil
gas will flow into the structure if there are
openings and cracks and the pressure
differential is favorable. Foundation open-
ings are of two types: deliberate openings
serving a purpose, such as control joints;
and unintended openings such as cracks
in slabs-on-grade.
Radon-resistant housing requires that
these two types of openings be controlled
and, if possible, eliminated. Quite different
strategies are needed to control these dif-
ferent types of openings. In principle, as
the deliberate openings are designed into
the building, they can be either eliminated
by a change in design, or closed by the
application of sealants during the building
process. Unintended openings, such as
unplanned cracks, are common in many
concrete slab-on-grade structures. Since
these cracks are normally not a structural
concern, the causes for their development
and design options to minimize their ex-
tent have not been fully studied.
The purpose of this study is to deter
mine the causes of cracking in slab-on
grade construction, particularly for single
family residential structures in Florida.
The objective of this study is to identify
design and construction procedures that
will lead to crack-free slabs in Florida
Crack-free or limited-crack slabs will con
tribute to the overall goal of radon resis
tant foundations for residential buildings
in Florida. The objective of radon resistant
construction is to produce a foundation
free of openings connected to the soil
The radon concentration in soil gas is
typically 1,000 times higher than the 1-2
pCi/L concentration desired in buildings. If
the soil gas flow-rate into a building is less
than 1/1,000 of the ventilation air flow
rate, then the building will be radon resis
tant. The natural pressure differential be
tween building and soil is a few pascals,
which implies that the effective leakage
area of cracks and openings in a typical
house slab must be less than that of an
unobstructed 1/4-in. (0.6 cm) hole. In prac-
tice the effective leakage area of cracks is
much less than the apparent size, but it is
clear that only a small amount of cracking
will severely reduce the effectiveness of a
concrete slab as a soil gas and radon
barrier.
Many factors affecting drying shrinkage
are related to concrete materials and to
construction practice in regard to slab con-
struction.
To identify the causes of cracking and
recommend construction methods for their
control, the following methodology was
adopted:
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1. Literature search to identify variables
that influence and contribute to crack
development and their importance.
2. Batch plant monitoring in Florida, con-
sisting of visiting batch plants, collect-
ing concrete mix design data, and in-
terviewing batch plant operators.
Construction practice monitoring in 5.
Florida, consisting of monitoring of slab
construction and interviewing contrac-
tors relating to drying shrinkage.
Crack development monitoring of slabs-
on-grade in Florida. 6.
Evaluation of field data, to identify
which major variables that influence, in
general, cracks in slabs-on-grade also
affect cracking in Florida's residential
houses.
Recommendation of construction meth-
ods to control cracking in slabs-on-
grade in Florida.
'U.S. Government Printing Office: 1993 — 750-071/80028
R. Eggink, E. Gazetas, and D. Steuernagel are with Acres International Corp.,
Amherst, NY 14228, and A. Scott is with American ATCON, Inc., Wilmington, DE
19899
David C. Sanchez is the EPA Project Officer (see below)
The complete report, entitled "Recommended Foundation Barrier Construction
Standard of the Florida Radon Research Program" (Order No. PB93-199 388/AS;
Cost: $17.50, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Air and Energy Engineering Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
Official Business
Penalty for Private Use
$300
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
EPA/600/SR-93/091
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