EPA-600/R-95-032
February 1995
Radon Generation and Transport
In Aged Concrete
by
Vern C. Rogers, Kirk K. Nielson, and Rodger B. Holt
Rogers & Associates Engineering Corporation
P.O. Box 330, Salt Lake City, UT 84110-0330
EPA Interagency Agreement RWFL933783-01
Florida Department of Community Affairs Contract 93RD-66-13-00-22-003
University of Florida Subcontract (Acct. 1506481-12)
EPA Project Officer: David C. Sanchez
U.S.Environmental Protection Agency
Air and Energy Engineering Research Laboratory
Research Triangle Park, NC 27711
Univ. of Florida Project Director: Paul D. Zwick
Department of Urban and Regional Planning
431 ARCH, University of Florida
Gainesville, FL 32611
Prepared for:
State of Florida
Department of Community Affairs
2740 Centerview Drive
Tallahassee, FL 32399
DCA Project Officer: Mohammad Madani
and
U.S. Environmental Protection Agency
Office of Research and Development
Washington, DC 20460

-------
_ 	 TECHNICAL REPORT DATA - 	 	..
.	 _	¦ (Plecse read !nuruetions on the reverse before completi
i. REPOR" NO. 12.
EPA-600/R-95-032 j
3, I
4. TITLE ANDSUBTITLE
Radon Generation and Transport in Aged Concrete
5, REPORT OATE
February 1995
6. PERFORMING ORGANIZATION CODE
7. AUTHORiS)
Vern C. Rogers, KirkK. Nielson, and
Rodger B. Holt
8. PERFORMING ORGANIZATION REPORT NO.
RAE-9226/1- 10R1
9. PERFORMING OFOANIZATION NAME AND ADDRESS
Rogers and Associates Engineering Corporation
P. C. Box 330
Salt Lake City, Utah 84110-0330
10. PROGRAM ELEMENT NO.
1WAIA^RmO933783-0l
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Air and Energy Engineering Research Laboratory
Research Triangle Park, NC 27711
13. type of report and period covered
Final; 10/92 - 11/93
14. SPONSORING AGENCY CODE
EPA/600/13
15. supplementary NOTES AEERL project officer is David C. Sanchez, Mail Drop 54, 919/
541-2979.
-16'A9STRACTrr-? • -	-	 	
----- 'v rePort gives results of a characterization of radon generation and trans-
port in Florida concretes sampled from 12- to 45-year-old residential slabs. It also
compares measurements from the old concrete samples to previous measurements
on newly poured Florida residential concretes. Radon generation in the aged slabs
was characterized in terms of concrete radium concentrations and radon emanation
coefficients, and radon transport was characterized by radon diffusion coefficients
and air permeability coefficients.^The radium concentrations and radon emanation
coefficients (0.11 +/- 0.04) ofJ:he~ old concretes in the study are about the same as
those measured previously for newly poured residential concrete samples. The
measured radon diffusion coefficients ranged from 1. 5 to 5. 5 x 10 to the minus 7th
power sq m/sec7>Cn the average, these values are about a factor of 2 higher than /
average values for new residential concretes. The measured air permeability coef-
ficients also average about a factor of 2 higher than those for new concretes, -r——
17. KEY WORDS AND DOCUMENT ANALYSIS
a. DESCRIPTORS
b.IDENTIFIERS/OPEN ENDEDTERMS
c. COSATI Field/Gioup
Pollution
Concretes
Radon
Transport Properties
Slabs
Residential Buildings
Pollution Control
Stationary Sources
Generation
13B
13	C
07R
14	G
13M
19. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
29
20. SECURITY CLASS /This page)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)	R~ 2

-------
NOTICE
This document has been reviewed in accordance with
U.S. Environmental Protection Agency policy and
approved for publication. Mention of trade names
or commercial products does not constitute endorse-
ment or recommendation for use.
ii

-------
ABSTRACT
This report presents the results of a study to charactenze radon generation and transport in
Florida concretes sampled from 12 to 45 year old residential slabs. This report also compares
the measurements from the old concrete samples to previous measurements on newly-poured
Florida residential concretes. Radon generation in the aged slabs was characterized in terms
of concrete radium concentrations and radon emanation coefficients, and radon transport was
characterized by radon diffusion coefficients and air permeability coefficients. The radium
concentrations and radon emanation coefficients (0.11 ± 0.04) of the old concretes in this
study are about the same as those measured previously for newly poured residential concrete
70*	7
samples. The measured radon diffusion coefficients ranged from 1.5x10" m^ s"* to 5.5x10"
m2 s"1. On the average, these values are about a factor of two higher than average values
for new residential concretes. The measured air permeability coefficients also average about
a factor of two higher than those for new concretes.
i i i

-------
TABLE OF CONTENTS
Section	Page No.
1	INTRODUCTION	1-1
1.1	Scope	1-1
1.2	Background	1-1
1.3	Report Contents	1-2
2	MEASUREMENTS ON NEW FLORIDA CONCRETES	2-1
2.1	Previous Measurements	2-1
2.2	Measurements on Other New Concrete Samples	2-3
3	MEASUREMENTS ON AGED FLORIDA CONCRETES	3-1
3.1	Sample Description	3-1
3.2	Measurement Methods	3-1
3.3	Measurement Results	3-4
4	DISCUSSION 4-1
4.1	Diffusion Coefficients	4-1
4.2	Air Permeability	4-4
4.3	Radium, Emanation Coefficient, Density, and
Porosity	4-4
5	CONCLUSIONS	5-1
APPENDIX A - METHODS FOR MEASURING THE EFFECTIVE
POROSITY OF CONCRETE	A-l
APPENDIX B - QUALITY ASSURANCE FOR CONCRETE ANALYSIS	B-l
REFERENCES	R-l
v

-------
LIST OF FIGURES
Figure No.
1-1
2-1
2-2
4-1
4-2
4-3
4-4
A-l
B-l
Pa ye No.
Average air permeability of concrete as a function of the
age of the concrete	1-3
Radon diffusion coefficients measured in new residential
concrete	2-2
Air permeability measurements of new residential concrete	2-4
Diffusion coefficients for aged concrete and regression
line for new concrete	4-2
Ratio of D to versus age	4-3
Air permeability of aged concrete as a function of concrete
density	4-5
Ratio of K to versus age	4-6
Apparatus for measuring the interconnected porosity of
concrete samples	A-2
Individual radium measurements on the IPL standard in
QC chart format	B-4
I
vi

-------
LIST OP TABLES
Table No.	Page No.
3-1	General description of aged concrete samples	3-2
3-2	Measurement results	3^
B-l	Comparison of duplicate radium assays to estimate
analytical precision	B-2
B-2	Analyses of standard reference material for 226Ra	B-3
B-3	Replicate analyses of a blank sample for 226Ra	B-5
B-4	Comparison of duplicate radon emanation measurements	B-6
B-5	Diffusion measurements on standard reference materials	B-7
vi i

-------
Section 1
INTRODUCTION
Diffusion can be a significant mechanism for radon entry into dwellings (Scott and Gordon 1978;
Loureiro et al. 1990). While the diffusive flux of radon through concrete floors is much smaller
than the advective or diffusive flux of radon through cracks in the floor, the predominance of the
intact floor area over the crack area may compensate for the difference in the fluxes. Thus, it
is desirable to examine the radon transport properties of concrete used in floor slabs to better
assess radon entry into dwellings.
1.1	SCOPE
This report characterizes the radon generating and transport properties of Florida concretes
sampled from the floor slabs of 12 to 45 year old homes. Radon generation is characterized in
terms of radium concentrations and radon emanation coefficients. Radon transport is
characterized in terms of radon diffusion coefficients and air permeability. Rogers and
Associates Engineering Corporation (RAE) conducted this work as part of the Florida Radon
Research Program (FRRP), sponsored by the Florida Department of Community Affairs. A
previous companion report focuses on newly-poured residential concretes (Rogers et al. 1994).
The same measurement procedures used for the previous work with new concrete samples were
used for characterizing the older concretes in this report.
1.2	BACKGROUND
Radon generation and transport data from scientific literature are reported by Rogers et al. (1994)
for the radium concentration (Ra), the radon emanation coefficient (E), the diffusion coefficient
(D), and the air permeability coefficient (K) for concretes. The literature also contains
references to the effects of aging on the strength-related properties of concrete. For example,
Wood (1991) presents the compressive strength, flexural strength, and modulus of elasticity for
concrete samples up to 20 years old. The compressive strength data increase with age and fit
a least squares quadratic expression with a correlation coefficient of r = 0.96. The data also
1-1

-------
indicate that the compressive strength reaches about 90 percent of its maximum value in about
5 to 10 years.
Only one specific study on the age effects of either D or K for concrete was found in the
literature. Martialay (1987) reported measurements of air permeability for six concrete slabs
made over a period of 20 years. The slabs were constructed with identical compositions. They
had a water-to-cement ratio of 0.37, which is much less than values for typical residential
concretes. Martialay's K values increased with the applied air pressure. The initial K values
ranged from 2.4xl0"14 m2 to 2.0xl0"u m2, with an average of 9.2xl0"14 m2 for the lowest pressure
tested, which was 3.9X104 Pa. The factor of eight spread in these values indicates the effects of
heterogeneity among the replicate samples. The average K values for the lowest pressure are
shown in Figure 1-1 as a function of time (t). Martialay reported that a quadratic expression fit
the data very well. The curve in Figure 1-1 is a least squares quadratic fit to Martialay's
averaged data. It is given by
K = 2.7xl0~14 + 1.3xl0"13 t - 2.9xl0"15 t2	t1"1)
The fitted equation has a correlation coefficient of r > 0.999. The data and curve indicate that
K reached its maximum value at about 20 years and that K increased to about 80 percent of its
maximum value at 12 years. Thus, most of the increase in K occurred in the first 10 to 12
years.
1.3 REPORT CONTENTS
Section 2 of this report summarizes the previous measurements on new concretes from Rogers
et al. (1994), plus the D measurements of an additional new residential concrete and a new
polymer concrete. This information is used in this report to provide a baseline for comparison
with the present measurements on older concrete samples. Section 3 describes the present
samples, the measurement techniques, and the results. The measured values for Ra, E, D, and
K from the aged samples are interpreted and discussed in Section 4. Section 5 presents the
conclusions of this study.
1-2

-------
Section 2
MEASUREMENTS ON NEW FLORIDA CONCRETES
2.1 PREVIOUS MEASUREMENTS
Measurements of radon generation and transport were made on 25 samples of new residential
concretes from Florida, as reported by Rogers et al. (1994). The Ra concentrations in the new
concrete samples ranged from 0.5 to 2.4 pCi g"\ with an average of 1.2 pCi g"1 and a standard
deviation, of 0.6 pCi g"1. The E values ranged from 0.02 to 0.17, with an average of 0.08 and
a standard deviation of 0.04. The measured dry densities of the new samples averaged 2.06xl03
kg m'3 with a standard deviation of 81 kg m"3, and ranged from 1.91X103 kg m"3 to 2.26xl03 kg
irr3. Similarly, the average total porosity of the samples was 0.21 ± 0.03. These data serve as
a useful baseline for estimating the effects of aging on Florida residential concretes.
The D values for these samples ranged from 2.1xl0'8 to 5.2xl0"7 m2 s"1, with an arithmetic
mean of 1.9xl0"7 m2 s"1 and a standard deviation of 1.4xl0"7 m2 s"1. The 95 percent confidence
in the mean was ± 5.8xl0"8 m2 s'1, assuming a Student's t distribution. The D values generally
decreased with increasing concrete density (d), and with increasing water-cement ratio. Figure
2-1 illustrates the variation of D with the concrete density. The line shown in Figure 2-1 is a
least squares fit to the measured data as reported by Rogers et al. (1994). The data used for the
fit also include six other literature values. The least-squares expression is
D = 0.084 exp(-0.0064d)
(2-1)
where
D
radon diffusion coefficient (m2 s"1)
d
concrete density (kg m"3).
The fitted line has a correlation coefficient of r = 0.73.
2-1

-------
Density (103 kg nr3)
RAE-105192
Figure 2-1. Radon diffusion coefficients measured ill new residential
concrete (from Rogers et al. 1994). The line is a least-
squares fit to the data.
2-2

-------
Air permeability measurements also were made on 21 of the new concrete samples. The data
from these measurements, shown in Figure 2-2, ranged from 8.0xl0"18 to 7.1xl0"16 m2, with a
geometric mean of 1.3x 10'16 m2, with a geometric standard deviation of 3.5. The K values also
generally increased with decreasing concrete densities. The line in Figure 2-2 is a least-squares
fit to the data. This least-squares expression is represented by
K = 2.2x10 "5 exp(-0.0126d)	<2"2>
This fitted line has a correlation coefficient of r = 0.80.
2.2 MEASUREMENTS ON OTHER NEW CONCRETE SAMPLES
One of the aged concrete samples was only about one year old and therefore was not included
in the aged concrete analysis. However, its D and K values were measured and were consistent
with the values for new concretes presented in Section 2.1. The sample, designated as sample
B, had a density of 2.10 g cm'3, and a porosity of 0.19. Its measured D value was 2.0xl0'7 m2
s'1 and its measured K value was 4.4xl0*17 m2.
RAE also tested a polymer concrete for comparison to the conventional floor-slab concrete
samples. The sample was supplied by Enviromates, Inc., located in Pensacola, Florida. The
Ra-226 content of the polymer concrete sample was less than 0.1 pCi g'\ and its D value was
less than 7.3x10"10 m2 s°. Thus, if it is economically practical, the polymer-based concrete could
serve as an effective barrier against the diffusion of radon into residences.
2-3

-------
Density (103 kg rrr3)
RAE-105194
Figure 2-2. Air permeability measurements of new residential
concrete (Rogers et al. 1994). The line is a least-
squares fit to the data.
2-4

-------
Section 3
MEASUREMENTS ON AGED FLORIDA CONCRETES
3.1	SAMPLE DESCRIPTION
Twenty-two concrete samples were obtained from residential floor slabs in Miami, Boca Raton,
Pompano Beach, and Delray Beach. The slab ages ranged from 12 to 45 years. Duplicate
samples were obtained at 11 separate locations. Each sample consisted of a 0.09-rn diameter
cylinder core-drilled through the slab (generally 0.10 m long). Table 3-1 gives the general
description of the samples and the sample densities. The samples from location B were about
one year old; consequendy, their results were not included in the analyses of results for the older
samples. The concrete densities ranged from 1.96X103 kg m'3 to 2.12x10s kg m"3. The
descriptions and estimates of the extent of their alkali-aggregate reaction, shown in the last two
columns of Table 3-1, are from visual observations of the samples. The extent of observable
alkali-aggregate reaction generally increased with age, and should also depend on the type of
aggregate.
3.2	MEASUREMENT METHODS
The measurements of D, K, Ra, and E were made with the same equipment and procedures used
by Rogers et al. (1994). The porosity of the concrete samples was determined both from the
measured dry density, as described by Rogers et al. (1994), and from an air intrusion method.
The density method gives an estimate of the total porosity (p,), and the intrusion method gives
an estimate of the interconnected porosity (pj). The interconnected porosity is more closely
related to the transport of radon through concrete.
To prepare the samples for the diffusion measurements, each cylinder was epoxied into standard
diffusion sample holders (Williamson and Finkel 1991) using an epoxy that has negligibly low
radon diffusion and permeability coefficients. The air permeability measurements were also
made in the same diffusion sample holder to minimize disruptive handling of the samples.
3-1

-------
TABLE 3-1. GENERAL DESCRIPTION OF AGED CONCRETE SAMPLES

Sample
Location
Description
Age
(yr)
Dry Density
(103 kg m"3)
Hardness of
Aggregate
Carbonate
Reactivity
Aggregate
A
mortar grey, angular and subrounded aggregate, white
with little light brown, Dmax=1.9 cm, well-sorted low
porous limestone, contains 50 percent aggregate
12
2.07
Hard
None
B
mortar dark grey, angular aggregate, white and some
light brown, Dmax= 1.9cm, well sorted low porous
limestone, contains 55 percent aggregate
1
2.10
Hard
None
C
mortar white, uniformly sand cement mixed, angular
and subrounded aggregate, white, Dmax=1.3 cm, well
sorted medium porous limestone, contains 45 percent
aggregate, cement may include lime
25
1.99
Medium
Moderate
D
mortar grey, angular and subrounded aggregate, white
and some light brown, Dmax=1.9 cm, nonuniformly-
sorted low porous limestone included crystal and friable
types, contains 55 percent aggregate
18
2.01
Most hard, a
few soft
Mild
E
mortar white, angular and subrounded aggregate, white
and some light brown, Dmax=1.9 cm, soft, fine and
well-sorted low porous limestone, contains 45 percent
aggregate, cement may include lime
20
2.07
Soft
Severe
F
mortar white, angular and subrounded aggregate, white
and some light brown, Dmax=1.3 cm, soft, fine and well
sorted low porous limestone, contains 45 percent
aggregate, cement may include lime
14
2.09 Most hard, a
few soft
(Continued)
Mild

-------
TABLE 3-1. CONTINUED

Sample
Location
Description
Age
(yr)
Dry Density
(103 kg m"3)
Hardness of
Aggregate
Carbonate
Reactivity
Aggregate
G
mortar grey, angular and subrounded aggregate, white
and some light brown, Dmax=1.9 cm, well-sorted
medium porous limestone, contains 45 percent
aggregate
45
1.96
Medium
Moderate
H
mortar white, angular and subrounded aggregate,
DmaX=l-9 cm, well sorted low porous limestone with
some dark grey and light brown conglomerate, contains
50 percent aggregate, cement may include lime
20
2.03
Medium
Moderate
I
mortar white, angular aggregate, white, some grey and
light brown, Dmax=1.9 cm, well-sorted low porous
limestone, contains 45 percent aggregate, cement may
include lime
15
2.12
Medium
Moderate
J
mortar grey, uniformly mixed sand and cement, angular
and subrounded aggregate, Dmax=1.9 cm, well-sorted
medium porous limestone, contains 50 percent
aggregate
40
2.09
Medium
Moderate
K
mortar light grey, uniformly mixed sand and cement,
angular and subrounded aggregate, white, Dmax=1.6 cm,
well-sorted limestone, medium porosity, contained 50
percent aggregate
21
1.98
Medium
Moderate
L
mortar grey, angular and subrounded aggregate, white
and some light brown, Dmax=1.0 cm, soft, well-sorted
medium porous limestone, contains 45 percent
aggregate
36
2.01
Soft
Severe

-------
The air intrusion method was used to measure the interconnected porosity with the concrete
samples in the same diffusion sample holders. The sample holder was sealed closed on one end
and evacuated using a vacuum pump. Air was then introduced back into the sample, and the
volume of air needed to re-establish equilibrium with the ambient pressure was measured with
a bubble-burette system. Appendix A provides a more detailed description of this procedure.
The Ra concentration measurements were made with the sealed-can, gamma counting method.
The emanation coefficients were determined by extracting the free radon from the sealed can into
a Lucas cell, and counting to determine the free radon-222 concentration.
3.3 MEASUREMENT RESULTS
Table 3-2 presents the results of the D, K, Ra, E, p(, and p, measurements on the samples of the
aged concretes.
TABLE 3-2. MEASUREMENT RESULTS
* #
No.
Age (yr)
D(m2 s"1)
K(ro*)
Ra(pCi g'1)
E
Pi
P.
A-l
12
3.5xl0"7
2.2xl0"16
1.7
0.085
**
0.20
A-2
12
1.5xl0"7
2.6x10"


**
0.20
C-l
25
2.3xl07
1.5xlfr,s
0.9
0.13
0.25
0.23
C-2
25
3.4xl0'7
1.5x1015


0.25
0.24
D-l
18
4.2xl0'7
1.4xl0',s
2.1
0.03
0.18
0.23
D-2
18
3.9x107
1.4xl0"16


0.17
0.22
E-l
20
1.8xl0"7
5.7x10"
0.9
0.19
0.12
0.20
E-2
20
2.4xl0'7
8.0xl0n


0.12
0.20
F-l
14
2.0xl0'7
7.5xlfr17
1.5
0.11
0.15
0.19
F-2
14
2.1xl0"7
7.5xl0",?


0.16
0.19
G-l
45
2.3xl0"7
3.9xl0"16
1.0
0.06
0.2
0.24
G-2
45
2.5xl0'7
6.4xl0",fi


0.24
0.24
(Continued)
3-4

-------
TABLE 3-2. CONTINUED
* *
No.
Age (yr)
D(m2 s'1)
K(m2)
Ra(pCi g l)
E
Pi
Pi
H-l
20
4.9xl0"7
5.3xl016
0.6
0.13
0.24
0.22
H-2
20
3.7xl0"7
8.9xl0"16


0.24
0.22
1-1
15
1.8xl0"7
l.lxlO'16
1.7
0.14
0.18
0.21
1-2
15
2.4xl0~7
5.3xl0"17
1.8
0.12
0.17
0.16
J-l
40
3.1xl0"7
4.7xl0'15
0.5
0.12
0.19
0.19
J-2
40
3.5xl0"7
3.4xl0"16
0.3
0.17
0.2
0.20
K-l
21
4.8xl0"7
4.4xl0"16
1.3
0.14
0.22
0.24
K-2
21
5.5xl0'7
4.4xl0'16


0.22
0.24
L-l
36
3.2xl0'7
3.7xl0"16
2.2
0.11
0.21
0.22
L-2
36
2.8xl0'7
2.9xl016


0.21
0.23
* Ra & E Values generally obtained for 1 sample per pair
**Not measured
The D values ranged from 1.5xl0"7 m2 s"1 to 5.5xl0'7 m2 s1, with an arithmetic mean of 3. lxlO"7
m2 s'1 and a standard deviation of l.lxl0"7 m2 s'1. The 95 percent confidence interval about the
mean was 2.6xl0'7 to 3.6xl0"7 m2 s"1.
The K values ranged from 5.3xl0"17 m2 to 4.7xl0"15 m2, with a geometric mean of 2.7xl0'16 m2
and a geometric standard deviation of 3.1. The 95 percent confidence interval about the mean
was 1.6xl0'16 to 4.4xl0'15 m2.
The Ra concentrations for the aged concrete samples ranged from 0.3 pCi g'1 to 2.2 pCi g"1, with
an arithmetic mean of 1.3 pCi g"1 and a standard deviation of 0.6 pCi.g"1. The E values ranged
from 0.03 to 0.19, with an arithmetic mean of 0.11 and a standard deviation of 0.04.
Except for samples C and H, the p; values were all generally less than or equal to the pt values,
within measurement uncertainties. The p, values exceeded the pt values by about 8 percent for
3-5

-------
samples C and H. The p; values ranged from 0.12 to 0.25, with an arithmetic mean of 0.19, and
the pt values ranged from 0.16 to 0.24 with a mean of 0.21. Thus, the ratio of the average pi
to p, was 0.88. The relative uncertainties associated with the duplicate measurements were 21
percent for the D data, 37 percent for K, 15 percent for the radium concentrations, and 30
percent for the radon emanation coefficients. Section 4 provides an interpretation and discussion
of these data, and Appendix B contains a detailed discussion of their quality assurance analyses
and results.
3-6

-------
Section 4
DISCUSSION
In this section the data from the aged concrete measurements are analyzed and compared to the
new concrete data summarized in Section 2.
4.1 DIFFUSION COEFFICIENTS
The D values for the aged concretes average about a factor of 1.6 greater than for the new
concretes. This difference in the means is significant at the 95 percent level of confidence.
However, since D varies with density, this difference may be attributed to differences in concrete
density. The densities and total porosities of the new and aged concrete samples are equivalent
within the measured variations. Their means differ by only a few percent. Thus, different
density values should not account for the differences in the D values between the new and aged
concrete samples. This fact is further illustrated in Figure 4-1, which presents the aged concrete
D values as a function of density. The line in Figure 4-1 is the new concrete correlation, given
in Equation 2-1. About two-thirds of the data points for the aged concrete are above the
correlation line for the Dcor of new concrete. This result suggests that the D for concrete may
increase slightly with age, independent of its density dependence.
In order to remove the density dependence from the aged concrete D values, the aged-concrete
D values were divided by the estimate of each D value using the new-concrete correlation
(Equation 2-1). The resulting ratio is the relative variation of the measured D values for the aged
concrete from the new concrete correlation value. Biased deviations of this ratio from unity
should then correlate with the age of the concrete if D increases with age, independent of density.
The D/Dcor ratio is plotted in Figure 4-2 as a function of the age of the concrete. The average
value of D/DCOI is 1.9. However, the data show no general trend with age. A linear
least-squares fit to the data, also shown in Figure 4-2, has a correlation coefficient of only r =
0.23. Therefore, on the average, the D value for residential concretes more than 10 years old
is about a factor of two higher than the average D value for new concrete in Florida, when
4-1

-------
Concrete Density (103 kg m-3)
RAE • 10S196
Figure 4-1. Diffusion coefficients for aged concrete (dots) and
regression line for new concrete (Rogers et al. 1994).
4-2

-------
corrected for density effects, but the D value for any one aged concrete sample is within the
range of variability of D for new concrete.
The lack of a trend in D/D:or with time for periods greater than 10 years generally is consistent
with the trend in the literature for the change in K and the change in compressive strength with
age, as discussed in Section 1. However, other unmeasured or unknown parameters may also
influence D for aged concrete. As stated in Section 1, the alkali-aggregate reaction may occur
over time in concrete. While this may contribute to an increase in D, there is no significant
evidence in the present data to confirm this.
4.2 AIR PERMEABILITY
The variation of K with age is similar to the variation with D. On the average, the K value for
the aged concrete is about 2.2 times greater than the K value for new concrete, and the range
extends about six times higher than the range of K for new concrete. Both the aged and the new
concrete K values are significantly less than the K values reported by Martialay.
Figure 4-3 presents the K values for the aged concrete as a function of density. The figure also
shows the correlation line of K versus density for the new concrete measurements. The effect
of density on K can be reduced by again dividing the aged concrete values by the corresponding
correlation estimate. The resulting ratios, shown versus concrete age in Figure 4-4, show no
general trend with age. This is consistent with the results from Martialay, who reported that K
for concrete reaches about 80 percent of its maximum value by about 12 years of age.
Therefore, the decrease in K with density suggested in Figure 4-3 is a density trend that is not
otherwise associated with concrete age.
4-3

-------
4.3 RADIUM, EMANATION COEFFICIENT, DENSITY, AND POROSITY
The average radium concentrations, emanation coefficients, densities, and total porosities are the
same for the aged Florida concretes as for the new concretes, within the measurement
uncertainties. These variables also do not show any significant trends with age.
4-4

-------
CM
E
2.0	2.1
Concrete Density (103 kg rrr3)
RAE • 105197
Figure 4-3. Air permeability of aged concrete as a function of
concrete density. The line is the correlation from
the new concrete K values (Rogers et al. 1994).
4-5

-------
Section 5
CONCLUSIONS
Radon diffusion and air permeability coefficients have been measured for Florida residential concretes
ranging from 12 to 45 years old. In general, the D values for the aged concrete average about 1.6 times
the values for the newly poured Florida concretes, but are within the range of D values for the new
concretes. The aged K values also average about a factor of two higher than for the new concretes, but
the range of K values increases by over a factor of 6 for the aged concretes. The Ra-226 concentrations
and radon emanation coefficients for the aged concretes are about the same as for the new concretes.
5-1

-------
Appendix A
METHODS FOR MEASURING THE EFFECTIVE POROSITY OF CONCRETE
This appendix contains the laboratory procedures used to measure the interconnected porosity of concrete
samples.
A.l EQUIPMENT
The following equipment is required to perform the interconnected porosity measurements:
1.	Vacuum pump, 0.7 CFM,* 5-micron, 1/8-HP (Model DD20, Precision Scientific
Group, Chicago, 111., or equivalent).
2.	Graduated burette, 100-cc (min) with two bottom vents as shown in Figure A-l.
3.	Metal plate for connecting the top edge of the diffusion tube with the clear tubing
(see Figure A-l). The plate must have a center hole and a hose barb for
connecting the tubing.
4.	Tubing, 1/4-inch O.D., 1/8-inch I.D., clear PVC, vinyl or equivalent.
5.	Epoxy for mounting the concrete sample in the diffusion tube. DURO Master
Mend 90-minute epoxy or equivalent.
6.	Vacuum bag sealant tape. Richmond Aircraft Products RS200.
A.2 PROCEDURES
A nondestructive test has been developed to measure the interconnected porosity of concrete samples.
Figure A-l illustrates the test apparatus. To perform this test, the concrete sample is mounted in a
diffusion tube using an impermeable epoxy. The sample is then sealed on one edge and evacuated using
a vacuum pump. The sample is then allowed to re-equilibrate, and the volume of air necessary to
re-establish equilibrium is measured using a bubble in a graduated burette. The detailed procedure is as
follows:
(*) 1 CFM = 0.00047 m3/s; 1 micron = l^m; 1HP = 746W; and 1 in. = 0.025m
A-l

-------
Clear Tubing
Vacuum Pump
Diffusion Tube
Containing Concrete
Sample
Graduated-
Burette
Bottom Vent	>•
Rubber Bulb
RAE - 105140
Figure A-l. Apparatus for measuring the interconnected porosity
of concrete samples.
A-2

-------
Appendix B
QUALITY ASSURANCE FOR CONCRETE ANALYSIS
The quality assurance of all analyses is determined by three data quality parameters: precision, accuracy,
and completeness. The following sections present the summary statistics of the analytical results in terms
of these data quality parameters for radium assays, radon emanation, radon diffusion, and permeability
coefficients. Completeness of the laboratory tests is estimated from the total number of measurements
compared to the total number of samples available for testing. According to this basis, the completeness
percentage for all analyses was 100 percent.
B.l RADIUM CONCENTRATION MEASUREMENTS
There are no numerical data quality indicators for radium concentration measurements in concrete due
to the lack of prior testing and of radium levels and variability in concrete. However, comparisons
between the data quality indicators for soils (Nielson and Rogers, 1991) and concrete illustrate the
precision of the sealed-can, gamma counting method. The precision of the radium determinations is
defined as the relative measurement uncertainty.
All the uncertainties in the radium determinations are less than ±20 percent at >2 pCi g'1. As expected,
numerous measurements are associated with higher uncertainties, but these are all in a radium range low
enough to approach the detection limit.
A second estimate of the precision of the radium determinations is based on comparing the results of
duplicate assays for a selected number of samples. Three duplicates were counted in the radium and
emanation determinations. TableB-1 summarizes the results for radium concentrations. The final column
lists the differences between the duplicate assay results and those given in the report. The average
absolute difference is -0.2 pCi g'1. The relative standard deviation between the duplicate measurements
is 14.6 percent. The relative standard deviation is computer as (Rogers, et aJ., 1994).
RSD^ = ^2n I (x, - Xj)2 / I (x, + x,)	(B"1)
where
B-l

-------
RSDdU[) = relative standard deviation among duplicates
x, = first observation
x2 = second observation
n = number of pairs being compared.
TABLE B-l. COMPARISON OF DUPLICATE RADIUM ASSAYS TO ESTIMATE
ANALYTICAL PRECISION
Duplicate Radium	Original Radium	Difference
Sample No.	(pCi g1)	(pCi g1)	(pCi g'1)
A-l 1.6	1.7	-0.1
C-l 0.8	0.9	-0.1
D-l 1.6	2.1	-0.5
Average absolute difference (pCi g'1)	0.2
Relative standard deviation (all detected)	14.6 percent
The agreement of similar analyses with standard reference material demonstrates the accuracy of the
radium concentration measurements. An Isotope Products Laboratory (IPL) reference material was spiked
into several powdered quartz sand aliquots to prepare the standard at 1014 + 16 pCi g"1. The material
was sealed in a can similar to those used for the concrete samples and was analyzed regularly at the
beginning and end of each batch of samples. Table B-2 presents the results of these analyses.
B-2

-------
REFERENCES
Loureiro, C.O., Abriola, L.M., Martin, J.E., and Sextro, R.G., 1990, "Three-Dimensional Simulation
of Radon Transport into Houses with Basements Under Constant Negative Pressure,"
Environmental Science and Technology 24: 1338-1348.
Martialay, R., 1987, "Concrete Air Permeability Age Effects on Concrete," In Concrete Durability, ed.
J.M. Scanlan, ACI-SP-100 VI, American Concrete Institute, Detroit, MI.
N'ielson, K.K., and Rogers, V.C., 1991, "Development of a Prototype Map of the Soil Radon Potentials
in Alachua County Florida," Rogers and Associates Engineering Corporation report, RAE-9137/3-
1, Salt Lake City, UT, October.
Rogers, V.C., Nielson, K.K., Lehto, M.A., and Holt, R.B., 1994, "Radon Generation and Transport
Through Concrete Foundations," EPA-600/R-94-175, September.
Scott, A.G. and G.W.S. Gordon, 1978, "Radon Diffusion Through Concrete," Health Physics Soc.
Conf., June.
Williamson, A.D., and Finkel, J.M., 1991, "Standard Measurement Protocols, Florida Radon Research
Program," EPA-600/8-91-212 (NTIS PB92-115294), November.
Wood, S.L., 1991, "Evaluation of the Long-Term Properties of Concrete," American Concrete Institute
Materials Journal 88: 630-643.
R-l

-------