low cost techniques for improving the surface …docs.trb.org/prp/13-1573.pdfkevern and sparks 1 low...

Kevern and Sparks 1

Low Cost Techniques for Improving the Surface Durability of Pervious Concrete

John T. Kevern

Assistant Professor of Civil Engineering

University of Missouri-Kansas City

370H Flarsheim Hall

5100 Rockhill Rd.

Kansas City, MO 64110-2499

Office: 816-235-5977 Fax: 816-235-1260

E-mail: [email protected]

Joseph Dan Sparks

Testing Project Manager

INTEC

1910 Merrill Creek Parkway

Everett, WA 98203

Phone: 425-293-0340

Fax: 425-293-0341

Email: [email protected]

Abstract 198 (250)

Text 3761

Tables 6(250) = 1500

Figures 5(250) = 1250

Total 6511 (7500 max)

November 15, 2012

TRB 2013 Annual Meeting Paper revised from original submittal.

Kevern and Sparks 2

ABSTRACT

This paper presents the results of a laboratory study to improve the durability of pervious

concrete using readily available and low cost techniques. Surface raveling of pervious concrete is

a concern for long term use and remediation techniques have not previously been investigated. In

this study a high void content pervious concrete was cured in worst case hot and dry conditions

to produce poor surface durability. Pervious concrete mixtures included a traditional binder and

one which included a super absorbent polymer for internal curing. Various remediation methods

including overlaying with fresh pervious concrete, latex paint, epoxy, and a surface densifier

were applied to the pavement before abrasion testing using the ASTM C944 rotary cutter

method. Results showed that the internally-cured mixture had superior durability to the

traditional mixture. Of the surface applied techniques, epoxy provided the best improvement in

durability followed by latex paint and the densifier. Material analysis showed that modifying a

mixture to include super absorbent polymer was the lowest cost option. On a poorly performing

pervious pavement, latex paint or a thin overlay both had low material costs. The summary

concludes that low-cost methods are effective techniques to improve the surface durability of

pervious concrete.


Kevern and Sparks 3

INTRODUCTION

Pervious concrete has become more popular in recent years primarily due to its environmental

benefits. When compared to traditional pavements, pervious concrete pavements provide

superior stormwater runoff control, reductions in potential for hydroplaning, and reduced glare

among other benefits (1). Until recently pervious concrete has been utilized only for parking

areas, primarily on private projects. Various state environmental departments and the

Environmental Protection Agency (EPA) have been considering including roadways in required

stormwater management areas. The limited available space within typical roadway right of ways

does not accommodate many traditional stormwater best management practices (BMPs) such is

detention/retention areas. Pervious concrete shoulders are an attractive option for near-roadway

stormwater management because no additional land area is required. The current national interest

in pervious concrete shoulders has resulted in the first pervious concrete shoulders installed on a

50,000 average annual daily traffic (AADT) highway in St. Louis, MO, pervious concrete

shoulders under construction on several state-owned roads in Nevada, and a NCHRP project

investigation design options for permeable shoulders with stone reservoirs (25/25: Task 82).

Although much progress has been made towards turning pervious concrete into a widely

used pavement material, durability concerns are still present. One of the most prevalent

durability distresses presently encountered when using pervious concrete is raveling. Raveling is

surface abrasion caused by the separation of individual cement-coated aggregate pieces from

pavement surface (2, 3). Pervious concrete is characterized by minimal fine aggregate and a near

zero slump (1). The open structure of pervious concrete requires specific construction techniques

to ensure adequate permeability and strength performance. As with any concrete, proper curing

is the most important step towards achieving the optimum durability of the pavement. Previous

studies have shown that covering pervious concrete with plastic sheeting immediately after

placement for a minimum of 7 days, is the best means of ensuring proper curing and reducing

abrasion (4).

Many pervious concretes experience some raveling in the early weeks after removal of

curing plastic, especially around sawed joints (5). However, severe raveling typically results

from poor curing practices. The main causes for surface raveling are improper curing, low

strength mixtures from poor compaction, and heavy early loading (2). Figure 1 shows a pervious

concrete where poor workability resulted in a high void content of 40% and isolated locations of

excessive raveling when poorly cured. The opposing sections with good durability were cured

under plastic. The darker sections had poor durability and excessive raveling caused when the

fresh paste on the surface dried when not covered with plastic. The only solution presently

available when severe raveling occurs is to remove and reinstall the pervious concrete pavement.

Remediation options for less severe raveling include continued vacuuming over time to remove

loose particles. Removal and replacement or continuous vacuuming are undesirable from time,

financial, and sustainability perspectives.


Kevern and Sparks 4

FIGURE 1 Excessive Raveling of Poor Durability Surface

PROJECT SIGNIFICANCE AND OBJECTIVE

When poor surface durability results in excessive raveling of pervious concrete the remediation

option is removal and replacement. The objective was to determine what the effect of pervious

concrete mixture, curing conditions, and surface applied remediation techniques provided the

best reduction in surface raveling. The pervious concrete mixtures investigated included a

conventional low water-to-cement mixture and one internally cured with a super absorbent

polymer. The curing conditions included optimum curing in lime water, curing under plastic, and

curing in a hot and dry environmental chamber. The surface-applied techniques included

densifier, epoxy, cement slurry, latex paint, and thin overlay. Results indicated that all techniques

provided significant improvement in surface raveling with the internally cured mixture having

the best raveling resistance.

MATERIALS AND METHODS

Mixture Proportions

A typical pervious concrete design void content of 20%-25% produces acceptable strength and

surface durability; however impacts from long haul times, hot weather, slow placement from

difficult site geometry, improper compaction, or admixture ineffectiveness can cause the in-place

void content to be significantly higher than the design, as shown in Figure 1. For this study a

typical mixture was selected and cylinder samples were placed at three densities as shown in

Figure 2. All pervious concrete mixtures follow a linear compaction density relationship which

allows prediction of any in-place void content using the unit weight measurement (6). For this

Good Durability

Poor Durability


Kevern and Sparks 5

study the highest void content (37%) was selected to ensure excessive raveling and the ability to

measure improvements to surface durability. The selected mixture would have unacceptable

performance related to raveling in the field and be subject to removal and replacement.

FIGURE 2 Compaction density relationship of the selected mixture

Mixture proportions for the two pervious concretes tested are shown in Table 1. One was

a typical pervious concrete control (PC) mixture and the second pervious concrete mixture (SAP)

contained a super absorbent polymer used for internal curing. The SAP consisted of crushed

crystalline partial sodium salts of cross-linked polypromancic acids rated at 2000 times

absorption in plain water. The selected SAP has previously been shown to improve the properties

of pervious concrete and reduce moisture loss (7). Additional water was added to satisfy SAP

absorption which raised the dosed water-to-cement ratio from 0.34 to 0.40. Void content was

maintained by reducing the overall cement paste content. Other admixtures included a vinsol

resin air entraining agent, a polycarboxylate water reducer, and a hydration stabilizing

admixture. The extra water present in the SAP mixture also allows a reduction in required

admixtures as shown in Table 1 for the water reducer and hydration stabilizer. The coarse

aggregate was ASTM C33 size 8 limestone (8) with a specific gravity of 2.59 and absorption of

1.8%. The fine aggregate was Missouri river sand conforming to ASTM C33 with specific

gravity of 2.62 and absorption of 0.4%. ASTM C150 cement marketed as Type I/II was utilized

(9).


Kevern and Sparks 6

TABLE 1 Mixture Proportions

Mixing and Testing Methods

Concrete was mixed according to ASTM C192 (10). Fresh concrete was preweighed for all

specimens before placing to ensure all samples had the same unit weight and voids. The high

void content of 37% did not require any compaction techniques and represented the loosest state

possible for the selected mixtures. Triplicate 100mm by 200 mm (4 in by 8in) cylinders were

cast for unit weight and void content testing determined according to ASTM C1754 (11). In

addition to the cylinders, both the PC and SAP mixtures were used to cast slab samples for

curing method investigation on abrasion. Fresh unit weight of the slab samples was also

controlled and the same as the cylinders. Slab samples had surface area of 750 cm2 (120 in

2) and

were 50mm (2 in.) thick. Samples were cured for 7 days 1) in a standard lime-water bath per

ASTM C192 (10), 2) under plastic sheeting commonly used for pervious concrete, and 3) cured

in a climate controlled cabinet at 38°C (100°F) and 32% relative humidity.

ASTM has a standard for potential raveling of pervious concrete ASTM C1747 (3). The

test abrades cast specimens in the LA abrasion apparatus and is suitable for comparing overall

durability between mixtures, but is not appropriate for measuring changes to surface-applied

materials. Rotary cutter surface abrasion was selected for its ability to physically measure

differences between surface treatments. Testing was performed according to ASTM C944 (12)

which uses a weighted rotary cutter to induce surface wear. Figure 3 shows the rotary cutter

device which is used to apply a 98N (22lbf) force during a 2 minute cycle. Pervious concrete

specimen weight was recorded before and after testing. A stiff-bristled broom and shop-type

vacuum were used to remove loose particles from the surface pores before weighing.

PC SAP

kg/m3 (lb/yd

3) kg/m

3 (lb/yd

3)

Cement 280(470) 260(430)

Coarse Agg. 1050(1770) 1050(1770)

Fine Agg. 80(130) 80(130)

Water 90(160) 100(170)

Air Entraining Agent

HR Water Reducer 3 mL/kg (4 oz/cwt) 2 mL/kg (2 oz/cwt)

Hydration Stabilizer 4 mL/kg (6 oz/cwt) 2 mL/kg (3oz/cwt)

SAP

Material

1.3 mL/kg (2 oz/cwt)

1.3 g/kg of cement (2 oz/cwt)


Kevern and Sparks 7

FIGURE 3 Surface Abrasion Testing Using ASTM C944, a) Rotary Cutter Head

Surface Treatments Table 2 shows the curing regimes and surface treatments performed on the two mixtures. The

curing regime was selected to represent a worst-case scenario for pervious concrete placement in

addition to the high void content. All specimens for investigating the surface treatments were

first cured in an environmental cabinet at 38°C (100°F) and 32% relative humidity for 7 days

before surface treatments were applied.

Previous research has shown that the use of recycled latex paint in concrete mixtures

improves surface durability (13). Additionally, research has shown that the use of latex polymers

in pervious concrete improves the resistance to abrasion when compared to other pervious

concrete mixtures (14). The use of latex admixtures has also been recommended as a means of

improving freeze-thaw durability of pervious concrete (15). Research shows that the use of

colloidal silica as a densifier in concrete mixtures improves the strength of the concrete (16). In

order to test the beneficial use of densifier as a repair for raveling of pervious concrete, colloidal

silica was applied directly to the surface of a pervious concrete so that the silica reacted with the

calcium hydroxide present in the concrete to create additional calcium silicate hydroxide gel

(CSH). The additional CSH present in the concrete surface was expected to improve surface

durability. Previous research has shown that the use of epoxy in concrete mixtures can improve

the compressive strength and freeze-thaw durability of the concrete (17). Pervious concrete used

as an overlay on traditional, non-pervious pavements is known to reduce both the risk for

hydroplaning and noise pollution (18).

A high solids latex paint was applied at 7400 m2/m

3 (300 ft

2/gal.). The paint was thinned

with equal parts water before application to prevent clogging of the surface pores. Colloidal

silica densifier was applied at 9800 m2/m

3 (400 ft

2/gal.). The colloidal silica densifier had a

consistency similar to water and was applied at twice the dosage as recommended for a flat,

impervious application. A cementitious slurry was created using 1:3 Portland cement to latex

admixture ratio. The latex admixture is marketed as a mortar bonding agent and contains 7%

solids. The cement slurry was applied at a rate of 580 m2/m

3 (177 ft

2/ ft

3). The application rate

was selected by visually balancing a sufficient surface coating of the slurry while maintaining

surface voids. A low viscosity marine grade cycloaliphatic clear epoxy was used at 4900 m2/m

3

(200 ft2/gal.). The low epoxy viscosity allowed coating of the surface particles without reducing

surface porosity. After abrasion testing on a set of pervious concrete control samples cured in the

environmental cabinet (PC-C), the SAP mixture was applied as an overlay at a thickness of 12.5

mm (1/2 in.) directly on the abraded surface. The existing surface was cleaned and dried before


Kevern and Sparks 8

overlaying. The paint, densifier, and epoxy were allowed to cure at ambient conditions for 7 days

after application. The slurry and overlay samples were cured under plastic for 7 days.

TABLE 2 Mixtures and Surface Treatments

RESULTS AND DISCUSSION

Testing on hardened cylinders verified that both mixtures achieved an average of 37% voids at a

unit weight of 1600 kg/m3 (100 pcf). The only treatment that caused a noticeable visual decrease

in surface voids, and presumably permeability, was the cementitious slurry. All other treatments

only provided a thin coating to the surface particles. Figure 4 shows the visual results of abrasion

testing on the sample surfaces. On samples with higher mass loss values the abrasion resulted in

loss of entire aggregate particles and aggregate wearing. Figure 4a shows the control mixture

before testing and Figure 4b shows the control after testing where a high mass loss was observed

from aggregate raveling. Figure 4c shows the SAP mixture before testing; the picture is of fresh

concrete. Figure 4d shows the SAP mixture after testing where all of the mass loss was aggregate

wear. Figure 4e shows a latex paint sample after testing and Figure 4f shows an epoxy sample

after testing. The other treatments not shown in Figure 4 had no distinguishable visual difference

from the control before or after testing.

Results of the curing regime trials are shown in Table 3 and represent an average of six

trials. Previous studies using ASTM C944 to determine abrasion on pervious concrete have

produced similar variability (4). Surface abrasion testing on pervious concrete has a coefficient

of variation (COV) higher than observed for other tests such as compressive strength. Because of

the high variability, six tests were required for statistical analysis to show differences between

groups. Statistical significance was determined using an analysis of variance (ANOVA) with

α=0.05. In both mixtures the hot and dry conditions in the environmental cabinet produced

higher abrasion from surface raveling (PC-C, SAP-C). There was statistically no difference in

abrasion for either mixture between samples cured in the lime-water tank (PC, SAP) and those

cured under plastic for 7-days (PC-P, SAP-P). The SAP mixture had significantly less raveling

than the control mixture for all conditions, but similar standard deviation which resulted in SAP

samples having higher COV. Raveling of the control mixture increased by 110% when cured in

the environmental cabinet, however the SAP mixture only increased by 41%. The included SAP

has been previously shown to reduce moisture loss from pervious concrete specimens, providing

increased cement hydration and strength (7).

Specimen ID Surface Treatment Curing Technique

PC - Lime Water Bath

PC-P - Under Plastic

PC-C - 32°C, 32% RH

SAP - Lime Water Bath

SAP-P - Under Plastic

SAP-C - 32°C, 32% RH

PC-Paint Latex Paint Ambient

PC-Dense Silicate Densifier Ambient

PC-Slurry Polymer-modified cement slurry Under Plastic

PC-Epoxy Marine Epoxy Ambient

PC-Over SAP Overlay Under Plastic


Kevern and Sparks 9

FIGURE 4 Abrasion Test Results (a) Control Before Testing, (b) Control After Testing, (c)

SAP Before Testing, (d) SAP After Testing, (e) Latex Paint After Testing, and (f) Epoxy

After Testing

a b

a

c

a

d

a

e

a

f

a


Kevern and Sparks 10

TABLE 3 Curing Regime Results

The abrasion results for the various surface treatments are shown in Figure 5 and

represent an average of six trials. The error bars represent one standard deviation. All surface

treatments provided a significant reduction in raveling when compared to the control samples

cured in the environmental cabinet (PC-C), which had the greatest mass loss. The epoxy coating

(PC-Epoxy), slurry (PC-Slurry), and thin overlay (PC-Over) had similar performance. The thin

overlay had similar performance to the full-depth specimen cured under plastic (SAP-P).

FIGURE 5 Abrasion Results

A full statistical comparison of results is shown in Table 4. Where two treatments

intersect an “O” represents no difference between groups and “X” shows a statistically

significant difference. There was no difference in durability for either mixture cured in lime

water or cured under plastic. Generally there were three levels of performance with no difference

between the high durability samples of SAP, SAP-P, PC-Slurry, PC-Epoxy, and PC-Over. The

moderate durability specimens of PC, PC-P, SAP-C, PC-Paint, and PC-Dense had statistically

less raveling than the cabinet-cured control, but more raveling than the higher durability samples.

All treatments had statistically less raveling than the control mixture cured in the environmental

cabinet.

Specimen Avg. Mass Loss (g) Std. Dev. (g) COV (%)

PC 10.5 1.2 11.6

PC-P 10.4 2.9 27.7

PC-C 22.0 7.3 33.1

SAP 6.8 2.1 30.7

SAP-P 6.3 1.7 27.2

SAP-C 9.6 2.2 22.7



TABLE 4 Statistical Comparison of Results

Remediation costs were determined for a 929 m2 (10,000 sf) pervious concrete parking

lot 150mm (6 inches) thick. Presented costs only represent material costs determined using

prevailing local material and admixture costs and do not incorporate labor for the repairs or

material delivery costs. The prevailing costs used for the concrete materials are shown in

TABLE 5. The materials only remediation costs are shown in TABLE 6. The pervious concrete

control mixture cost $60/m3 ($46/cy), while the SAP mixture cost $63/m

3 ($48/cy). The SAP

mixture line represents the cost difference between using the SAP mixture and the control

mixture for the project initially. The observed ease of remediation from least to most intensive

was: SAP mixture, densifier, paint, epoxy, SAP overlay, and slurry. If the control mixture was

changed to the SAP mixture no additional labor would be required. The paint and epoxy both

had low viscosity and flowed into the surface pores with relative ease. The slurry also had low

viscosity from the water-to-cement ratio of 3, but had to be carefully applied to prevent clogging

surface pores. Based only on material cost and durability, the thin SAP overlay was a superior

remediation technique, but would require significantly more labor than an option like paint or

densifier. The additional height created by an overlay may not be allowable at certain locations.

Those locations might necessitate milling the pavement before overlaying or option for a

surface-applied strategy. While pervious concrete has been successfully overlaid on conventional

concrete, the thin 12.5 mm (1/2 in.) overlay used in this study has not evaluated under traffic.

Epoxy was superior for surface-applied strategies, although latex paint provided a 51% reduction

in abrasion and had a lower cost.

TABLE 5 Prevailing material costs

PC PC-P PC-C SAP SAP-P SAP-C PC-Paint PC-Dense PC-Slurry PC-Epoxy PC-Over

PC - O X X X O O O X X X

PC-P O - X O X O O O X X X

PC-C X X - X X X X X X X X

SAP X O X - O X X X O O O

SAP-P X X X O - X X X O O O

SAP-C O O X X X - O X X X X

PC-Paint O O X X X O - O X X X

PC-Dense O O X X X X X - X X X

PC-Slurry X X X O O X X X - O O

PC-Epoxy X X X O O X X X O - O

PC-Over X X X O O X X X O O -

Treatment

Material Cost

Portland Cement $91/mton ($100/ton)

Limestone $15.4/mton ($17/ton)

Sand $10.9/mton ($12/ton)

Water $0.4/10,000l ($1.5/10,000 gal)

HRWR $4.5/l ($17/gal)

AEA $1.00/l ($3.75/gal)

HS $4.23/l ($16/gal)

SAP $28.6/kg ($13/lb)



TABLE 6 Remediation Costs

CONCLUSIONS

Surface raveling is the material related distress most common for pervious concrete. Loose

particles on the surface are unattractive, create a difficult walking surface, contribute to clogging,

cause further abrasion when driven over, and cause vehicle and windshield damage. Current

options for poor surface durability are continued vacuuming to remove the loose particles or

complete removal and replacement. This study investigated available low cost techniques to

reduce surface abrasion. Pervious concrete was created with high voids (37%) and was

subsequently cured in worst-case hot and dry conditions. Abrasion was measured before and

after applying treatments to the surface. From this study the following conclusions can be drawn:

The mixture containing the super absorbent polymer for internal curing had less abrasion

in all curing conditions than the control mixture.

No difference in abrasion resistance was observed between mixtures cured in a lime

water tank or cured under plastic for 7-days.

All remediation techniques tested resulted in improved surface durability.

Latex paint and epoxy were both effective at improving surface abrasion resistance.

The thin overlay had similar surface abrasion resistance to properly cured samples of the

same mixture.

Results from surface abrasion laboratory testing indicate that low-cost methods are

promising methods to improve the surface durability of pervious concrete.

ACKNOWLEDGEMENTS

The authors would like to thank Geiger Ready Mixed Concrete for providing the

aggregate for the study, Lafarge North America for the cement, BASF construction chemicals for

the admixtures, Protecrete for the densifier, and ProCure USA for the super absorbent polymer.

Findings are those of the authors and do not represent the opinion or position of the material

suppliers.

REFERENCES

1. American Concrete Institute (ACI) Pervious Concrete. “522-R10: ACI 522 Committee

Report,” Farmington Hills, MI: ACI, 2010.

2. Kevern, J.T. (2011). “Operation and Maintenance of Pervious Concrete Pavements,” 90th

Annual Transportation Research Board Annual Meeting, CD-ROM, Transportation

Research Board of the National Academies, Washington D.C.

Material Application Rate Cost Amount Required Additional Cost

SAP Mixture 1.3g/kg (2 oz/cwt) $28.5/kg ($0.81/oz) 45kg (100 lb) $310

SAP Overlay 12.5mm (1/2 in.) $63/m3 ($48/cy) 11.8 m

3 (15.4 cy) $731

Paint 7400 m2/m

3 (300 ft

2/gal.) $10.5/l ($40/gal) 125l (33 gal) $1,333

Epoxy 4900 m2/m

3 (200 ft

2/gal.) $16.1/l ($61/gal) 189l (50 gal) $3,033

Slurry 580 m2/m

3 (177 ft

2/ ft

3) $3091/m

3 ($2349/cy) 47m

3 (61 cy) $4,995

Densifier 9800 m2/m

3 (400 ft

2/gal.) $14.8/l ($56/gal) 380l (100 gal) $5,600



3. ASTM Standard C-1747, “Standard Test Method for Determining Potential Resistance to

Degradation of Pervious Concrete by Impact and Abrasion,” Annual Book of ASTM

Standards, West Conshohocken, PA, Vol. 4, No. 2, 2011.

4. Kevern, J. T., Schaefer, V. R., and Wang, K. “The Effect of Curing Regime on Pervious

Concrete Abrasion Resistance,” Journal of Testing and Evaluation. Vol. 37, No. 4,

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Association, Silver Spring, Maryland, 2004.

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Concrete Quality Assurance Program,” ACI Concrete International magazine, March

2010.

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8. ASTM, Standard C-33, “Standard Specification for Concrete Aggregates,” Annual Book

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International, 2003.

9. ASTM Standard C-150, “Standard Specification for Portland Cement,” Annual Book of

ASTM Standards, West Conshohocken, PA, Vol. 4, No. 1, 2012.

10. ASTM Standard C-192, “Standard Practice for Making and Curing Concrete Test

Specimens in the Laboratory,” Annual Book of ASTM Standards, West Conshohocken,

PA, Vol. 4, No. 2, 2003.

11. ASTM Standard C-1754, “Standard Test Method for Density and Void Content of

Hardened Pervious Concrete,” Annual Book of ASTM Standards, West Conshohocken,

PA, Vol. 4, No. 2, 2012.

12. ASTM Standard C944, “Standard Test Method for Abrasion Resistance of Concrete or

Mortar Surfaces by the Rotary-Cutter Method,” Annual Book of ASTM Standards, West

Conshohocken, PA, Vol. 4, No. 2, 1999.

13. Nehdi, M. and Sumner, J. “Recycling Waste Latex Paint in Concrete.” Cement and

Concrete Research, Vol. 33, No. 6, pp. 857-863, 2003.

14. Kevern, J.T., Schaefer, V.R., and Wang, K. “Mix Design Development and Performance

Evaluation of Pervious Concrete for Overlay Applications,” ACI Materials Journal, July-

August, Title No. 108-M47, Vol. 108, No. 4, 2011.

15. Kevern, J.T., Wang, K., and Schaefer, V. R. “Pervious Concrete in Severe Exposures:

Development of pollution-reducing pavement for northern cities”, ACI Concrete

International magazine, pg 43-49, July, 2008.

16. Bigley, C. and Greenwood, P. “Using Silica to Control Bleed and Segregation in Self-

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17. El-Hawary, M. and Abdul-Jaleel, A. “Durability Assessment of Epoxy Modified

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18. Schaefer, V.R., Kevern, J.T., Izevbekhai, B., Wang, K., Cutler, H., and Wiegand, P.

“Construction and Performance of the Pervious Concrete Overlay at MnROAD,”

Transportation Research Record: Journal of the Transportation Research Board (TRB),



No. 2164, Transportation Research Board of the National Academies, Washington D.C.,

pp. 82-88, DOI 10.3141/2164-11, 2010.


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