Journal of ASTM International, Vol. 5, No. 2Paper ID JAI101320

Available online at www.astm.org

J. T. Kevern,1 V. R. Schaefer,1 K. Wang,1 and M. T. Suleiman1

Pervious Concrete Mixture Proportions for ImprovedFreeze-Thaw Durability

ABSTRACT: Recent stormwater management regulations from the Environmental Protection Agency�EPA� and greater emphasis on sustainable development has increased interest in pervious pavement asa method for reducing stormwater runoff and improving stormwater quality. Pervious concrete is one ofseveral pervious pavement systems that can be used to reduce stormwater runoff and treat stormwater onsite. Pervious concrete systems have been used and are being proposed for all parts of the United States,including northern climates where severe freezing and thawing can occur. The purpose of the research isto develop pervious concrete mixtures that have sufficient porosity for stormwater infiltration along withdesirable porosity, strength, and freeze-thaw durability. In this research, concrete mixtures were developedwith single-sized river gravel aggregate �4.75 mm� and constant binder contents, together with high rangewater reducer. River sand was used as a replacement for up to 7 % coarse aggregate. Two different typesof polypropylene fibers �a shorter fibrillated variable-length and a longer fibrillated single-length� wereincorporated at several addition rates from 0 to 0.1 % by volume of concrete. The engineering properties ofthe aggregate were evaluated along with the porosity, permeability, strength, and freeze-thaw durability ofselected concrete mixtures. The results indicate that the use of sand and fibers provided beneficial effectson pervious concrete properties, including increased strength, maintained or improved permeability, andenhanced freeze-thaw resistance.

KEYWORDS: pervious concrete, freeze-thaw durability, freeze-thaw resistance, stormwatermanagement

Introduction

Pervious pavements are mainly used to allow stormwater to percolate through the voids of the pavement,which reduces the amount of runoff water. In the United States, pervious pavements are used in sidewalks,parking lots, and low traffic density areas �1�. Unlike other pavement systems, the pervious layer needs notonly to possess the required strength to support the applied loads and freeze-thaw durability to resistenvironmental conditions, but is required to have adequate permeability for the design storm of a specificregion. There are many examples of pervious concrete installations in severe freeze-thaw environments�2–4�. The general recommendation for pervious concrete systems in freeze-thaw environments is to installa layer of aggregate base below the pervious concrete pavement to store stormwater in order to avoidsaturation of the pervious concrete during freeze-thaw events �5�. There are no documented cases offreeze-thaw failures of existing installations when these recommendations are followed. However, there isstill some potential for saturation of the pervious concrete layer and it is therefore prudent to designpervious concrete mixtures to be freeze-thaw resistant in case the pervious concrete does become saturatedduring freeze-thaw events.

This paper summarizes the results of research performed at the National Concrete Pavement Technol-ogy Center �CP Tech Center� located at Iowa State University, to develop a freeze-thaw resistant portlandcement pervious concrete �PCPC� that has the required compressive strength and adequate permeability,utilizing sand and polypropylene fibers. The engineering properties of the aggregate and the porosity,permeability, strength, and freeze-thaw durability of pervious concrete mixtures were evaluated and aresummarized herein.

Manuscript received June 21, 2007; accepted for publication January 7, 2008; published online February 2008.1 Ph.D. Student, Professor of Civil Engineering, Associate Professor of Civil Engineering, and Lecturer, respectively, Iowa State

University Department of Civil, Construction, and Environmental, Engineering, Ames, Iowa 50011, e-mail: kevernj@iastate.edu

Copyright © 2008 by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959.

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Background

Advantages of Using Pervious Concrete

To meet the requirements of the Federal Water Pollution Control and Flood Disaster Protection Acts of theUnited States Government, Franklin Institute Research Laboratories used porous asphalt pavement sys-tems in the early 1970s �6�. More recently the amendments of the Clean Water Act, which requirereduction in the quantity of stormwater runoff and initial water quality treatment, increased the interest indeveloping new porous pavement materials and enhancing the properties of currently available materials�7�.

Pervious concrete is one of a number of methods employed to reduce the volume of direct water runofffrom pavements and to enhance the quality of stormwater �8�. Other reported advantages of perviousconcrete include: reducing noise, improving skid resistance, reducing cost, and preserving native ecosys-tems, while minimizing the heat island effect in large cities �5�.

Typical Mixture Proportions and Material Properties

The Environmental Protection Agency �EPA� �9� reported that approximately 75 % of current porouspavement systems have failed, due to a variety of mechanisms including poor design and constructionpractices. The National Ready Mixed Association �NRMCA� �3� reported the mixture proportions of tenprojects where pervious concrete was used in the United States. These mixture proportions have water tocement ratios ranging from 0.27 to 0.43 and contain no fine aggregate �i.e., sand�. The cement contentsranged from 177 kg �300 pcy� to 355 kg �600 pcy� per cubic metre along with coarse aggregate amountsfrom 1422 kg �2400 pcy� to 1600 kg �2700 pcy� per cubic metre. The single-sized coarse aggregatereported in the literature ranges from 2.54 cm to 4.75 mm �1 in. to No. 4 sieve�. Only one of the reportedmixtures was installed in a hard wet-freeze environment with an average temperature below freezing for90 days.

Ferguson �5� and the NRMCA �3� reported properties of pervious concrete used in the United States,which includes porosity ranging from 14 to 31 %, permeability coefficients ranging from 0.03 to 0.6 cm /s.�85 to 1700 ft /day�, and 28-day compressive strengths ranging from 6.7 to 17.5 MPa �972 to 2540 psi�,with most mixtures having strength less than 13.8 MPa �2000 psi�. In general, pervious concrete compres-sive strength of 13.8 MPa �2000 psi�, or perhaps even lower, is adequate for most parking and light streetapplications. However, in some cases it may be desirable to achieve higher compressive strength.

Failure Mechanisms of Pervious Concrete

When subjected to loading, pervious concrete made of single-sized aggregate transfers stress through theaggregate to the cement paste. Generally, the strength of coarse aggregate is high when compared with thatof the paste and the interface between the aggregate and the paste �10�. To improve the strength ofpervious concrete, the strength of the paste, and the interface between the aggregate and the paste needs tobe improved �11�. These improvements can be achieved by using lower water-to-binder ratios �w/b�,smaller-sized aggregates, and proper admixtures, as well as by altering the mixing process.

Experimental Work

Materials

Type II cement marketed as a Type I/II cement, with a Blaine fineness of 384 m2 /kg and a specific gravityof 3.15, was used in all mixtures. A type of single-sized river gravel coarse aggregate was used. Thesingle-sized river gravel had 100 % of the material passing a 9.5-mm sieve �3 /8 in.� and being retained ona 4.75-mm sieve �No. 4�. The dry rodded unit weight was 15.61 kN /m3 of the aggregate, porosity of38.5 %, specific gravity of 2.62, the abrasion obtained using a Micro Deval device of 14.4 %, andabsorption of 1.7 %.

River sand was used to replace up to 7 % of the coarse aggregate. The sand had a fineness modulus of

2.90, with 90 % passing a 2.36-mm sieve �No. 8�. It had a specific gravity of 2.62 and absorption of 1.1 %.

KEVERN ET AL. ON CONCRETE MIXTURE PROPORTIONS 3

Polypropylene fibers �Propex� were incorporated into the pervious concrete proportions and their materialproperties are also provided in Table 1. An air entraining agent �AEA� and high-range water reducer�HRWR� were used in all of the pervious concrete mixtures. The specific gravity and pH were 1.01 and 10for the AEA �Master Builders Everair plus� and 1.07 and 7.8 for the HRWR �Master Builders Glenium3400 NV�, respectively.

Mixture Proportions

The mixture proportions consisted of seven groups, each group included one mixture with sand and onemixture without sand, for a total of 14 mixtures. Fibers were added to the baseline mixtures at varyingquantities and the proportions are summarized in Table 2. The manufacturer’s recommended fiber dosageis 0.9 kg /m3 �1.5 lb /yd3� of concrete, which represents 0.1 % by volume �12�.

Specimen Preparation

Initial trial batches were mixed using a 0.01 m3 �0.5 ft3� open pan mixer for evaluation of porosity,permeability, unit weight, and seven-day compressive strength. Selected mixtures were mixed again usinga larger 0.04 m3 �1.5 ft3� rotating-drum mixer in order to determine strength development with time,splitting tensile strength, and freeze-thaw resistance, in addition to the previously mentioned characteris-tics. For the mixtures included in this study, data reported for those mixtures containing no fibers and fibersadded at 0.3 and 0.9 kg /m3 were samples placed from the larger mixer �Mixtures 1-3 and 6 and 7�.Mixtures containing fibers added at 0.6 kg /m3 were mixed using the smaller mixer �Mixtures 4 and 5�.

Since initially the concrete strength was hindered by poor bonding characteristics between the cementpaste and the smooth, yet strong river gravel aggregate, two different sample preparation procedures wereused to increase the strength of the pervious concrete. The first procedure was the one traditionally used forconcrete where aggregate, water, and admixtures were combined before the addition of the cement. Usingthis procedure for Mixture 1, it was observed that the samples failed at the interface between the cementpaste and the aggregate. The bond between the cement paste and the aggregate was increased by dry

TABLE 1—Properties of fibers used in preparing the pervious concrete mixtures.

Fiber Name Fibermesh 300 Fibercast 500

Fiber Type fibrillated fibrillated

Specific Gravity 0.91 0.91

Length 12.7 mm, 19.1 mm 50 mmDenier 360 360

Surface Area 20.65 cm2 /g 188.45 cm2 /g

TABLE 2—Mixture proportions used in this study.

Water Fibers

MixtureID

Cement�kg /m3�

Gravel�kg /m3�

Sand�kg /m3� �w/c� �kg /m3� Type �kg /m3�

1 343 1602 … 0.27 93.0 … …1S 343 1498 104 0.27 93.0 … …2 343 1602 … 0.27 93.0 FM300 0.3

2S 343 1498 104 0.27 93.0 FM300 0.3

3 343 1602 … 0.27 99.5 FC500 0.3

3S 343 1498 104 0.27 99.5 FC500 0.3

4 343 1602 … 0.27 93.0 FM300 0.6

4S 343 1498 104 0.27 93.0 FM300 0.6

5 343 1602 … 0.27 99.5 FC500 0.6

5S 343 1498 104 0.27 99.5 FC500 0.6

6 343 1602 … 0.27 93.0 FM300 0.9

6S 343 1498 104 0.27 93.0 FM300 0.9

7 343 1602 … 0.27 99.5 FC500 0.9

7S 343 1498 104 0.27 99.5 FC500 0.9

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mixing a small amount of cement ��5 % by mass� with the aggregate until completely coated �about oneminute�. Next, the remaining cement and water �with HRWR� were added. Finally, the concrete was mixedfor three minutes, allowed to rest for three minutes, and then mixed for an additional two minutes beforecasting. Samples that employed this modified mixing procedure failed more often through the aggregate,which increased the seven-day compressive strength of the mixture. All specimens were placed by lightlyrodding 25 times in three layers to ensure uniform compaction in each lift. In addition to rodding, thesamples were placed on a vibration table for five seconds after rodding each layer to ensure the layersproperly meshed together, since the rodding did not penetrate the underlying layer. This procedure wasdesigned to uniformly compact the specimens without consolidation, thereby creating uniform densityacross the samples. The samples were demolded after 24 hours, placed in a fog room at 98 % relativehumidity, and cured according to ASTM Standard C192-02, “Standard Practice for Making and CuringConcrete Test Specimens in the Laboratory,” �13�. Before compression testing, the cylinders were cappedusing a sulfur capping compound following ASTM Standard C617-98, “Standard Practice for CappingCylindrical Concrete Specimens,” �14�. When specimens were tested with unbounded caps containing aneoprene rubber pad with a durometer hardness of 50, according to ASTM Standard C1231, “StandardPractice for Use of Unbonded Caps in Determination of Compressive Strength of Hardened ConcreteCylinders,” �15�, the failure occurred at the ends of the sample, whereas sulfur capped samples failedthrough the center in a similar manner to standard concrete compression failure.

Cylinders of 100 mm �4 in.� in diameter and 200 cm �8 in.� in length were used for both compressionand tensile strength tests. Cylinders of 75 mm �3 in.� by 150 mm �6 in.� were used to perform the porosityanalysis and cylinders of 75 mm �3 in.� in diameter and length were used to measure the permeability.Beams with a cross section of 75 mm �3 in.� by 100 mm �4 in.� and a length of 400 mm �16 in.� wereused for freeze-thaw testing.

Testing Procedures

Workability of the fresh concrete was determined by a standard slump cone test using ASTM StandardC143-00, “Standard Test Method for Slump of Hydraulic-Cement Concrete,” �16�. Although, slump is notapplicable to pervious concrete as it often has zero slump or collapses without providing any useful data.Compressive strength tests were performed according to ASTM Standard C39-01, “Standard Test Methodfor Compressive Strength of Cylindrical Concrete Specimens,” �17� and splitting tensile tests were per-formed using ASTM Standard C496-96, “Standard Test Method for Splitting Tensile Strength of Cylin-drical Concrete Specimens,” �18�.

The porosity of the pervious concrete was determined by taking the difference in weight between asample oven dry and submerged under water and using Eq 1 �19� and the procedure developed at theUniversity of South Carolina �20�.

P = �1 − �W2 − W1

�wVol��100�%� �1�

where:

P�total porosity, %W1�weight under water, kgW2�oven dry weight, kgVol�volume of sample, cm3

�w�density of water @21°C, kg /cm3

The permeability of mixtures was determined using a falling head permeability test apparatus �Fig. 1�.A flexible sealing gum was used around the top perimeter of a sample to prevent water leakage along thesides of a sample. The samples were then confined in a latex membrane and sealed in a rubber sleevewhich was surrounded by adjustable hose clamps. The test was performed using several water heightswhich represented values that a pavement may experience. The average coefficient of permeability �k� was

determined using Eq 2, which follows Darcy’s law and assumes laminar flow.

KEVERN ET AL. ON CONCRETE MIXTURE PROPORTIONS 5

k =aL

AtLN�h1

h2� �2�

where:

k�coefficient of permeability, cm/sa�cross sectional area of the standpipe, cm2

L�length of sample, cmA�cross-sectional area of specimen, cm2

t�time in seconds from h1 to h2

h1�initial water level, cmh2�final water level, cm

Mixtures with adequate porosity and seven-day compressive strength were further investigated by theirstrength development with time and freeze-thaw resistance using ASTM Standard C666-97, “Standard TestMethod for Resistance of Concrete to Rapid Freezing and Thawing,” procedure A �21�, in which sampleswere frozen and thawed in the saturated condition. One of the assumptions in this test is constant massloss, which allows direct comparison of the initial fundamental frequency with that of the sample as itdeteriorates. Since pervious concrete specimens have significantly more mass loss than standard concrete,the rate of deterioration of the dynamic modulus is often over estimated. There was also difficulty obtain-ing consistent, reproducible sonometer readings. Consequently, a less sensitive approach was employed todetermine freeze-thaw durability using the aggregate soundness requirements from ASTM Standard C33-97, “Standard Specification for Concrete Aggregates,” �22�. When using a magnesium sulfate solution theallowable aggregate mass loss is 18 %, and 12 % is allowed for sodium sulfate solutions. By combiningthe two values, the test was completed when a sample reached 300 cycles or 15 % mass loss. Mass losswas tested every 20 to 30 cycles. The results of other mixtures and more details are summarized inSchaefer et al. �23� and Kevern �24�.

Results and Discussion

Engineering properties of all pervious concrete mixtures included in this study are presented in Table 3.The data values in the table represent the average of three test specimens. The slump of all mixtures rangedbetween 0.00 and 1.27 cm �0 to 1 /2 in.�. The porosities ranged from 15.0 to 33.1 %. The seven-daycompressive strength ranged from 9.9 to 22.7 MPa �1440 to 3290 psi�.

A statistical analysis was performed using SAS and the General Linear Model �GLM� procedure witha Type III sum of squares error to determine which variables have a significant effect on the concrete

FIG. 1—Permeameter used to test pervious concrete samples.

properties. An alpha value of 0.05 was used to identify statistical significance. Table 4 shows the results of

6 JOURNAL OF ASTM INTERNATIONAL

the GLM analysis. The statistical analysis was performed as a series of one-way ANOVA trials testing thesignificance of each of the individual variables and interactions on the specific concrete property. Theanalyzed mixture proportion variables are identified as yes or no �y/n� as either present or not present inthe analysis. The effect of fiber addition was considered for no addition compared individually with eachof the three addition levels.

The Effect of Sand on Material Properties

The effect of using sand in pervious concrete mixtures was investigated by using 7 % sand, �by weight� asreplacement for coarse aggregate. Figure 2 shows the average effect of sand on material properties for allthe mixtures discussed in this paper. The addition of sand had a statistically significant effect on all thevariables.

Among the mixtures, Mixture 1S �baseline mixture with sand and no fibers� had the highest seven-daycompressive strength, although it did not occur at the lowest porosity. When sand was added to thebaseline Mixture 1 �Mixture 1S�, the seven-day compressive strength increased from 14.5 MPa �2100 psi�to 22.7 MPa �3290 psi�, with a corresponding 7 % decrease in porosity. The average seven-day compres-sive strength for the mixtures not containing sand was 14.4 MPa �2090 psi�, while the strength was17.0 MPa �2460 psi� for the mixtures containing sand. The average tensile strength increased from2.05 MPa �295 psi� to 2.55 MPa �370 psi�, an increase of 24 %, when sand was added. Consequently, theporosity was reduced by an average of 4.2 % with the inclusion of sand. The addition of sand also reduced

TABLE 3—Engineering properties of pervious concrete mixtures.

Compressive StrengthTensile

Strength

MixtureID

Porosity�%�

Unitweight

�kg /m3�7 day�MPa�

21 day�MPa�

28 day�MPa�

28 day�MPa�

k�cm/s�

1 25.3 1,882 14.5 16.4 17.3 2.00 0.25

1S 18.3 2,046 22.7 23.3 25.2 2.95 0.10

2 18.9 1,929 17.8 20.3 21.4 2.40 0.27

2S 16.0 1,992 16.7 18.7 20.3 2.60 0.01

3 21.7 1,916 15.4 17.1 17.8 1.30 0.02

3S 15.0 2,029 17.4 19.3 19.5 2.20 0.01

4 32.1 1,769 9.9 … … … 1.18

4S 28.9 1,832 11.7 … … … 0.57

5 33.1 1,759 10.1 … … … 1.03

5S 27.3 1,867 12.8 … … … 0.49

6 22.1 1,913 17.9 19.1 21.4 2.45 0.68

6S 19.0 1,963 20.6 22.2 26.5 2.40 0.30

7 20.4 1,888 15.3 17.7 17.7 2.05 0.20

7S 19.4 1,935 16.9 16.9 17.0 2.45 0.02

1000 psi=6.90 MPa1 in. /h=7.1�10−4 cm /s.

TABLE 4—Results of GLM statistical analysis.

Mixture Proportion Variables

Fiber Type Fiber Addition Rate

ConcreteProperties

Sand�y/n� FM300 �y/n� FC500 �y/n� FM300 or FC 500 0-0.3 0-0.6 0-0.9

Unit Weight S S S N N S S

Voids S N N N S S S

Permeability S S N S N S N

7-day compressivestrength

S S S N S S N

Note: S�A statistically significant factor.

Note: N�Not a statistically significant factor.

KEVERN ET AL. ON CONCRETE MIXTURE PROPORTIONS 7

the average permeability of the mixtures from 0.52 to 0.21 cm /s �747 to 298 in. /h� a decrease of 60 %,which is still higher than the maximum required permeability to drain the maximum 25-year/24-hourstorm across the United States �i.e., 30.5 cm �12-inch�� �25�.

The Effect of Fibers on Material Properties

The effect of fibers on pervious concrete behavior was investigated by the incorporation of two differentfibers �FM300 and FC500� at three addition rates. Figures 3 and 4 show the effects of fiber addition onconcrete material properties for the 0.0, 0.3, and 0.9 kg /m3 addition rates. The fiber addition rate produceda significant effect above the 0.3 kg /m3 rate; the fiber type did not affect the air voids or compressivestrength.

When the shorter fibers �FM300� were added to the baseline Mixture 1 �no sand, no fibers�, theporosity of Mixture 2 and Mixture 6 decreased by 6.4 and 3.2 %, and 28-day compressive strengthincreased 24 % for both addition rates used �Fig. 3�a��. Even though the porosity decreased, the perme-ability increased by 8 % at the 0.3 kg /m3 �0.5 pcy� addition rate and by 172 % for the 0.9 kg /m3

�1.5 pcy� addition rate. Splitting tensile strength also increased by an average of 23 %, from 1979 kPa�287 psi� to 2434 kPa �353 psi�.

When the longer fibers �FC500� were added to Mixture 1, the porosity decreased by 3.6 and 4.9 %,Mixture 3 and Mixture 7, respectively. A decrease in porosity was observed along with a slight increase instrength of 6.2 % at the 0.3 kg /m3 �0.5 pcy� addition rate and of 5.5 % at the 0.9 kg /m3 �1.5 pcy�

FIG. 2—Effect of sand on material properties.

FIG. 3—Effect of fibers on material properties (mixtures without sand) (a) FM300 fibers (b) FC500 fibers.

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addition rate at seven-days �Fig. 3�b��. Although, when the longer fibers were added to Mixture 1, thepermeability decreased from the baseline mixture �Mixture 3 and Mixture 7�. There was not a clear effecton tensile strength from addition of the longer fibers, with a 34 % decrease for Mixture 3 and a 4 %increase for Mixture 7.

When the shorter fibers �FM300� were added to the baseline mixture containing sand �Mixture 1S�, thetrend is different from that of the fibers added in the mixtures with no sand �Fig. 4�. The porosity decreased2.3 % when 0.3 kg /m3 �0.5 pcy� of the fibers were added �Mixture 2S�, but it increased 0.7 % when0.9 kg /m3 �1.5 pcy� of the fibers were added �Mixture 6S�. Compressive strength trends followed that ofthe porosity with a decrease at the lower addition rate and an increase at the higher addition rate. Perme-ability also showed a decrease for Mixture 2S of 90 % and an increase for Mixture 6S of 200 %. Tensilestrength was decreased for both addition rates compared to the baseline mixture containing sand.

The results of the mixtures with long fibers �FC500� and sand were similar to that of the short fibers.The porosity decreased 3.3 % at the lower addition rate �Mixture 3S� and increased 1.1 % at the higherrate �Mixture 7S�. The 28-day compressive strength decreased for both addition rates as well as perme-ability and splitting tensile strength.

Material Property Relationships

The relationships between unit weight and porosity are presented in Fig. 5, between compressive strength,permeability, and porosity in Fig. 6, and between splitting tensile strength and compressive strength inFig. 7.

As expected, the unit weight of the pervious concrete decreased linearly as the porosity increased. Forall reported mixtures, the seven-day compressive strength linearly reduced as a function of porosity.However, the permeability exponentially increased as a function of porosity, especially above 25 % voids.Figure 6 illustrates that mixtures with a porosity between 15 and 20 % achieve both the adequate seven-day strength ��20 MPa �2900 psi�� and acceptable permeability ��0.01 cm /s �14 in. /h��, which is indi-

FIG. 4—Effect of fibers on material properties (mixtures containing sand).

FIG. 5—Relationship between unit weight and porosity.

KEVERN ET AL. ON CONCRETE MIXTURE PROPORTIONS 9

cated as the limits of the target region. The observed relationships between the material properties andporosity are consistent with those presented in the American Concrete Institute �ACI� pervious concrete522 committee report �26�.

It has been observed that mixtures which lie in the target region have a unit weight of about 1900 to2000 kg /m3 �119 to 125 pcf� for this particular aggregate type. This suggests that unit weight may beconsidered as a key factor that controls quality of pervious concrete.

The relationship between splitting tensile strength and compressive strength, at 28 days, is slightlyhigher than the 10 % ratio between tensile strength and compressive strength normally assumed forcommercially available, conventional density concrete. Other reported values for pervious concrete sug-gest that the splitting tensile strength values represent between 65 and 90 % of the three point tensilestrength �23�.

Freeze-Thaw Durability

The freeze-thaw durability as a function of mass loss is shown in Fig. 8 and indicates:1. Use of sand replacement significantly increased the freeze-thaw resistance of the pervious con-

crete. When compared with Mixture 1 �no sand�, Mixture 1S �with sand� had better freeze-thawresistance.

2. Addition of fiber �0.03 or 0.1 % by volume� in the concrete without sand also improved theconcrete freeze-thaw resistance. However, the degree of the improvement was not as high as thatprovided by use of sand. Compared with Mixture 1, which had more than 15 % weight loss atapproximately 145 freeze-thaw cycles, Mixtures 2 and 6 had more than 15 % weight loss atapproximately 200 and 175 freeze-thaw cycles, respectively.

3. Use of sand and fiber together greatly enhanced freeze-thaw resistance of the concrete, especiallythe freeze-thaw resistance at the early-age cycles. Compared with Mixture 1 �without sand and

FIG. 6—Relationship between seven-day compressive strength, permeability, and porosity.

FIG. 7—Relationship between splitting tensile strength and compressive strength.

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fiber� and Mixture 1S �with sand but no fiber�, Mixture 6S �with sand and 0.9 % FM300 fiber� hadimproved freeze-thaw resistance at the early freeze-thaw cycling �up to 200 freeze-thaw cycles�although its freeze-thaw resistance was reduced later �lower than that of Mixture 1S at 300 cycles�.

Figure 9 shows beams of Mixtures 1, 1S, and 2 before and after freeze-thaw cycling. As observed, thebeam made with Mixture 1 �no sand and no fiber� had 19 % weight loss at 156 cycles. The beam madewith Mixture 2 �no sand but 0.3 % fiber� had 15 % mass loss at 210 cycles. The samples containing fibersmaintained a more uniform shape after failure than those samples that did not contain fibers. For allsamples, the initial mass loss was through splitting of the aggregate, beginning this process after only fewcycles. As the test progressed towards failure, the mechanism of mass loss was paste deterioration causingthe raveling of entire pieces of aggregate. However, the beam made with Mixture 1S �with sand but nofiber� had only 2 % weight loss at 300 cycles, primarily from the splitting of a few less durable aggregateparticles located on the beam surface. Further research is necessary to better understand the frost damagemechanism in pervious concrete.

Conclusions

This study found that pervious concrete mixture proportions can be optimized for strength, permeability,

FIG. 9—Effect of sand on the pervious concrete freeze-thaw resistance (a) Mixture 1, (b) Mixture 1S, (c)Mixture 2.

FIG. 8—Freeze-thaw results.

porosity and freeze-thaw resistance with sand, or sand and fibers. Well designed pervious concrete mix-

KEVERN ET AL. ON CONCRETE MIXTURE PROPORTIONS 11

tures can meet strength, permeability, and freeze-thaw durability requirements for cold weather climates.Mixture 1S which included 4.75-mm river gravel, 7 % sand, and air entrainment, showed the best freeze-thaw durability with 2 % mass loss after 300 cycles. The addition of fibers further improved the freeze-thaw durability of the mixtures.

From this study the following conclusions can be made:1. Use of sand in a pervious concrete mixture significantly increased strength although it slightly

decreased the voids and permeability of the concrete.2. Use of the short fibers improved the strength, permeability, and freeze-thaw durability of the

mixtures which did not contain additional sand. The long fibers improved the strength and freeze-thaw durability of the mixtures which did not contain additional sand but did not improve perme-ability.

3. A target unit weight can be used to design mixtures for the best combination of strength, perme-ability, and freeze-thaw durability.

4. Pervious concrete mixtures that possess optimized strength, permeability, porosity and freeze-thawresistance can be developed by incorporating sand and fibers.

Acknowledgments

This study was sponsored by the National Concrete Pavement Technology Center at Iowa State Universitythrough the Sponsored Research Fund by Iowa Department of Transportation, the Iowa Concrete PavingAssociation, and the Iowa Ready Mixed Concrete Association. Various admixtures were donated by Mas-ter Builders. The cement was donated by LaFarge and the aggregate by Hallett Materials. The fibers weredonated by Propex. The opinions, findings and conclusions presented here are those of the authors and donot necessarily reflect those of the research sponsors.

References

�1� Tennis, P. D., Leming, M. L., and Akers, D. J., “Pervious Concrete Pavements,” EB302, PortlandCement Association, Skokie, IL, and National Ready Mixed Concrete Association, Silver Spring,MD, 2004.

�2� Florida Concrete and Products Association Inc., Portland Cement Pervious Pavement Manual,Florida Concrete and Products Association, Orlando, FL, 2000.

�3� National Ready Mixed Concrete Association �NRMCA�, Freeze-Thaw Resistance of PerviousConcrete, NRMCA, Silver Springs, MD, 2004.

�4� Delatte, N., Miller, D., and Mrkajic, M., “Portland Cement Pervious Concrete: Field PerformanceInvestigation on Parking Lot and Roadway Pavements,” Final Report of the RMC Research andEducation Foundation, Silver Springs, MD, 2007. http://www.rmc-foundation.org/newsite/images/Long%20Term%20Field%20Performance%20of%20Pervious%20Final%20Report.pdf

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