Concrete International20

Keywords: coarse aggregates; laboratories; no-finesconcretes; research; voids.

Laboratory researchSeveral research series were con­

ducted in the National AggregatesAssociation (NAA) - NationalReady Mixed Concrete Association(NRMCA) Joint Research Labora­tory to develop information con­cerning proportioning methods aswell as methods of measuring thestrength and permeability of no­fines pervious concrete. Batch sizesranging from 1 to 3 ft3 (0.028 to0.085 m') were mixed in rotatingdrum laboratory mixers. Labora­tory stock Type I cement was usedwith two sizes of stock coarse ag­gregate: moderately rounded gravelaggregates of % in. (9.5 mm) maxi­mum size (ASTM C 33, No 8 size),and % in. (19 mm) maximum size(ASTM C 33, No. 67 size). Fig. 2shows the end of a broken 6 x 12 in.(152 x 305 mm) strength cylinderand a 4 x 14 in. (102 x 356 mm) cyl­inder used in freezing and thawingtests (both cylinders were madefrom laboratory concrete contain­ing No. 8 size aggregate).

The properties of no-fines con­crete depend not only on its pro­portions but also on its compac­tion. To better understand the ef­fect of compaction on concrete airvoid content, unit weight, and com-

No-fines concrete is also used forpaving in greenhouses and nurserieswhere it is undesirable to have freewater on paved surfaces. It permitsthe surface to appear relatively drywith no streams or puddles of waterfrom irrigation of plants or nurserystock. Use of pervious concrete alsoallows a parking lot to be builtaround trees, without cutting off airand moisture to the roots below.

In extreme cases, to impound theneeded amount of rainfall in heavystorms, parking lots are being de­signed to store water not only invoids of the pavement or base ma­terial, but also on top of the pave­ment. These parking lots temporar­ily store an additional 6 in. (15 cm)of rainfall up to the curb line on acompletely fIat 101. Their entranceaprons must be humped up enoughto retain the design storm wateramount and not allow it to run outinto the adjacent road or gutter.

No fines pervious concrete hasbeen used as an open-graded drain­age material in bases under side­walks and light duty pavement, andalso as drainage layers under high­way shoulders, to allow water trap­ped under pavements to flow morerapidly out of the pavement struc­ture. A double-barrelled approachuses no-fines concrete plus a drainpipe to a small storm water reten­tion basin (Fig. 1).

Data and references are available from NRMCA­NAA, 900 Spring St., Silver Spring, MD 20910.

No-fines, pervious concrete isbeing used for paving in sit­uations where it is desired tohave rainfall or surface wa­

ter percolate through the pavementinto a permeable base. The elimina­tion of fine aggregate producesconcrete in which the coarse aggre­gate particles are coated with a wa­ter-cement paste that bonds themtogether at their contact points. Thefairly large voids left between thecoarse aggregate particles allow theconcrete to be permeable to water.

This concrete is used in Florida toeliminate storm water run-off fromparking lots and reduce the need forseparate storm water retentionponds in shopping centers and de­velopments. It is particularly usefulin areas where local or state regula­tions require that storm water beretained on the site to recharge thegroundwater system with fresh wa­ter and to reduce the need for stormsewers.

Results of a laboratory study of no­fines pervious concrete for paving arepresented. Conclusions are drawnregarding the percent air voids neededfor adequate permeability, the optimumwater-cement ratio range, and theamounts of compaction and curingrequired. Recommendations are maderegarding appropriate uses for this typeof concrete.

Fig. 1 - No-fines concrete facilitates drainage to a stormwater retention basin.by Richard C. Meininger

No-FinesPerviousConcretelar Paving

21August 1988

b .t~ 4'~~"~·"~;"~~~~¡__JL~ZL:~~...LUL~:':.Fig. 5 - Bottom surface of percolation specimens withblocked channels (no flow).

120 to 122 Ib/ft3(1922 to 1954 kg/ru')

Compressive strength range:2100 to 2480 psi

(14.5 to 17.1 MPa)The tamper used for the 5 and 15

tamp compaction level was madefrom pipe fittings. It weighs 5.0 lb

111 to 1141b/ft3(1778 to 1826 kg/rri')

Compressive strength range:1400 to 1550 psi

(9.6 to 10.7 MPa)Heavy (C 31 rodding compaction [3layers])Unit weight range:

Compressive strength range:980 to 1360 psi

(6.8 to 9.4 MPa)Medium (15 tamps on each of twolayers)Unit weight range:

107 to 111 Ib/ft3(1714 to 1778 kg/rn ')

Fig. 4 - Bottom surface of percolation specimens withopen channels (flow).

Light (5 tamp compaction of eachof two layers)Unit weight range:

• C 31 rodding compaction; 25strokes on each of 3 layers.

The resulting cylinder unitweights and strengths are shown inFig. 3. Unit weight ranged from alow of about 105 lh/ft ' (1682 kg/m') with no compaction up to about120 lb /ft" (1922 kgz'rn') with theASTM C 31 rodding procedure.The cylinders with no compactionwere unsatisfactory because theycontained large voids and discon­tinuities, so three levels represent­ing different amounts of cornpac­tion that might be obtained in pav­ing were chosen for future work:

Fig. 3 - Cylinder unit weights and strengths for eightdifferent compaction methods.

7 8METHODS OF COMPACTION (AND 28-DAY COMPRESSIVE STRENGTH

OF CYLINDER FROM BATCH A, BATCH B)

l. NO COMPACTION, CONCRETE SCOOPED INTO MOLO2. 2 LAYERS, TILT ANO OROP MOLO3. 2 LAYERS, 5 TAMPS EACH OF THE TAMPER (1355, 975 psi)4. 2 LAYERS, 5 OROPS EACH OF THE TAMPER (1340 psi, 1050 psi)5. 2 LAYERS, 5 DROPS EACH, PROCTOR HAW1ER (1360 psi, 1100 psi)6. 2 LAYERS, 15 TAMPS EACH OF THE TAMPER (1550 psi, 1395 psi)7. 3 LAYERS, 25 DROPS EACH, PROCTOR HAMMER (1945 psi, 1540 psi)8. ASTM C 31 ROOOING PROCEOURE, 3 LAYERS (2475 psi, 2095 psi)

~.>. .)

/)-:BATCH A, w/c = 0.34

~ 1/ ~v// ./.ATCH B, W/C = 0.31

/

125

120

e:115:I:

8¡,¡~;::z 110::>Il:we~~ 105><u

100

• No compaction (just scoop con­crete in).

• Fill in two layers; tilt and dropcylinder after each.

• Two layers; five tamp cornpac­tion of each with 5 lb circulartamper.

• Two layers; five drops of thetamper for each layer.

• Two layers; five drops each usinga proctor hammer.

• Two layers; 15 tamps each layer.• Three layers; 25 drops each withthe proctor hammer.

pressive strength, concrete batcheswere mixed at two different water­cement ratios (0.31 and 0.34) and 6x 12 in. (152 x 305 mm) cylinderswere then made using eight differ­ent procedures:

Fig. 2 - No-fines pervious concrete strength test andfreeze-thaw test cylinders.

~ t.~'... )

......'~ f' \.

Concrete International22

vious concrete was measured in apercolation test rig consisting of a 6x 12 in. (152 x 305 mm) plastic cyl­inder mold with the bottom cut outplaced over a cured half-height (6 x6 in. [152 x 152 mm]) cylinder madefrom the test concrete. Mastic wasplaced on the sides of the 6 x 6 in.(152 x 152 mm) cylinder to preventwater flowing out the sides, andthen the plastic cylinder mold wasslid down about 3 in. (76 mm) overthe percolation cylinder.

Water was run through the per­colation cylinder for a few minutesto condition it, and then the waterlevel aboye the cylinder was raisedto more than 5 in. (127 mm) aboyethe cylinder and the hose shut off.The percolation rate was measuredby timing the drop in the water SUf­face from a point 5 in. (127 mm)aboye the top surface of the cylin­der to a point 1 in. (25 mm) aboyethe cylinder. This was converted toinches of rainfa11 transmitted perminute by dividing 240 by the num­ber of seconds it took the waterlevel to drop 4 in. (102 mm).

Fig. 4 (flow) and Fig. 5 (no flow)shows the bottom surface of sorneof the percolation specimens. Thevoids between the coarse aggregateparticles of specimens with a higherpaste content can become blockedso that the channels in the specimen

CoarseCement Water aggregate Air Strength Percolation

w/c (lb/ydJ) (lb/yd') (lb/yd') (OJo) (psi) (in./min)

0.51 440 224 2640 22 1350 50.47 430 203 2575 23 1370 40.43 430 184 2570 25 1500 100.39 425 165 2550 27 1400 300.35 415 145 2520 29 1250 400.31 410 125 2430 32 1010 510.27 395 106 2370 33 870 59

Table 1 - Detailed data for light compaction tests(5 tamp compaction; No. 8 coarse aggregate;aggregate·cement ratio = 6)

Flexural strength was measured on6 x 6 x 36 in. (152 x 152 x 914 mm)beams using two breaks per beamwith third-point loading (ASTM C78). Beams were prepared to simu­late the same two compaction levelsused on cylinders. For the lightcompaction they were prepared inone layer using the 5 lb (2.3 kg)tamper, and for the heavy cornpac­tion using two layers and the ASTMC 31 rodding procedure.

Air void content of the concretewas calculated gravimetrically fromthe unit weight data determinedfrom a11 types of specimens (unitweight bucket, 6 x 12 in. [152 x 305mm] cylinders, and flexural beams).

The rate at which water couldpercolate through the no-fines per-

Fig. 7 - Relationship between 28-day compressivestrength and water-cement ratio.

WATER-CEMENTRATIO

.50.45.40.35.30

.~ 2500Ulo.

:2E-<t!)z 2000""P::E-<U)

"":>H 1500U)U)

""P::e,zou1000

><~Cl

coN

500

3000

Test methodsunit weight of the concrete was

measured in a 0.25 fe (0.007 m ')unit weight bucket using the 5 tamptwo layer compaction. Unit weightswere also determined on cylindersmade by both the light compaction(5 tamps, 2 layers) and heavy com­paction (C 31 rodding, 3 layers),and on flexural beams made at twocompaction levels.

Compressive strength was mea­sured on 6 x 12 in. (152 x 305 mm)cylinders made using the light corn­paction and heavy compaction.

(2.3 kg) and has a vertical handlewith a horizontal circular metal, 4-in. (l02-mm) diameter tampinghead.

WATER-CEMENT RATIO

Fig. 6 - Relationship between w/c and air content for twocompaction levels.

8 20Zril~Zo MIXER HOLDBACKu¡:¡:; DRYH 15.:¡; .25 .30 .35 .40 .45 .50

~~ 25r------+------~~~~~----~----~~u¡:¡:;ril~

~ 30~~--~~----+------+------4------4--43::

~

6, NO. 8 COARSE AGGREGATE

Pervious Concretecontinued

23August 1988

Effect of adding sandThe strength of no-fines concrete

irnproves when a srnall arnount ofsand is added (10 to 20 percent as apercentage of the total aggregateweight) (Fig. 9). As sand is added tothe mixture it tends to fill the voids,reducing the air content frorn 26percent to 22 and 17 percent in thiscase, and raising the compres sivestrength frorn about 1500 psi (10.3MPa) to about 2500 psi (17.2 MPa).

The strength data frorn thesemixtures is shown in Fig. 7, alongwith the strength data for those us­ing No. 8 size coarse aggregate.Again, the trend is to have better

strengths in the rnid-range of water­cernent ratios for both sizes ofcoarse aggregate. The traditionalwater-cernent ratio law does nothold for these mixtures beca use ofthe large differences in air-voidcontent and the difficulty of han­dling and cornpacting mixtures withvery low water-cernent ratios.The percolation rate becornes verylow (or no flow was observed) whenthe air void content of the speci­rnens become as low as 15 percent(Fig. 8). It appears that void con­tent values need to be 15 percent ormore to assure flow.

Fig. 9 - Adding 10 to 20% sandincreases compressive strength.

PERCENT SAND

Test results for No. 67coarse aggregate

A series of batches were rnixedusing the % in. (19 mm) rnaxirnurnsize coarse aggregate (No. 67) andthree cernent content ranges gov­erned by the aggregate-cement andwater-cernent ratios used (Table 2).

tended to cause balling and stickingof the concrete in the mixer, result­ing in substantial hold-back of con­crete when the drum was tilted fordischarge. High water-cernent ra­tios gave a thin paste that could runoff the aggregate during placernentresulting in increased variability andblockage of water flow channels.Table 1 shows detailed data for

the light cornpaction. As the aircontent increased frorn 22 percentto 33 percent, the rate of percola­tion increased from about 5 to 50in./rnin (127 to 1270 rnrn/rnin). Thecornpressive strength appeared to beoptirnurn in the mid-range of water­cernent ratios. At high water-ce­rnent ratio the strength was lower,and at very low water-cernent ratios(where the air content is higher)strengths becarne very low, becausethe past volurne was greatly re­duced and did not bind the aggre­gate particles together as well.

Fig. 8 - Minimum air void content of15% is needed for flow.

AIR CONTENT, PERCENT

100

80

e'e<,e 60 •..< 3000

Ulo.Z ;;8 E-<E-< oo<t: 40 ~ 2000Ho 1>:U E-<1>: Ul¡:iIe, ¡..¡ IW. 67 C. AGG~20 Ul 1000

Ul A/C = 6¡:.¡1>:p.. W/C = 0.38~o(.)

10 20 30 40 10 20 30

Water-cernent ratioTo investigate the effect of wa­

ter-cernent ratio, a series of batcheswere rnixed with ratios varying frorn0.51 down to 0.27. In this series afixed aggregate-cernent ratio (a/c =6) was used with the No. 8 coarseaggregate. Here basically relativelyfixed cernent and aggregate con­tents were used, and as the watercontent of the batches increased, thewater-cernent paste occupied moreof the voids in the coarse aggregate,thus lowering the air void content.

Fig. 6 shows the gravirnetric aircontent of the light and rnediurncornpaction batches calculated frornthe unit weight data. As water-ce­rnent ratio increased the air voidcontent decreased in a linear rela­tionship, with the light cornpactionhaving air voids about 2 percenthigher than the rnediurn cornpac­tion. Observation of the consis­tency of the water-cernent paste andhow the concrete handled in themixer indicated that water-cernentratios in the 0.35 to 0.45 range arebest for efficient coating of the ag­gregate. Low water-cernent ratios

are not continuous in sorne cases,causing a no flow condition.

b/bo

5-Tarnp C 31070

Sand NO.8 No. 67 No.8 No. 67

O 0.92 0.92 0.99 0.9910 0.84 0.85 0.93 0.9320 0.78 0.78 0.85 0.86

Table 3 - Effective b/bovalues

Cernenta/c w/c (lb/ydJ)

4 0.25 to 0.49 600 to 6806 0.25 to 0.49 400 to 45010 0.27 to 0.51 250 to 270

Table 2 - Cernent contentranges for strength testresults shown in Fig. 7 (No.67 coarse aggregate)

Concrete International24

20-30% - highly permeable; poor strength7. Calculate absolute volume of air8. Calculate absolute volume of sand, (if any)9. Calculate sand batch weight (if any)10. Calculate absolute volume of water-cement paste11. Calculate batch weight of cement12. Calculate batch weight of water13. Mix trial batch and determine:unit weight; air void content; yield; strength; etc.

for compaction level desired (or several compactionlevels)14. Adjust batch weights

1. Required data on coarse aggregate:SSD specific gravity; absorption; dry-rodded unit

weight2. Select a mid-rangc w!c

(0.33 to 0.45)3. Select a trial b/b: (Table 3)4. Calculate batch weight of coarse aggregate

(b/bo) (dry-rodded unit weight) (batch volume);correct to SSD5. Calculate absolute volume of coarse aggregate6. Select target air void content

10-15% - little or no flow; good strength15-20% - permeable; fair strength

Proportianing procedure

strength to an unacceptable level).For example, one could pick a se­

ries of batches along the 20 percentair line at a w/c = 0.38. In increas­ing order of paste content the trialbatches would befor C 31 compaction:

13OJo paste volume; 20% sand15% paste volume; 10% sand17% paste volume; 0% sand

for 5 tamp compaction:18% paste volume; 20% sand20% paste volume; 10OJo sand22% paste volume; 0% sand

An example of the data for the Vsin. (9.5 mm) aggregate (No. 8) isshown in Fig. 10 for light cornpac­tion (5 tamp; solid lines) and heavycompaction (C 31; dashed lines).For each condition sand contents ofO, 10, and 20 percent are shown.The family of curves for the % in.(19 mm) aggregate (No. 67) are verysimilar. These curves could be usedto proportion concrete within thedesired air content range of about15 to 22 pecent (enough voids to al­low water flow but not reduce

PASTE CONTENT, %

Fig. 11 - Relationship between paste content and b/b, fortwo levels of compaction and three sand contents.

0.9

1.0

A series of batches of concretewas mixed, all using the same mid­range w/c of 0.38, and two size ofcoarse aggregate - No. 8 and No.67. For each aggregate size, sandpercentages were varied from O per­cent up to 50 percent. At sand con­tents over about 30 percent the con­crete became more normal in con­sistency and did not have thecontent of larger voids necessary toallow water to flow through.

Proportioning relationships

PASTE CONTENT, PERCENT

Fig. 10 - Relationship between paste and air contents fortwo levels of compaction and three sand contents.

NO. 8 C. AGG.

OO

E-<Z>ilUtt:>il 30o..~

E-<Z>ilE-<Zo 20uo:;H,c¡;

10

40

0.8

o.c<,.c

0.75-TAMP

0.6

NO. 8 C. AGG.

0.510 20 30 40 50 o 10 20 30 40 50

Pervious Concretecontinued

25August 1988

define the fIow Ino flow boundaryfor air void contents in the lOto 25percent range, using a series of mix­tures with O, 10, and 20 percentsand. Water percolation rate wasmeasured on specimens made fromeach mixture, and both compressiveand flexural strength was deter­mined.

Fig. 13 shows the relationship ofcompressive strength to air voidcontent as calculated gr avirnetri­cally from the unit weight of thecylinders. All test conditions are in­cluded in this data. Fig. 14 showsflexural strength data versus the aircontent calculated from the unitweight of each beam specimen.These mixtures are highly depen­dent on the void content.

Fig. 15 shows the relationship offlexural strength to compressivestrength for this series and for otherfairly low strength regular concretedata from the NAA-NRMeA JointResearch Laboratory. The heavycompaction data (black circles) ap­pear to be more in line with pre­vious laboratory data, while thelight compaction (open circles) showa higher flexural strength thanmight be expected for the corre­sponding compressive strength.Sorne of the explanation for this

Comprehensive exampleA series of batches were mixed at

two compaction levels (light [5 tampcompaction] and heavy [e 31 corn­paction]) and with two sizes ofcoarse aggregate (No. 8 and No.67). All were mixed using a water­cement ratio of 0.39. The principal­purpose of this series was to better

compensates for the effect of dif­ferent coarse aggregate particleshape, grading, and specific grav­ity. Therefore, these values shouldbe usable for trial batches with anynormal weight coarse aggregate.They can be used to estimate theamount of coarse aggregate per cu­bic yard, if the level of compactionin the resulting construction can beselected accurately.

The same data can be plotted in adifferent way (Fig. 12) to showvoids in the mineral aggregate(VMA) in the same way that as­phalt technicians look at the voidsbetween the aggregate skeleton inan asphaltic concrete mixture. Inthat context VMA is the voids in themixture of coarse aggregate andfine aggregate (i f any is used).However, I feel the b/b; approachis easier to use.

Another approach to proportion­ing that appears to work well is theuse of the b rb ; concept as ern­ployed in A'C] 211.1 for propor­tioning normal weight concrete.Here the ratio b/b; compares theamount of coarse aggregate in aunit volume of concrete with theamount of coarse aggregate in a likevolume of dry rodded coarse aggre­gate (ASTM e 29 Test Method).

Fig. 11 shows calculated b/b; val­ues for the series of batches withNo. 8 coarse aggregate at variouspaste contents, for 2 levels of com­paction and O, 10, and 20 percentsand contents. For practical paste­contents aboye about 10 percent thecurves are relatively flat, indicatingthat b/b; (amount of coarse aggre­gate in the concrete) is relativelyconstant and not affected by thepast content. However, compactionlevel and sand content do affect theamount of coarse aggregate in theconcrete. The b/b; curves for the %in. (19 mm) (No. 67) coarse aggre­gate are very similar to those for theVs in. (9.5 mm) (No. 8) size.Table 3 shows the effective b/b,

values for the series of concretebatches. The b/b; concept, in usingthe dry-rodded unit weight ofcoarse aggregate, automatically

AIR CONTENT, PERCENT

Fig. 13 - Relationship between gravimetric air contentand 28-day compressive strength of cylinders.

25201510

PASTE CONTENT, PERCENT

Fig. 12 - Relationship between paste content and VMAfor two levels of compaction and three sand contents.

5040 305302010oo

6000

50COMPACTION-- 5 TAMP

~ 5000 -- C 31:>

• .-1fJJ PERCENT SAND~ o. O, 10, 20E-<

oex: 40 ::Co~ E-< 4000cr; t!lo Zo ~oex: cr;

E-<.....:¡ 30 ti)

oex:cr; ~ 3000~ :>z H

H ti)

::E ti)~Z cr;

20 P<H ~ti) O 2000Q UHO:>E-< 10z 1000w NO. 8 C. AGG.Ucr;WP<

Concrete International26

Example parking lotsFig. 16 shows a good job where

no- fines pervious concrete has beenused to advantage.

Raveling can occur when there isinsufficient hardened paste to holdthe top coarse aggregate, when thetop aggregate pieces are not cor­rectly seated into the concrete, andwhen poor curing allows the cementpaste to dry before sufficient hy­dration has taken place. Fig. 17shows a hand screed finish on aparking lot. No additional compac­tion and seating of the coarse ag­gregate was accomplished, and thatcoupled with poor curing caused theparking lot to have a rough, ravel­ing surface one year after construc­tion.

where it might beco me saturatedprior to a hard freeze. Sorne con­crete producers are using air-en­trainment in the paste; this may im­prove durability, but it may affectthe permeability characteristics aswell. Caution must also be exer­cised in using pervious concrete inexposures where sulfates or acidsmay be involved since the perrnea­bility of the product would allowsuch aggressive solutions to pene­trate and attack the interior of theconcrete.

Flexural strength:320 psi (2.2 MPa)

Percolation rate:7.3 in./min (185 mm/min)

The specimens were cured in astandard moist room for 30 days, atwhich time half of the specimenswere subjected to ASTM C 666Procedure A (freezing and thawingin water) and half to Procedure B(freezing in air and thawing in wa­ter). AH of the specimens failedfairly quickly in both freezing ex­posures, indicating that the voids inthe concrete became saturated andthe water was not able to drain outquickly enough to prevent freezingdamage in the rapid (5 cyc1es perday) freeze-thaw exposure.The cylinders appeared to crack

and tend to split lengthwise, indi­cating a build up of pressure due tofreezing of water in larger internalvoids. It was not the type of failurewhere material sloughs off the out­side surface. The rapid freezingfrom all directions may have drivenwater to the interior of the speci­mens, and when the internal waterfroze there was no avenue of pres­sure relief. For a situation wherefreezing is slower, and from one di­rection, there may be more oppor­tunity for water to drain out of theno-fines paving material.

Caution needs to be exercisedwhen using a product such as this

121 lb/yd' (72 kg/rn')Compressive strength:

1910 psi (13.2 MPa)

Unit weight:21 percent.

Air void content:

No admixtures were used. Themix characteristics were:

497 lb/yd' (295 kg/rn')194 lb/yd' (115 kg/rri')

26001b/yd3 (1543 kg/rri')0.39

CementWaterGravelw/c

Limited freezing andthawing testsFreezing and thawing specimens

(4 x 14 in. [102 x 356 mm] cylinderswith gage studs in the ends) weremolded from no-fines concrete withNo. 8 coarse aggregate containing:

appears to be related to a differenceof about 2.5 percent air content ofthe concrete as compacted in thebeam mold versus that in the cylin­der mold using light compaction.The air content was higher in thecylinders than that in the beams,probably due to the more confinedshape of the cylinders and greaterprobability of friction and confine­ment in the center porion of a beammoldo

Fig. 15 - Relationship between flexural strength andcompressive strength.

Fig. 14 - Relationship between gravimetric air contentand flexural strength of beams.

40003000 6000500020001000

COMPRESSIVE STRENGTH, psi

100 ~----~----~----~----~----~----~

3025

AIR CONTENT, PERCENT

2015105

500...,UJo.

iE-< 400oZWp:;E-<Ul

H 300~::JXWHtLo

200

700

D

D600

/f..•.-1Ul .a.

500 ..:iE-< e . ..(él .. a:z: e D¡,:¡ . .¡:>:;E-< 400 e • ·aUl

l' •e,_:¡ e~ ..p ... . ..>< o¡,:¡

300,_:¡ -:rx..

200

27August 1988

ACI member Rich·ard C. Meiningeris Vice President ofResearch of theNational ReadyMixed ConcreteAssociation andthe National Ag­gregates Associa­tion, Silver Spring, Maryland. Theseassociations sponsor the NAA-NRMCAJoint Research Laboratory in CollegePark, Maryland, where this researchwas conducted. He is a member of theACI Technical Activities Committee,and Committees 211, ProportioningMixtures, 221, Aggregates, and 226,Fly Ash, other Pozzolans, and Slag.Mr. Meininger was a recipient of theACI Construction Practice Award in1984.

,.\~ , ,. ..

b·l' .1:....•11~·~.:~~~:ii~~..'.....'~ .~

'.. ,t 'r...·1... L~,,\~u.Fig. 18 - Proper compaction andcuring gives a tight surface.

porous concrete can dry out veryrapidly if not quickly covered withplastic sheeting. Curing is vital tothe continued hydration, and resis­tance to abrasion, of the top sur­face.

The level of compaction must beconsidered in the design of the mix­ture. Too much compaction can re­duce the air voids to below 15 per­cent and plug the flow channels.Too little compaction will leave thestructure with very high air voidsresulting in low strength and a rav­eling surface. Compact test speci­mens to the same density as will beobtained in the field. It may takesorne experimenting to obtain com­parable compaction in the field andlaboratory. The CSA CanadianStandard s have sorne informationon how this can be done.

No-fines pervious concrete is aviable option for automobile park­ing lots in warm climate areas.There is concern that this lowerstrength concrete will not stand upwell where frequent truck or bustraffic may be involved. Regularnormal-weight concrete should beused for bus or truck lanes in park­ing lots and also in areas with fre­quent abrasion or turning maneu­versoThe use of no-fines concrete insurface courses should be confinedto automobile parking areas orother light duty uses.

Fig. 17 - Hand screed finish of no-fines permeable concrete paving providesinadequate compaction and seating of aggregate.

ConclusionsIt appears that at least 15 percent

air void content is required to ob­tain the needed percolation in no­fines concrete. A water-cement ra­tio in the range of 0.35 to 0.45 doesa better job of coating the coarseaggregate without causing too muchballing in the mixer or , at the op­posite extreme, being so wet thatthe paste tends to run off the aggre­gateo

Construction methods are criticalto proper performance. Sorne com­paction is needed during placementand the coarse aggregate on the topsurface needs to be properly seatedto reduce ravelling of the surface.Curing is very important since the

Fig. 18 shows the surface and aconstruction joint of a new parkinglot where extra effort was applied inproperly seating the top layer ofcoarse aggregate and in curing theconcrete. The screed used to strikeoff the concrete had a rounded edgewhich tended to compact the topsurface and a manually operatedsteel lawn roller was run over thesurface just behind the screedingoperation to properly embed theaggregate. Immediately followingthat the concrete was covered withsheet plastic to insure proper curingof the concrete.

Fig. 16 - A quality job using no-finespervious concrete.