3.-No-Fines Pervious Concrete for Paving - Meininger (1988).pdf

No-Fines Pervious Concrete lar Paving by Richard C. Meininger Results of a laboratory study of nofines pervious concrete for paving are presented. Conclusions are drawn regarding the percent air voids needed for adequate permeability, the optimum water-cement ratio range, and the amounts of compaction and curing required. Recommendations are made regarding appropriate uses for this type of concrete.

o-fines, pervious concrete is being used for paving in situations where it is desired to have rainfall or surface water percolate through the pavement into a permeable base. The elimination of fine aggregate produces concrete in which the coarse aggregate particles are coated with a water-cement paste that bonds them together at their contact points. The fairly large voids left between the coarse aggregate particles allow the concrete to be permeable to water. This concrete is used in Florida to eliminate storm water run-off from parking lots and reduce the need for separate storm water retention ponds in shopping centers and developments. It is particularly useful in areas where local or state regulations require that storm water be retained on the site to recharge the groundwater system with fresh water and to reduce the need for storm sewers.

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

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Fig. 1 - No-fines concrete facilitates drainage to a storm water retention basin.

No-fines concrete is also used for paving in greenhouses and nurseries where it is undesirable to have free water on paved surfaces. It permits the surface to appear relatively dry with no streams or puddles of water from irrigation of plants or nursery stock. Use of pervious concrete also allows a parking lot to be built around trees, without cutting off air and moisture to the roots below. In extreme cases, to impound the needed amount of rainfall in heavy storms, parking lots are being designed to store water not only in voids 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 a completely fIat 101. Their entrance aprons must be humped up enough to retain the design storm water amount and not allow it to run out into the adjacent road or gutter. No fines pervious concrete has been used as an open-graded drainage material in bases under sidewalks and light duty pavement, and also as drainage layers under highway shoulders, to allow water trapped under pavements to flow more rapidly out of the pavement structure. A double-barrelled approach uses no-fines concrete plus a drain pipe to a small storm water retention basin (Fig. 1).

Laboratory research Several research series were conducted in the National Aggregates Association (NAA) - National Ready Mixed Concrete Association (NRMCA) Joint Research Laboratory to develop information concerning proportioning methods as well as methods of measuring the strength and permeability of nofines pervious concrete. Batch sizes ranging from 1 to 3 ft3 (0.028 to 0.085 m') were mixed in rotating drum laboratory mixers. Laboratory stock Type I cement was used with two sizes of stock coarse aggregate: moderately rounded gravel aggregates 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. 2 shows the end of a broken 6 x 12 in. (152 x 305 mm) strength cylinder and a 4 x 14 in. (102 x 356 mm) cylinder used in freezing and thawing tests (both cylinders were made from 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 air void content, unit weight, and comKeywords: coarse aggregates; laboratories; no-fines concretes; research; voids.

Concrete International

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appears to be related to a difference of about 2.5 percent air content of the concrete as compacted in the beam mold versus that in the cylinder mold using light compaction. The air content was higher in the cylinders than that in the beams, probably due to the more confined shape of the cylinders and greater probability of friction and confinement in the center porion of a beam moldo

Limited freezing and thawing tests Freezing and thawing specimens (4 x 14 in. [102 x 356 mm] cylinders with gage studs in the ends) were molded from no-fines concrete with No. 8 coarse aggregate containing: Cement 497 lb/yd' (295 kg/rn') Water 194 lb/yd' (115 kg/rri') Gravel 26001b/yd3 (1543 kg/rri') w/c 0.39 No admixtures were used. The mix characteristics were: Air void content: 21 percent. Unit weight: 121 lb/yd' (72 kg/rn') Compressive strength: 1910 psi (13.2 MPa)

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Flexural strength: 320 psi (2.2 MPa) Percolation rate: 7.3 in./min (185 mm/min) The specimens were cured in a standard moist room for 30 days, at which time half of the specimens were subjected to ASTM C 666 Procedure A (freezing and thawing in water) and half to Procedure B (freezing in air and thawing in water). AH of the specimens failed fairly quickly in both freezing exposures, indicating that the voids in the concrete became saturated and the water was not able to drain out quickly enough to prevent freezing damage in the rapid (5 cyc1es per day) freeze-thaw exposure. The cylinders appeared to crack and tend to split lengthwise, indicating a build up of pressure due to freezing of water in larger internal voids. It was not the type of failure where material sloughs off the outside surface. The rapid freezing from all directions may have driven water to the interior of the specimens, and when the internal water froze there was no avenue of pressure relief. For a situation where freezing is slower, and from one direction, there may be more opportunity for water to drain out of the no-fines paving material. Caution needs to be exercised when using a product such as this

where it might beco me saturated prior to a hard freeze. Sorne concrete producers are using air-entrainment in the paste; this may improve durability, but it may affect the permeability characteristics as well. Caution must also be exercised in using pervious concrete in exposures where sulfates or acids may be involved since the perrneability of the product would allow such aggressive solutions to penetrate and attack the interior of the concrete.

Example parking lots Fig. 16 shows a good job where no- fines pervious concrete has been used to advantage. Raveling can occur when there is insufficient hardened paste to hold the top coarse aggregate, when the top aggregate pieces are not correctly seated into the concrete, and when poor curing allows the cement paste to dry before sufficient hydration has taken place. Fig. 17 shows a hand screed finish on a parking lot. No additional compaction and seating of the coarse aggregate was accomplished, and that coupled with poor curing caused the parking lot to have a rough, raveling surface one year after construction. Concrete International

Fig. 16 - A quality job using no-fines pervious concrete.

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

Fig. 18 shows the surface and a construction joint of a new parking lot where extra effort was applied in properly seating the top layer of coarse aggregate and in curing the concrete. The screed used to strike off the concrete had a rounded edge which tended to compact the top surface and a manually operated steel lawn roller was run over the surface just behind the screeding operation to properly embed the aggregate. Immediately following that the concrete was covered with sheet plastic to insure proper curing of the concrete.

porous concrete can dry out very rapidly if not quickly covered with plastic sheeting. Curing is vital to the continued hydration, and resistance to abrasion, of the top surface. The level of compaction must be considered 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 the structure with very high air voids resulting in low strength and a raveling surface. Compact test specimens to the same density as will be obtained in the field. It may take sorne experimenting to obtain comparable compaction in the field and laboratory. The CSA Canadian Standard s have sorne information on how this can be done. No-fines pervious concrete is a viable option for automobile parking lots in warm climate areas. There is concern that this lower strength concrete will not stand up well where frequent truck or bus traffic may be involved. Regular normal-weight concrete should be used for bus or truck lanes in parking lots and also in areas with frequent abrasion or turning maneuverso The use of no-fines concrete in surface courses should be confined to automobile parking areas or other light duty uses.

Conclusions It 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 does a better job of coating the coarse aggregate without causing too much balling in the mixer or , at the opposite extreme, being so wet that the paste tends to run off the aggregateo Construction methods are critical to proper performance. Sorne compaction is needed during placement and the coarse aggregate on the top surface needs to be properly seated to reduce ravelling of the surface. Curing is very important since the August 1988

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1... L~,,\~u. Fig. 18 - Proper compaction and curing gives a tight surface. ACI member Rich· ard C. Meininger is Vice President of Research of the National Ready Mixed Concrete Association and the National Aggregates Association, Silver Spring, Maryland. These associations sponsor the NAA-NRMCA Joint Research Laboratory in College Park, Maryland, where this research was conducted. He is a member of the ACI Technical Activities Committee, and Committees 211, Proportioning Mixtures, 221, Aggregates, and 226, Fly Ash, other Pozzolans, and Slag. Mr. Meininger was a recipient of the ACI Construction Practice Award in 1984. 27