The delayed curing but the mechanical strength is

Thecompressive, split-tensile, and flexural strengths are contrarily correlated topermeability. As the permeability increased, the strength properties of perviousconcrete mixtures decreased (57, 132, 30).

It is also observed that thecompressive strength of the pervious concrete increases linearly with theincrease of the tensile strength (30). It has been observed that addition of smallamount of sand was efficient in increasing mechanical property (2, 6, 92). It is also reported that Sandand/or latex increase the strength but reduce permeability of pervious concrete(131).The mixes containing only sand, had bigger increase in strength than the mixescontaining sand and latex. Mixes containing silica fume had higher voids ratiosand lower strengths than mixes without.

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              The compressive, split-tensile,and flexural strengths of the single-sized aggregate gradations slightlydecreased as the nominal maximum aggregate size increased, but thesedifferences were not statically significant (57,132). The mechanical strengthis strongly related to mix proportion (23) and porosity of pervious concrete (140).Shu etal. (22)reported higher compressivestrength using limestone aggregate and incorporation of latex. Also, reportedby H. Wu et al (64)adding latex desirably improved the strength whereas fiber did not showsignificant effect on mechanical properties of pervious concrete. Huang et al.

(24) mentioned intheir study that addition of polymer, sand, fiber enhance the mechanicalstrength. Giustozzi (6) mentioned in their study that polymer modifiedmixes showed delayed curing but the mechanical strength is significantlyimproved. It was also observed that pervious concrete reached 80-90 % ofcompressive strength after 7 days of curing as observed after 28 days of curing(61).Widely reported by many researchers (18, 15,132) that the increase in paste volumeresulted in improving the mechanical properties regardless of aggregate sizeand for a given paste volume the use of lower maximum size aggregate resultedin higher strength values. Yangand jiang (31) foundthat compressive strength of 50 MPa and flexural strength of 6 MPa could beachieved by the addition of Silica fume, and using smaller size aggregate. Deo & Neithalath (56) used image analysis method to study material structure andcompressive response. The result indicate that the large size aggregate andincrease in paste volume fraction are observed to be increase the compressivestrength and it is mainly influenced by pore sizes , their distribution andspacing.

Moreover, small size fraction of aggregate produce small size pores inpervious concrete (95).Many researchers have reported that higher compressive strength could beachieved for mixtures containing smaller size aggregate (22, 4, 12, 31, 132, 151) and increase in cement paste (18, 49, 15). It is also observed thatcompressive strength increases with decrease in porosity (59).

Also, compressive strength of 35 Mpawas reported by Chang et al. (7)using Electric arc furnace slag and alkali activated slag cement.It was also reported by Zhong & wille (12) that the matrixstrength, aggregate size and a/b ratio significantly affect the strengthproperties.Suozzo and Dewoolkar (67) investigated the effect of sulphur mortarcapping and elastomeric pad capping on the compressive strength measurementsand found that there is no statically significant difference in compressivestrength measurement. Rehder et al.

(44, 24) from their studyreported that fibers generally not found to influence the compressive strengthto any significant degree, as is expected for conventional concretes also.Among the pore structure features, porosity exerted the maximum influence oncompressive strength. However, Rangelov et al.

(126) investigated fresh and hardeneddensity/porosity and 28-day compressive strength, and found that the two-weekair curing followed by two-week moist curing method yield higher 28-daystrengths for both specimen sizes. Moreover, longer periods of moist curing didnot result in higher strengths. Attemptshave been made to make the pervious concrete using locally available coarseaggregates i.

e. 1st classbrick aggregate, crushed stone aggregate and recycled brick aggregate and foundthat pervious concrete with compressive strength range from 4.5 to 11.72 Mpaand permeability from 60 to 15 mm/sec can be made (125).

Kevern et al (47) studied17 different types of aggregates and showed corresponding strengths. Bhutta et al. (60) fromtheir experimental investigation reported the reduction in compressive strengthusing recycle aggregate, but the compressive strength significantly increasedue to polymer modification for both normal and recycle aggregate. It isbelieved that the addition of polymer have improved the internal cohesion andwater retention between cement matrix and aggregate and increased the bondingforce between neighboring aggregate particles. Gaedickeet al (8) found outthat compressive strength of RCA found to be 8% lower than pea gravel and 15%lower than limestone aggregate for porosity of 20%. Sata et al. (127) used crushedstructural concrete and crushed clay bricks aggregates (Both RCA) to makegeopolymer concrete and analyzed that these can be used but strength loosesignificantly.

Although Compressive strength greatly affected by RCA (151). Moreover, Nguyen etal. (19)reported that by partially replacing natural aggregates with sea shell byproducts, a compressive strength of 15 mpa could be achieved. Hence, itcan be summarized that the strength of pervious concrete can be increased (withcompromise in permeability) by factors such as paste volume, small sizeaggregates, addition of sand, mineral admixture and mix design. Variation of compressive strength with porosity by usingnatural aggregate from 11 studies is shown in fig.4 and by using recycleaggregate is shown in fig.5.