The

compressive, split-tensile, and flexural strengths are contrarily correlated to

permeability. As the permeability increased, the strength properties of pervious

concrete mixtures decreased (57, 132, 30). It is also observed that the

compressive strength of the pervious concrete increases linearly with the

increase of the tensile strength (30). It has been observed that addition of small

amount of sand was efficient in increasing mechanical property (2, 6, 92). It is also reported that Sand

and/or latex increase the strength but reduce permeability of pervious concrete

(131).

The mixes containing only sand, had bigger increase in strength than the mixes

containing sand and latex. Mixes containing silica fume had higher voids ratios

and lower strengths than mixes without.

The compressive, split-tensile,

and flexural strengths of the single-sized aggregate gradations slightly

decreased as the nominal maximum aggregate size increased, but these

differences were not statically significant (57,132). The mechanical strength

is strongly related to mix proportion (23) and porosity of pervious concrete (140).

Shu et

al. (22)

reported higher compressive

strength using limestone aggregate and incorporation of latex. Also, reported

by H. Wu et al (64)

adding latex desirably improved the strength whereas fiber did not show

significant effect on mechanical properties of pervious concrete. Huang et al.

(24) mentioned in

their study that addition of polymer, sand, fiber enhance the mechanical

strength. Giustozzi (6) mentioned in their study that polymer modified

mixes showed delayed curing but the mechanical strength is significantly

improved. It was also observed that pervious concrete reached 80-90 % of

compressive 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 volume

resulted in improving the mechanical properties regardless of aggregate size

and for a given paste volume the use of lower maximum size aggregate resulted

in higher strength values. Yang

and jiang (31) found

that compressive strength of 50 MPa and flexural strength of 6 MPa could be

achieved by the addition of Silica fume, and using smaller size aggregate. Deo & Neithalath (56) used image analysis method to study material structure and

compressive response. The result indicate that the large size aggregate and

increase in paste volume fraction are observed to be increase the compressive

strength and it is mainly influenced by pore sizes , their distribution and

spacing. Moreover, small size fraction of aggregate produce small size pores in

pervious concrete (95).

Many researchers have reported that higher compressive strength could be

achieved for mixtures containing smaller size aggregate (22, 4, 12, 31, 132, 151) and increase in cement paste (18, 49, 15). It is also observed that

compressive strength increases with decrease in porosity (59). Also, compressive strength of 35 Mpa

was 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 matrix

strength, aggregate size and a/b ratio significantly affect the strength

properties.

Suozzo and Dewoolkar (67) investigated the effect of sulphur mortar

capping and elastomeric pad capping on the compressive strength measurements

and found that there is no statically significant difference in compressive

strength measurement. Rehder et al. (44, 24) from their study

reported that fibers generally not found to influence the compressive strength

to any significant degree, as is expected for conventional concretes also.

Among the pore structure features, porosity exerted the maximum influence on

compressive strength. However, Rangelov et al. (126) investigated fresh and hardened

density/porosity and 28-day compressive strength, and found that the two-week

air curing followed by two-week moist curing method yield higher 28-day

strengths for both specimen sizes. Moreover, longer periods of moist curing did

not result in higher strengths.

Attempts

have been made to make the pervious concrete using locally available coarse

aggregates i.e. 1st class

brick aggregate, crushed stone aggregate and recycled brick aggregate and found

that pervious concrete with compressive strength range from 4.5 to 11.72 Mpa

and permeability from 60 to 15 mm/sec can be made (125). Kevern et al (47) studied

17 different types of aggregates and showed corresponding strengths.

Bhutta et al. (60) from

their experimental investigation reported the reduction in compressive strength

using recycle aggregate, but the compressive strength significantly increase

due to polymer modification for both normal and recycle aggregate. It is

believed that the addition of polymer have improved the internal cohesion and

water retention between cement matrix and aggregate and increased the bonding

force between neighboring aggregate particles. Gaedicke

et al (8) found out

that 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 crushed

structural concrete and crushed clay bricks aggregates (Both RCA) to make

geopolymer concrete and analyzed that these can be used but strength loose

significantly. Although Compressive strength greatly affected by RCA (151). Moreover, Nguyen et

al. (19)

reported that by partially replacing natural aggregates with sea shell by

products, a compressive strength of 15 mpa could be achieved.

Hence, it

can be summarized that the strength of pervious concrete can be increased (with

compromise in permeability) by factors such as paste volume, small size

aggregates, addition of sand, mineral admixture and mix design. Variation of compressive strength with porosity by using

natural aggregate from 11 studies is shown in fig.4 and by using recycle

aggregate is shown in fig.5.