The delayed curing but the mechanical strength is

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).

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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.