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Waste rubber aggregates 93

density was 2.47%, 4.81%, 7.42% and 11.81% with the addition of 10%, 20%, 30%
and 40% rubber sand, respectively.

4.4 Properties of rubberised mixes at the hardened state

4.4.1 Hardened density

The replacement of natural aggregates with crumb rubber reduced the mortar or
concrete mass density. Pierce and Blackwell (2003) reported a reduction from 32%
to 57%, by volume, which increased as the rubber sand content increases.
Mohammed et al. (2012) reported that hollow concrete blocks containing rubber
(particle size of 0.6 mm) as a natural sand replacement were lighter than conven-
tional hollow blocks.
Pelisser et al. (2011) found a 13% reduction in the concrete density by partially
replacing natural sand with 10% recycled tyre rubber (size ,4.8 mm).
Raj et al. (2011) found a reduction in the hardened density of SCCs when natural
sand was partially replaced with rubber (0 4.75 mm) at 0%, 5%, 10%, 15% and
20%, by volume. Reduction increased as the rubber sand content increases.
Pedro et al. (2013) found a reduction in the dry bulk density of mortar specimens
by partially replacing natural sand with shredded rubber (size 0 2 mm) at different
contents. The reduction after 28 days of curing was about 4%, 7% and 10% with
the addition of 5%, 10% and 15% of rubber sand, respectively, while it was 5%,
8% and 11% after 90 days.
Corinaldesi et al. (2011) used styrene butadiene rubber (SBR) and waste rubber-
shoe (SR) as a part of fine aggregate in mortars. Natural sand (size 0 5 mm) was
partially replaced with either SBR (size 0 12 mm) or SR (size 0 8 mm) up to
30%, by volume. The reduction in the dry unit weight was 3.84% and 16.35% with
the addition of 10% and 30% of SBR sand, respectively, while it was 2.86% and
13.54% with the addition of 10% and 30% of SR sand, respectively.
Sukontasukkul (2009) partially replaced natural sand in concrete with two differ-

ent particle sizes of rubber (passing sieve n 6 and n 26) at 0%, 10%, 20% and

30%, by volume. A reduction in the hardened density of concrete specimens was
observed. The reduction was about 14%, 17% and 20% with the addition of 10%,
20% and 30% of rubber sand with a large size, respectively, while it was 17%, 22%
and 28%, respectively, with the addition of rubber sand with a small size.
Grdi´ c et al. (2014) reported a reduction in the hardened density of concrete spe-
cimens by partially replacing natural sand with rubber (size 0.5 4 mm) at 10%,
20% and 30%, by volume. The reduction in the hardened density increased by
increasing rubber sand content. The reduction in the hardened density was about
4%, 9% and 13% with the addition of 10%, 20% and 30% of rubber sand, respec-
tively. Hilal (2011) reported a reduction in the hardened density of foamed concrete
specimens by partially replacing natural sand with crumb rubber (size 0.7 5 mm)
at 20% and 30%, by weight. The reduction in the 28 days density was 6.4% and
10.4% with the addition of 20% and 30% of rubber sand, respectively.