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Waste rubber aggregates 91

workability of concrete mixes by partially replacing natural sand with rubber (size
0.5 4 mm) at 10%, 20% and 30%, by volume, was also observed by Grdi´ c et al.
(2014).
Bravo and de Brito (2012) partially replaced natural sand in concrete mixes with
rubber aggregate coming from used tyres (with the same size of natural sand) at
0%, 5%, 10% and 15%, by volume. Various w/c ratios were used. Results showed a
reduction in the workability with the addition of 5% and 15% of rubber sand, while
an increase was observed with the addition of 10% of rubber sand.
Wang et al. (2013) reported an increasing bleeding effect with the addition of
rubber as a natural sand replacement in concrete mixes up to 40%, by volume.
Youssf et al. (2014) partially replaced natural sand in concrete mixes with crumb
rubber (particle size 1.1 2.3 mm) at 0% 5%, 10% and 20%, by volume. Results
showed that the addition of 5% rubber sand exhibited similar workability to the
control mix, while for higher replacement contents the workability decreased with
increasing rubber content.
On the other hand, Onuaguluchi and Panesar (2014) observed an increase of
workability by replacing the natural fine aggregate in concrete mixes with crumb
rubber at 0%, 5%, 10% and 15%, by volume.
Antil et al. (2014) and Parveen et al. (2013) reported an increase in concrete mix
workability by partially replacing natural sand with 5% and 10% crumb rubber
(size 4.75 0.075 mm), by volume. The addition of a higher amount of crumb rub-
ber decreased workability.
Balaha et al. (2007) investigated concrete mixes containing ground waste tyre
rubber (size ,4 mm) as a partial replacement of natural sand at 0%, 5%, 10%, 15%
and 20%, by volume. Results showed an increase in the workability as the rubber
sand content increased.
An increase in the workability of concrete mixes by replacing natural sand with
crumb rubber (size 2.36 2 mm) at 0%, 10%, 15%, 20% and 30%, by volume, was
also reported by Azmi et al. (2008). The workability increased with increasing the
rubber sand content.
Wang et al. (2013) studied the workability and initial setting time of low strength
rubber concrete mixes by replacing natural sand with rubber (size 4.75 mm) at 0%,
10%, 20%, 30% and 40%, by volume. W/b ratio was kept constant and a fixed con-
tent of accelerating agent was used. Results showed 3.46% increase in the slump
value with the addition of 10% rubber sand, while the reduction in the slump value
was 4.33%, 1.3% and 14.72% with the addition of 20%, 30% and 40% of rubber
sand, respectively. The slump flow increased with the addition of 10% and 20% of
rubber sand, while it decreased with the addition of 30% and 40% of rubber sand.
The initial setting time increased as the amount of rubber sand increases.
From these studies it can be concluded that the addition of waste rubber sand
in the mix reduced the workability. This is probably related to the higher water
absorption of rubber sand compared to natural sand. The reduction of workability
mainly depends on the rubber content and its particle size. However, some studies
reported that the addition of rubber to the concrete mix could increase
workability.