Page 123 - New Trends in Eco efficient and Recycled Concrete

Waste rubber aggregates 97

(particle size of 0.59 mm), respectively, while it was approximately 71% and
97%, respectively, with a particle size of 0.29 mm.
A reduction in the concrete mechanical properties was also found by Skripkiunas
et al. (2007), with the replacement of natural sand with 3.2% of rubber (size
0 1 mm), by weight. Compressive strength, static and dynamic modulus of elastic-
ity were reduced by 1.46%, 10.82% and 2.47%, respectively.
Pelisser et al. (2011) found a reduction of 67% and 49% in the compressive
strength and elastic modulus in concrete containing 10% recycled tyre rubber
(0 4.8 mm) as natural sand replacement, after 28 days of curing.
Chunlin et al. (2011) found a reduction of the compressive and flexural strength
of 5.73% and 29.47%, respectively, by partially replacing natural sand in concrete
with 10% of crumb rubber (1 5 mm), by volume. Studies by Holmes et al. (2014)
showed a reduction in the compressive strength and Young’s modulus of concrete
by partially replacing 7.5% of natural sand with crumb rubber (0.425 4.75 mm). In
this case, the flexural strength increased with the addition of rubber sand.
Bravo and de Brito (2012) used rubber aggregate made from used tyres to
replace natural sand in concrete at 0%, 5%, 10% and 15%, by volume. Results
showed a reduction of the compressive strength after 28 days of curing.
Compressive strength decreased as the rubber sand content increases.
Najim and Hall (2012) reported a reduction in the compressive, flexural, splitting
tensile strength and modulus of elasticity with the addition of crumb rubber (size
2 6 mm) in SCC as natural sand replacement. The reduction of the compressive
strength was about 42%, 52% and 67% with the addition of 5%, 10% and 15% of
rubber sand, respectively.
Azevedo et al. (2012) partially replaced natural sand in high performance mor-
tars with tyre rubber waste (particle size between 1 2.4 mm) at 0%, 5%, 10% and
15%, by weight. The compressive strength decreased by increasing rubber sand
content. The reduction of the compressive strength after 28 days of curing was
about 31%, 54% and 64% with the addition of 5%, 10% and 15% of rubber sand,
respectively.
Lijuan et al. (2014) used different rubber sizes as partial replacement of natural
sand in concrete, at 0%, 2%, 4%, 6%, 8% and 10%, by cement mass. The addition
of rubber reduced the compressive strength and elastic modulus of the concrete.
The reduction increased by increasing rubber content and decreasing the particle
size.

4.4.2.3 Replacement of natural aggregates with crumb rubber in
concrete (up to 25%)

Balaha et al. (2007) replaced natural sand with ground waste tyre rubber (0 4 mm)
in concrete, at 0%, 5%, 10%, 15% and 20%, by volume. Results showed a reduc-
tion of the compressive strength of about 7%, 12%, 18% and 28% with the addition
of 5%, 10%, 15% and 20% of rubber sand, respectively.
Experimental studies by Geso˘ glu and G¯ uneyisi (2007) showed a reduction in the
compressive strength of concrete where natural coarse aggregates were replaced by