Page 129 - New Trends in Eco efficient and Recycled Concrete

Waste rubber aggregates 103

Najim and Hall (2012) partially replaced natural sand in SCCs with crumb rub-
ber (size 2 6 mm) at up to 15%, by weight. Toughness was increased by 54%,
17% and 33% with the addition of 5%, 10% and 15% of rubber sand, respectively.
Liu et al. (2013) partially replaced natural sand (0 5 mm) in concrete with
recycled tyre rubber (0 2 mm) at up to 15%, by volume. Concrete toughness
increased by increasing rubber sand content. The flexural strength to compressive
strength ratio of concrete with 5%, 10% and 15% of rubber was 1.08, 1.16 and 1.26
times greater than the plain concrete, respectively.
Huang et al. (2013) replaced IOTs with crumb rubber (average size 0.135 mm)
at up to 40%, by volume. Rubber particles led to a substantial reduction of fracture
toughness by about 50% compared to the control. The increasing porosity of ECC
may have weakened the interfacial bond between tyre rubber particles and sur-
rounding cement paste allowing a crack to easily develop around the tyre rubber
particles.
It can be noted that the addition of rubber sand in concrete mixes as a partial
substitution of natural aggregates is able to increase their fracture toughness. This
improvement can be explained by the ability of the rubber to absorb some energy
before fracturing (Taha et al., 2008). The enhancement of the concrete toughness
with the addition of rubber sand is one of the advantages of using this recycled
material in cement-based matrices.
Guo et al. (2014a,b) showed that appropriate rubber content is able to improve
the concrete ductility. However, beyond a certain limit, the use of rubber may be
detrimental.
Jingfu and Yongqi (2008) found that mortar and concrete containing rubber
aggregates exhibited ductile failure and great deformation before failure. The ulti-
mate deformations increased up to four times that of control specimen. Grdi´ c et al.
(2014) reported an increase of the concrete ductility by replacing natural sand with
crumb rubber (0.5 4 mm) at up to 30%, by volume. The ductility index increased
by increasing rubber sand content. The ductility index increased by 25%, 81% and
93% with the addition of 10%, 20% and 30% of rubber sand, respectively.
Hilal (2011) found that foamed concrete containing up to 30% of crumb rubber
(0.7 5 mm) as natural sand replacement, by weight, showed a more ductile behav-
iour under compression, with respect to the reference specimen. Vadivel et al.
(2014) found an improvement in the concrete ductility by partially replacing natural
sand with 6% of rubber (0.1 4.75 mm), by weight.
Lijuan et al. (2014) replaced natural sand in concrete with rubber at up to 10%,
by cement mass. They used different rubber sizes (up to 4 mm). The addition of
rubber is able to improve the concrete’s deformability. As a consequence, the ulti-
mate strain of normal concrete increased. The ultimate strain of rubberised concrete
increased as the rubber content increases and particle size reduces.
Mohammed (2010) replaced natural sand in concrete slabs with crumb rubber
(0 0.6 mm) at up to 10%, by volume. Rubberised slab improved their ductility
when subject to bending loads.
Ganesan et al. (2013a,b) replaced natural sand in beam-column concrete joints
with rubber (up to 4.75 mm) at 0% and 15%, by volume. The addition of shredded