Page 134 - New Trends in Eco efficient and Recycled Concrete

108 New Trends in Eco-efficient and Recycled Concrete

Bravo and de Brito (2012) observed a reduction in the carbonation resistance of
concrete specimens containing rubber aggregate made from used tyres as natural
sand replacement at up to 15%, by volume. The carbonation depth slightly
increased by increasing the rubber sand content. This is probably due to the greater
void volume between rubber aggregate and the cement paste. There is still a lack of
studies on what concerns the effect of rubber sand on the carbonation resistance of
cement-based matrices. The carbonation resistance of mortar/concrete containing
rubber sand needs further investigations.
Onuaguluchi and Panesar (2014) observed a reduction in the rapid chloride per-
meability of concrete specimens by partially replacing 5%, 10% and 15% of natural
fine aggregate with crumb rubber (0 2.3 mm), by volume.
It can be concluded that the addition of rubber sand in cement-based mixes may
increase water absorption and porosity, as reported by many studies, and that the
rubber particle size and content play a crucial role. The water absorption increase
may be the result of the formation of porosity during mixing process. Rubber parti-
cles are able to entrap air bubbles in their rough surface during the mixing process
because of their non-polar nature and this may increase the porosity of the matrix.
On the contrary, the addition of rubber particles of small size (,0.5 mm) reduce
the water absorption. The smaller rubber particles, indeed, acting as fillers to fill up
capillary pores in the matrix reduce the water absorption (Sukontasukkul and
Tiamlom, 2012).
The increase in the water absorption of cement-based matrices with the addition
of rubber particles is one of the drawbacks of using this type of material.
The chloride ion penetration depth increased by increasing rubber sand content.
However, chloride penetration depth can be reduced by replacing 10% of cement
with silica fume (Geso˘ glu and G¯ uneyisi, 2007) or by replacing part of cement with
fly ash (Geso˘ glu and G¯ uneyisi, 2011).

4.5.3 Drying shrinkage and cracking resistance

Turatsinze et al. (2005, 2007) observed an increase in the free shrinkage of mortars
with partial replacement of natural sand with 20% and 30% of rubber (0 4 mm),
by volume.
Jingfu et al. (2009) replaced natural sand with tyre rubber particles (0 1.5 mm)
3
in concrete mixes, at up to 120 kg/m . Results showed an increase of the drying
shrinkage with the addition of rubber sand. The drying shrinkage increased by
increasing rubber sand content.
¸
Uyguno˘ glu and Topcu (2010) found an increase in the drying shrinkage of self-
consolidating mortars where natural sand was partially replaced with tyre rubber
(1 4 mm) at up to 50%, by weight, with a w/c ratio of 0.4. By increasing the w/c
ratio to 0.51, the addition of rubber at up to 30% reduced the drying shrinkage,
while 40% and 50% significantly increased it.
Chunlin et al. (2011) observed a reduction of free shrinkage of concrete with nat-
ural sand replaced by 10% of crumb rubber (1 5 mm), by volume.