Page 135 - New Trends in Eco efficient and Recycled Concrete

Waste rubber aggregates 109

Bravo and de Brito (2012) found an increase in the shrinkage by replacing natu-
ral sand in concrete with rubber coming from used tyres at up to 15%, by volume.
The shrinkage increased by 43% with a rubber sand content of 15%.
Sukontasukkul and Tiamlom (2012) replaced natural sand in concrete with rub-
ber particles of two different sizes at up to 30%, by volume. Results showed an
increase in the free drying shrinkage as the rubber sand content increases.
Specimens containing rubber sand of smaller size showed higher free shrinkage
than those containing large size.
Pedro et al. (2013) observed an increase in the shrinkage of mortar specimens
with partial replacement of natural sand with 15% of shredded rubber (0 2 mm),
by volume. Yung et al. (2013) observed the length change of concrete prisms con-
taining waste tyre rubber (0.3 0.6 mm) as natural sand replacement at up to 20%,
by volume. An increase in the shrinkage by increasing rubber sand content was
observed. The average length change was 35% higher than the control length. With
a replacement of 20% of natural sand with waste tyre rubber powder, the average
length change was 95% higher with respect to the control specimen.
The shrinkage of mortar and concrete with rubber particles is influenced by the
particle size and the content of rubber in the mix. It can be observed that the addi-
tion of rubber sand in mortar or concrete mix generally increase the free shrinkage.
The higher shrinkage of rubberised mortar/concrete is partly due to the lower com-
pressive strength and stiffness of rubber particles, compared to natural sands.
Sukontasukkul and Tiamlom (2012) observed that, as the replacement rate
increase, the lack of fine aggregate causes a greater decrease of internal restraints
and led to higher shrinkage of the matrix. In terms of rubber sand particle size, the
smaller size caused a higher shrinkage than the larger size.

4.5.4 Freeze/thaw and ageing resistance
Paine and Dhir (2010) observed that the replacement of natural sand in concrete
with 4% of rubber particles (sizes up to 25 mm) improved the resistance of freeze/
thaw cycles.
Al-Akhras and Smadi (2004) found a better freeze/thaw resistance of mortars
containing rubber ash (0 0.15 mm) as natural sand replacement at 5% and 10%, by
weight. The freeze/thaw resistance increased as the rubber ash content increases.
Topcu and Demir (2007) exposed concrete specimens, containing rubber sand
¸
(1 4 mm) as natural sand replacement at up to 30%, by volume, to 30 freeze thaw
cycles, according to ASTM C 666. Results showed that concrete containing 10% of
rubber sand was less damaged than the control specimen.
Karahan et al. (2012) exposed concrete specimen with rubber particles
(0.15 4.75 mm) to 300 freeze/thaw cycles. The addition of 20% and 30% of rubber
sand led to a reduction in the flexural strength of 12.5% and 13.16%, respectively,
after freeze/thaw cycles.
Turgut and Yesilata (2008) observed higher freeze thaw resistance of concrete
blocks containing crumb rubber (0.075 4.75 mm) at contents exceeding 50%, by
volume.