Page 138 - New Trends in Eco efficient and Recycled Concrete

112 New Trends in Eco-efficient and Recycled Concrete

4.6.2 Sound absorption

Sukontasukkul (2009) replaced natural sand in concrete with two different particle
sizes of crumb rubber at up to 30%, by volume. Results showed an increase in the
noise reduction coefficient of 40%, 41% and 22% with the addition of 10%, 20%
and 30% of rubber sand.
Khaloo et al. (2008) replaced natural sand in concrete with rubber (0 4.75 mm)
at 25%, 59%, 75% and 100%, by volume. The sound absorption by concrete
increased by increasing rubber sand content.
Mohammed et al. (2012) reported better sound absorption of concrete containing
rubber (0 0.6 mm) compared to the conventional concrete. The noise reduction
coefficient increased by increasing the rubber sand content. Najim and Hall (2012)
found that SCCs containing crumb rubber (2 6 mm) at up to 15%, by weight,
exhibited superior vibration damping behaviour compared to the control specimen.
Gisbert et al. (2014) observed that mortars containing crumb rubber at up to
40%, by weight, showed superior damping behaviour compared to the control mor-
tar. The damping increased by increasing the rubber sand content. Researchers also
observed that if the crumb rubber percentage is higher, the presence of rubber can
cause sound absorption if a finer size distribution is involved (size 0.25 mm).
The literature reported above showed that the addition of rubber sand in concrete
matrix increased its sound insulation. For this reason, rubberised concrete could be
used as a sound barrier.

4.6.3 Electrical resistance
Yung et al. (2013) observed higher electrical resistance of rubberised concrete in
comparison with reference concrete. The electrical resistance increased by increas-
ing the rubber sand content. The addition of rubber (0 0.6 mm) increased the sur-
face resistance by 17%.
Mohammed et al. (2012) found an increase in the electrical resistivity of hollow
concrete blocks made by partial replacement of natural sand with crumb rubber
(0 0.6 mm) at up to 50%, by volume, with respect to the reference specimens. The
electrical resistance increased by increasing the content of rubber sand.
Although there is still a lack of experimentation and knowledge on electrical
resistance of rubberised cement-based matrices, it can be concluded that the electri-
cal resistance increases with the addition of rubber particles in substitution of natu-
ral aggregates.

4.7 Fields of application

The use of rubber as a natural aggregate substitution in mortars and concrete shows
many advantages, such as lower matrix density, higher ductility, toughness,
improved impact load resistance, increased freeze/taw resistance, higher thermal
and sound insulation, increased strain capacity and improved energy absorption.