Page 128 - New Trends in Eco efficient and Recycled Concrete

102 New Trends in Eco-efficient and Recycled Concrete

Furthermore, fine aggregates were totally replaced by crumb rubber. A general
reduction of the compressive strength, equal to 17%, 36%, 58% and 83% by repla-
cing crushed sand at 15%, 25%, 50% and 100%, respectively, was detected. When
fine aggregate was fully replaced with rubber sand the compressive strength
decrease was about 96%.
The literature showed that the addition of rubber sand (with different particle
sizes) as partial replacement of natural sand decreased the mechanical strength of
concrete. This reduction can be related to the lower adhesion at the interface
between rubber sand and cementitious matrix. Turatsinze et al. (2006) and
Corinaldesi et al. (2011) related the low strength of mortar containing rubber parti-
cles to the low quality of the interfacial transition zone between rubber particles
and cement paste. Turki et al. (2009a,b) observed that the lower mechanical proper-
ties of mortars containing rubber particles may be due to the void spaces between
rubber aggregate and cement matrix. Albano et al. (2005) related the lower mechan-
ical strength to the increased porosity. Taha et al. (2008) related the low strength of
rubberised concrete to three main reasons: first, the deformability of the rubber par-
ticles compared to the surrounding cement paste, that results in initiating cracks
around the rubber particles; secondly, the weak bond between rubber particles and
the cement paste; third, the possible reduction of the concrete matrix density. Many
other studies (Eldin and Senouci, 1993; Khatib and Bayomy, 1999; Chung and
Hong, 1999; Taha et al., 2008; Ozbay et al., 2011; Karahan et al., 2012) related the
lower strength of rubberised concrete to the weak bond between rubber particles
and cement paste and to the increased matrix porosity.
The reduction of concrete strength by using rubber sand is one of the limitations
of using this recycled material in the civil engineering community. To reduce the
decrease of mechanical properties caused by substitution of natural sand with rub-
ber sand, some studies (Geso˘ glu and G¯ uneyisi, 2007; Guneyisi et al., 2004) recom-
mended to replace part of cement with silica fume. Other researchers (Bowland
et al., 2012) recommend to mix rubber particles with latex before in order to
improve the adhesion at the rubber to cement paste interface.

4.4.3 Toughness, ductility and strain capacity
Topcu (1995) replaced natural sand in concrete with rubber (0 1, 1 4 mm) at up
¸
to 45%, by volume. Ductility of concrete improved with the addition of rubber
sand.
Sukontasukkul and Chaikaew (2006) found an increase in the toughness with the
addition of rubber as natural fine and coarse aggregate replacement.
Balaha et al. (2007) found that concrete containing ground waste tyre rubber
(0 4 mm) as a partial replacement of natural sand increased its toughness. The
damping ratio of the concrete containing 20% of rubber sand was 63% higher than
that of normal concrete.
Taha et al. (2008) replaced natural sand in concrete with crumb rubber (size
1 5 mm) at up to 100%, by volume. Fracture toughness increased with the addition
of rubber sand.