Civil Engineering Reference
In-Depth Information
Table 4.17 Dynamic and static elastic moduli of concrete with ground and crushed rubber as
coarse aggregates replacement (Zheng et al.
2008a
)
Properties
Conventional
Concrete prepared by replacing coarse aggregates with
Ground rubber in volume (%)
Crushed rubber in volume (%)
15
30
45
15
30
45
E
d
(GPa)
43.7
41.2
35.2
31.2
35.4
36.5
32.8
E
s
(GPa)
31.8
27.1
24.1
22.3
23.1
24.3
22.1
respectively, referred to the control mix. A decrease in flexural strength with the
increase in particle size of rubber aggregates was reported in other studies too
(Benazzouk et al.
2003
; Mavroulidou and Figueiredo
2010
).
4.7.2.5 Modulus of Elasticity
Just like strength properties, the incorporation of crumb or chip rubber as aggre-
gates in concrete considerably reduces both the static and dynamic moduli of
elasticity. Aggregates characteristics affect the modulus of elasticity: concrete with
aggregates with higher stiffness normally has high modulus of elasticity. Since the
rubber aggregates have very low stiffness as compared to NA, the addition of
rubber aggregates lowers the modulus of elasticity of the resulting concrete.
The type of rubber (i.e. chips or ground rubber) may have some effect on the
modulus of elasticity. Zheng et al. (
2008a
) reported higher values of both static
and dynamic moduli for concrete with 15 % by volume of coarse aggregate
replaced by ground rubber than for concrete with crushed rubber at similar
replacement level (Table
4.17
). However, at higher replacement level the elasticity
behaviour of concrete with ground and crushed rubber aggregates becomes similar.
Skripkiunas et al. (
2007
) observed a reduction of about 11 % in the modulus of
elasticity of concrete due to the addition of rubber aggregates that replaced fine
aggregate by about 3 % by weight. Mavroulidou and Figueiredo (
2010
) observed a
higher static modulus of elasticity for concrete with coarse rubber aggregates
(19-10 mm) than for concrete incorporating finer rubber aggregates
(10-4.75 mm). Both types of aggregates were used to replace 10 % by weight of
natural coarse aggregates.
Azmi et al. (
2008
) found reductions in the modulus of elasticity with increasing
rubber aggregates content in concrete as well as with increasing w/c value. The
authors found a reduction of about 30 % in modulus of elasticity when the
replacement ratio of fine aggregates by crumb rubber increased from 0 to 30 % by
volume. According to the authors, the inclusion of crumb rubber implies defects in
the internal structure of the composite material, producing a reduction of strength
and stiffness. Benazzouk et al. (
2003
) reported that the decrease in dynamic
modulus of elasticity was greater with expanded type rubber aggregates compared
with compacted rubber aggregates for the same size and same amount of rubber
