Civil Engineering Reference
In-Depth Information
Table 4.18 Toughness indices and some other parameters of rubberized concrete (Aiello and
Leuzzi
2010
)
Amount of rubber
in concrete (%)
Toughness indices
a
Residual strength factor
a
Toughness
(kN/mm
3
)
I
5
I
10
I
20
R
5,10
R
10,20
50
4.06
8.72
14.4
93.2
56.8
113
75
4.96
9.92
17.8
99.2
78.8
196
a
For details, see ASTM C1018-97
needed, such as bunkers and jersey barriers, or where vibration damping is
required such as foundation pads in railway stations. Due to the positive influence
of rubber aggregate, substantial work has been done to evaluate the stress-strain
curve and the toughness behaviour of concrete with rubber aggregates. This
behaviour is generally evaluated during the determination of various strength
properties.
Aiello and Leuzzi (
2010
) observed substantial improvement of post-cracking
behaviour of concrete due to the addition of coarse rubber aggregates. In
Table
4.18
, the toughness indices and energy absorption capacities (toughness)
measured during the determination of the flexural strength of concrete with rubber
aggregates used to replace 50 and 75 % by volume of natural coarse aggregates are
presented. The toughness indices determined from the curves were in the specified
limit of the standard range defined in ASTM C1018-97 and these increased with
rubber content. However, in the same investigation insignificant enhancement of
toughness behaviour due to the incorporation of fine rubber aggregates used to
replace 25 and 50 % by volume of natural fine aggregates in concrete was also
reported.
Batayneh et al. (
2008
) also found two distinct behaviours in the stress-strain
curves of concrete depending on rubber content (Fig.
4.49
). 0.075-4.75 mm
rubber aggregates were used to replace fine NA in concrete. The stress-strain
behaviour of specimens with rubber content up to 40 % follows a trend similar to
that of the control specimen. In this case, concrete behaved like a brittle material
i.e. there was a linear increase of stress until it reached its peak value before
specimen's fracture. However, the curves became nonlinear for concrete mixes
with 60 and 80 % rubber, which indicated that concrete behaves like a ductile
material. Kang et al. (
2009
) observed a similar type of ductility behaviour for
concrete with shredded rubber aggregates. Concrete with rubber aggregates did not
disintegrate and some cracks closed after unloading.
Benazzouk et al. (
2003
) also observed increasing ductility in the stress-strain
curve of concrete due to increasing addition of rubber aggregate as well as due to
increasing particle size of rubber aggregates. The brittleness index (BI) was also
measured to estimate the ductility of different concrete specimens. These values
for different mixes as a function of rubber aggregates volume are presented in
Fig.
4.50
. The peak was obtained at a rubber addition level of 10 % for all
aggregate sizes and characterised the transition from brittle to ductile material after
