Civil Engineering Reference
In-Depth Information
Fig. 4.54 Drying shrinkage
of concrete with various
amounts of rubber aggregates
(Kang et al.
2009
)
shrinkage of self-consolidating mortar prepared by replacing 10 and 20 % of sand
by rubber aggregates. However, at higher substitution levels it increases sharply.
Ho et al. (
2009
), from a test according to ASTM standard C 1581-04, reported
that the incorporation of rubber aggregate in concrete reduced the sensitivity of
concrete to cracking due to shrinkage-related length change. This was due to the
enhanced strain capacity of rubberized concrete. The compressive strain developed
in the steel ring caused by the restrained shrinkage of the concrete specimen
measured from the time of casting show that in comparison with the control
concrete, the development of compressive strain in the steel ring slowed down for
rubberized concretes, which confirms the stress relaxation resulting from the
presence of rubber particles. The incorporation of rubber into concrete delayed the
time of crack initiation and increasing rubber amounts further delayed it. These
results are presented in Table
4.21
.
4.7.3.2 Water Absorption
The amount of water absorbed is related to the porosity of the test specimens and
gives an insight of the internal microstructure. Several reports are available on the
water absorption behaviour of concrete due to incorporation of rubber aggregates.
The water absorption behaviour of concrete with rubber aggregates depends on
their particle size. In general, the presence of large size rubber aggregates
Table 4.21
Effect of rubber aggregate on the cracking potential of concrete (Ho et al.
2009
)
Potential for cracking
a
Mix
Time to cracking (day)
Average stress rate (MPa/day)
C0R
9.25
0.39
High
C20R
15.50
0.16
Moderate-low
C40R
33.25
0.05
Low
a
According to ASTM C1581-04
C0R conventional concrete
C20R and C40R concrete prepared by replacing 20 and 40 % of sand by an equal volume of
rubber aggregates
