Civil Engineering Reference
In-Depth Information
Fig. 4.11
Modulus of elasticity of concrete with CBA (Andrade et al.
2007
)
for 100 % replacement by coarse CBA and 100 % replacement by a mixture of
fine and coarse CBA were, respectively, 22.5 and 51 %.
Andrade et al. (
2007
) also observed significant reduction in elastic modulus
value for concrete with fine CBA as partial or full replacement of fine aggregate
fraction (Fig.
4.11
). This reduction was prominent at the early stage of curing.
However, at the latter stages of curing the pozzolanic reaction of CBA made the
microstructure of concrete denser and improved the mechanical properties
including the elasticity modulus. However, changes in water content during con-
crete the mix preparation by considering the water content in CBA can improve
the elastic modulus behaviour of hardened concrete. The authors refer this fraction
as CRT4 in Fig.
4.11
.
The same authors plotted stress-strain curves for concrete with CBA aggre-
gates. However, they did not find too much difference for CRT4 type concrete, but
other types gave scattered results at all ages.
4.2.3 Durability Behaviour
4.2.3.1 Drying Shrinkage
The drying shrinkage of concrete is generally affected by the addition of CBA
aggregates, as this material is porous by nature and therefore absorbs a large
amount of water. Bai et al. (
2005
) reported that the concrete with CBA as a
replacement of sand fraction at constant w/c value exhibited lower drying
shrinkage than conventional concrete. This is due to the release of moisture
absorbed by CBA during dry condition that keeps the mortar in a moist condition.
On the other hand, for constant slump value, shrinkage increased with increasing
content of CBA. However, in this condition, the authors found a comparable
drying shrinkage of concrete with CBA replacing 30 % by weight of natural sand.
Their results are presented in Fig.
4.12
.
