Civil Engineering Reference
In-Depth Information
vast work is already available on the evaluation of various durability behaviours of
concrete containing CDW aggregate. In this section these properties are presented
based on the collected references.
5.4.1 Drying Shrinkage
Concrete begins to shrink as soon as the hardening process starts by losing
unconsumed water (i.e. that does not take part in the cement hydration reaction).
The shrinkage of concrete can affect several mechanical and other durability
properties of concrete due to the formation of micro cracks. In this section, the
shrinkage (especially drying shrinkage) performance of concrete containing CDW
aggregate is presented based on the literature. Normally, the incorporation of
CDW aggregate in concrete increases the drying shrinkage. The increase in paste
content in concrete due to the incorporation of CDW aggregate was identified as
the main reason for drying shrinkage of concrete to increase (Kou et al.
2011b
;
Limbachiya et al.
2000
). Table
5.20
shows a few typical examples of drying
shrinkage of concrete containing RCA as coarse aggregate.
Limbachiya et al. (
2000
, Limbachiya (
2010
) observed higher drying shrinkage
in RCAC with 30, 60 and 70 MPa design strength than in equivalent conventional
concrete (Table
5.20
). The shrinkage of concrete increased with the RCA content
and design strength. The reasons for this trend were: the increase in cement content
to reduce the w/c value and achieve the same 90-day strength as conventional
concrete; and the presence of old cement paste in RCA. Like in conventional
concrete, they observed lower shrinkage in RCAC with higher CS. In comparison
to conventional concrete, Hansen and Boegh (
1985
) observed an increase of about
40-60 % in 440-day drying shrinkage of three different classes of structural
concrete containing three types of coarse RCA as the only coarse aggregate by
comparison with the parent concrete from which the RCA were generated
(Table
5.20
). The reasons for this trend were the same as in the previous research.
Hasaba et al. (
1982
) observed a drying shrinkage about 70 % higher in concrete
with RCA as a full replacement of fine and coarse NA. In comparison to con-
ventional concrete, Poon et al. (
2006
) observed about 33 and 20 % higher 112-day
drying shrinkage of two types of RCAC where 100 % by volume of coarse NA
were replaced by RCA and at w/c of 0.55 and 0.45, respectively.
Sagoe-Crentsil et al. (
2001
) observed a 35 % increase of the 365-day drying
shrinkage due to the complete replacement of coarse basalt aggregate by RCA in
concrete; however, the decreasing trend of drying shrinkage of both types of
concrete with time was similar. The 56-day drying shrinkage strain of both types
of concrete was less than the 700 l, the recommended limit in the Australian
standard, AS 3600. Khatib (
2005
) observed a higher drying shrinkage of con-
ventional concrete and RCAC's containing fine RCA at various levels in the first
10 days of curing (Fig.
5.56
). The shrinkage increased with the content of RCA in
concrete. Kou and Poon (
2009a
) observed increasing drying shrinkage of concrete
