Use of Industrial Waste as Aggregate: Properties of Concrete - Recycled Aggregate in Concrete - page 119

Fig. 4.6 Compressive strengths of concrete with CBA (Andrade et al. 2007 )

in compressive strength of concrete due to increasing addition of CBA for constant
w/c.
Kim and Lee ( 2011 ) did not observe any significant changes in the compressive
strength of concrete with constant w/c value due to the incorporation of coarse and
fine CBA as partial and full replacement of coarse and fine aggregate, respectively.
According to the authors, this was due to the presence of higher amounts of cement
paste than those observed in other studies. Kuruma et al. ( 2009 ) observed higher
compressive strength in autoclaved aerated concrete with fine CBA replacing
50 % of natural sand than in similar conventional concrete, and compressive
strength further decreased with increasing replacement level. This was mainly due
to the pozzolanic activity of CBA, which increased at autoclaved aerated condi-
tions and therefore forms additional amounts of products like calcium silicate
hydrate gel, and strengthen the structure.
Andrade et al. ( 2007 ) reported that the consideration of water content in CBA
during the preparation of a concrete mix has profound effect on the compressive
strength of hardened concrete. Their results are presented in Fig. 4.6 . The authors
prepared two types of concrete: in one type the moisture content in CBA was not
considered to determine the water amount in the mix (CRT3) and in the other type
the moisture content in CBA was considered for that effect (CRT4).
As the CBA is slightly pozzolanic by nature, the strength development pattern
with respect to elapsed time for concrete with CBA is different from that of
conventional concrete. In most studies, it was reported that this type of concrete
gains strength at a slower rate in the initial period of curing and grows faster at the
latter stage of curing (Andrade et al. 2007 ; Agarwal et al. 2007 ; Ghafoori and
Bacholc 1996 ). According to these authors, bottom ash takes parts in hydration
reaction at the latter stages of curing and forms other products. In Fig. 4.6 , the
strength development behaviour of two types of concrete with CBA aggregate is
presented. Park et al. ( 2009 ) reported that the failure of concrete with coarse CBA
aggregate was predominantly by aggregate fracture instead of binder fracture and
interface fracture, due to the lesser hardness of CBA versus that of normal
aggregate.