Use of Industrial Waste as Aggregate: Properties of Concrete - Recycled Aggregate in Concrete - page 116

that of coarse CBA and therefore concrete with fine CBA absorbs negligible
amounts of cement paste and water during mixing, which does not affect the slump
value of the resulting concrete mix. Their results are presented in Fig. 4.1 b.
Kasemchaisiri and Tangtermsirikul ( 2008 ) also observed reduction in slump
value due to incorporation of CBA as a partial substitution of fine aggregate.
According to these authors, this was due to an increase in frictional forces between
aggregate particles as CBA is highly irregular in shape and it has rough surface
texture.
Bai et al. ( 2005 ) reported an increase in slump due to the partial substitution of
sand with fine CBA in the concrete mix (Fig. 4.1 c). According to the authors, the
presence of a ''ball-bearing effect'', due to the replacement of irregular shaped
normal sand by spherical shaped fine CBA aggregate increases the slump value of
the concrete mix.
Kou and Poon ( 2009 ) also reported increasing slump of fresh concrete mix due
to the incorporation of fine CBA as partial or total replacement of normal sand
(Fig. 4.1 d). An increase in free water content in the concrete mix with fine CBA by
comparison with that of the conventional concrete mix, due to the high water
absorption capacity of CBA, increases slump.
4.2.1.2 Bleeding Behaviour
Andrade et al. ( 2009 ) observed bleeding of water during the preparation of a fresh
concrete mix with CBA as aggregate. The authors reported that the concrete mix
started to segregate (i.e. the aggregates and cement particles tended to occupy the
bottom of the container) during the concrete preparation and moulding process due
to the difference in weight of various constituents in the concrete mix. The water
loss due to the addition of CBA as partial replacement of sand fraction in the
concrete mix is presented in Fig. 4.2 a. The bleeding of water increases with
increasing content of CBA. Ghafoori and Bucholc ( 1996 ) observed a similar
behaviour for concrete with fine CBA as partial substitution of sand (Fig. 4.2 b).
According to these authors, the higher bleeding of fresh concrete mix due to
Fig. 4.2 Water loss due to bleeding of concrete mixes with various amounts of fine CBA
aggregates. a Andrade et al. ( 2009 ); b Ghafoori and Bucholc ( 1996 )