Use of Industrial Waste as Aggregate: Properties of Concrete - Recycled Aggregate in Concrete - page 143

Fig. 4.21 Comparison of
slump of AAS concrete with
BFS and basalt as coarse
aggregates and conventional
concrete with basalt coarse
aggregates (Collins and
Sanjayan 1999 )
4.4.1 Fresh Concrete Properties
There are vast differences in results presented in various references on the slump
behaviour of concrete mix due to the addition of BFS aggregates. Etxeberria et al.
( 2010 ) observed a slight increase in slump when 25 % by volume of coarse NA
were replaced by BFS aggregates. The mix was workable just like conventional
concrete. On the other hand, replacing 50 % by volume of NA by BFS aggregates
considerably reduced the slump of the resulting concrete. However, slump
increased again when natural coarse aggregates were completely replaced by BFS
aggregates. Collins and Sanjayan ( 1999 ) observed a slump of 65 mm for alkali-
activated slag (AAS) concrete with BFS coarse aggregates and a slump of 115 mm
for a similar concrete with basalt coarse aggregates. In this study, the BFS
aggregates were presaturated with water before being used as aggregates due to
their higher water absorption capacity (4.4 %) in comparison to that of basalt
aggregates (1.2 %) (Fig. 4.21 ). The observed low slump of BFS aggregates was
due to the differences in surface texture, shape and porosity from basalt aggregates.
However, in some studies, no significant difference was found in terms of slump or
workability between conventional concrete and concrete with BFS as coarse
aggregates (Demirboga and Gul 2006 ; Haque et al. 1995 ). The incorporation of
BFS as fine aggregates replacement also decreases the slump of the resulting
concrete and increasing their content further decreases it (Yüksel et al. 2011 ).
The density of concrete with BFS aggregates depends on the bulk density of
BFS aggregates. Demirboga and Gul ( 2006 ) observed an increase in fresh density
of about 7.9-8.5 % in HSC with different w/c values due to BFS-aggregates
incorporation. The bulk density of BFS aggregates was equal to 2.78 g/cm 3 and
higher than that of natural coarse aggregates. Etxeberria et al. ( 2010 ) reported
lower dry density for concrete with BFS aggregates than for conventional con-
crete. The dry density was further decreased as the content of BFS aggregates
increased due to the lower bulk density of BFS aggregates (2.36 g/cm 3 ) than that
NA (2.56 g/cm 3 ). The air content of alkali-activated concrete with BFS coarse
aggregates and basalt coarse aggregates were 1.6 and 1.2 %, respectively (Collins
and Sanjayan 1999 ).