Use of Industrial Waste as Aggregate: Properties of Concrete - Recycled Aggregate in Concrete - page 147

Fig. 4.25 Residual
compressive strength of
concrete after high
temperature exposure of
BFS-aggregates concrete (C-
series) along with CBA
aggregates concrete (K-
series) (Yüksel et al. 2007 )
Increasing addition of aggregates slightly improved these properties, which was
more noticeable in the dynamic elasticity modulus results. In another work, Yüksel
et al. ( 2007 ) observed higher residual strength for concrete where up to 40 % by
weight of fine aggregates were replaced by BFS aggregates than for conventional
concrete. In this study, the maximum strength was observed at 20 % replacement
level. The residual strength was lower than that of the conventional concrete for
50 % replacement of fine aggregates by BFS aggregates, possibly due to changes
in concrete microstructure and the generation of more porosity because of the
substitution of fine aggregates by porous BFS aggregates. However, the residual
strength of concrete with CBA as partial replacement of fine aggregates was better
than that of the BFS-aggregates concrete (Fig. 4.25 ).
Yüksel et al. ( 2007 ) found higher freeze-thaw resistance for concrete with BFS
as partial replacement of fine aggregates than for conventional concrete as well as
CBA aggregates with concrete. The specimens were subjected to 50 cycles of
repeated freezing and thawing. This resistance increased with the replacement
ratio of fine aggregates by BFS aggregates and at 20 % replacement level it
reached a maximum; further increasing the replacement level up to 50 % by
weight decreased the resistance even though the performance was still better than
that of conventional concrete. Their results are presented in Fig. 4.26 .
Yüksel et al. ( 2007 ) observed an insignificant effect of wet-dry cycles on the
strength loss of concrete with BFS fine aggregates as 0-50 % by weight replacement
of NA, when the specimens were subjected to 25 cycles. Collins and Sanjayan ( 1999 )
observed lower drying shrinkage for AAS concrete with BFS as coarse aggregates
than for concrete with basalt aggregates. The experiment was undertaken at 23 C
with 50 % room humidity. However, similar autogenous shrinkage in concrete with
basalt and BFS aggregates indicated that the improvement of shrinkage because of
BFS-aggregates addition was attributed to the internal curing caused by the moisture
present in these aggregates. Ashby ( 1996 ) also observed lower drying shrinkages for
concrete with air-cooled BFS aggregates than for conventional concrete with river
gravel up to a period of 56 days. Haque et al. ( 1995 ) reported lower drying shrinkage
for high-performance concrete with air-cooled BFS aggregates than for conventional
concrete.