Civil Engineering Reference
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Fig. 4.39 Stress-strain
curves for a reference
concrete (plain line) and a
concrete with PET waste
aggregates (dotted line)
(Frigione
2010
)
peak shapes of the two curves also suggested that the concrete with PET waste
aggregates is less brittle than the reference concrete and this type of concrete could
withhold a larger deformation still keeping its integrity (Fig.
4.39
). Kou et al.
(
2009
) observed increasing Poisson's ratio values with increasing contents of PVC
waste aggregates in concrete. Since the higher Poisson's ratios meant higher
ductility, the addition of PVC improved the ductility of the resulting lightweight
aggregates concrete, due to the elastic nature of PVC.
4.6.2.6 Failure Characteristics
After failure during the determination of compressive strength, specimens with
plastic aggregates do not exhibit the typical brittle type of failure, obtained for
conventional cement mortar and concrete. As the plastic aggregates content
increased, the failure became more ductile. The specimens with plastic aggregates
can carry load for a few minutes after failure without full disintegration, as was
observed by various researchers (Hannawi et al.
2010
; Marzouk et al.
2007
, Saikia
and de Brito
2010
). The recycled PET-aggregates can delay crack initiation and
prolong the crack propagation interval thereby increasing structural strength.
Albano et al. (
2009
) found various types of failure including normal cone type
for concrete specimens with PET-aggregates, where 20 % of fine aggregates were
replaced. As the smooth surface of the PVC particles and the free water accu-
mulated at the surface of PVC granules may have caused weaker bonding between
PVC particles and cement paste, most of the PVC granules in the concrete matrix
did not fail but were debonded from the cement paste after reaching the ultimate
strength of concrete (Kou et al.
2009
). Fraj et al. (
2010
) reported that the rupture
mechanism of concrete with PUR-foam aggregates was different from that of the
normal weight control concrete: in the first case, the rupture occurred on the mortar
matrix/PUR-foam aggregates interfaces as well as in the middle of the PUR-foam
aggregates. In normal weight concrete, the rupture mainly took place in the ITZ
because of the poor properties of this zone compared to the other concrete com-
ponents. By observing the splitting behaviour of concrete blocks after tensile
