Page 104 - New Trends in Eco efficient and Recycled Concrete

78 New Trends in Eco-efficient and Recycled Concrete

Figure 3.16 SEM micrographs of PP fibre concrete (A) before fire test and (B) after fire test
(Han et al., 2005). PP, Polypropylene; SEM, scanning electron microscope.

PET aggregates exhibited more significant compressive strength and elastic modu-
lus reductions than those seen in the conventional concrete when exposed to 600
and 800 C, and the difference became more pronounced with an increase in RPA%.

Ozbakkaloglu et al. (2017) reported a similar trend for the compressive strength
reduction of concrete containing PP coarse aggregates (with melting point of
160 C) when exposed to 200 C. Han et al. (2005) showed that concrete containing

PP fibres had a higher residual compressive strength than that of the conventional

concrete after exposure to elevated temperatures in a furnace at 850 C for 40 min.
This is because of the severe spalling failure of conventional concrete caused by
the generation of high vapour pressure at high temperatures, whereas no spalling
occurs in concrete containing PP fibres as the vapour pressure is released when PP
fibre melted. Fig. 3.16 shows the SEM image of concrete containing PP fibre at

ambient temperature and after exposure to 600 C(Han et al., 2005). The
figure clearly shows that the PP fibre melted after exposure to 600 C, resulting in

the release of the vapour pressure. Furthermore, an increase in RPF% resulted in an
increase in the residual compressive strength of PP fibre concrete even when the

concrete was heated up to 850 C, which is attributed to the bridging effect of PP
fibres to prevent the spalling failure in concrete (Han et al., 2005).

3.7.2 Thermal conductivity
Recycled plastic concrete develops a lower thermal conductivity in comparison to
the conventional concrete, which is because the thermal conductivity of recycled
plastics is lower than that of NAs. There are very limited studies on the thermal
conductivity of recycled plastic concrete. Yesilata et al. (2009) showed that the
replacement of natural fine aggregates by PET fine aggregates by 15% with square,
stripped and irregular shapes resulted in, respectively, a 10.3%, 17.1% and 17.2%
decrease in the thermal conductivity of concrete, suggesting that the thermal con-
ductivity of PA concrete is influenced by the geometry of PAs. Wang and Meyer