Civil Engineering Reference
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Fig. 4.43 Flexural strength behaviour of concrete with fine PET-aggregates before and after heat
treatment (Albano et al.
2009
)
4.6.4.1 Fire Behaviour
Albano et al. (
2009
) determined the fire behaviour of concrete with various per-
centages of shredded PET-aggregates as partial replacement of natural fine
aggregates. The authors placed the cured slabs in a muffle furnace, the temperature
inside the furnace was increased up to a given temperature, the slabs were kept at
that temperature for 2 h and then the heating was stopped immediately. The
temperatures chosen for this study were 200, 400 and 600 C. After cooling the
specimen to room temperature, the flexural strength was determined. In parallel,
unheated specimens were tested. Their results are presented in Fig.
4.43
.
As the temperature increased, the flexural strength decreased regardless of the
substitution ratio and the PET particle size. However, the decrease in flexural
strength was more significant when PET content was 20 % than 10 % due to the
presence of more porosity (voids), which act as stress concentration spots.
Moreover, PET-aggregates were more susceptible to temperature than natural fine
aggregates. The volume change and the degradation of the PET particles produce
less cohesion between concrete components and a greater number of voids. The
decrease in flexural strength also increased with the w/c value. According to the
authors, at high w/c value the thermal stability of PET-aggregates decreased due to
the hydrolytic degradation of PET particles. The formation of carboxyl and
hydroxyl end groups occurred due to the reaction of one water molecule with one
PET molecule, which accelerated its decomposition. Besides, the water vapour
was difficult to discharge at high temperatures, so the vapour pressure favours
crack formation in concrete.
4.6.4.2 Thermophysical Properties
Mounanga et al. (
2008
) observed significantly low thermal conductivity for con-
crete with PUR-foam aggregates used to partially replace fine NA due to the
porous nature of PUR-foam aggregates. These pores contain air, whose thermal
conductivity is much lower than that of the other concrete constituents. The
