Civil Engineering Reference
In-Depth Information
composite with high thermal conductivity. PeT concrete composites show
an interesting thermal insulation performance. however, a high PeT waste
volume is needed to ensure a low thermal conductivity coefficient and that
implies a high mechanical strength loss.
Durability
Silva et al. (2005) found that, with time, PET fibres degraded in the alkaline
environment of the cement paste. The mechanism of PeT degradation
involves a depolymerization reaction that breaks the polymer chain, splitting
it in two groups (the aromatic ring and the aliphatic ester). The infrared
spectrum of PET fibre after immersion in alkaline solutions that reproduce
the alkaline conditions of pore solution shows the presence of bands assigned
to the aromatic ring. As a result of PET fibre degradation the toughness
performance of cementitious composites decreases with time. These authors
mentioned a 20% loss between specimens with 42 curing days and 104 curing
days.
Ochi et al. (2007) mentioned that treated indented PET fibres showed high
resistance to chemical degradation in an alkaline medium. These authors
compared the alkali resistance of treated PET fibres with the resistance
of PP and polyvinyl acetate (PVA) fibres reporting that the former retains
99% of their tensile strength while PP only retains 86% and PVa shows a
severe degradation retaining only 56% of its tensile strength. Benosman et
al. (2008) reported that the partial replacement of cement by PeT wastes
contributed to the reduction of the chloride ion diffusion coefficient.
Won et al. (2010) studied the durability of embossed PET fibres composites.
although the results of chloride permeability were similar to the control
concrete and freeze-thaw resistance was better than the control concrete,
the results related to exposure to an alkaline environment and to sulphuric
acid revealed a performance that is not acceptable when it comes to real
applications.
galvão et al. (2010) compared the performance of PeT-based concrete
composites versus the performance of concrete with low-density polyethylene
fibres and tyre waste fibres. The results showed that PET composites had the
highest compressive strength with almost 30 MPa for the worst case scenario
(7.5% volume replacement). even for the tensile strength PeT composites
outperformed the other wastes. as to the erosion-abrasion under water test
the best results were obtained for mixtures with 5% PeT and 5% low-density
polyethylene fibres. When compared with the reference concrete erosion-
abrasion resistance, the 5% PeT mixture presented less than 23% of mass
loss and and 5% low-density polyethylene fibres mixture presented less than
40% of mass loss.
