Study on the effects of different forms of polyethylene terephthalate plastic - aggregates on the compressive strength of concrete.

Abstract

This study describes the effects of polyethylene terephthalate (PET) plastic-aggregates forms on the properties of the resulting concrete, with particular focus on the compressive strength and workability properties. The waste plastic was obtained from various recycling industries and three forms were considered i.e. Coarse plastic aggregate, fine shreds and solid pellets. The various forms were added to concrete replacing natural aggregate at varying percentages and the tests for both workability and compressive strength carried according to British Standard. It was found that concrete mixed with coarse plastic aggregates produced the lowest slump value which translates to the least workable mix. This result was attributed to the fact that the coarse plastic aggregate had a large surface to volume ratio and would have needed more mortar to produce a more workable mixture. The coarse plastic, due to its nature also produced a greater degree of interlocking. On the other hand, concrete mixed with plastic pellets produced the highest slump value hence most workable mix because of the cylindrical nature of the pellets that allowed the mix to flow easily. While the majority of the concrete samples achieved an acceptable level of strength for domestic purposes, the mix with plastic pellets and that with coarse plastic aggregate produced concrete with the highest and least compressive strength with an average 28- day strength of 22MPa and 18MPa respectively. The higher strength of the former is owed mainly to their higher density as they were produced in a controlled environment (vacuum) compared to the coarse plastic aggregate which was melted and crushed by the team, in open air. It was concluded that using plastic pellets as replacement in concrete produced the better results as regards to workability and compressive strength.