Lightweight PET based composite aggregates in Portland cement materials - Microstructure and physicochemical performance

Abstract

This article presents testing results of cement mortars, in which Composite Lightweight Aggregates (CLA) obtained in laboratory conditions substitutes a part of natural aggregates. The new aggregates are sustainable products obtained by using 100% waste by-products: PET flakes and sewage sludge fly ash (ssFA) streams or siliceous fly ash (FA). The level of natural aggregate replacement by CLAs in mortars was 10% and 25% by vol. The purpose of the research was to assess the physicochemical properties of fresh and hardened mortars in the context of the quality assessment of two methods of producing CLAs and the type of fly ash used as their integral components. Surface modification of PET using both types of fly ash improves the useable properties of the obtained mortars compared to mortar using unmodified PET. In case of CLA aggregate based on PET and FA, no symptoms of depolymerization of polyethylene terephthalate were observed in the presence of alkali from cement paste. In case of mechanical properties modelled with CLA composite, an increase in compressive or flexural strength has been observed due to the possibility of lowering the w/c ratio in CLAs mixtures without loss of workability. Replacing only a small part of the natural aggregate with CLA aggregate allows for a double ecological aspect: saving of natural resources and full management of problematic plastic and mineral waste. Cement composites with composite lightweight aggregates may be ecosolution for a number of applications for building engineering like ordinary concrete, small pre-cast or modulus concrete.