Concrete with crushed, graded and washed recycled construction demolition waste as a coarse aggregate replacement

Purpose – A current trend is to use waste and by-products in concrete to replace binders and aggregates. This trend reduces the impact on the environment and the use of finite natural resources. This paper aims to investigate whether concrete which includes crushed, graded and washed recycled construction demolition waste, used as a coarse aggregate, can be manufactured to a comparable strength as concrete manufactured from virgin aggregates. Design/methodology/approach – Laboratory testing investigated the strength development of concrete manufactured with varying degrees of coarse aggregate replacement. All of the concrete samples were tested at five, seven, 14 and 21 days and the concrete with the recycled aggregate was compared to a plain control sample manufactured with virgin aggregates. The mixes tested against the control sample were: 100 per cent gravel replacement with recycled aggregate, and the same mix with a viscosity modifying agent. A 50 per cent partial coarse aggregate replacement was used in one batch to compare against the control and the 100 per cent recycled aggregate concrete. Compressive strength was used to compare the different concrete batch performance. Density was used to indicate the degree of particle packing and void content which was measured across the range of samples to evaluate the relationship between the different concrete mixes. Findings – The optimum concrete mix design using recycled construction waste was obtained by using a 50-50 per cent mix of virgin gravel and recycled aggregates. Using recycled construction waste as a 100 per cent coarse aggregate replacement produces concrete with a lower compressive strength when compared to concrete made with virgin aggregates. Originality/value – The paper investigates ways of incorporating construction demolition waste as recycled aggregate to reduce the environmental impact of the production of concrete