Characterisation and behaviour of recycled concrete and bricks as engineered fill.

Demolition waste materials mainly consist of concrete and bricks and arise from the demolition of existing structures and buildings. Environmental and economical reasons make their recycling necessary but up to date little research has been undertaken to what is perceived as low level reuse of these materials.This project tries to understand the behavioural characteristics of three types of recycled materials to determine their potential for engineering fill applications. For this purpose their physical and mechanical characteristics have been extensively investigated. Two types of crushed concrete, one obtained straight after demolition and the other further processed to industry specifications, and one type of crushed bricks were tested. Due to the variable nature of recycled materials large quantities were tested and their grading, particle shape and aggregate crushing and impact values established. In addition, large scale equipment was developed for the determination of their compaction and permeability characteristics. An extensive large scale shear box test regime was used to determine the shear strength behaviour of the materials. Two different densities and maximum particle sizes were used, and their influence on the shear strength established. The degree of particle breakage was also quantified by sieving the shear box specimens before and after testing. The comparison of the behaviour of the materials during shearing has shown that the two crushed concrete based materials behave similarly despite the different degrees of processing, but there is difference between them and the crushed brick material. The friction angles of the materials decrease with decreasing density and maximum particle size, with the reduction of the latter affecting the friction angles values more. The results show that the friction angles reduce with increasing normal stress, the shear-normal stress envelopes exhibit curvature at low normal stresses and the materials exhibit dilatancy at low normal stresses that decreases with increasing normal stress. This behaviour during shearing is similar to the behaviour exhibited by natural granular materials from literature. For all the three types of materials tested, the friction angles fall above the lower limits of strength for rockfill set by Leps (1970), which indicates their suitability for use as engineered fill.