Crushing treatment on recycled aggregates to improve their mechanical behaviour for use in unbound road layers

Abstract

The application of mixed recycled aggregates (MRA) and recycled concrete aggregates (RCA) in road works has been studied intensively over the last two decades. One of the properties that has not been studied enough is the self-cementing capacity of recycled aggregates (RA), which favours improving the bearing capacity of compacted recycled aggregates. This research aims to analyse the variables that influence the self-cementing of recycled aggregates, both concrete and mixed. Elaborating recycled aggregate is carried out by crushing the material in a treatment plant which favours self-cementing. In this research part of the recycled material is crushed again in the laboratory in order to produce a better self-cementing process when the material is crushed and used in a short period of time. One of the causes for which the bearing capacity is improved is the appearance of old unhydrated cement particles, which can favour residual setting in the medium-term. In this work two series with different treatments, based on crushing and sieving part of the material, were studied to determine the influence of these changes on the bearing capacity: a series called All-in-one (AO) with a particle size of 0–20 mm, which includes coarse fraction (C) and fine fraction (F) and a second series, called Fine (F), which only include fine fraction with a particle size of 0–4 mm. In both series different samples of RA were processed by sieving, crushing and compaction in different ways. In addition, natural aggregate samples were studied to compare with recycled ones. The results show that the influence of the treatment in the material, mainly crushing and fresh compaction, as well as particle size, significantly improves the loading capacity of recycled aggregates.