Assessment of different shapes and grain sizes of bentonite aggregates in lightweight concretes

This study deals with the production of lightweight concretes from bentonite aggregates. Bentonite ball pellets of different grain sizes were prepared and the green pellets were then dried for 48 h in open air to allow the water of workability to release. They were then fired in a muffle furnace at a rate of 20 K/min for 1 h at 1150 °C. This temperature is the best temperature and yields the lowest density and higher bloatability without complete melting of the pellets. The bloatability of the investigated clay pellets was followed by the bulk density. The bentonitic materials were investigated for their chemical and mineralogical composition (XRD, SEM and EDX). The physico-mechanical properties including compressive strength were investigated on concrete pastes. Also, the phase composition was determined by XRD, SEM and EDX. The results of the compressive strength, density and bulk density showed that these lightweight concretes were affected by the type, shape and the percentage of aggregates, the cement paste and the interfacial zone between cement and aggregates. Strength minerals represented by calcium silicate-hydrate (CSH) and calcium aluminate-hydrate (CAH), which lead to the concrete strength.