The effect of additives on the properties of lightweight aggregates produced from clay

In an attempt to improve the properties, lightweight aggregates were produced from clay with the addition of Na2CO3, SiO2, Fe2O3, and Fe in quantities between 2 and 10 wt% and examined with respect to strength, density and expansion behavior. The additives were mixed into dry clay powder, water was added and pellets were formed by hand and fired at 1120 °C in a chamber furnace. Particle densities of the products ranged from 0.31 to 0.57 g/cm3, porosities from 78% to 89% and the solid strength from 0.54 to 1.58 MPa. The addition of Na2CO3 proved to decrease the viscosity of the glass phase at the surface of the pellets but resulted in a reduced expansion, irregular shape and pellets sticking together. SiO2 addition did not give any major change in properties. The addition of Fe2O3 increased the pore size in the center of the pellets, however with insignificant change in strength and density. Adding 5 wt% metallic iron powder led to LWA pellets with increased porosity, reduced density, larger pores and low mechanical strength and could be a useful additive in applications where low density is more important than strength.