Orimulsion fly ash in clay bricks. Part 2: technological behaviour of clay/ash mixtures

In order to appraise the technological feasibility of the Orimulsion ash recycling in clay bricks, a laboratory simulation of the brickmaking process was carried out with various clay/ash mixtures up to 6% waste. Two different clays were selected and mixes were characterized by XRF, XRPD, TGA-DTA, TDA, and PSD analyses. Plasticity, extrusion and drying behaviour, and mechanical strength were determined on unfired mixtures, while shrinkage, water absorption, bulk density, modulus of rupture, pore size distribution, microstructure and phase composition were measured on fired bricks. Orimulsion ash caused some detrimental changes of technological properties of both unfired and fired products, concerning particularly plasticity, drying rate and drying sensitivity, porosity, and colour. These effects were slightly different on the two raw materials, being the carbonate-rich clay less sensitive to the presence of ash in respect of the carbonate-free clay. At all events, drawbacks appeared to be tolerable, in technological terms, for low waste additions, approximately 1-2% ash.