Use of gypsum panels waste in clay materials

Abstract

The aim of this thesis is to investigate the influence of the addition of crushed gypsum panels waste to poured earth. In particular, the effect on shrinkage and crack formation during the drying process, the rheological and mechanical properties and the chemical reaction which leads to coagulation are analyzed. The drying process is accelerated thanks to the addition of crushed gypsum panels. Furthermore, the apparition of cracks is reduced by approximately a factor 2 and, most importantly, their width is reduced by an average factor 1.5 with respect to pure earth. It has been shown that water absorption by the gypsum panel does not influence the rheological properties of the mixes but the coagulation is rather due to a chemical reaction be- tween gypsum (CaSO4·2H2O) and the dispersant sodium hexametaphosphate ((NaPO3)6). The compressive strength of the earth-gypsum mix with 7.5% clay replacement by crushed gypsum panel is increased by approximately 18%, from averagely 2.35MPa to 2.78MPa. Furthermore, the ecological and economical impact of the new material was estimated and compared to the one of concrete: 30 times less CO2 per mass unit and 3 times less CO2 per mass unit and MPa compressive strength are emitted by the developed mix compared to concrete, while the costs of the used raw materials are comparable (0.06-0.08CHF/kg). The created mix is largely recy- clable with little effort. More research is required to examine other properties of the investigated earth-based construction material, in particular it would be interesting to analyze durability.