Evaluation of the calcination parameters of the gypsum waste on the properties of recycled plaster

Abstract

Industrial activities have contributed to the generation of gypsum waste, so the high volume and inappropri-ate disposal contributes to environmental problems and represents waste of material. The objective of this work was to characterize the waste of gypsum and to evaluate the influence of parameters such as granu-lometry, temperature and calcination time on the properties of the recycled gypsum, seeking the reduction of residues and obtaining better properties of the final product with the use of 100% of recycled plaster. The gypsum waste was beneficiated, characterized and separated into three different granulometries: sieve ABNT nº 200 (0.075 mm); ASTM nº 50 (0.3 mm) and ABNT nº 10 (2.0 mm). They were then calcined at tempera-tures of 130, 136, 150 and 170ºC for 1, 2, 4, 6, 8, 17 and 24h. Its workability, heat of hydration, mechanical properties, mineralogical characterization and morphology were analyzed in the recycled plaster. The recycled gypsum was influenced in its properties in the evaluated parameters, besides the presence of impurities. The main phases formed in the recycled gypsum were affected by the calcination time: calcium sulfate hemi-hydrate, calcium sulfate dihydrate, anhydrite and calcite. The workability did not show a clear trend of behavior independent of grain size, time and calcination temperature. The best results for the compressive strength were obtained at the temperature of 136ºC (17h) and 150ºC (8h). The recycled plaster had an aver-age hardness of 12.71 N∙mm-2. The recycling of gypsum waste can contribute to the reduction of waste and make possible the use of new technologies in civil construction.