Properties of recycled gypsum from gypsum plasterboards and commercial gypsum throughout recycling cycles

The increasing consumption of gypsum products compels their producers and consumers to behave in accordance with the precepts of sustainability. Despite the necessity of the integral recycling of gypsum products, only a part of the waste plaster is reused, which leads to the development of products with large quantities of plaster to meet this growing demand. The objective of this research was to investigate the variation of the physical and mechanical properties of residues of gypsum plasterboard sheets and commercial gypsum during recycling cycles on bench scale. The experiment addressed the crushing, milling, calcination, hydration, formation and breaking of test bodies. The microstructure of the recycled gypsum was characterized according to its chemical and mineralogical composition by using scanning electron microscope (SEM) and X-ray spectroscopy (EDX). The characteristics of the powder and the physical and mechanical properties in the fresh and hardened states were determined for five proportions of recycled gypsum and commercial gypsum throughout the recycling cycles. The results showed that it is possible to obtain 8.40 MPa for axial compression strength at 28 days in the first three recycling cycles for gypsum from gypsum boards, recycled gypsum plaster and the suggested mixtures, except for gypsum recycled in the first cycle and commercial gypsum plaster. Values higher than 30 N mm(-2) were obtained for surface hardness in all samples. The reversibility of the reactions was verified during the recycling cycles, proving the technical viability of the process up to the third recycling cycle. The third cycle gypsum presented similar results to the original gypsum and met the technical norms requirements. Hence, the potential of producing components containing large quantities of recycled gypsum is notable, thus encouraging not only reverse logistics but also the incorporation of waste products and increasing products cycles. (C) 2018 Elsevier Ltd. All rights reserved.