Mechanical and acoustic properties of gypsum composites with cellulose waste

Gypsum building materials are widely used in the construction sector and their use is growing steadily. At the end of the life cycle of a building, these gypsum materials become demolition waste. Thus, the increased consumption of gypsum building materials leads to an increased amount of demolition waste. The recycling of such demolition waste is becoming more and more relevant and important, as the recycling of gypsum waste would save natural raw materials and reduce waste. The main objective of this study was to investigate the effect of waste cellulose fibers on the physical and mechanical properties of gypsum samples. First of all, gypsum waste board was shredded and the cellulose separated from the gypsum. The gypsum particles were then ground in a ball mill to a fine powder. Calcination was carried out at 160 °C for 1,50 hours of 1 kg of gypsum. Citric acid was used as a set retarder and the amount was 0,05 wt. % by weight of the gypsum powder. The amount of waste cellulose fibers was 1, 3, 5 and 10 wt. % and as reference sample used gypsum sample without cellulose. The density, flexural and compressive strength were determined for all the samples. The microstructure was assessed by optical microscopy and the acoustic insulation properties were determined. The results showed that it is possible to obtain 5,75 MPa of compressive strength and 1,2 MPa of flexural strength by including 3 and 5 wt. % of waste cellulose fibers. The results of the sound insulation performance of gypsum composites with different amounts of waste cellulose fibers show that the highest levels of sound insulation were achieved when the composite contained 3 % and 5 % by weight of waste cellulose fibers. The findings of the study indicate that the utilization of recycled gypsum can yield environmental benefits when compared with the use of natural gypsum.