Application of Recycled Gypsum Wallboards in Cement Mortar

Abstract

Gypsum is a naturally formed mineral that is already known to be added to cement at small percentages in order to reduce the speed of reaction with water, however it seems that substantial technical research has not been done concerning larger proportions of gypsum. The primary objective of this study is to use recycled wallboard/drywall powder (hereafter is called gypsum) as a partial replacement for cement in cement mortar mixtures to introduce a more sustainable and environmentally friendly solution that lowers carbon dioxide (CO2) emissions by using recycled materials, while maintaining adequate strength and durability. Used gypsum wallboard is often sent to landfills instead of being recycled, which can cause leachates with harmful environmental and health effects. Eight mixtures containing different combinations of cementitious material including cement, gypsum and fly ash were mixed with water and aggregates and placed in 50 mm mortar cube molds. After curing in a moist room, the mortar cubes were tested for compressive strength at the age of 3, 7, 28, and 56 days. Superplasticizers were used to regulate mixture consistency, as adding gypsum was found to dehydrate the mixture. Fly ash was also used, though requiring a longer initial setting time than cement. This study showed that mixtures containing only recycled gypsum and cement showed lower compressive strength at all ages, becoming increasingly weak with increased proportions of gypsum. However, combining gypsum and fly ash as partial replacement for cementitious material showed increased compressive strength, especially at later ages.