2019 CSCE Annual Conference - Laval (Greater Montreal)

2019 CSCE Annual Conference - Laval (Greater Montreal) Conference


Title
Application of Recycled Gypsum Wallboards in Cement Mortar

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Author(s)
Ms. Sarah Hansen, Dalhousie University (Presenter)
Dr. Pedram Sadeghian, Dalhousie University
Abstract

Gypsum wallboards have been used extensively in the construction industry, however waste gypsum wallboards are often disposed of in landfills instead of being recycled. Landfill sites with large volumes of waste containing gypsum cause leachates with harmful effects on human health and on the environment. Large amounts of carbon dioxide are emitted during the production of cement, so partially replacing cement with recycled gypsum would also help prevent harmful emissions. Gypsum is already known to be added to cement at small percentages in order to reduce the speed of reaction with water, however substantial technical research has not been done using recycled gypsum wallboards containing other materials such as paper, fiber, and paint particles. The primary objective of this research is to use recycled gypsum as a partial replacement for cement in concrete mixtures to introduce a more sustainable solution using recycled materials that is environmentally friendly, while maintaining adequate strength and durability. Several mixtures containing different combinations of cementitious material including Portland cement (50-100%), gypsum (0-40%) and fly ash (0-40%) 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 days 3, 7, 28, and 56. Superplasticizers were used in effort to regulate the consistency of mixtures, as gypsum was found to dehydrate the mixture more than regular cement. Fly ash can increase the workability of concrete mixes, although it is known that large amounts of fly ash require a longer initial setting time and show low early strength. Research showed that mixtures containing only recycled gypsum and Portland 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,