Optimization of fresh properties and durability of the green gypsum-cement paste

Abstract

Despite the fact that gypsum materials have many advantages, such as fast hardening, low cost, environmental friendliness, their field of application is limited by low values of compressive strength, water resistance and durability. An urgent task is to increase the efficiency of the gypsum composite through the use of Portland cement, as well as a natural and man-made waste. The novelty of the work lies in the identification of scientific regularities of the influence of industrial waste on the structure formation and properties of green gypsum-cement paste (GGCP). For the first time, the genesis and technogenesis of quartz in the waste of ferruginous quartzites is generalized and studied. The features of the formation of the structure and hardening of GGCP are studied taking into account the chemical, structural and morphological features of dehydrate gypsum, Portland cement and man-made waste of various genesis. Gypsum β-modification of the G-5B II grade and technogenic wastes were used as a binder component and mineral additives, respectively. The fresh properties and durability of the GGCP were studied according to standardized test methods. However, the influence of different fineness of grinding of components on the performances of GGCP was investigated. It was revealed that with a decrease in the fineness of concrete waste, from 200 to 600 m2/kg, the compressive strength significantly increases, 4 times. This is due to the fact that when concrete waste is ground; previously unhydrated cement particles are exposed, which undergo hydration later. It was revealed that the maximum compressive strength of 22 MPa of the GGCP is achieved at a specific surface area of 600 m2/kg, a further increase in the specific surface area would lead to a decrease in compressive strength, which is explained by an increase in water demand. As a result of research for two years, both in water and air, it was found that there were no signs of destruction and decrease in the strength of the specimens. In accordance with the experimental data obtained, a three-stage model of the structure formation of the GGCP with mineral additives of industrial waste was proposed.