INFLUENCE OF ADDITIVES ON THE HYDRATION AND DISSOLUTION KINETICS AND PROPERTIES OF SEMI-HYDRATE GYPSUM

Abstract

In this work, the influence of citric acid, methylcellulose and polymer additives on semi-hydrate gypsum hydration and dissolution kinetics and physical and mechanical properties has been investigated. These additives are commonly used in dry construction mixtures of gypsum production. The citric acid additive was found to slow down 1.3–1.5 times semi-hydrate gypsum hydration and dissolution. The methylcellulose additive during the period up to 40 min marginally affects the hydration and dissolution rate and the suspension pH variation, but later the effect does not occur. The polymer additive during the period up to 40 min increases the rate of hydration of calcium sulphate, but later (60 min) it has but little influence. The additive acts as a plasticizer, it reduces the setting time and compressive strength of samples. After using all three additives, the V/G of forming mixture decreases, and the initial setting time extend to 62 min. The compressive strength of wet samples decreased almost 2-fold compared to samples without additives, but the compressive strength of dry samples was almost 1.5 times higher.