Evolution of Ettringite and Thaumacite in Cement Stone

Abstract

The processes of hydration and hardening of cement systems are still one of the urgent problems of modern building materials science. In particular, this concerns the role of the expansive phases of ettringite and thaumacite, especially in the late stages of structure formation. The difficulty lies in the fact that these two phases are isomorphic to each other and can transform into one another throughout the evolution of cement stone. Many attempts have been made by researchers from different countries to explain the nature and mechanism of action of these structural neoplasms. In the course of numerous studies, it has been found that under certain conditions in the presence of iron compounds and other polyvalent metals, ettringite does not cause destructive phenomena in cement stone even in the late stages of hardening. In the presence of plasticizers, sucrose and carbamide solutions play a positive role. However, special attention is paid to the processes of carbonation, sulfate and carbon dioxide corrosion and the introduction of carbonate additives, which even in the presence of two-water gypsum do not lead to the expansion of the products of hydration and hydrolysis of cement. Experiments on forced carbonation of cement stone have been carried out and the positive role of carbonate additives, especially dolomite, the formation of hardening structures and durability has been shown. The authors propose a technology for the care of concrete after thermal moisture treatment by holding products in an atmosphere of carbon dioxide. It is shown that even in the presence of two-water gypsum used as a cement setting retarder and plasticizer, carbonate additives in combination with sucrose and urea solutions prevent concrete corrosion and increase the durability of cement systems.