Optimization of the Composition of Cement Pastes Using Combined Additives of Alumoferrites and Gypsum in Order to Increase the Durability of Concrete

Abstract

The reliability of concrete structures is closely related to the durability of the concrete materials stable under external environmental conditions. The present study is aimed at analysing the effect of a prospective hardening additive containing calcium alumoferrites and calcium sulfate (AFCS) as a substitute (5–15%) for Portland cement. The hardened cement pastes were characterized by water absorption, shrinkage, strength and corrosion resistance. It was shown that replacing a part of Portland cement with the AFCS additive results in an increase in the strength of fine-grained concrete and in the water resistance grade of concrete. The use of the AFCS additive in the mixed cements reduces the shrinkage of cement stone, resulting in shrinkage-free fine-grained concretes. The increased corrosion resistance of the hardened cement paste is caused by a chemical (saturation) equilibrium between corrosive medium and a cement stone. Penetration of sulphate ions from corrosive solution into the hardened cement paste is much lower, unlike Portland cement. Following saturation of the hardened cement paste with sulphate ions, their further penetration into the cement stone does not occur. Based on the results of the study, recommendations were developed for the use of the hardening alumoferrite-gypsum additive to Portland cement, which allows to improve the mechanical and corrosion characteristics of concrete.