Use of sulfoferrite additives in heavy and fine-grained concretes

Abstract

The study is devoted to the development of a sulfoferrite expanding additive based on neutralized phosphogypsum and iron-containing scale for compensating concrete shrinkage. The relevance of the work is determined by the need to utilize large-tonnage wastes from the chemical and metallurgical industries, including phosphogypsum and rolling scale, as well as by the acute problem of shrinkage cracking in concrete structures, which reduces their durability and operational reliability. During the experiment, the effect of the additive dosage in the range of 5-15% of the cement mass on the physical and mechanical properties of heavy and fine-grained concretes was studied. The microstructure of cement stone was investigated by X-ray phase analysis and scanning electron microscopy. It was established that the introduction of the proposed additive converts shrinkage deformations into expansion and increases the strength and crack resistance of the material. The optimal dosage was 5% of the cement mass, providing the maximum increase in compressive strength (by 56,8%) and flexural strength (by 14,2%) at the age of 28 days without signs of destruction of the cement matrix. The positive effect is explained by the formation of iron-substituted ettringite-like hydrates, which contribute to the creation of an internal micro-reinforcing framework and the reduction of internal stresses. The proposed additive can be considered an effective resource-saving alternative to traditional expanding components, such as sulfoaluminate cements, and a promising method for utilizing technogenic wastes in the construction industry while reducing the cost of concrete works.