Concrete placement technologies at low temperatures

Abstract

The article examines technologies for ensuring the required strength and performance characteristics of cast-in-place concrete and reinforced concrete structures at subzero temperatures, where the critical constraint is the risk of premature ice formation in the pore space of the cement stone and the associated microdestruction of the early structure. A comprehensive analysis is presented of the influence of “cold” curing with antifreeze components and thermally controlled regimes on hydration kinetics, temperature fields, process energy intensity, and durability indicators. Experimental strength data at ages of 3, 7, and 28 days record a nonlinear deterioration of strength development as temperature decreases to −15 °C, even with increased dosages of modifiers, while an effect of delayed hydration in the 7–28 day interval is revealed. Comparison of heating methods according to the “strength–energy consumption” criterion shows the advantage of more uniform heat input, whereas the thermos method ensures maturity without direct energy expenditures but requires reliable heat retention. Microstructural studies and porometry confirm an increase in total and open porosity during cold curing, deterioration of water impermeability, and a reduction in the frost resistance coefficient, with the relationship between the volume of open pores and frost resistance being distinctly inverse. The practical relevance of a combined approach, integrating chemical modification with moderate heating until the attainment of critical strength, is substantiated as a compromise between the rate of hardening, energy efficiency, and durability.