Improvement of the technology of winter concreting of monolithic reinforced concrete structures with substantiation of a rational concrete curing regime

Abstract

The specificity of winter concreting of monolithic reinforced concrete structures in regions with a prolonged period of negative temperatures determines the need to optimize thermal curing regimes to prevent premature freezing of the mixing water, which causes irreversible disruption of the crystalline structure of the cement stone accompanied by a loss of 40-60% of the design strength, a 1,5-2-fold reduction in frost resistance and water impermeability, as well as to minimize temperature gradients provoking crack formation under conditions combining exothermic heating of internal volumes and intense cooling of external surfaces. A comprehensive analysis of various technological approaches, including the thermos method with insulation, electrode heating with rod electrodes, heating with PNSV heating wire and the use of thermal mats in combination with modified concrete mixtures on Portland cement with superplasticizers and antifreeze additives, reveals their influence on the formation of temperature fields and the kinetics of structure formation. Experimental data demonstrate that electrode heating ensures a rapid rise to the maximum temperature of 58,2° C in 9,4 hours with a gradient of 2,17° C/cm and high early strength of 12,86 MPa at the age of one day; however, it leads to the formation of a less dense structure with a final strength of 28,54 MPa, unlike the heating wire, which creates a more uniform field (gradient 1,46° C/cm, coefficient of variation 12.4 %) and reaches 30,18 MPa by 28 days with balanced strength gain. The thermos method is characterized by minimal gradients of 0,83° C/cm and a long active phase of 62,3 hours, which affects the rate of formwork turnover, whereas thermal mats offer a compromise solution with a temperature of 47,3° C. Technical and economic indicators, including specific energy consumption from 0 to 87,4 kWh/m³ and total costs 612,8-937,4 rub./m³, emphasize the dependence of efficiency on climatic conditions and the surface modulus of structures, where for elements with a modulus of more than 15 m⁻¹ intensive electric heating is preferable, and for massive ones (less than 5 m⁻¹) – measures to limit gradients. Numerical modeling of heat transfer processes using the Arrhenius kinetic model ensures prediction with an error of up to 6.2 % and confirms optimal parameters in the range of maximum temperatures 45-55° C, gradients not higher than 1,5° C/cm. The revealed correlations, in particular the negative relationship of the maximum curing temperature with the 28-day strength (coefficient -0,873) and the positive one of the uniformity of the field with frost resistance (0,791), substantiate a systemic approach to the choice of regimes. The obtained dependencies contribute to the introduction of adaptive systems for monitoring the maturity of concrete, reducing energy consumption by 18-24%, increasing performance characteristics and reducing construction time, opening prospects for the integration of artificial intelligence, nanocomposite heaters and low clinker compositions for the sustainable development of the construction industry, which allows information systems to effectively assess the relevance of the material for solving practical engineering tasks.