The influence of cyclic temperature and humidity effects on the compressive strength of heavy concrete

Abstract

The paper presents the results of experimental studies of the effect of cyclic exposure to elevated temperatures up to 90оС and 150оС and moistening to full water saturation on the strength of heavy concrete. Quantitative data on the change of concrete strength properties depending on the influence factors are obtained. Proposals are formulated to take into account in calculations the influence of heating and moistening modes on the strength of concrete in axial compression. Under cyclic exposure to elevated temperatures and subsequent moistening at normal temperature, there are significant changes in the compressive strength of concrete at different stages of each cycle. At the short-term heating stage, the reduction in the prismatic strength of the concrete amounted to 15 - 22% of the concrete strength before heating. Prolonged isothermal heating results in a 13 - 25% increase in concrete strength. At the stage of subsequent moistening of concrete after heating, there is a decrease in strength by 25 - 27%, while the relative magnitude of strength reduction does not significantly depend on the number of previous cycles. In the investigated interval of up to twenty-five cycles of exposure to elevated temperatures and moistening, the greatest reduction in concrete strength was observed in the first and last cycles. For cycles with heating temperature up to 90⁰C at short-term heating at the beginning of the second cycle the concrete strength drop was 45.5%, and the concrete strength drop at short-term heating for the 25th cycle was 9.7%. For cycles with heating temperature of 150⁰C the strength drop was 45.9% and 52.5%, respectively. The accepted experimental mode according to the formula of cycle (6+1) + (6+1) is the most unfavorable for the strength of concrete under cyclic effects of elevated temperatures and subsequent moistening.