INFLUENCE OF PRE-CURING PERIOD AT SUB-ZERO TEMPERATURE （-20℃） ON THE COMPRESSIVE STRENGTH OF CONCRETE

Abstract

Average temperatures over most of Mongolia are below freezing from November through March. The lowest temperatures in January are as low as -36℃ to -40℃. However, in the extremely cold climate of Mongolia, it is often executed the concrete works even outside temperature is below -20℃. Therefore, in this experimental work, we investigated the required time span of pre-curing in order to achieve the potential strength at 28 days before being exposed to extremely low temperature（-20℃）, simulating Mongolian weather conditions. Moreover, internal temperature changes and microstructure analyses have been executed. We have found that concrete freezing temperature decreases remarkably from 0℃ to -15.6℃ with increasing pre-curing time, however, depending on the water-cement （W/C） ratio. Our experiments have shown that there was no freezable water after 14 days when the W/C ratio is below 0.39. Our research concluded that concrete should at least be cured at 20℃ for 14 days before being exposed to sub-zero temperatures, in order to reach in fair to middling potential strength at 28 days.