Experimental study of mechanical properties of normal-strength concrete exposed to high temperatures at an early age

In China, accidental fires are known to occur during construction, causing concrete to be exposed to high temperatures when it is at an early age (i.e. “young”). In this paper, compressive and splitting tensile strengths of concretes cured for different periods and exposed to high temperatures were obtained. The effects of the duration of curing, maximum temperature and the type of cooling on the strengths of concrete were investigated. Experimental results indicate that after exposure to high temperatures up to 800 °C, early-age concrete that has been cured for a certain period can regain 80% of the compressive strength of the control sample of concrete. The 3-day-cured early-age concrete was observed to recover the most strength. The type of cooling also affects the level of recovery of compressive and splitting tensile strength. For early-age concrete, the relative recovered strengths of specimens cooled by sprayed water are higher than those of specimens cooled in air when exposed to temperatures below 800 °C, while the changes for 28-day concrete are the converse. When the maximum temperature exceeds 800 °C, the relative strength values of all specimens cooled by water spray are lower than those of specimens cooled in air.