The aim of this study is to quantitatively determine the effect of elevated temperatures on the pore structure and compressive strength of concrete. To minimize the effect of the hydration process, thermal and endogenous shrinkage, concrete cured in water for 12 months was tested. Evolutions of pore structure under elevated temperatures (40, 105, 150, 200, and 250°C [104, 221, 302, 392, and 482°F]) were characterized by mercury intrusion porosimetry (MIP), N2 adsorption, and scanning electron microscope (SEM) tests.

Compressive strength tests were carried out to characterize the mechanical properties. The experimental results showed that with the increase of temperature, the porosity increased and the pore structure destroyed gradually. The changes in porosity and pore structure can be explained by the loss of water in concrete. In addition, the compressive strength decreased with increasing temperature.

The relationship between compressive strength and porosity after heating at elevated temperatures fitted well with the strength-porosity logarithmic relation proposed by Schiller. The correlation coefficient is 0.994, which indicated that the effect of elevated temperature on the compressive strength of concrete can be quantitatively determined by Schiller function.

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