ABSTRACT
When the concrete is exposed to high temperature, its strength and Young’s modulus decreases and microdefects appear at micro (less than 1 μm) and mesolevels (between 1 μm and 1 cm).
Different types of aggregates have various processes happening under high temperature. The majority of aggregates tend to be more or less stable until the temperature is about 500°C. For the non-siliceous aggregates, the temperature when reactions like transformation and decomposition will start is at about 600°C (Harmathy & Aleen 1973). Limestone (calcareous) aggregates experience decomposition of the carbonates, decarbonation at temperatures between 600°C and 900°C, when a significant amount of CO2 is expelled. The chemical and physical changes happen not only to aggregates, but to hardened cement paste as well. When dehydration of hardened cement paste takes place, it changes porosity and water evaporates from aggregates (Bazant 1996).
