Long-term progressive deterioration following fire exposure of OPC versus slag blended cement pastes

Abstract

The normal practice of repairing fire-damaged concrete structures is to remove the visibly damaged portions and restore them with new concrete. However, little attention has been given to the long-term performance of fire exposed concrete which is not removed from the structure. This paper addresses this issue. Ordinary Portland cement (OPC) pastes, when exposed to a critical temperature of 400°C, undergo complete breakdown. This behaviour was attributed to the dehydration of Ca(OH)2, followed by the expansive rehydration of CaO. In contrast, partial replacement of the OPC binder with slag, had a beneficial effect in the mechanical properties of the paste after exposure to high temperatures, as slag significantly reduces the amount of available Ca(OH)2 in the cement paste. The present work provides new data regarding the long-term (after the exposure event) effect of CaO rehydration in the OPC and OPC/slag pastes. After 1 year the ongoing effect of the CaO rehydration was severe in the OPC paste while OPC/slag blends were not affected by rehydration. Compressive strength and thermogravimetric results are presented to explain this behaviour.