Behaviour of modified lightweight aggregate concrete after exposure to elevated temperatures

Abstract

An inorganic polymer compound was used to coat lightweight expanded clay aggregates (ceramsites) with a thin layer. These modified aggregates were then used to manufacture modified ceramsite concrete specimens. The spalling and mechanical properties, including cube and cylinder compressive strengths, tensile strength, flexural strength, elastic modulus and stress–strain relationship, of the concrete specimens at room temperature and after exposure to high temperatures (200–1200°C) were tested. Furthermore, chemical changes of the inorganic polymer compound and macro- and microstructures of the concrete were also detected after exposure to the different temperatures by means of Fourier transform infrared spectroscopy, charge-coupled device high-temperature in situ digital image collection and scanning electron microscopy, respectively. Normal ceramsite concrete and crushed limestone concrete were also produced as references for comparison. It was found that only 4·2% of the modified ceramsite concrete specimens spalled, while 69·4% of the normal ceramsite concrete specimens and 33·3% of the crushed limestone concrete suffered spalling. After exposure to 1200°C, modified ceramsite concrete still had considerable residual mechanical properties. The polymer used as the modification material decomposed gradually with increasing temperature, which could generate channels for vapour release to reduce the possibility of concrete spalling.