Thermal behaviour of novel lightweight concrete at ambient and elevated temperatures: Experimental, modelling and parametric studies

This paper reports a study based upon experimental investigation and analytical simulation which assesses the behaviour of a new type of lightweight concrete at both ambient and elevated temperatures. Different ratios of by-product materials, including recycled glass and metakaolin, were used in conjunction with expanded clay to produce the lightweight concrete mixes. Their fundamental mechanical properties of compressive and splitting tensile strengths were determined at ambient temperature. In order to characterise their overall thermal behaviour, their density, thermal conductivity and specific heat characteristics were first measured at ambient and high temperatures. A heat flow test was then carried out using a unidirectional heat flow regime and the results obtained were analytically simulated in terms of the time–temperature aspect. A parametric study was conducted using a simulation model to identify the most influential factors governing the thermal behaviour of this type of concrete.The results showed improvements in mechanical and thermal properties in comparison with conventional types of lightweight concrete. Compressive strength exceeded the value required for structural lightweight concrete by about 11%, whilst superior performance was recorded for the modified concrete mixes in terms of thermal conductivity, with percentage decreases reaching 42% at ambient temperature. The best resistance to the effects of high temperatures was observed for concrete mixes containing 15% and 30% recycled glass with 10% metakaolin. Close agreement was obtained between the simulated and measured results. The parametric study showed that the coefficient of thermal convection had the most influential role on the insulation criterion.

► Addition of MK improved the durability of lightweight mixes at high temperatures.
► Reductions in thermal conductivity were observed for the modified concrete mixes.
► Samples with high glass content showed type of spalling at elevated temperatures.
► Satisfactory strength values of structural lightweight concrete were achieved.
► Close agreement between the measured and simulated results were obtained.