Thermal properties of fibre-reinforced alkali-activated concrete in extreme temperatures

Abstract

The thermal conductivity and specific heat capacity of paste and concrete prepared with alkali-activated fly ash were investigated. Along with a reference plain concrete mix, two other mixes were reinforced with a blend of steel and polypropylene fibres to examine the role of fibre reinforcement on the thermal constants. The mixtures were exposed to a range of extreme temperatures in the sub-zero and elevated regimes, from −30°C to 300°C, for a duration of 2 h. The thermal constants were measured using the transient plane source method on a hot-disc thermal analyser system. The results showed that there was no phase change in the alkali-activated system within the range of exposures. The thermal conductivity increased with a drop in ambient temperature, especially in the sub-zero regime. Adding fibres tended to lower the thermal conductivity, probably due to the finer pore size and consequent lowering of the freezing point of water. The specific heat capacity was found to rise with an increase in ambient temperature. A rule-of-mixtures approach was found to closely approximate the thermal constants at room temperature.