Effect of electrical arc furnace slag, lead slag and steel fibres on thermal properties of one-part alkali-activated materials for sensible heat storage

This study investigates one-part alkali-activated materials incorporating lead slag (LS) as fine aggregate, steel fibres (SF), and electric arc furnace (EAF) slag as partial replacement of natural coarse aggregate. An integrated experimental, statistical, analytical, and microstructural approach was adopted, with optimised mortars scaled to concrete and subjected to 10-time cyclic heating up to 400 °C. At the mortar scale, SF was identified as the dominant factor governing strength and thermal conductivity, enhancing crack resistance and forming effective heat-transfer pathways. Increasing the LS fine aggregate content improved thermal conductivity and specific heat capacity with a slight reduction in strength at higher levels. Analytical modelling showed that the parallel model well predicted thermal conductivity under ambient conditions, whereas none of the conventional models adequately captured post-heating behaviour. At the concrete scale, partial replacement of natural aggregate with EAF slag improved thermo-mechanical performance, with 10% replacement providing the most balanced enhancement in strength, thermal insulation, and heat storage capacity. These findings demonstrate the potential of waste-derived alkali-activated composites for sustainable concrete-based thermal energy storage applications. • One-part alkali-activated materials were developed using lead slag, steel fibres, and EAF slag for TES. • Steel fibres governed strength and thermal conductivity through conductive crack-bridging networks. • Lead slag increased thermal conductivity and specific heat capacity at the mortar scale. • Cyclic heating to 400 °C preserved strength but reduced thermal conductivity. • A 10% EAF slag replacement enhanced the mechanical performance and heat storage of concrete.