Thermal and mechanical properties of structural lightweight concrete containing lightweight aggregates and fly-ash cenospheres

Abstract

This study investigates the effects of mix proportion, aggregate type, and microstructures on the thermal and mechanical behaviors of structural lightweight concrete (LWC) containing lightweight aggregates and lightweight functional fillers such as fly-ash cenospheres (FAC). Particularly, FAC are incorporated into the mixtures to reduce the materials’ density and thermal conductivity while maintaining high mechanical strength. The experimental results indicate that the elastic modulus and thermal conductivity of LWC decrease linearly with respect to the reduction in concrete density, while compressive strength depend largely on material microstructures. The hierarchically porous microstructure of FAC-containing LWC were investigated using scanning electron microscopy (SEM) and the interactions between lightweight fillers and other phases in concrete – i.e., the cementitious binder and aggregates – are investigated. SEM images taken on mechanically tested LWC samples indicated that the strong FAC shell may provided barriers to hinder micro-crack formation and propagation. Lastly, a two-step homogenization scheme was proposed to estimate the thermal properties of lightweight concrete containing both FAC and aggregates. The results calculated using this method shows good agreement with experimental data.