Lightweight structural cement composites with expanded polystyrene (EPS) for enhanced thermal insulation

The development of Expanded Polystyrene (EPS) concrete involves two major concerns: (a) poor strength resulting in the EPS concrete unsuitable for structural applications, and (b) segregation of the ultra-light weight of EPS during mixing (EPS is approximately 100 times lighter than concrete). Though EPS displays high insulation (thermal conductivity approximate to 0.04 W/m-K), these issues limit its usage in concrete. This study aims to develop a lightweight-EPS cement composite (LECC) having enhanced insulating capacity as well as satisfactory compressive strength for structural applications. To mitigate the deteriorating effect of EPS on strength, the LECC is developed using the base material of ultra-high performance concrete (UHPC). EPS beads of 3-5 mm diameter are mixed in UHPC in five proportions by volume of 0, 16, 25, 36, 45% and the resulting composites are tested for mechanical and thermal properties. Microstructural characterization is performed using micro-computed tomography (mu CT). The choice of the UHPC ingredients proportion is found successful in achieving a balance between an optimum viscosity and satisfactory workability for uniform dispersion of EPS, confirmed by the flow values and mu CT results. McLachlan's general effective media approximation, based on percolation theory, is used to homogenize the composite and estimate its thermal conductivity with satisfactory accuracy. The LECC thus developed displays a strength 45 MPa with a corresponding density of 1677 kg/m(3) and thermal conductivity of 0.58 W/m-K.