Use of a form-stable phase change material to improve thermal properties of phosphate sludge-based geopolymer mortar

Abstract

The development of eco-innovative building materials has become increasingly important due to their unique characteristics and environmental benefits. One such technology, the inclusion of phase change materials (PCMs), is highly effective in reducing energy consumption and increasing the thermal inertia of buildings. This study focuses on a novel PCM that encapsulates fatty acids in polyurethane foam and is incorporated into a geopolymer mortar matrix developed from phosphate industry by-products. The paper first outlines the structural and thermal properties of the developed geopolymer mortar (GP) and the form-stable phase change material (PU@PCM). It then investigates the influence of PU@PCM on the mechanical performance of the geopolymer mortar by conducting compressive tests, and the thermal performance by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and thermal conductivity (LFA) measurements. Results indicate that the prepared geopolymer mortar consists of a continuous three-dimensional network and that the developed PU@PCM provides a suitable operating temperature range (10–22 °C) for designing energy-efficient buildings, with good energy storage capacity (ΔHf = 164 J/g). Although the addition of PU@PCM resulted in a loss of compressive strength, the developed composites still meet the mechanical requirements for concrete applications, with the PU@PCM-rich composite reaching 29.5 MPa. Furthermore, the study of thermal performance shows that the inclusion of PU@PCM significantly improves the heat capacity and slightly reduces the thermal conductivity of the composites, with the PU@PCM-rich composite exhibiting 1.1 J/g.°C and 0.84 W/m.°C, respectively. Finally, cyclic DSC tests demonstrate that the composites are thermally stable even after 20 heating/cooling cycles. Overall, the geopolymer mortar with the highest PU@PCM content shows promise as a potential candidate for developing sustainable and energy-efficient buildings in the future. The developed material offers a combination of good thermal performance and acceptable mechanical strength, which are essential features for practical applications in construction.