Sustainable geopolymers incorporating PCM-impregnated paper pulp sludge for energy-efficient building applications

The integration of phase change materials (PCMs) into building components is an effective strategy to enhance thermal energy storage and reduce energy demand. This study presents a metasilicate-activated waste-based geopolymer composite produced by incorporating PCM-impregnated paper pulp sludge (PPS) into a binder system composed of blast furnace slag and silica fume. PPS was impregnated with 45 wt% methyl palmitate to obtain a leakage-resistant geopolymer composite. The mixtures were prepared with varying silica fume contents (0–5 wt%), Si/Al ratios (3.2–3.4), and a silica modulus (Ms≈2.8–3.1) under ambient curing at 30°C. The effects of PCM loading and silica fume content on physical, mechanical, and thermal behavior were examined through density, porosity, compressive strength, DSC, and solar thermoregulation tests. Calorimetric results confirmed that PPS effectively acted as a stable PCM carrier, ensuring reliable thermal storage with a melting enthalpy of ~110 J/g and excellent cyclic stability. PPS/PCM-based panels reduced peak room-center temperatures by up to 12.3%, while the maximum lower-surface temperature reduction reached approximately 5°C compared with the reference geopolymer panel. The predicted thermal-economic analysis demonstrated significant energy savings and feasible cost payback periods. These results highlight the potential of PPS/PCM integrated geopolymers as sustainable and energy-efficient building materials.