Mechanical and thermal properties of fiber-reinforced concrete incorporating shape-stabilized phase change materials: Evaluation of paraffin-silica fume and PEG-silica fume

The integration of phase change materials (PCMs) into concrete enhances thermal regulation, though structural applications are often constrained by reduced strength. This study investigates the use of shape-stabilized PCMs (SSPCMs) as partial cement replacements in fiber-reinforced concrete (FRC) to produce load-bearing elements with both mechanical integrity and improved thermal performance. Paraffin and polyethylene glycol (PEG) 1000 were stabilized with silica fume (SF) through vacuum-assisted impregnation to prevent leakage and ensure uniform distribution. A key novelty of this work lies in the comparative evaluation of paraffin- and PEG-based SSPCMs under identical stabilization conditions to assess their relative efficiency in optimizing the mechanical–thermal performance of structural concrete. SSPCMs replaced 10–30% of cement by weight, while hybrid steel–glass fibers (0.4%) were incorporated to enhance mechanical properties. When 20% of cement was replaced with paraffin/SF, compressive and flexural strengths showed only minor reductions, whereas thermal conductivity decreased by 56%, water absorption decreased by 28%, and surface temperature under sunlight reduced by 25.5%. Similarly, a 20% PEG/SF replacement led to slight reductions in mechanical strength, a 51% decrease in thermal conductivity, a noticeable surface cooling effect, and a 7% increase in water absorption. The addition of hybrid fibers enhanced mechanical performance by approximately 13%, with modest additional improvements in thermal conductivity and water absorption. These results demonstrate that SSPCM-integrated FRC can significantly improve the thermal management of structural elements with minimal compromise to mechanical performance. The comparative analysis further guides the design of load-bearing concrete components with optimized mechanical–thermal compatibility.