Performance of PCM-Enhanced Cementitious Composites and Textile-Reinforced Walls: Mechanical Characterization and OpenFOAM Numerical Investigation for Energy-Efficient Buildings

This study investigates the integration of phase change materials (PCMs) and recycled textile fibers into cementitious composites to improve the thermomechanical performance and energy efficiency of building envelopes. Experimentally, eco-efficient mortars were developed by partially replacing sand with recycled textile fibers (0–40% by volume) and microencapsulated PCM (0–30% by volume) across sixteen distinct formulations. The fresh-state workability, apparent density, compressive strength, and flexural strength were systematically characterized after 28 days of curing. Results show that while PCM addition lowers composite density and mechanical resistance, textile fibers effectively mitigate compressive strength loss and enhance flexural strength by up to 70% through crack-bridging mechanisms. Numerically, an open-source conjugate heat transfer (CHT) framework was developed in OpenFOAM using the chtMultiRegionFoam solver and a temperature-dependent apparent heat capacity formulation to simulate the thermal response of concrete walls lined with an inner textile-reinforced mortar (TRM) skin. The numerical framework was experimentally validated against the literature’s benchmark data, reproducing diurnal surface temperature profiles with high fidelity. A parametric investigation of the inner composite skin thickness (2, 4, and 6 mm in the numerical model, corresponding to 20, 40, and 60 mm prototype layers) was conducted. The analysis reveals that incorporating a PCM-loaded TRM skin dampens internal thermal swings, lowers the required cooling demand, and reduces occupant thermal stress by over 20% compared to plain concrete. This integrated approach establishes an eco-efficient route for valorizing industrial textile waste while embedding passive thermal regulation directly within structural envelopes.