Thermal energy storage-enhanced self-leveling mortars made of pre-placed perlite aggregates filled with bio-based phase change materials

This study investigates the development and performance of Self-Leveling Mortars (SLMs) enhanced with Phase Change Materials (PCMs) and expanded perlite aggregates to provide Thermal Energy Storage (TES) functionality for energy-efficient buildings. A cementitious encapsulation method was used to coat PCM-saturated perlite, forming durable macro-encapsulated aggregates. To preserve the structural integrity of these inclusions during casting, the pre-placed aggregate method was employed in combination with a highly flowable self-consolidating mortar matrix. Three mortar formulations were produced and analyzed: (a) reference SLM, (b) SLM with expanded perlite, and (c) SLM with PCM-filled perlite. Thermal performance was assessed through dynamic “DKK” tests and a custom ASTM C1363 Hot-Box apparatus. Tests reveal that PCM-enhanced mortars achieved the highest thermal buffering effect, exhibiting plateaus at 25–30 °C and reduced heat flux values. The apparent thermal conductivity, during the PCM phase change, dropped to 0.28 W/m × K, demonstrating effective latent heat absorption. The results clearly demonstrate enhanced passive thermal regulation with delayed heat transfer responses, supporting the use of PCM-perlite SLMs as energy-storage building materials. Complementary tests were then performed to verify material, mechanical and durability feasibility of the composites. Mechanical tests showed that the reference SLM achieved the highest compressive and flexural strengths, at 60.14 MPa and 5.79 MPa, respectively. The incorporation of expanded perlite reduced the compressive strength to 29.02 MPa, while PCM-enhanced aggregates further reduced it to 17.62 MPa. A slight improvement in flexural strength was observed for the PCM composite (i.e., 3.46 MPa) compared to the uncoated perlite (3.08 MPa), indicating potential reinforcement by the encapsulation shell. Water absorption tests revealed that PCM-enhanced perlite mortars exhibited low absorption within the first 180 min but experienced a sharp increase at 72 h (i.e., 3 days), surpassing all other mixes and suggesting long-term permeability issues. SEM-EDS analyses indicated high Ca/Si ratios (∼7.75) in the shell, and TGA results showed minimal portlandite decomposition, both supporting the hypothesis of calcium hydroxide consumption by silica fume to form additional C–S–H gels. Overall, PCM-perlite SLM shows strong potential for TES-enabled building applications.