High-temperature behavior of expanded-perlite-modified cement mortars: An experimental investigation

This study investigates the mechanical, thermal, and microstructural response of cement mortars incorporating expanded perlite (EP) as a volumetric replacement for natural sand (25–40 %). A 50:50 blend of fine and coarser EP grades was preconditioned to a saturated-surface-dry (SSD) state, enabling the target workability to be achieved without superplasticizer (SP), unlike the reference mortar. Increasing EP content reduced bulk density and mechanical strength due to the low stiffness of the aggregate and a weakened interfacial transition zone. Upon exposure to elevated temperatures (100–1000 °C), EP-modified mortars exhibited higher mass loss below 400 °C associated with the release of absorbed water, while at temperatures exceeding 800 °C the porous EP inclusions effectively mitigated explosive spalling and preserved physical integrity. Thermogravimetric (TG–DTG) analysis confirmed that the fundamental hydration chemistry remained unchanged, with apparent peak amplification attributable to binder-fraction normalization effects rather than altered phase composition. SEM–EDS observations showed that the thermally stable silicate skeleton of EP remains intact after binder dehydration and contributes to post-heating structural continuity. In addition to confirming the expected density–strength trade-off, the study provides a controlled high-temperature performance dataset based on quantified EP moisture conditioning and a closed water budget, a gradation-engineered EP aggregate blend, and standardized ISO 834 fire exposure up to 1000 °C. The results support mix-design-oriented guidance, indicating that 25–30 % EP offers a balanced compromise between mechanical capacity and density reduction, whereas 40 % EP provides the highest integrity and spalling resistance at 800–1000 °C but with very limited residual strength at 1000 °C, indicating suitability mainly for protective and non-load-bearing roles. • Mechanical thermal response of cement mortars incorporating expanded perlite as volumetric replacement for natural sand (25-40%). • Increasing expanded perlite content reduced compressive strength and density. • EP replacement offers balance trade-off between strength.