Influence of very high temperatures on properties of medium grained lightweight aggregate mortars containing perlite and various cement types

This article examines the effects of very high temperatures (300–1000 °C) on the physical, mechanical, and thermal behaviour of medium-grained lightweight mortars incorporating expanded perlite (EP) and three cement types: Ordinary Portland (OPC), Calcium Sulphoaluminate (CSAC), and Calcium Aluminate (CAC). Mortars with 0–100% EP replacement were tested for compressive strength, density, absorbability, thermal conductivity, and microstructure. Increasing EP content reduced density and strength but enhanced thermal insulation and dimensional stability. Above 650 °C, OPC and CSAC underwent dehydration, ettringite loss, and microcracking, while CAC developed stable phases that preserved cohesion and colour. Strong correlations were found between thermal conductivity and compressive strength, allowing predictive modelling across temperatures. Polynomial correlations best described the strength–temperature relationship for OPC and CAC, while logarithmic models were optimal for CSAC. Overall, CAC-EP mortars demonstrated superior thermal stability, mechanical retention, and durability, highlighting their suitability for refractory and energy-efficient construction applications.