Experimental investigation of the compressive stress–strain response of desert sand mortar under elevated temperatures

Purpose This study aims to systematically investigate the compressive stress–strain behavior of desert sand mortar (DSM) after exposure to elevated temperatures ranging from 100°C to 700°C. The research specifically evaluates the influence of the desert sand replacement ratio (DSRR) to isolate the intrinsic “matrix effect” of desert sand on thermal stability, independent of coarse aggregate interference. Design/methodology/approach Prismatic DSM specimens were prepared using Maowusu desert sand at six replacement ratios (0%–100%) and cured for 28 days. Samples were subjected to a 4°C/min heating regime and tested under displacement-controlled uniaxial compression (0.006 mm/s) to capture complete stress–strain curves. The thermo-mechanical response was quantified through microstructural analysis (XRD/SEM) and the development of a modified Popovics-type constitutive model. Findings Experimental results indicate that a DSRR of 40% optimizes peak stress and elastic modulus. A strength rebound occurs at 200°C due to C–S–H gel densification and “internal autoclaving,” followed by linear degradation beyond 300°C. DSM retains 15–30% higher residual strength at 700°C compared to conventional mortar. The proposed constitutive and empirical models achieve high accuracy, with mean square percentage errors below 15% and R2 values exceeding 0.96. Originality/value This work provides the first comprehensive thermo-mechanical dataset for DSM, establishing a quantitative foundation for the fire-resistant design of desert-sand-based cementitious materials. It reveals the intrinsic degradation mechanisms of the mortar phase, offering essential input parameters for the multi-scale numerical modeling of desert sand concrete structures.