Experimental investigation on compressive performance of recycled aggregate concrete (RAC) incorporating diatomite as supplementary cementitious material after exposure to elevated temperatures

Diatomite can enhance the thermal resistivity of cement-based materials, but the combined effect of diatomite and recycled coarse aggregate (RCA) on the performance of RAC after high-temperature exposure remains unexplored. This study proposes that incorporating diatomite as supplementary cementitious materials enhances the high-temperature performance of RAC. The effects of RCA replacement ratio, diatomite substitution rate, and elevated temperature on critical compressive performance indicators, such as surface morphology, ultrasonic pulse velocity, elastic modulus, failure mode, compressive strength, peak strain, and stress–strain behavior, were systematically investigated. Key findings include: (1) Owing to the porous structure and pore optimization properties of diatomite, 1 % or higher diatomite reduced cracking and spalling under high-temperature exposure, thereby improving the integrity of RAC during compression. (2) A critical transition temperature of 300°C was identified, beyond which ultrasonic pulse velocity exhibited accelerated deterioration, concrete damage intensified. (3) Both dynamic and static elastic moduli decreased progressively with increasing exposure temperature, with their ratio also diminishing. (4) All diatomite-incorporated groups exhibited significantly higher residual compressive strength at 300°C compared to 25°C, with a maximum increase of 17.2 %. 1 % diatomite resulted in higher residual strength, with improvements of 5.5 %, 18.9 %, and 10.6 % at 300°C, 500°C, and 800°C, respectively. The strength of the prism was particularly sensitive to high temperatures. (5) At 800 °C, all stress–strain curves showed a noticeable flattening trend. The RCA exerted a greater influence on peak strain at 25°C than the diatomite, but the diatomite’s effect became more pronounced above 300°C, with 1 % diatomite increased by 10.0 %, 29.0 %, and 32.0 % at 300°C, 500°C, and 800°C, respectively. (6) Compared with natural aggregate concrete (NAC), appropriate diatomite incorporation synergistically enhanced strength, toughness, and crack resistance, effectively improving the high-temperature performance of RAC. • Investigated the effects of diatomite on compressive performance of RAC after exposure to elevated temperatures. • 1 %∼2 % diatomite reduced cracking and spalling under high-temperature exposure. • Improvement in micro-pore structure and hydration products were observed through TGA and XCT when using diatomite. • Diatomite-incorporated groups exhibited significantly higher residual compressive strength at 300°C. • 1% diatomite synergistically enhanced strength, toughness, and crack resistance at elevated temperatures.