Mechanical properties of ECC incorporated with micro-powder of construction waste after elevated-temperature exposure

With the increasing demand for resource utilization of construction waste and advancing research on the elevated-temperature behavior of engineering materials, incorporating micro-powder of construction waste (MPCW) into engineered cementitious composites (ECC) and studying their mechanical properties under elevated temperatures are of great practical value. This study investigates the mechanical behavior of ECC where natural aggregates are partially replaced by MPCW, within the temperature range of 20 °C to 600 °C, with control groups including ECC without MPCW and ECC with 20 % MPCW substitution. Results show that MPCW incorporation reduces ECC strength, but the compressive strength loss (13.34 %) meets the engineering design standard (maximum allowed loss<25 %). As temperature rises, the compressive, tensile, and flexural tensile strengths of MPCW-ECC, along with their corresponding strains, first increase and then decrease. When the temperature exceeds 300 °C, the failure mode becomes more brittle, and flexural failure no longer follows the multi-cracking mechanism; above 400 °C, its compressive strength drops to <75 % of the control group. X-ray diffraction (XRD) analysis reveals that the crystal phase transformations of ECC and MPCW-ECC matrices at different temperatures are highly consistent with macroscopic performance trends, while scanning electron microscopy (SEM) further clarifies the microstructural evolution and its impact on mechanical behavior. Additionally, a regression model established for MPCW-ECC mechanical properties shows high predictive accuracy, with R² values of 0.911, 0.880, and 0.865 for compressive, tensile, and flexural tensile strengths, respectively. Overall, this study provides a scientific basis for the elevated-temperature safety evaluation of MPCW-ECC and valuable insights into the sustainable utilization of construction waste in cement-based composites.