Improvement of concrete performance through a ternary aggregate system: Microstructural insights into pore structure and ITZ characteristics

Durability remains one of the key factors determining the long-term performance and service life of concrete structures. This study investigated a novel way to use waste dolomite powder (WDP) in concrete, aiming to develop a ternary aggregate system that simultaneously improves mechanical properties and durability. Experimental results showed that incorporating WDP in the concrete increased the 90-day compressive strength by up to 21.06% and the splitting tensile strength by 10.84%. Meanwhile, durability was significantly enhanced: compared to that of the control concrete, the reductions in drying shrinkage, water absorption and chloride migration coefficient of the concrete containing WDP were up to 17.27%, 35.59%, and 43.20%, respectively. The XRD, FTIR, and TGA results verified that WDP provided a stable crystalline phase dolomite (CaMg(CO 3 ) 2 ) which contributes to maintaining long-term dimensional stability. Acting as a micro-aggregate, WDP effectively filled into pores and refined the interfacial transition zone (ITZ). Pore structure analysis confirmed that the cumulative pore volume decreased by up to 21.83%, while the content of the harmless pore content (≤ 20 nm) increased by 35.49%. The SEM-EDS and Vickers hardness measurements further showed a narrower ITZ. Notably, the microhardness of the ITZ and the matrix were improved by 38.38% and 39.62%, respectively. In addition, the life-cycle assessment results show that incorporating WDP in concrete effectively reduced CO 2 emissions, energy consumption, and economic costs. These findings demonstrate that WDP can be effectively utilized to produce more sustainable concrete with superior durability and mechanical performance.