Degradation of recycled heterogeneous aggregate concrete with supplementary cementitious materials under sulfate erosion and dry - wet cycles

The extensive use of materials in the construction industry imposes risks of depleting natural aggregates and increased carbon emissions, thereby motivating the search for sustainable alternatives. This work investigates the influence of supplementary cementitious materials (SCMs), including fly ash (FA), silica fume (SF), and ground-granulated blast-furnace slag (GBFS) on the durability and mechanical behavior of recycled heterogeneous aggregate concrete (RAC) subjected to sulfate erosion and dry–wet cycles (SEDWCs). Durability performance was evaluated through observation of surface appearance and mass variation, and digital image correlation (DIC) was used to monitor crack evolution and failure modes under uniaxial compression. Microscale mechanisms were examined using X-ray diffraction (XRD), scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP). Incorporating SCMs mitigated surface deterioration, stabilized mass change, and enhanced compressive strength. DIC observations revealed delayed crack initiation and less severe damage in SCM-modified RAC, with failure modes shifting from predominant shear to combined shear–cohesion failure. Microstructural analyses confirmed that SCMs densified the cement matrix and refined the interfacial transition zone (ITZ). Among the SCMs, silica fume exhibited the strongest resistance to SEDWCs, while fly ash and GBFS also improved durability compared with RAC without SCMs. These results demonstrate that the combined use of recycled aggregates and supplementary cementitious materials can significantly enhance the long-term performance of concrete in sulfate-rich cyclic environments, advancing the development of sustainable construction materials.