Uniaxial Dynamic Compressive Mechanical Properties of Alkali-Activated Recycled Aggregate Concrete Modified by Single and Combined Incorporation of CNTs/GO

To investigate the synergistic reinforcement mechanism of single and combined incorporation of carbon nanotubes (CNTs) and graphene oxide (GO) on the dynamic mechanical properties of alkali-activated recycled aggregate concrete (AARAC), 81 cylindrical specimens were designed with varying dimensions, recycled coarse aggregate (RCA) replacement ratios, and single/combined nanomaterial incorporation schemes. Uniaxial compression tests were conducted to obtain the stress–strain curves of AARAC under different strain rates (10−5 s−1, 10−3 s−1, and 10−1 s−1), and a dynamic constitutive model for AARAC was established. The results indicate that under static conditions (strain rates of 10−5 s−1 and 10−3 s−1), the coupling law between the RCA replacement ratio and nanomaterial dosage is determined by the balance between the defect degree of recycled aggregates and the improvement effect of nanomaterials. Specifically, at a 50% RCA replacement ratio, the single incorporation of 0.1% CNTs can enhance the mechanical properties of AARAC; at a 100% RCA replacement ratio, the synergistic effect of the combined incorporation of 0.1% CNTs and 0.05% GO can mitigate the defects of fully recycled aggregates. In contrast, under dynamic conditions (strain rate of 10−1 s−1), Nanomaterials (CNTs and GO) optimize load transfer efficiency and slow down the process of crack propagation, leading to a much greater improvement in the mechanical properties of AARAC compared to static conditions, with the combined incorporation achieving better performance at a 100% RCA replacement ratio. As the specimen size increases from 75 mm to 150 mm, the increase in static peak strain is relatively small, which is attributed to the more uniform deformation distribution and stronger deformation coordination capability of larger specimens under static loading. Under dynamic loading, the influence law of peak strain and elastic modulus is consistent with that of peak stress. Based on these findings, a dynamic constitutive model for AARAC modified by single and combined incorporation of CNTs/GO was established. The predicted curves of the model are in good agreement with the experimental curves, with an error range of 2.3–7.1%, which can well describe the constitutive relationship of the tested material.