Syncretic Investigation of the Size Effect on the Constitutive Behavior of Sustainable Geopolymer Recycled Aggregate Concrete under Compression via Macroscale Experiments and Mesoscale Simulations

ABSTRACT Geopolymer recycled aggregate concrete (GRAC), incorporating industrial byproducts as binder substitutes and recycled concrete aggregates (RA) replacing natural aggregates, offers significant potential for reducing carbon emissions and promoting resource recovery. This study presents a systematic investigation into the size effect of GRAC under compression, integrating experimental testing, mesoscale numerical modeling, and theoretical analysis. A refined mesoscopic finite element model is established and then compared with the test results. The effects of specimen size, water-to-binder (w/b) ratio, and RA substitution rate on the compressive behavior of GRAC are analyzed. Based on the macro- and meso-observations, the failure mechanism of GRAC specimens and the size effect mechanism are deeply discussed. The results show that the specimen failure predominantly occurs via oblique shear, initiated by damage propagation from the RA into the surrounding matrix. Smaller specimens exhibit greater localized damage intensity, whereas larger specimens demonstrate more pronounced surface spalling. Furthermore, decreasing the w/b ratio from 0.5 to 0.35 increases the peak stress and elastic modulus of GRAC specimens with a diameter of 150 mm and a 50 % RA by 28.53 % and 12.64 %, respectively, whereas the peak strain decreases by 11.87 %. The addition of RA enlarges the population of weak regions within the concrete, which causes the damage to almost entirely surround the recycled coarse aggregates, forming an intricate network-like pattern. Consequently, as the RA replacement ratio increases from 0 % to 100 %, the peak stress and elastic modulus decrease by 30.00 % and 32.78 %, respectively, and the peak strain increases by 16.67 %. The main reason related to the size effect behavior of GRAC primarily stems from material heterogeneity, inherent brittleness, and weak interfacial transition zones. Based on the experimental results, size effect laws for the peak stress and peak strain of GRAC are obtained, within the scope of Weibull statistical theory.