Shear behaviour of reinforced construction and demolition waste-based geopolymer concrete beams

Geopolymer concrete (GPC) is a promising candidate to replace conventional concrete (CC) as geopolymer concrete depends on alkali-activated binders instead of Portland cement. The elimination of cement from the mixture results in the reduction of the greenhouse gas release. From the literature, it is known that the micro-scale characteristics of the geopolymer concrete are similar to its counterparts. However, the structural performance of geopolymer elements should be investigated in detail. Therefore, in this study, the deficiently reinforced beams' structural performance was compared by conducting bending tests to determine the shear behavior of new geopolymer concrete manufactured from entirely construction and demolition wastes (CDW). In these experiments, geopolymer concrete with recycled aggregates, geopolymer concrete with natural aggregates, concrete with recycled aggregates, and concrete with natural aggregates were used in order to study the possibility of reaching fully-recycled construction materials. Three shear span-to-effective depth ratio were used to examine the different failure modes. The mechanical performances of geopolymer concretes were assessed by using load-deflection/momentcurvature curves, and crack propagations. Test results revealed that geopolymer concrete beams exhibited similar performance to the concrete beams of the same grade. Besides, the insertion of recycled aggregates caused a shift in the failure mechanism from flexure-dominated to shear dominated, especially in specimens with larger a/d ratios. Finally, the capacity prediction performance of current codes, i.e., TS500 and ACI318, were also examined, and the calculations resulted that the current code equations had a percentage error of approximately 55% on average, although TS500 equations performed slightly better.