Evaluating Structural Integrity of Green Concrete Modified with Supplementary Cementitious Materials Using        Non-Destructive Testing

The growing demand for environmentally friendly construction materials has led to the partial replacement of Portland cement with supplementary cementitious materials (SCMs) such as fly ash and bentonite. This study aims to determine the non-destructive strength of concrete in which cement is blended with fly ash and varying dosages of bentonite. The concrete specimens were created, in which cement was replaced with 0%, 10%, 20%, 30%, 40%, and 50% bentonite, along with a constant dosage of 10% fly ash. The mechanical characteristics of concrete were assessed using non-destructive testing (NDT) methods, such as Ultrasonic Pulse Velocity (UPV) and Schmidt Rebound Hammer test, to determine the strength and surface hardness of the concrete specimens. Study shows that concrete specimens containing 10% fly ash along with 10% bentonite exhibited higher values of pulse velocity and rebound index, which predicts higher compressive strength of concrete due to the formation of dense microstructure and refinement of internal pores of the concrete. However, the specimens containing higher dosages of bentonite and fly ash exhibited a low rebound index, likely due to their porous and loose microstructure. Therefore, non-destructive testing methods can be effectively used for monitoring the structural health of sustainable concrete.