Mode Ⅰ dynamic fracture toughness of rubberised concrete using a drop hammer device and split Hopkinson pressure bar

The utilization of recycled rubber particles (RPs) made from waste tyres in concrete is a sustainable method. Many studies have found that RPs can improve the strain-rate sensitivity of strength for concrete materials. To further investigate the mechanisms of the strain-rate effect of strength on rubberised concrete under dynamic loads, dynamic fracture toughness tests were conducted with a drop hammer device and split Hopkinson pressure bar on cracked straight through Brazilian disc (CSTBD) specimens. The sand in rubberised concrete was replaced with RPs at six proportions: 0, 10, 20, 30, 40, and 50%. After verifying the force balance of the stress on two sides of a specimen in the loading direction, the propagation law of the main crack was observed using a high-speed camera. It was found that the crack started from the crack tips on both sides and propagated along the loading direction. With help from the strain gauge method, the crack initiation time was captured, and the stress intensity factor of the CSTBD specimens was determined. There was a positive correlation between fracture toughness and loading rate. As the rubber content increased up to 30%, the rate sensitivity of the fracture toughness was enhanced. After observing the failure modes, the reasons for the enhancement effect of fracture toughness by RPs were analysed. The results obtained in this study are of great value for the analysis of the strain-rate effect of strength and crack propagation in rubberised concrete under impact loads.