FRACTURE PROPERTIE ANALYSIS OF RECYCLED AGGREGATE CONCRETE BASED ON DIGITAL IMAGE CORRELATION TECHNIQUE

Three point bending fracture tests of recycled aggregate concrete beams with different recycled coarse aggregate replacement ratio (0%, 30%, 50%, 70%, 100%) have been carried out, with results analyzed by digital image correlation (DIC) method and the traditional electrometric method. The double-K fracture parameters, crack-mouth-opening displacement (CMOD), crack-tip-opening displacement (CTOD), crack extension length (\Delta a) and fracture growth path were obtained, and the validity of DIC method was verified. The results show that when the replacement rate is 100%, the crack initiation fracture toughness and unstable fracture toughness of recycled aggregate concrete decrease by 15.81% and 15.39%, respectively. With the increase of the replacement rate of recycled aggregate, the slopes of the descending sections of P-CMOD, P-CTOD and P-\Delta acurves increase. DIC method can effectively capture the fracture propagation process. The CMOD values measured by DIC method and clip type extenometer are in good agreement. The variation trends of DIC measured value and formula-calculated value of CTOD are relatively consistent. Based on the test results, the estimated values, \Delta a, of specimens with different replacement rates of recycled aggregate under different loads can be obtained by fitting the curve between P/P_\max and \Delta a/\Delta a_\textc.