A fracture mechanics model to predict the rate sensitivity of mode I fracture of concrete

The mechanical properties of cementitious composites have been observed to be sensitive to the rate of loading and this rate sensitivity has been attributed to the strain rate effects on cracking. A nonlinear fracture mechanics model is proposed to predict the strain rate effect on mode I fracture of concrete. This model requires three material properties (Critical Stress Intensity Factor, K_Ic^s Critical Crack Tip Opening Displacement, CTOD_c and Young's Modulus, E) which can be determined from static tests. The analytical procedure is based on the observation that the pre-peak nonlinearity is due to the pre-peak (or stable or pre-critical) crack growth and that this pre-critical crack growth decreases with increase in rate of loading. K_Ic^s and E are assumed to be rate independent while CTOD_c is assumed to decrease exponentially with the logarithm of the relative strain rate. The model predicted values correlated well with the experimentally observed trends in the strain rate effects on mode I fracture of concrete.