A comparative study of nil-SIF-based and initial fracture toughness-based criteria for prediction of mode-I crack propagation in concrete at low temperatures

Proper understanding of crack growth mechanism in concrete at low temperatures is of vital importance in ensuring safety and serviceability design of concrete structures in cold regions. Although stress intensity factor (SIF)-based criteria have been widely employed to assess the concrete cracking, there is little information available regarding the applicability of different SIF-based criteria in predicting crack growth in concrete exposed to low temperatures. In this research, a numerical procedure was developed to predict the mode-I crack growth in concrete at low temperatures based on the nil-SIF-based and K_ini-based criteria. Empirical equations for temperature-dependent material properties of concrete employed for numerical calculations, including the tensile strength, elastic modulus, fracture energy and initial fracture toughness, were proposed using a large number of datasets. The predictive performance of nil-SIF-based and K_ini-based criteria was verified by comparing the numerical results against three sets of test data on three-point bending (TPB) concrete beams under low temperatures as low as − 80℃. The results demonstrate that the predictions using the K_ini-based criterion exhibit superior performance in evaluating the crack growth in concrete in terms of P-CMOD response, peak load, and CMOD_c compared to those using the nil-SIF-based criterion. It is also found that low temperatures result in increased initial fracture toughnesses and more pronounced differences in crack extension behaviors between these two criteria. As the temperature decreases, the K_R values predicted by the K_ini-based criterion are larger than those derived from the nil-SIF-based criterion until the value of Δa/(D − a₀) reaches around 0.6, beyond which a contrasting trend emerges. When employing the nil-SIF-based and K_ini-based criteria, decreasing the temperature from 20 °C to − 40℃ leads to a reduction in the maximum FPZ length by 7.02 % and 11.89 %, respectively. These results demonstrate that the utilization of the K_ini-based criterion is more appropriate for determining mode-I crack growth in concrete, both in terms of accuracy and efficiency, particularly under low temperature conditions.