Experimental investigation and multi-objective optimization of fracture properties of asphalt mixtures containing nano-calcium carbonate

The low temperature fracture is one of the most important challenges in asphalt mixtures, which, if not paid, will lead to high maintenance costs. Therefore, researchers are looking for different materials to enhance the fracture behavior of mixtures. As the asphalt surface is affected by different types of loading throughout their operational lifetime, this study explores the impact of nano-calcium carbonate (NCC) on the fracture behavior of mixtures in different fracture modes. For this purpose, semi-circular bending (SCB) tests were applied to specify the fracture toughness. Two bitumen types of PG 64-22 and PG 58-28 were modified with 1%, 3%, 5% and 7% NCC. Finally, the fracture toughness of samples in pure mode-I, pure mode-II and mixed-mode I/II was investigated at -10 degrees C. Moreover, the prediction models of multivariate regression (MVR), group method of data handling (GMDH) and genetic programming (GP) were provided to present the best model with higher accuracy in order to obtain optimum NCC content with two objectives of K-If and K-IIf (the fracture toughness in modes I and II). The results indicated that NCC had a notable influence on the fracture toughness. However, in each mode and bitumen, the additive percentage that is associated with the highest fracture toughness was different. From the fracture tests, the most optimal percentage of NCC was determined between 3% and 7% and 3% to 5% for mixtures made with bitumen types of PG 64-22 and PG 58-28, respectively. Among the various models, GMDH had the greatest R-2 so that the R-2 amount of GMDH for K-If and K-IIf was 98.68% and 99.02%, respectively. The two-objective optimization results showed that 4.17%, 3.62% and 6.29% NCC were the best optimal amounts to maximize K-If and K-IIf amounts simultaneously for all mixtures and mixtures made with bitumen types of PG 64-22 and PG 58-28, respectively. (C) 2021 Elsevier Ltd. All rights reserved.