On the effect of nano calcium carbonate on the flexibility and tensile-shear cracking resistance of greener WMA asphalt concretes containing RAP contents

Asphalt mixtures are widely used materials for paving roads, however, they need a significant amount of virgin materials, and their preparation process is environmentally unfriendly. In this regard, using less harmful production processes and using recycled materials can be beneficial. In the current study, the cracking resistance parameters (fracture toughness and fracture energy) of warm mix asphalt (WMA) mixtures, prepared with high contents of reclaimed asphalt pavement (RAP) were investigated, while different contents of nano calcium carbonate (NC) were used as a modifier. The cracking resistance studies were done for the full range of mode I/II fracture conditions. From the results, it is seen, that the addition of RAP increases both fracture toughness and fracture energy, regardless of the mode mixity and NC contents (respectively by an average, of 30 and 20%). The NC also made the mixture more resistant to cracking, so the enhancement of fracture energy by up to 30% and the enhancement of fracture toughness by up to 20% is observed. The NC optimum content was calculated in the range of 2 to 4% (in weight of binder), varied based on the considered variables. As a result of increasing the material’s brittleness by adding RAP and NC, the flexibility index showed a decrease. In separate evaluations, the effect of variables on strength parameters was studied statistically, showing that the fracture toughness in mode II, is about 1.2 to 1.5 times higher than fracture toughness in mode I. Also, theoretical frameworks were used to predict the trend of fracture data, showing the consistency of experimental results and theoretical predictions.