Abstract: In order to avoid insufficient selection of the optimal gradation curve using empirical methods when optimizing the gradation design of asphalt mixtures, the response surface method was used to optimize the gradation design of RAP plant mixed hot recycled asphalt mixtures with a large content (30%) of AC-20 gradation type. The optimal design result can be obtained when the 19 mm sieve pass rate of the aggregate was 97.2%, the 4.75 mm sieve pass rate was 39.3%, the 0.075mm sieve pass rate was 6.0%, and the oil stone ratio was 4.48%. Under optimal conditions, the predicted values of the model were void rate of 4.00%, void ratio of 13.17%, saturation of 70%, and stability of 11.75kN. The experiment shows that the relative error between the measured values and the predicted values of the model is small (both not more than 3%), indicating that the established second-order model has good fitting results. The response surface method can effectively predict the performance of asphalt mixture mix design and provide optimization results for the grading of 40% to 70% RAP content.

Key words: thermal regeneration, high RAP content, response surface method, gradation optimization design