Evaluation of mixing temperature impact on warm mix asphalt performance

This study presents a new approach for determining an optimum mixing temperature for a chemical and an organic WMA additive based on correlating the mixing temperatures with performance measures including the Indirect Tensile Stiffness Modulus (ITSM) and the Indirect Tensile Strength (ITS). WMA was produced at 145, 130 and 115°C and compacted at 110°C, while the control HMA was mixed at 160 and compacted at 150°C. The results revealed that the WMA produced using the chemical additive did not have any dependency on mixing temperature, and the ITSM and ITS results were comparable to the performance of the control HMA at all mixing temperatures with insignificant reduction (10%) in the ITSM, as confirmed by statistical analysis. Therefore, its mixing temperature can be determined based on other factors such as the distance between the construction site and the asphalt plant. However, the WMA produced using the organic additive showed a significant dependency on mixing temperature; the higher the mixing temperature, the higher the ITSM and ITS values. Furthermore, the ITSM results were comparable or improved in comparison with the control HMA, but the ITS results were significantly lower than those of the control HMA when the mixing temperature was 115°C based on statistical analysis. Based on the relationship between the ITS and the mixing temperature, the same ITS as the control HMA was achieved at 135°C;at lower temperatures, the ITS started dropping. Therefore, this temperature is suggested as an optimum mixing temperature for the wax additive in this case.