# Laboratory Performance Evaluation of Hot-Mix
###### Abstract  
Aggregate gradation and asphalt type are traditional variables that affects mix design of Hot-Mix Asphalt (HMA). Recently, the number of design gyrations (\(N_{\text{des}}\)) has been increasingly accepted as another variable parameter during the design process. Due to the growing shortage of high-quality raw materials, it is necessary to make full use of the combined roles between these design parameters, instead of solely relying on their individual effect, to improve the HMA properties. Therefore, this study comprehensively explored the effect of aggregate gradation, \(N_{\text{des}}\), and asphalt type on the performance of HMAs. Seven different combinations of aggregate gradation, \(N_{\text{des}}\), and asphalt type were evaluated. The volumetric indicators, uniaxial penetration shear test (UPST), unconfined compression test (UCT), low-temperature bending test (LBT), four-point bending test (FPBT), and dynamic modulus test (DMT) were used to assess the performance of HMAs designed by various parameter combinations. It was found that the contribution of adopting harder asphalt binder was able to make up for the high-temperature resistance loss caused by lower \(N_{\text{des}}\) or coarser gradation. The dynamic modulus exhibited the similar phenomenon. By contrast, the harder asphalt binder led to the worse tenacity of HMAs at low temperature; however, the tenacity can be restored through using lower \(N_{\text{des}}\) or coarser gradation by increasing asphalt content. In addition, the fatigue life of HMAs went up significantly by about \(36\sim 41\%\), when both \(N_{\text{des}}\) and asphalt penetration grade decreased to one lower level. asphalt mixture; performance; aggregate gradation; design gyration; low/high-temperature properties 2020 21 April 202021 April 202028 April 202020 April 202021 April  
the rutting resistance of the mixture increased by about 2.0 to 2.5 times. As the number of \(N_{\text{des}}\) increased by 25, the rutting resistance was improved by approximately 15% to 25%; Moreover, as the high-temperature PG-grade of the asphalt increased by one level (6 \({}^{\circ}\)C), the rutting resistance of HMA went up by about 2.5 times [7]. The above NCHRP project only focused on the mixture's high-temperature performance. The assessments for other HMA properties (i.e., low-temperature performance and fatigue performance), however, were not performed in this project. Some other studies also explored the individual influence of design parameters on the mixture properties. In terms of the effect of aggregate gradation, [PERSON] et al. found that the HMA with coarse gradation (below restricted zone) exhibited weak deformation resistance under high temperatures [8]. [PERSON] et al. found the similar patterns as [PERSON] et al. [9]. [PERSON] et al. found that HMAs using fine gradation (above or through restricted zone) had better fatigue performance as compared with those using coarse gradation [10]. In terms of the effort of \(N_{\text{des}}\), [PERSON] et al. discovered that with an increase in \(N_{\text{des}}\), the high-temperature properties and dynamic modulus of the mixtures were significantly improved [3; 11]. Moreover, [PERSON] et al. reported that the rise in \(N_{\text{des}}\) by 25 resulted in a decrease in fatigue life by 10-20%, and a decrease in low-temperature flexural-tensile strain by 10-50% [2]. As for the effect of asphalt type, the HMAs with modified binder (i.e., PG 76-22) were found to suffer less rutting by about 60% compared with those using neat binder (i.e., PG 67-22) [12]. Above studies indicated that all design parameters, including aggregate gradation, asphalt type and \(N_{\text{des}}\), affected the HMA properties notably. Previous studies mainly evaluated the individual influence of design parameter on the mixture properties. The combined effects of those parameters, however, need to be further investigated. In addition, several other essential properties of HMAs (i.e., low-temperature cracking) also need to be further included during investigation.