粗集料接触参数对沥青混合料损伤演化的影响

为了揭示沥青混合料内部细观损伤对宏观性能的影响，基于DIC方法与四点弯曲疲劳试验，对不同粗集料接触状态的混合料细观损伤尺度效应进行研究。首先以颗粒堆积理论与粒子干涉理论为基础，提出可表征细观主骨架结构状态的颗粒接触主力链配位参数（n_pfc）计算方法。采用SAC设计方法，通过控制关键筛孔2.36~4.75 mm的分计筛余质量百分比，设计4组可反映不同粒径尺寸集料组合形式的SAC16级配（B60S00~B60S15），计算不同级配沥青混合料对应的npfc。其次，结合DIC方法与四点弯曲疲劳试验，分析疲劳荷载作用下沥青混合料小梁试件水平应变场演化特征，并提出混合料疲劳损伤因子定量分析方法。最后对不同粗集料接触参数的沥青混合料的细观损伤演化特征、疲劳损伤因子D_FD及表征宏观抗疲劳性能的K_m进行分析。研究结果表明：随着疲劳荷载作用次数的增加，4种不同n_pfc混合料的水平应变量逐渐增大，各D_FD也均显著增加；随着n_pfc的增大，D_FD明显减小，当n_pfc=7.73~9.55时，D_FD较小，混合料的疲劳细观尺度损伤叠加效应较小；同时，随着n_pfc增加，K_m呈先增大后略微减小的趋势；当n_pfc=7.73~9.55时，对应的宏观抗疲劳性能较好；因此，选取合理的n_pfc可优化沥青混合料内部主骨架细观结构状态，减少细观尺度损伤叠加效应影响，提高沥青混合料的宏观抗疲劳性能。

Influence of Contact Parameters of Coarse Aggregate on Damage Evolution of Asphalt Mixture

Research based on a digital image correlation method and four-point-bending fatigue tests was conducted to determine the relationship between meso-damage and macro-performance of asphalt mixtures. The different contact states of coarse aggregate were investigated to determine the scale effect of meso-damage of the asphalt mixtures. First, the three-dimensional packing and filling theory and the particle interference theory was used as a basis for proposing a computing method of the coordination number of particle contact force (n_pfc) and characterizing the stable state of the framework structure. By controlling the unit screening rate of the key screen mesh (2.36-4.75 mm) and using the SAC design method, four different SAC16 gradations, which reflect the combinations of the different particle size aggregates, were designed. Moreover, n_pfc was calculated for asphalt mixtures with different aggregate gradations. Then, combining the digital image correlation method and the four-point-bending fatigue tests, the evolution of the horizontal strain field of asphalt mixture beam specimens was analyzed using the DIC method; a quantitative analysis method for fatigue damage factors of asphalt mixtures was proposed. Finally, the evolution of the meso-damage and the fatigue damage factor of asphalt mixtures were analyzed using the different contact parameters of coarse aggregate. Moreover, the analysis extended to the K_m value, which indicates the macro-fatigue resistance. The results show that with increasing fatigue loading, the horizontal strain distribution of the four different n_pfc asphalt mixtures changes from non-uniform to uniform, the strain variable increases from small to large, and the fatigue damage factors increases significantly. The fatigue damage factor decreases significantly with increasing n_pfc. When n_pfc is from 7.73 to 9.55, the fatigue meso-damage scale superposition effect of this graded asphalt mixture is small. Simultaneously, the K_m value, which characterizes the macroscopic fatigue resistance performance, tends to first increase and then decrease slightly as n_pfc increases. When n_pfc is from 7.73 to 9.55, the corresponding macro-fatigue resistance is better. Therefore, selecting a reasonable n_pfc optimizes the meso-structural state of the main skeleton inside the asphalt mixture, reduces the effect of the meso-damage scale effect, and improves the macro-fatigue resistance of the asphalt mixture.