热再生沥青混合料间接拉伸试验离散元数值模拟研究

发布时间：2018-12-28 20:41

【摘要】：再生沥青混合料属于组分复杂的非连续介质材料,其宏观性能与细观结构息息相关,但当前关于再生沥青混合料细观结构特性的研究较少。从细观角度阐释破损过程,剖析再生沥青混合料损伤规律,实现细观结构力学响应与宏观表象的统一,不仅使得细观力学模拟方法成为传统室内试验的有效补充,而且还能理论指导室内试验方法的选择。因此运用离散单元法构建再生沥青混合料细观结构模型,实现宏细观相结合的方法对再生沥青混合料的损伤规律研究具有重要的理论指导意义。论文通过采用化学染色剂预处理新集料,成型不同回收沥青路面材料(简称RAP)掺配率的再生沥青混合料马歇尔标准试件进行室内间接拉伸试验,测试劈裂强度。借助数码相机拍照获取试件横切面图,应用图像均衡、图像锐化、边缘检测和图像分割等数字图像处理技术实现图像细节凸显和各颗粒边缘清晰可辨等目的,并完成集料图像粒径分类。然后利用体视学方法完成横切面图像从二维实体向三维实体转换,计算图像颗粒的均匀性系数。最后根据上述分析结果合理确定二维离散元数字试件级配,在二维颗粒流程序基础上进行二次开发,数字重构再生沥青混合料细观模型,使用实际边界信息并合理进行材料细观参数比选,运用伺服机制控制荷载施加,实现间接拉伸试验数值模拟,分析再生沥青混合料细观力学特性。研究结果表明:(1)0%、10%、20%和40%RAP掺配率下的劈裂强度分别为1.57MPa、1.43MPa、1.38MPa和1.33MPa,劈裂强度随掺配率增加呈下降趋势,对于新拌沥青混合料劈裂强度而言,10%、20%和40%RAP掺配比例的试件强度下降率分别为8.9%、12.1%和15.3%;(2)利用体视学方法修正集料图像级配,得到骨料修正系数=π/4,=0.86,使得集料图像级配与设计级配基本吻合;(3)集料均匀性系数达到0.9左右,表明其横向分布均匀,新旧料空间分布的卡方拟合趋势图呈直线关系,证明新旧集料空间分布达到均匀状态;(4)通过细观参数校准后建立的再生沥青混合料间接拉伸试验数字试件模型的模拟结果与室内试验值之间虽然存在一定的误差,但是可从细观角度阐释再生沥青混合料速度矢量图及力链发育规律,证明了再生沥青混合料力学试验虚拟化模拟室内试验的有效性。
[Abstract]:Recycled asphalt mixture is a kind of discontinuous material with complex components, and its macroscopic performance is closely related to its meso-structure. However, there is little research on the meso-structure characteristics of recycled asphalt mixture at present. The damage process of recycled asphalt mixture is explained from the point of view of meso, the damage law of recycled asphalt mixture is analyzed, and the unity of mechanical response and macroscopic appearance of micro structure is realized, which not only makes the meso-mechanical simulation method an effective supplement to the traditional indoor test. It can also guide the selection of indoor test methods theoretically. Therefore, using discrete element method to construct the meso structure model of recycled asphalt mixture and realizing the method of combining macro and micro view have important theoretical guiding significance for the research of damage law of recycled asphalt mixture. In this paper, through pretreatment of new aggregate with chemical dye agent and formation of recycled asphalt mixture Marshall standard specimen with different recycled asphalt pavement material (RAP) blending ratio, indirect tensile test is carried out in laboratory to test the splitting strength. With the help of digital camera, the cross-sectional images of the samples are obtained, and the digital image processing techniques such as image equalization, image sharpening, edge detection and image segmentation are applied to realize the purpose of image detail highlighting and the distinct and discernible edges of each particle. The particle size classification of aggregate image is completed. Then the horizontal section image is transformed from two dimensional solid to three dimensional entity by stereology method, and the uniformity coefficient of image particle is calculated. Finally, according to the above analysis results, the gradation of two-dimensional discrete element digital specimen is reasonably determined, and the secondary development is carried out on the basis of two-dimensional particle flow program, and the mesoscopic model of recycled asphalt mixture is reconstructed digitally. Using the actual boundary information and reasonably selecting the meso-parameters of the material, the servo mechanism is used to control the load applied to realize the numerical simulation of indirect tensile test, and the meso-mechanical properties of recycled asphalt mixture are analyzed. The results show that: (1) the splitting strength is 1.57 MPA and 1.33 MPA, respectively, and the splitting strength is 1.57 MPA and 1.33 MPA, respectively, and the splitting strength tends to decrease with the increase of the blending ratio, and the results show that: (1) the splitting strength is 1.57 MPA, 1.43 MPA and 1.33 MPA, respectively, and the splitting strength decreases with the increase of the blending ratio. For the split strength of fresh asphalt mixture, the drop rate of strength of 10% or 20% and 40%RAP ratio is 8.9% and 15.3%, respectively. (2) the aggregate image gradation is corrected by stereology method, and the aggregate correction coefficient = 蟺 / 4 / 0.86 is obtained, which makes the aggregate image gradation basically coincide with the design gradation; (3) the uniform coefficient of aggregate is about 0.9, which indicates that the horizontal distribution is uniform, and the chi-square fitting trend diagram of spatial distribution of new and old materials is linear, which proves that the spatial distribution of new and old aggregates is uniform; (4) although there is a certain error between the simulation results of the digital specimen model of indirect tensile test of recycled asphalt mixture and the indoor test value, However, the velocity vector diagram and the law of force chain development of recycled asphalt mixture can be explained from the viewpoint of meso, which proves the validity of virtualization simulation laboratory test of recycled asphalt mixture mechanical test.
【学位授予单位】：长安大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：U414

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