基于CT图像的粗集料颗粒接触特性细观尺度研究

采用工业CT获取沥青混合料断面扫描图像,利用数字图像处理方法将粗集料从图像中分离,并解决了颗粒粘连问题,使粗集料颗粒成为单独个体.确立了粗集料颗粒之间接触的判定准则,并设计5像素×5像素大小的窗格沿颗粒边缘进行接触搜索.对640张断面图像遍历处理后获得的数据进行定性分析,尝试建立了接触度指标C.采用4种概率密度分布函数...     

沥青拌和楼集料振动筛分理论分析

振动筛是沥青混凝土搅拌设备保证混合料级配的重要装置,本文对振动筛振动系统进行了动力学分析,并对集料颗粒及集料粒群在筛面上的运动进行了分析,为提高集料的筛分效率及保证沥青混合料的级配提供了理论基础。     

沥青拌和楼集料振动筛分理论分析

介绍了振动筛是沥青混凝土搅拌设备保证混合料级配的重要装置，对振动筛振动系统进行了动力学分析，并对集料颗粒及集料粒群在筛面上的运动进行了研究，从而为提高集料的筛分效率及保证沥青混合料的级配提供了理论基础。     

沥青混合料集料离析的数值模拟与分析

采用颗粒力学的基本理论分析了颗粒相互作用时的运动规律及沥青混合料集料离析的机理,提出以混合料中滚落距离大的集料颗粒比例判断集料离析的模型。利用离散元颗粒流计算软件PFC2D对沥青混合集料离析进行数值模拟,验证了集料离析模型的合理性。以沥青混合料集料料仓的实际尺寸为依据,对AC-13、AC-20沥青混合料集料进行下落试验,试验结果与理论分析及数值模拟结果吻合,并表明密级配沥青混合料集料粒径分布范围广、公称粒径大,集料易产生离析。沥青混合料生产过程中,应严格控制粗、细颗粒粒径大小及其级配含量,以避免混合料集料离析的产生。     

基于灰色系统理论的RAP材料颗粒组成特征分析

针对废弃沥青混凝土(RAP)颗粒组成复杂,不利于再生沥青混凝土级配准确控制的问题,利用灰色系统理论,以RAP制备的多孔沥青混凝土的孔隙率偏差值作为灰色系统的主行为,以不同虚拟系数(Kc)在合成筛分中所占的比例作为影响系统主行为的相关因素行为,对RAP材料颗粒组成进行灰色关联分析,得到代表再生沥青混凝土级配准确程度与RAP颗粒组成关系的灰色关联度序列.结果表明:不同粒径范围的RAP颗粒组成规律不同,粒径越大对再生沥青混凝土级配的影响越明显;通过关联度对比分析,可模拟出1条接近再生后RAP颗粒真实存在状态的虚拟筛分曲线,经验证,该虚拟筛分曲线能够更准确地控制再生沥青混凝土级配,从而为RAP在骨架型沥青混合料中的应用提供理论指导.     

公路沥青路面集料级配波动范围控制指标研究

集料是沥青混凝土路面的主要组成部分,单粒径集料级配的波动范围直接影响沥青混合料矿料级配的稳定。通过收集公路沥青路面用四档规格单粒径集料筛分数据,分析了集料级配标准差及变异系数,确定了各档集料变异性最大的筛孔尺寸。根据正态分布确定了各档集料允许波动范围控制指标,为公路沥青路面施工质量稳定性控制提供参考。     

集料分布特征对混合料疲劳性能的影响分析

根据建立的集料三维体积级配与二维数量级配关系式,编制了沥青混合料二维数字试件生成程序;结合离散元基本原理,建立了包括沥青混合料离散元模型、离散单元接触模式选择和疲劳失效判断标准在内的一整套沥青混合料虚拟疲劳试验方法;通过沥青混合料小梁虚拟疲劳试验,分析了集料分布特征对混合料疲劳性能的影响.结果表明:沥青混合料虚拟疲劳试验能真实模拟其疲劳过程,虚拟试验结果与真实试验结果相差无几,所建立的虚拟疲劳试验方法可以作为沥青混合料疲劳性能分析的辅助手段;集料分布均匀性对混合料疲劳寿命影响较大,混合料内粗集料分布较为密集的区域是最易疲劳损坏之处.     

沥青混合料集料微观结构的三维重构与计算

基于Matlab(R)自编程序对沥青混合料CT图片进行集料微观结构的三维重构与分离,并对分离后的集料颗粒等效直径、表面积、体积等三维几何信息进行了计算与论证.结果表明:基于CT技术进行沥青混合料集料微观结构的三维重构与分离切实可行,并且集料的三维几何信息计算结果与实际数据非常吻合.     

基于Mimics沥青混合料三维数值模型建立

为了建立沥青混合料的三维数值模型,采用德国Compact-225型X-ray工业CT对AC-16级配的沥青混合料标准马歇尔试件进行断层扫描,将扫描图导入医学软件Mimics,通过双峰法进行阈值分割实现对沥青混合料细观结构的识别,经过局部修正处理后进行三维重构。用Magics软件对重构模型进行光滑处理后导入Ansys有限元软件进行体网格划分和优化,再通过Mimics的Materials功能来进行材质赋值,经系统运算后生成三维数值模型,可直接用于虚拟力学分析。     

沥青混凝土集料级配的分形特征研究

以散粒体分形模型为基础 ,推导了沥青混合料矿料分布函数。在双对数坐标系里画出 19(或 2 0 )的几种沥青混合料的级配上限、下限、中值曲线 ,经过回归分析 ,得到每种级配集料的分形维数。沥青混合料的矿料分形维数主要由 0 .0 75 mm以下颗粒的多少决定。 0 .0 75 mm以下颗粒越多维数越高 ,反之越少。分形维数的相关性越高 ,集料级配越连续。分形维数越高 ,集料越细。分形维数和相关性可以作为集料级配评价的量化指标。     

基于厂拌热再生技术的集料密度影响规律

研究了厂拌热再生技术中回收沥青路面材料（RAP）中矿料与新集料的密度差异对混合料空隙率和级配的影响规律,改进了RAP矿料密度的测试方法,提出热再生混合料空隙率法则和广义级配法则： 当RAP矿料掺量和油石比一定时,混合料中矿料的合成毛体积相对密度越小,其空隙率越大;在混合料级配曲线上,受较小密度集料影响的部分曲线段向级配上限靠近,受较大密度集料影响的部分曲线段向级配下限靠近.沥青路面施工必须严格控制集料密度波动.     

贝雷法三参数级配控制的探讨

介绍了贝雷法级配设计的一些基本概念，评述了贝雷法在Superpave混合料设计中的应用，着重介绍了三参数级配控制法，结果表明经贝雷法设计的Superpave混合料既能抗车辙又能防渗水，是一种较好的级配设计方法。     

Three dimensional distribution of the mastic in asphalt composites

The microstructure of the fine aggregate matrix has a significant influence on the mechanical properties and evolution of damage in an asphalt mixture. This paper presents the findings from a study conducted to identify a quantitative method to characterize the three-dimensional microstructure of the matrix in an asphalt mixture. The influence of binder content, coarse aggregate gradation, and fine aggregate gradation on the microstructure of the matrix was also investigated. Results indicate that for a given aggregate type, binder content and aggregate gradation influence the degree of anisotropy whereas gradation of the coarse aggregate has the most influence on the direction of anisotropy of the asphalt mastic. Addition of asphalt binder or adjustments to the fine aggregate gradation also resulted in a more uniform spatial distribution of the asphalt mastic.     

集料级配变异性对沥青路面压实度的影响

集料级配是保证沥青混合料质量的重要指标之一,而压实度是沥青混合料路面质量的评价指标之一,那么集料级配对压实度的影响如何呢?文中将以绥满公路哈尔滨到大庆高速公路沥青混凝土加铺工程第五标段工程为依托,用定量分析的方法对集料级配的变异性对沥青路面的压实度影响程度进行分析,指出影响集料级配变异性的因素,提出相应的控制措施。     

Characterize packing of aggregate particles for paving materials: Particle size impact

Aggregate packing directly affects the way of aggregate particles forming a skeleton to transmit and distribute traffic loads, thus influencing the stability and mechanical performance of the mixtures. Although some efforts have been conducted to evaluate the quality of a designed aggregate structure, such as the Bailey’s method for hot mix asphalt (HMA) mixture, there is a lack of fundamental understanding of the aggregate packing properties. Also how the packing and degree of aggregate interlock can be related to mixture performance is not clear. Major reason is because the aggregate structure is a very complicated system whose packing characteristics can be affected by both particle size distributions and the particle shape (angularities) distribution. To understand this complex packing system, our study developed a two-step procedure. As the first step, the size distribution effect is evaluated and the results are presented in this paper. The second step will investigate the combined effect of size distribution and shape impact and the results will be presented in a later paper. Specifically, in this paper we conducted a particle packing analysis using a discrete element modeling (DEM) simulation method. An HMA mixture gradation typically used in the State of Washington was utilized as a case study example for the analysis. By correlating the gradation parameter to the volumetric properties of the structure, this paper theoretically demonstrated the roles of aggregate particles with different sizes in an HMA mixture. Contact force chains and mean contact force were calculated using PFC^3D DEM simulation, which provided an indication of the capability of the aggregate structure to transmit stresses through aggregate skeleton, and thereby, to resist permanent deformation. The study conducted here demonstrated the aggregate size distribution played a significant role in the packing characteristics, affecting both volumetrics and the contact characteristics of a packed structure. Such findings are critical for evaluating the combined effect of size and shape distribution on packing, and achieving a performance based aggregate gradation design.     

花岗岩SMA混合料的配合比设计

采用黏附性试验分析了花岗岩与沥青的黏附性,据此确定了普通沥青和改性沥青添加抗剥落剂的最佳剂量;基于级配型抗滑沥青混凝土的设计理论,采用马歇尔体积设计法对花岗岩SMA混合料进行了目标配合比设计;参考所在地区(辽宁省)的技术指导经验,根据设计空隙率确定了花岗岩SMA混合料的最佳油石比;性能检验表明,花岗岩SMA混合料的各项性能指标均满足施工技术规范要求,特别是水稳定性能良好;经过2年试验路段的路面跟踪检测发现,试验路段的路用性能良好.     

Virtual modeling of asphalt mixture beam using density and distributional controls of aggregate contact

The characteristic indicators of aggregate contacts in asphalt mixtures, including the number, orientation, and area of contact regions, significantly affect skeleton morphology and mixture stability. To investigate the influence of indicators on mixture stability, structures with diverse characteristics of aggregate contacts are required. This study proposes an algorithm for the virtual modeling of asphalt mixture beams, which supports the density and distributional controls of aggregate contacts in the microstructure. The methodology comprises three main steps: (1) three-dimensional models of coarse aggregates conforming to the predefined gradation and volumetric content are randomly selected from a digital library of realistic aggregates, (2) contact relations of aggregates are established during the adaptive arrangement of aggregates in samples with prescribed control parameters of aggregate contact using self-developed codes, and (3) air voids are randomly scattered in the sample without overlapping aggregates according to the volumetric content of the air voids, and an asphalt mortar model is then constructed using Boolean operations. Four beam samples with different contact characteristics were obtained using the proposed method to conduct simulations of three-point bending tests. The number and spatial distribution of aggregate contacts in beam models are consistent with the prescribed parameters, showing the reliability of the proposed method for the control of aggregate contact in asphalt mixtures. A comprehensive comparison of the results of the laboratory test and simulations validates the ability of the digital beam to capture the macroscale response of asphalt mixtures. Furthermore, simulation results indicate that the sample with the greatest number and distribution uniformity of aggregate contacts has the largest peak strength and fracture energy, which is beneficial for the understanding of the relationship between the indicators of aggregate contacts and the rutting and fatigue resistance of mixtures.     

沥青混合料配合比设计中的影响因素

沥青混合料是一种比较复杂的复合型材料,它的力学性能与矿料的组成直接相关。介绍了骨架密实型、骨架空隙型和悬浮密实型等3种矿料级配类型的结构特点和工程特性。结合通化市的实际工程经验,指出采用骨架密实型的沥青混合料矿料级配比较理想。在沥青混合料配合比设计中,还应考虑关键性筛孔和最大公称尺寸的影响。     

Image analysis for detecting aggregate gradation in asphalt mixture from planar images

The mechanical properties of bituminous mixture strongly depend on the gradation of the aggregate that represents the mineral skeleton of the mixture, since for open and gap-graded mixtures, stresses due to vehicles in movement on the pavement are mainly transmitted through their contacts. Internal structure of bituminous mixture is, therefore, of great interest for road and infrastructure engineering and it is appropriate to study it with recently developed image analysis method. The purpose of this study was to finalize an effective analysis of asphalt section image for automatically extracting aggregate gradation without the need of separation of the bitumen from the aggregate. This paper proves that, thanks to the synergic use of different segmentation methods of the digital images taken on slices of cores from the pavement, it is possible to obtain a reliable gradation of the mineral skeleton of the mixture. The proposed methodology allows one to estimate the aggregate gradation that, otherwise, it would be necessary to establish via specially equipped laboratory, undertaking time-consuming tests that also imply health risks for the operators, due to the use of solvents and other hazardous materials.