沥青混凝土永久变形预估方法研究

提出了一种新的沥青混凝土永久变形预估模型,该模型理论明确,有效考虑了剪切因素,用单轴贯入抗剪强度表征沥青混合料本身的抗变形能力,用面层内剪应力表示结构的抗车辙属性.通过不同温度、压力及厚度下的车辙试验,基于分层叠加的基本思想确定了沥青混凝土永久变形预估模型;同时根据波尔兹曼线性叠加原理,在永久变形预估模型中考虑了行车速度;最后采用不同的沥青混合料对该模型进行了验证.结果表明:永久变形预估模型能够较精确模拟沥青混凝土的变形规律,对不同的沥青混合料具有通用性,从而为建立正确的车辙预估方法奠定了基础.     

沥青混合料永久变形过程中粗集料空间运动分析

编写了三维不规则多面体粗集料的随机生成程序,重构了包含粗集料、沥青砂浆及空隙的沥青混合料车辙试件的三维离散元模型.通过对三维离散元模型进行数字切割获取了沥青混合料车辙试件的二维离散元模型,对沥青混合料车辙试件二维离散元模型中微观组成结构之间的接触赋予了相应的微观接触模型及模型参数.进行了沥青混合料车辙试验的二维离散元模拟,分析了沥青混合料永久变形过程中粗集料的平动和转动.结果表明:二维离散元模型能够较为精确地描述粗集料在沥青混合料永久变形过程中的空间运动情况,从而为今后沥青混合料车辙形成机理的探讨提供新的研究方式.     

高等级道路沥青路面车辙的预估方法

根据在MTS试验机上对沥青混合料所进行的不同温度、不同应力及不等加载方式下的蠕变试验,对沥青混合料的高温变形特性进行了较为全面的分析,提出了一种有效地表征沥青混合料变形特性的流变学模型,并采用曲线拟合法确定了沥青混合料的模型参数。借助于粘弹性理论和所提出的流变学模型,建立了一种高等级道路沥青路面车辙的预估方法。结合路面的实际条件,提出了车辙计算中有关参数的确定方法,并绘制了供车辙计算查用的诺模图。试验道路上车辙观测结果同预估值较为一致,证实了建议的车辙预估方法的可靠性。     

沥青混合料抗车辙性能研究

对几种沥青混合料进行了车辙试验,以评价其高温抗车辙性能,通过试验研究,认为大粒径沥青混合料和SMA具有较好的高温稳定性能,使用改性沥青有利于提高沥青混合料高温抗车辙能力。     

基于离散元的行车荷载作用下沥青砂浆迁移规律研究

为研究行车荷载作用下沥青砂浆的迁移规律,借助离散元软件PFC2D建立了沥青混合料二维离散元模型,通过改变沥青砂浆Burgers模型的宏观参数,模拟了40、50和60℃温度下的沥青混合料黏弹状态,并利用时温等效原理,进行虚拟汉堡车辙试验,分析了沥青砂浆的迁移规律和温度对沥青砂浆迁移的影响.研究结果表明:在行车荷载作用下,...     

沥青混合料抗车辙性能评价方法的对比分析

从沥青路面分析仪与法国车辙试验机两方面,介绍了用于评价沥青混合料抗车辙性能的两种试验方法,并分析了两者的优缺点与适用性,建议在进行沥青混合料抗车辙性能评价时,优先选用APA并辅以法国车辙试验结果数据进行参考。     

基于离散元法的沥青混合料单轴贯入试验分析

通过离散元方法对沥青混合料单轴贯入试验进行模拟,选择AC-13、SMA-13、OLSM-25三种材料作为研究对象。通过试验模拟,得出相应结论:颗粒间接触力沿外力作用线方向以大粒径颗粒为中心向两侧传递,且不同混合料接触力分布情况也有所差异,AC-13接触力分布比较均匀,SMA-13、OLSM-25接触力分布较为分散;颗粒位移矢量与混合料结构形式有关,AC-13颗粒位移较大,SMA-13、OLSM-25颗粒位移较小,同为骨架结构的SMA-13和OLSM-25,随着最大公称粒径和空隙率的增大,颗粒位移矢量减小;骨架型沥青混合料比连续级配沥青混合料抗车辙能力强,增大最大公称粒径有助于提高混合料的抗车辙能力。     

沥青混合料低温劈裂试验离散元数值模拟影响因素分析

基于颗粒流软件PFC2D,建立沥青混合料劈裂试验二维离散元模型,研究集料模型(clump模型和cluster模型)、几何形状、混合料孔隙率,以及加载方向对沥青混合料低温劈裂试验离散元数值模拟的影响。研究结果表明,集料模型、几何形状、混合料空隙率,以及加载方向等,都对沥青混合料低温劈裂试验离散元数值模拟产生明显的影响。     

沥青混合料抗车辙性能常用试验方法综述

车辙是沥青路面常见的破坏形式之一,沥青路面抗车辙性能试验方法的相关研究,对于沥青路面路用性能的改善、沥青混合料性能的评价具有显著意义。文章对沥青混合料抗车辙性能的多种试验方法进行比对分析。对比结果表明:径向加载试验中试件形状对结果影响较大;单轴试验设备复杂,且对试验结果构成影响的因素较多;三轴重复试验结果与沥青混合料抗车辙性能相关度较高,但设备复杂、昂贵、对试验过程要求更高,且指标标准存在差异;马歇尔试验不适用于沥青混合料高温稳定性的检验,更适用于配合比设计以及施工质量检验。因此,在对我国沥青路面抗车辙性能进行评价时,建议结合沥青路面实际情况,选择合理评价方法,以期得到可信度更高的评价结果。     

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.     

Evaluating permanent deformation in asphalt rubber mixtures

Permanent deformation or rutting, one of the most important distresses in flexible pavements, has long been a problem in asphalt mixtures, mainly in countries with high temperatures such as Brazil. Throughout the years, researchers have used different test methods to estimate the rutting performance of asphalt mixtures. One of the alternatives to reduce permanent deformation in asphalt pavement layers is through the use of mixtures produced with asphalt rubber. Crumb rubber from waste tires introduced into the asphalt is one of suitable application to dispose the tires and used as an additive to enhance the properties of the conventional asphalts. This work aims at comparing the rutting performance of asphalt rubber mixtures (with dense and gap-graded aggregate gradation) with the conventional dense graded mixture most used in Brazil. The asphalt rubber mixtures were produced by the wet process using continuous blend and terminal blend asphalt rubber. To study their performance, two laboratory tests, the Repeated Simple Shear Test at Constant Height (RSST-CH) and the Accelerated Pavement Testing Simulator Test (wheel tracking) were carried out. The testing results confirmed that the use of asphalt rubber binder improves significantly the resistance to rutting. The highest resistance is presented by the mixtures produced with continuous blend binders and gap-graded aggregate gradation. The results of both testing apparatus can be correlated by a linear relationship. The testing results allowed concluding that the characteristics of the asphalt rubber binders cannot be used to predict the permanent deformation resistance of the asphalt rubber mixtures.     

Fatigue and rutting performance of lime-modified hot-mix asphalt mixtures

This paper describes the effect of lime on composite hot-mix asphalt (HMA) mixtures of aggregate and asphalt binder evaluated using viscoelastic continuum damage analysis, which is based on predicting the effective stress vs. strain equations and microcrack growth. The performance characteristics evaluated in this study included fatigue cracking and rutting resistance in both moisture-damaged and undamaged states. The test methods used in this evaluation were the dynamic modulus test for stiffness characterization, the direct tension test for fatigue cracking characterization, and the triaxial repeated-load permanent deformation test for rutting characterization. The main contribution of this paper is the demonstration of advanced test methods and models that can be used to evaluate the performance of various mixtures with respect to the fatigue damage and rutting performance.     

Starch as a modifier for asphalt paving materials

This paper investigates the viability of using starch (ST) as a new modifier for asphalt paving materials. Different ratios of ST (2.5, 5.0, and 7.5% by weight of asphalt) were blended with 70/100 paving grade asphalt. Unmodified and modified asphalt binders were subjected to physicochemical, alkali, acid and fuel resistance tests. The performance tests including, Marshall stability, Marshall Quotient (MQ), tensile strength, tensile strength ratio, flexural strength, rutting resistance and resilient modulus (MR) were carried out on unmodified and modified stone matrix asphalt (SMA) mixtures. The analyses of test results show that the performance of ST-modified asphalt mixtures are better than conventional and styrene–butadiene–styrene (SBS)-modified mixtures. The rutting potential, moisture susceptibility and temperature susceptibility can be reduced by the inclusion of ST in the asphalt mixture. The laboratory MR values are lower than the calculated ones using the empirical equations. The results also revealed that this modifier can be used as anti-stripping agent. It also shows resistance to fuels and most common chemicals. A ST content of 5% by weight of asphalt is recommended for the improvement of the performance of asphalt concrete mixtures similar to that investigated in this study.     

复合式SMA桥面铺装混合料配比设计及高温抗车辙性能研究

为了提升桥面铺装的高温抗车辙性能,采用马歇尔配合比设计方法对3种SMA沥青混合料分别进行级配设计及体积指标验证,选用轮辙试验和车辙试验对所设计的5种复合式SMA桥面铺装结构组合的高温性能评价指标进行测试.结果表明,SMA混合料沥青析漏损失及飞散损失均满足技术要求,SMA具有合理的最大沥青用量,且粘附性良好;提出的5种复...     

Nonlinear properties analysis on rutting behaviour of bituminous materials with different air void contents

Rutting is one of the major distresses of flexible pavement. It is defined as the formation of longitudinal depressions along the wheel paths caused by the progressive movement of materials under traffic loading in the asphalt pavement layers or in the underlying base through consolidation or plastic flow. This structural damage has a negative financial impact to the economy. In this study, the rutting behaviour of bituminous materials with different air void contents was investigated. The dynamic cyclic compression testing was carried out to establish nonlinear material models with multiple regression technique. With the specified material models, finite element analysis was carried out to study the rutting behaviour of the wearing course materials with different air void contents in a flexible pavement structure. The simulation result shows that the rutting depth is small at the air void contents of 4.5–8% for wearing course materials. However, for the air void contents above or below this range, the rutting resistance reduces, and thus the rutting depth increases. To verify this simulation result, wheel tracking tests were performed to obtain laboratory data, and the test data was found to be very close to the simulated one. This proved that the developed nonlinear model is applicable to simulate the rutting performance of bituminous mixture and it is a convenient and economical method to be used for the design of bituminous mixtures for both new and rehabilitated pavements.     

High temperature properties of wax modified binders and asphalt mixtures

The influence of adding two commercial waxes (FT-paraffin and polyethylene wax) to binders of penetration grades 50/70 and 160/220 were investigated for high temperature performance of binders and asphalt concrete mixtures. Binder properties were determined by conventional test methods, dynamic mechanical analysis and bending beam rheometer testing. The high temperature properties of asphalt concrete were investigated using the French rutting tester.The addition of FT-paraffin and polyethylene wax increased the rutting resistance of mixtures for both types of binder. The FT-paraffin modified asphalt mixtures showed the best rutting resistance.Adding polyethylene wax showed the highest stiffening effect in terms of rutting factor by DMA for the binders. However, this could not be verified in asphalt mixture testing. Adding FT-paraffin improved the rutting resistance of asphalt mixtures containing low or high penetration binder, but for the mixture containing high penetration binder the specification limit was exceeded.     

Investigation of rutting performance of asphalt mixtures containing polymer modifiers

The purpose of this study is to evaluate mechanical properties of control and modified asphalt mixtures. Conventional and five modified asphalt mixtures were studied on hot mix asphalt permanent deformation resistance. Amorphous polyalphaolefin, cellulose fiber, polyolefin, bituminous cellulose fiber and styrene butadiene styrene were used as modifiers. Indirect tensile strength, indirect tensile, static and repeated creep and LCPC wheel tracking tests were used for different loading conditions and temperatures. Research was focused on comparing the interaction between LCPC wheel tracking and other mechanical tests. According to the LCPC wheel tracking and repeated creep test results SBS mixtures were found as the most resistance mixtures in view of the rutting. Additives performed different performance levels but showed more resistance to permanent deformation according to the conventional mixtures. As far as the static creep test results are concerned there are controversial results because conventional mixtures are better. It is thought that this result may stem from the static behavior of the load and rheological change of bitumen with modifiers.     

Fatigue of asphalt binder,mastic and mixture at low temperature

The fatigue damage is one of the most common distresses observed on the asphalt concrete pavement. To thoroughly understand the fatigue of asphalt concrete, the behaviors of the major components of asphalt concrete under cyclic loading are investigated respectively in this study. A new experiment method is developed to evaluate the performances of asphalt binder, mastic and fine aggregates mixture under cyclic tensile loading. The fatigue test results of asphalt binder show that the fatigue performance of asphalt binder is closely related with loading magnitude, temperature and loading rate. Mastic specimens with different filler content are tested and the results indicate that mastic specimens with 30% filler content show better fatigue resistance and higher permanent strain. The micro-structure analysis of mastic and mixture indicates that the fatigue resistance is closely related with the air void content of specimen. 3D digital specimens are developed to model the fatigue of the asphalt binder, mastic and mixture specimens based on the finite element method (FEM). Fatigue damage of asphalt concrete is simplified by a damage model. With proper selection of damage parameters, the simulation results agree well with laboratory test results and can be used as a basis for future fatigue research.