Fatigue behavior of SMA and HMA mixtures

Fatigue crack is a main form of structural damage in flexible pavements. Under the action of repeated vehicular loading, deterioration of the asphalt concrete materials in pavements caused by the accumulation and growth of the micro and macro cracks gradually takes place. The indirect tensile tests was carried out on hot mix asphalt HMA and stone matrix asphalt SMA mixtures comprising different nominal maximum aggregate sizes NMAS in three temperatures of 5, 25 and 40 °C. Stiffness modulus, fatigue lives and fatigue prediction equation of the mixtures were developed and characterized in terms of aggregate gradation type, coarseness and fineness of gradation, temperature and asphalt content.     

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.     

Effect of asphalt film thickness on the moisture sensitivity characteristics of hot-mix asphalt

Temperature, air and water are the common factors that profoundly affect the durability of asphalt concrete mixtures. In mild weather conditions, distresses such as permanent deformation, fatigue cracking can be encountered on the pavements due to traffic loading. But when a severe climate is in question, these stresses increase in poor materials; under inadequate control; with traffic as well as with water which are key elements in the degradation of asphalt concrete pavements. Many variables affect the amount of water damage in asphalt concrete layer. Among them, mixture design properties such as air void level, permeability, asphalt content and asphalt film thickness are the ones that must be investigated carefully.     

温拌沥青混合料的半圆弯抗与水敏感性试验研究

疲劳破坏和水损害是温拌沥青路面重要的破坏类型之一。采用由三个现场项目提供的8种温拌沥青混合料(Evotherm、Sasobit、Foamed),进行半圆弯抗(SCB)试验和改进Lottman试验(AASHTO T283)分别评价WMA的抗疲劳性能与水稳定性。结果表明:与相应的HMA比较, WMA表现出相近或更高的Jc值;WMA技术的使用提高了沥青混合料的抗断裂性能;温拌沥青混合料和普通热拌沥青混合料的水敏感性没有显著差异。     

连续配筋混凝土路面结构优化及性能评价

针对目前连续配筋混凝土路面(CRCP)的结构特征和缺陷,对CRCP结构进行了研发及优化设计,垫层用碎石,基层采用碾压混凝土,面层分上下两层,上面层采用橡胶水泥混凝土,基层和面层之间设沥青混凝土抗冲刷层|行车道及硬路肩1/2宽度范围内的面层设纵横向连续钢筋以及可滑移支座,硬路肩另外1/2宽度范围的部分为素混凝土,在硬路肩1/2宽度处设纵向接缝,在面层设横向诱导切缝|钢筋采用环氧树脂净浆涂层处理,横向钢筋和纵向钢筋呈30°～60°角|运用断裂力学、损伤力学理论和数值仿真法,对CRCP加铺改造后沥青层的损伤开裂进行了研究,结果表明：新的CRCP结构沥青加铺层的疲劳损伤寿命大幅提高,裂缝扩展强度大大减小,路用性能得到有效提升,经济效益显著。研究成果已有一定的工程应用,提出的设计理念及方法可为连续配筋混凝土路面的合理设计提供理论依据和参考,也可为我国道路设计理论的发展提供有益借鉴。     

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.     

Mix design and performance analysis of asphalt concretes with electric arc furnace slag

The paper presents the results of a laboratory study, aimed at verifying the possibility to use two particular typologies of electric arc furnace (EAF) steel slags, in substitution of the natural aggregates, in the composition of wearing course asphalt concrete for flexible pavements. The experimental research has been articulated in a preliminary study of the chemical, leaching, physical, and mechanical properties of the EAF steel slag, and in the following mix design and performance characterisation of the bituminous conglomerates, through gyratory compaction tests, permanent deformations tests, Stiffness Modulus tests at various temperatures, fatigue tests and indirect tensile strength tests. All the mixtures with EAF slag have satisfied the requisites for acceptance in the road sector technical standards, thus resulting as suitable for use in the construction of road infrastructures, moreover presenting higher mechanical characteristics than those of the corresponding asphalts with full natural aggregate.     

混凝土多轴等幅疲劳性能研究

利用大型多轴疲劳试验机,进行了双轴拉-压、三轴拉-压-压等幅循环荷载作用下混凝土的疲劳性能研究.分析了不同侧压比、不同应力水平下混凝土的多轴等幅疲劳破坏形态、疲劳强度以及残余应变的变化规律,得到了应力水平-疲劳寿命(S-N)曲线及其表达式.结果表明:在等幅疲劳荷载下,混凝土多轴疲劳破坏形态与侧压比无关;残余应变呈三阶段发展规律,受侧压比影响较大,几乎与应力水平无关.定义相对残余应变为损伤变量,建立了损伤演变方程,为混凝土多轴等幅疲劳试验研究及疲劳损伤评价提供参考.     

旧水泥混凝土路面沥青加铺层疲劳断裂分析

在道路的使用过程中,沥青加铺层一直经历着交通荷载及温度变化的循环作用,沥青加铺层结构中的裂缝扩展呈现为疲劳断裂特征.沥青加铺层的使用寿命（从开始承载直至破坏所经历的车辆荷载及温度循环次数或作用时间）可分为疲劳裂缝形成寿命和疲劳裂缝扩展寿命两部分.疲劳裂缝形成寿命为由微观缺陷发展到宏观可检裂缝所对应的寿命,目前仍由传统疲劳理论的方法确定;而疲劳裂缝扩展寿命则为由宏观可检裂缝扩展到临界裂缝而发生破坏这段区间的寿命,用疲劳断裂力学方法确定.论文着重对沥青混合料与沥青路面的疲劳断裂进行分析.     

Uncertainties in determining the responses of reinforced flexible pavements using in-situ tests

A 225m long full-scale testing lane was constructed at a local road in Australia to evaluate the performance of the flexible pavements over a weak soft subgrade. The pavements were reinforced with three types of geosynthetic products: High-density polyethylene (HDPE) geogrid, HDPE geocomposite and fibreglass geocomposite. The road was divided into 15 sections with different configurations such as the thickness of the base course, reinforcement types and locations, and base course materials. A series of in-situ tests were conducted on each section to compare the behaviour of the pavement structures, such as the moduli of the subgrade, base course and asphalt layer. The comparison shows that there is a large variation in the properties of the structures and great uncertainties in determining the properties even within the sections with the same configuration. When the base course is weaker, the FWD tests may be able to detect the effect of the reinforcements below the asphalt seal layer. Smaller plates are recommended when determining the modulus of thinner base course layers using FWD or LWD tests to minimize the influences from the subgrade.     

我国桥面铺装破坏原因的分析

针对桥面铺装层问题,介绍了常见的铺装层破坏形式,从设计、施工、材料、力学特性四方面具体分析了桥面铺装层出现破坏的原因,并探讨了解决办法,对浇筑式沥青混凝土,沥青玛脂等新型铺装材料作了说明,以期指导实践。     

多孔沥青混凝土路面的调研分析

多孔沥青混凝土具有排水、降噪等优良性能,广泛应用于表面层。通过调研和整理,介绍了多孔沥青混凝土路面的起源、发展以及在我国的实践。同时,调研分析了多孔沥青混凝土路面的强度机理、降噪机理与排水机理。最后指出了未来多孔沥青混凝土的研究方向。     

Hierarchical approach for fatigue cracking performance evaluation in asphalt pavements

In this paper, a hierarchical approach is proposed for the evaluation of fatigue cracking in asphalt concrete pavements considering three different levels of complexities in the representation of the material behaviour, design parameters characterization and the determination of the pavement response as well as damage computation. Based on the developed hierarchical approach, three damage computation levels are identified and proposed. The levels of fatigue damage analysis provides pavement engineers a variety of tools that can be used for pavement analysis depending on the availability of data, required level of prediction accuracy and computational power at their disposal. The hierarchical approach also provides a systematic approach for the understanding of the fundamental mechanisms of pavement deterioration, the elimination of the empiricism associated with pavement design today and the transition towards the use of sound principles of mechanics in pavement analysis and design.     

Performance evaluation of a high durability asphalt binder and a high durability asphalt mixture for bridge deck pavements

This paper describes the results of laboratory and full-scale performance tests for a high durability asphalt binder (HDAB) and high durability asphalt mixture (HDAM) applicable to the wearing course in a bridge deck system. The HDAB was developed using a styrene–butadiene–styrene (SBS) modifier and hydrocarbon for improving construction workability and resistance to fatigue cracking. Various binder tests were conducted on the HDAB, and test results showed that the resistance to fatigue and low temperature cracking of the HDAB increased significantly compared to that of the PG 64-22 and PG 76-22 binders. For the mixtures, the fatigue test results showed that the HDAM has a three times longer fatigue life than the SBS-modified asphalt mixture. It was also found that the HDAM has a higher resistance against moisture-induced damage. Results from full-scale accelerated testing on the bridge deck pavement system proved that the HDAM can significantly improve pavement performance.     

沥青路面耐久性分析

简要介绍了我国沥青混凝土路面使用现状,针对沥青路面的损坏问题进行了分析,分别阐述了影响沥青路面耐久性的内部因素和外部因素,从原材料、配合比、防水设计等方面入手提出了耐久性改善措施,以期指导实践。     

沥青混凝土路面常见病害成因及处治措施

通过对沥青混凝土路面常见病害进行分析,揭示沥青混凝土路面病害产生的原因,提出沥青混凝土路面病害的预防及处治措施,以提高路面使用性能,延长沥青道路寿命。     

高寒地区水泥混凝土桥面沥青铺装层抗疲劳开裂性能分析

混凝土桥面沥青铺装层在使用期间产生的疲劳开裂是世界各地桥面铺装常见的问题,该文依托内蒙古教来河大桥采用有限元分析软件ANSYS对于高寒地区混凝土桥面沥青铺装层的疲劳开裂性能进行分析研究。分析提出高寒地区混凝土桥面沥青铺装层深度0~2 cm区域可作为铺装层内部常温拉应力的峰值分布区域;铺装层内的常温拉应力均随着上面层/下面层厚度的增加而减小;通过增加高寒地区混凝土桥面沥青铺装层的厚度来改善桥面铺装层的抗疲劳性能。     

循环荷载作用下含缺陷岩石破坏特征试验研究

 采用水泥砂浆材料和充填材料模拟含缺陷岩石,分别对含孔洞、柔性充填物及刚性充填物试样进行低周疲劳试验,观察含缺陷试样的疲劳破坏特征,得出含缺陷试样的轴向不可逆变形阶段性规律,研究不同缺陷对岩石类材料的疲劳寿命、疲劳裂纹萌生及其扩展的影响。试验结果表明：循环荷载作用下含缺陷岩石试样的轴向不可逆变形经历初始变形、等速变形以及加速变形3个阶段;含缺陷试样疲劳裂纹首先在有较大应力集中的缺陷与基体材料界面边缘处萌生及扩展;在相同循环加卸载条件下,预制孔洞直径越大,对应的孔洞试样疲劳寿命越短;刚性充填物试样最容易发生疲劳破坏,孔洞试样次之,柔性充填物试样疲劳寿命最长。     

Estimation of relative performance of reinforced overlaid asphalt concretes against reflection cracking due to bending more fracture

Most of overlaid asphalt pavements are facing with reflection cracking in an early age of service life. In this study, a numerical prediction model for fatigue life was developed by modifying crack growth rate, da/dN, of Paris law with horizontal deformation rate, du/dN, to compare relative performance of the material choice based on experimental test result. Experimentally, an interlayer between old concrete pavement and overlay asphalt pavement, polymer modifiers and fiber were used to retard initiation and progress of reflection crack. An expedited reflection cracking test method was developed and applied to various bitumen mixture-concrete block test bodies. The results were compared with one another in terms of resistance against reflection cracking. The coefficient of determination of predicted life and measured life was very high (r² = 0.98). Therefore, it was shown that the fatigue life of each bitumen material and interlayer combination can be estimated using the prediction model developed in this study.     

钢渣沥青混合料疲劳性能及改善机理

采用钢渣替代部分粗集料,制备了4种钢渣掺量的沥青混合料,并对其进行不同应变水平下的四点弯曲疲劳试验,分析钢渣掺量和应变水平对混合料疲劳性能的影响,以揭示疲劳性能改善机理.结果表明:随着钢渣掺量的增加,沥青混合料疲劳寿命呈先增加后降低的趋势,峰值出现在钢渣掺量为30%(质量分数)时;钢渣沥青混合料初始劲度模量和疲劳寿命均随着应变水平的增大而降低;疲劳损伤演化过程可分为失稳、平衡、失效3个发展阶段,疲劳失效劲度模量衰减比S_r/S_(50)小于50%,并随着应变水平的增大而逐渐减小;疲劳裂纹扩展主要发生在矿料-沥青界面处,且受应变水平影响较大;钢渣的化学性质和表面构造在改善界面相结构方面起到了交互黏附和嵌入锚固作用,用钢渣作为粗集料可显著提升沥青混合料的疲劳性能.