Strain distribution along geogrid-reinforced asphalt overlays under traffic loading

While there is significant field evidence of the benefits of geosynthetic-reinforced asphalt overlays, their use has focused on minimizing the development of reflective cracks. Yet, geogrids in asphalt overlays are also expected to develop reinforcement mechanisms that contribute to the pavement structural capacity. Specifically, the use of geosynthetics in asphalt overlays may also improve the mechanical behavior of paved roads by controlling permanent displacements and reducing strains in the pavement layers. While relevant advances have been made towards identifying the mechanisms in geosynthetic stabilization of base courses, such mechanisms may differ from those that develop in geosynthetic-reinforced asphalt overlays. This paper investigates the development and distribution of tensile strains along geogrids used to reinforce asphaltic layers. Experimental data was collected from large-scale paved road models subjected to the repeated loading imparted by wheel traffic. Specifically, the study examines both the elastic and permanent components of displacements induced in geogrids by using mechanical extensometers attached to the geogrids. The testing program includes a number of geosynthetic-reinforced paved road models, as well as a control (unreinforced) section that was also instrumented for comparison purposes. Asphalt strain gauges were used to measure strains within the asphalt concrete layer, providing an additional source of information that proved to be highly consistent with the results obtained from the extensometers. The experimental results showed a progressive mobilization of permanent geogrid strains that reached a final profile beyond which additional traffic loading did not result in additional straining. In comparison, higher strains developed in the unreinforced model, which showed a continuously increasing trend. Elastic tensile strains in the asphalt mixture and rutting under the wheel load were comparatively smaller when using geogrids. Overall, the results generated in this study indicate that the presence of geogrids in asphalt overlays results in a lateral restraining mechanism that influences on the mechanical behavior of flexible pavements.     

Investigations on fracture characteristics of geosynthetic reinforced asphalt concrete beams using single edge notch beam tests

Reflective cracking is a major cause for premature deterioration of asphalt pavements. Different varieties of geosynthetics are used at the interfaces of surface layers to control the reflective cracks. The significant factors influencing their efficiency are the flexural strength and interfacial bonding. Fracture energy that leads to development of cracks and their propagation can be investigated by single-edge notched beam (SENB) tests with sufficient accuracy. Double layered asphalt samples were extracted from pavement sections purposely built as part of this investigation for conducting quasi-static SENB tests. The goal of this paper is two-fold (a) to present a methodology for conducting SENB tests to measure the fracture properties of geosynthetic reinforced samples at temperatures of 10 °C, 20 °C and 30 °C and (b) evaluation of the flexural and the fracture characteristics of unreinforced and geosynthetic reinforced samples. The geosynthetic reinforcement did not show much improvement of the Asphalt Concrete (AC) in the pre-cracking phase but slowed down the crack propagation. The failure pattern of reinforced specimens has changed from quasi-brittle to ductile. An equation is proposed to predict the crack initiation force of SENB sample knowing the bond strength of the corresponding reinforced AC layers at their respective temperature.     

Mode I reflection cracking resistance of strengthened asphalt concretes

This study was devised to evaluate the performance of polymer-modified asphalt mixtures and specially designed reinforcement techniques against reflection cracking for the typical asphalt pavement overlays. Selected polymers from previous studies were used as asphalt modifiers along with fibre; a polypropylene film (vinyl) and a grid were used as reinforcing materials. Using the reinforced asphalt mixtures with the optimum asphalt content from mix design, an asphalt mixture slab was made and cut into two specimens. A layer of grid or polypropylene film was placed at the bottom of each specimen to strengthen the pavement layer against cracking. Simulated-repeated loading was applied to the asphalt mixture specimens using a hydraulic dynamic loading frame. The asphalt mixture specimens were bonded to a cement concrete base which was cut to simulate a crack. Crack propagation under repeated loading was monitored and the effectiveness of the devised crack preventing techniques was evaluated. From the test results, a significant retardation of crack progress was monitored from some of the modified and reinforced asphalt mixtures.     

旧水泥混凝土路面沥青罩面层反射裂缝及防治

针对目前反射裂缝仍是旧水泥混凝土路面加铺沥青罩面层早期破坏的主要形式,通过有限元分析说明了夹层和加铺层厚度对加铺层底部应力的影响,然后简要介绍了国内减少反射裂缝的防治措施,以提高路面质量。     

老路拼接中土工格栅治理路面结构阻裂作用分析

结合滨河路老路改造工程,应用数值仿真,引进了奇异单元模拟裂缝尖端的应力应变场,建立了土工格栅治理新老路路面拼接的计算模型,对行车荷载偏载作用下老路拼接工程中土工格栅的阻裂作用进行分析。结果表明:老路拼接裂缝为张拉型,应力强度因子KI远大于KII,拼接位置主要发生弯拉破坏;新老路不均匀沉降作用下,铺设土工格栅应力强度因子小于未铺设土工格栅应力强度因子,土工格栅阻止裂缝的扩展,对路面裂缝有阻裂作用;在新老路路面拼接处,半刚性基层开裂先于面层,土工格栅铺设位置越靠上,越有利于发挥土工格栅的抗拉效果,建议在路面基层顶面铺设土工格栅。     

Evaluating long-term benefits of geosynthetics in flexible pavements built over weak subgrades by finite element and Mechanistic-Empirical analyses

Finite element (FE) models were developed to evaluate the benefits of geosynthetic reinforcement in flexible pavements built over weak subgrades. The parametric study was conducted to evaluate the effect of different variables such as base thickness, geosynthetic type, geosynthetic stiffness, and double-geogrid layers. FE analyses were performed for 100 load cycles, and the permanent deformation (PD) was used to calibrate the empirical parameters in MEPDG equations for each layer, which were used to extrapolate PD data for the service life of pavements. The PD curves for unreinforced and similar reinforced sections were used to evaluate the Traffic Benefit Ratios (TBR) at different rut depths. The results showed that the inclusion of one geogrid/geotextile layer at the base-subgrade interface could significantly reduce pavement rutting. The use of geogrid is more effective than geotextile in reducing pavement rutting. The derived TBR values range from 1.91 to 8.9 for one geogrid layer and from 1.71 to 5.92 for one geotextile layer. The TBR values increase with increasing the rutting depth and geosynthetic stiffness. The TBR value demonstrates an optimum at a base thickness of 10 in. The results demonstrated the superior benefits of using double geogrid layers compared to single-layer cases.     

Influence of asphalt thickness on performance of geosynthetic-reinforced asphalt: Full-scale field study

In this study, a series of controlled traffic loadings was conducted on unreinforced and geosynthetic-reinforced full-scale asphalt overlays. Unlike the common objective of using paving interlayers to mitigate the development of reflective cracks, the main purpose of adopting geosynthetics for this study was to render an increased roadway structural capacity. The project involved instrumented test sections constructed during the rehabilitation of an in-service roadway in Texas, USA. The rehabilitation involved repairing the pre-existing pavement, placing tack coat, installing a geosynthetic interlayer (except in the unreinforced section), and finally constructing a 75 mm-thick asphalt overlay. This overlay comprised a 50 mm-thick, dense-graded (TY-D) layer overlain by a 25 mm-thick, thin-overlay mixture (TOM) layer. Controlled traffic loadings were conducted, which involved driving standard and light axle loads directly above asphalt strain gauges that had been installed at mid-depth of the pre-existing asphalt layer. Comparison of tensile strains among the different test sections revealed significantly smaller tensile strains in the geosynthetic-reinforced sections compared to those obtained in the unreinforced section. Consequently, and even though geosynthetic interlayers have often been adopted to minimize reflective cracking in asphalt overlays, the field monitoring results generated in this study demonstrate that they also provide added roadway structural capacity.     

浅谈水泥路面加铺沥青层

通过对水泥路面加铺沥青层进行调查分析研究,探讨了水泥路面加铺沥青层技术中的几个关键性问题,结果表明：水泥路面加铺沥青层技术是处理旧水泥路面行之有效的方法之一,在旧水泥路面改建中发挥着重要作用。     

温度场作用下的反射裂纹应力场分析

考虑了沥青混合料的热粘弹特性,结合热传导理论,通过有限元数值模拟,研究在温度场作用下反射裂纹的应力场。分析表明,在较低温度环境下,会使基层裂纹附近存在高应力区,当其应力值大于沥青的抗拉强度时,会导致裂纹的产生并扩展到路面形成路面裂纹。提出了采用聚酯纤维增强型沥青的阻裂方案,通过数值模拟验证了其有效性。     

A preliminary study of the application of the strain-self-sensing smart geogrid rib in expansive soils

Flexible conductive materials are widely used in structural health monitoring; it is also known in geotechnical engineering. In this preliminary study, a strain-self-sensing smart geogrid rib was proposed to monitor the induced strain by wetting-drying cycles of the expansive soil. After the calibration, a physical modeling test was conducted with the smart geogrid rib reinforced in expansive soils under three wetting-drying cycles. Results demonstrated: that the smart geogrid rib was capable of self-sensing its strain; the strain self-sensed by the smart geogrid rib was in good agreement with that measured by FBG strain sensors before cracks were generated; it could capture the crack propagation of expansive soils during wetting-drying cycles by the discrepancy compared to FBG sensors. Further study will be continued for the mechanism of the geogrid instead of the geogrid rib and the application to real-time monitoring of the performance of the geosynthetic expansive soil slopes.     

旧水泥路面加铺沥青层方案的综合分析

反射裂缝是旧水泥路面加铺沥青层工程中常见的问题。依托工程实践经验并结合规范,分析了反射裂缝产生的原因,并讨论了不同路状下旧水泥混凝土路面加铺沥青层的处理方案。最后按JTGD50—2006《公路沥青路面设计规范》介绍了加罩措施分类标准和对旧水泥路面碎石化处理时的注意问题。     

沥青路面低温开裂问题的探讨

阐述了国内外沥青路面低温开裂研究的现状,介绍了沥青路面裂缝的两种形式,从沥青的性质、沥青混合料的性质以及环境因素对开裂的影响三方面分析了影响沥青路面低温开裂的因素,为研究新疆沥青路面的低温开裂提供了参考依据。     

The effect of waste tire thread mesh on the dynamic behaviour of asphalt mixtures

The crack potential of the pavement under various loading conditions and temperature variations has been a problem for the application of asphalt pavements. Crack generation in asphalt pavement increases the maintenance and rehabilitation costs. Two principal solutions for the problem of asphalt pavement cracking have been introduced: first, applying a thicker asphalt pavement and, second, making an asphalt mixture with modified characteristics. The effects of different types of reinforcement on the cracking potential of asphalt pavement as a substantial characteristic of asphalt mixture has been questioned, and a variety of different experiments have been developed to determine these effects. The use of tire cord mesh in reinforcing asphalt pavement has been introduced and accurately observed in this research. In this paper, the crack potential of asphalt pavement reinforced with tire cord mesh is evaluated with emphasis on introducing experimental methods and analysing their results. The results show that the tire cord mesh reinforcement significantly increases the asphalt pavement resistance against cracking and increases its service life while decreasing maintenance and rehabilitation costs.     

水泥混凝土路面加铺沥青罩面的病害成因分析与对策

通过对城市沥青罩面道路的病害调查和相关室内试验,分析了水泥混凝土路面加铺沥青罩面产生的主要病害类型及成因,并提出了相应的防治措施和对策,为完善水泥混凝土路面加铺沥青罩面的设计、施工和养护技术,以及提高路面质量和延长路面使用寿命提供了参考。     

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.     

混凝土桥面铺装层受力分析研究

本文对桥面铺装层建立一种分层剪滞模型,并结合线弹性断裂力学研究了混凝土公路桥中桥面板和铺装层组合体受车辆荷载作用下铺装层的破坏问题,求得了某工程实例中新、旧桥面铺装层中裂纹发生扩展时的强度.结果表明,新桥面铺装层（钢纤维增强混凝土）的强度极限明显高于旧桥面铺装层（普通混凝土）的强度极限.     

沥青路面低温开裂问题的探讨

沥青路面完全暴露于自然环境中,长期承受着车辆载荷的作用和外界自然环境的直接影响,导致沥青路面路用性能的下降。在我国北方地区,低温开裂是沥青路面常见的一种病害,因此,有必要对沥青路面的低温开裂性能进行深入研究。该文分析了我国东北地区沥青路面低温开裂产生的机理和原因以及半刚性基层的服役特点,提出了减少温缩裂缝的措施。     

沥青路面表面裂缝扩展研究

基于线弹性断裂力学,分析了沥青路面开裂以后,裂缝尖端的应力强度因子与路面温度分布和路面材料特性参数之间的关系,分析结果表明,在沥青路面的抗裂设计中,合理设计沥青面层的厚度和优选温缩性小的路面材料是提高沥青路面抗裂性能的两个重要方面。     

地震灾后旧水泥混凝土路面沥青加铺技术研究

结合震后四川某一级公路路面不同路段的损坏情况,决定采用旧水泥混凝土路面沥青加铺技术对其进行加固维修,归纳了维修方案设计的相关内容,指出该路面加铺技术运用效果好,改善了路面质量。     

沥青路面反射裂缝扩展有限元分析

通过介绍扩展有限元的概念及方法,应用ABAQUS有限元分析半刚性沥青道路在持续降温情况 下反射裂缝的扩展过程.通过模拟分析,发现只有当温度下降到一定值之后裂缝才开始扩展,而一旦超过该温度裂缝将会急速扩展贯穿面层,然后扩展速率下降趋于稳定;损伤能在面层出现张开量时急速增长直至面层完全张开时稳定不再变化.