Heat transfer model for microwave hot in-place recycling of asphalt pavements

In order to solve for temperature fields in microwave heating for recycling asphalt mixtures, a two-dimensional heat transfer model for the asphalt mixtures within the heating range is built based on the theory of unsteady heat conduction. Four onedimensional heat transfer models are established for the asphalt mixtures outside the heating range, which are simplified into four half-infinite solids. The intensity of the radiation electric field is calculated through experiment by using heating water loads. It is suggested that the mathematical model of boundary conditions can be established in two ways, which are theoretical deduction and experimental reverse. The actual temperature field is achieved by fitting temperatures of different positions collected in the heating experiment. The simulant temperature field, which is solved with the Matlab PDE toolbox, is in good agreement with the actual temperature field. The results indicate that the proposed models have high precision and can be directly used to calculate the temperature distribution of asphalt pavements.

Mass transfer analysis for microwave hot in-place recycling of asphalt pavements

In order to realize mass transfer analysis for microwave hot in-place recycling of asphalt pavements, a volume element is established including asphalt mixtures, liquid water and vapor. A mass transfer control model is built by the theory of multiphysics, phase transformation and diffusion. The model contains continuity equation, energy conservation equation, movement equation and vapor diffusion equation. To gain the solution of the mass transfer model, the formulas are simplified to one-dimensional differential equations. And then a mathematical model of boundary conditions is established. The mass transfer velocity and dissipative energy are obtained in different moisture contents through simulation of asphalt pavements recycling. The result indicates that when initial moisture content is certain, mass transfer velocity is almost uniform in depth direction at the same heating time and enertrv absorbed by water i,~ descendino with denletion of moisture.

Analytical prediction and field validation of transient temperature field in asphalt pavements

This work presented the development and validation of an analytical method to predict the transient temperature field in the asphalt pavement.The governing equation for heat transfer was based on heat conduction radiation and convection.An innovative time-dependent function was proposed to predict the pavement surface temperature with solar radiation and air temperature using dimensional analysis in order to simplify the complex heat exchange on the pavement surface.The parameters for the time-dependent pavement surface temperature function were obtained through the regression analysis of field measurement data.Assuming that the initial pavement temperature distribution was linear and the influence of the base course materials on the temperature of the upper asphalt layers was negligible,a close-form analytical solution of the temperature in asphalt layers was derived using Green's function.Finally,two numerical examples were presented to validate the model solutions with field temperature measurements.Analysis results show that the solution accuracy is in agreement with field data and the relative errors at a shallower depth are greater than those at a deeper one.Although the model is not sensitive to dramatic changes in climatic factors near the pavement surface,it is applicable for predicting pavement temperature field in cloudless days.

Low temperature cracking behavior of asphalt binders and mixtures: A review

Low temperature cracking(LTC)distress on pavement seriously affects road life.This paper finished a literature review of the research on the mechanism of LTC of asphalt composites(asphalt composites refers to asphalt binder and asphalt mixture in this article),test methods,factors contributing to LTC,measures to prevent and control the distress,and prediction of LTC in asphalt pavements.The following conclusions were obtained:the cracking mechanism of asphalt mixtures needs to be further revealed by means of simulation at the micro level,the BBR and 4 mm plate test(by DSR)methods are currently optimal,and a correlation between asphalt and asphalt mixture evaluation indexes needs to be established.Sensitivity analyses are needed for the factors affecting LTC of asphalt mixtures.It is necessary to calculate the contribution of each factor to the LTC of asphalt mixtures.The aim is to propose targeted improvement measures for the most unfavourable factors,as well as to carry out research and development of key materials for anti-cracking.Measures for the prevention and control of LTC of asphalt pavement are analyzed and discussed.Existing researches on the prediction of LTC of asphalt pavements is discussed.It is necessary to analyse the mechanical response of asphalt pavement,the damage process and the sensitivity of anti-cracking parameters on the basis of considering the complex geometrical characteristics and material properties of asphalt pavement materials.Finally,the mechanism of LTC,evaluation methods,factors influencing LTC,and remedial measures for asphalt composites were summarized,and future research prospects were suggested.This paper provides theoretical support for the further solution of LTC distress of asphalt pavement,which is effective on the improvement of pavement life.

Influences of Used Parameters of Screw Distributor upon Mixture Paving Segregation

The paving segregation of asphalt mixture was closely related to the structure size and using parameters for the screw distributor of paver,and the paving uniformity of the mixture was determined by the screw blade diameter,pitch,and the position of the mixture in the screw distributor.Through researching the kinematics of the mixture in the screw distributor,the mathematical model was established,and the mathematical model was related with structural parameters,used parameters and material parameters.Through the mathematical model,the various parameters on the screw distributor job performance were analyzed,and the unstable area,meta-stable area and stable area were determined.In the project,the full-scale test in actual project was conducted by using the AC25 mixture.By changing the using parameters compare the paving operations,the results show that,the reasonable parameter will greatly improve the uniformity of paving,and the surface proportion of structural depth of mixture decrease from the 2.13 to 1.60.

改性乳化沥青冷再生技术及设备改进分析

在我国经济建设稳步推进的背景下,交通运输线路肩负着重要的功能作用,为解决路面损坏的问题,缓解其对于出行与运输安全造成的阻碍,该文提出改性乳化沥青冷再生技术的应用,其作为一种新型的路面翻修施工技术具有显著的优势。通过对改性乳化沥青冷再生技术的分析,对该技术工艺与设备进行全面了解,由此得出改性乳化沥青冷再生技术及设备改进具体性能结论,为沥青路面施工创造出更好的经济效益。

高速公路沥青路面材料选择与性能提升研究

高速公路作为现代交通体系的重要组成部分,其沥青路面的性能直接影响着行车安全、舒适度以及道路的长期服役状况。近年来,随着交通运输量的持续增长、重型车辆比例的增加以及极端气候事件的频发,对沥青路面的耐久性、稳定性和环保性提出了更高要求。与此同时,新材料、新技术的快速发展为提升沥青路面性能提供了新的可能。因此,深入研究高速公路沥青路面材料的选择策略与性能提升技术,对于确保道路基础设施的长期高效运行,满足社会经济发展需求,以及实现交通领域的可持续发展目标具有重大意义。

探市政公用工程施工中沥青路面施工技术通病与改进措施

在现代城市化进程中,沥青路面施工的挑战和难点日益凸显。一方面技术难题和施工环境的复杂性给施工过程带来了不小的压力;另一方面材料选择和质量控制的不足也直接影响了路面的使用寿命和性能表现。此外,路面常见病害如裂缝、车辙、沉陷等问题的频繁出现,进一步加剧了施工质量和维护成本的难题。因此,深入探讨市政工程沥青路面施工的技术挑战、病害分析和改进措施,对于提高施工质量、延长路面使用寿命和降低维护成本具有重要意义。

沥青路面高密实振捣压实传递特性研究

为了提高沥青路面的摊铺密实度,需要研究摊铺机振捣机构对混合料的压实传递特性。针对振捣装置与材料组成的动力学压实系统,考虑摊铺下承层材料特性建立了振捣机构-沥青混合料相互作用动力学模型,提出压实传递力和压实传递率的理论计算方法。将振捣压实过程中的压实传递力作为振捣机构压实能力参数、压实传递率作为振捣压实效率参数,研究振捣频率、沥青混合料特性和下承层刚度对振捣压实传递特性的影响规律,得到了沥青路面高密实摊铺的振捣工作参数范围。基于振捣压实传递特性参数,探讨振捣压实传递力和压实传递系数与密实度之间关系,并进行仿真分析和试验研究。研究结果表明:振捣频率为最大振捣频率的10%(4 Hz左右),密实度出现第一个峰值点87%,之后密实度逐渐减小,在振捣频率百分比为45%(15 Hz左右)时,到达密实度低谷段84%后又逐渐增大,振捣频率百分比为65%(22 Hz左右)达到密实度第二个峰值点88%,密实度和振捣压实传递力理论计算结果之间存在对应关系。在小于振捣频率22 Hz的范围内,振捣压实传递力可以作为摊铺密实度变化的特征参数。研究结果可为摊铺机实现对铺层混合料的高效压实提供依据。

以乡村振兴为背景的农村公路提质改造设计研究

围绕乡村振兴战略,加速农村公路提质改造,研究以保证质量完成农村公路修建,并且节约造价为目的,充分利用旧路资源,结合已有公路进行技术改造、完善相关安全保障设施。以广东省汕头市农村公路改建为例说明农村公路改造设计过程,以现场旧路详细调查为依据,进行旧路路面病害分析,确定路面改造技术标准与设计参数。在改造路面的同时,完善安全设施,提高行驶安全性。

基于改进遗传算法的公路沥青混凝土路面黏弹性损伤演化模拟

沥青混凝土路面在低温状态下会有明显的开裂现象,一旦公路路面上出现裂缝,路面就会逐渐损坏,影响道路的平稳性与舒适性。为降低公路维护成本,基于改进遗传算法对公路沥青混凝土路面黏弹性损伤进行演化模拟。建立沥青混凝土路面结构模型,依据弹性柔量与摩擦系数的关系得到路面各层级之间的空间特征;基于改进遗传算法计算路面黏弹性损伤荷载,划定初始损伤与断裂区域的应力总值,计算路面黏弹性损伤荷载;设定路面损伤在环境温度以及各层级间相对位移量的边界条件,得到路面损伤模拟分析的方法。由试验数据可知:温度越低,路面的应力作用越大,且裂缝的长度与路面正应力成正比。

沥青混合料离析防治及路面压实技术研究——以兰州绕城高速公路为例

针对高速公路的路面离析问题,结合兰州绕城高速公路南绕城路段的施工经验和养护记录,对离析现象的种类和成因进行研究,提出防治沥青混合料离析的措施,研究影响路面压实的相关因素,提升北绕城路段的路面施工质量。研究表明,不同类型的沥青混合料中,沥青玛蹄脂碎石混合料(SMA)最易压实,但是运营阶段抵抗变形能力较弱;不同级配的沥青混合料,中值级配压实最容易,但上限级配在运营阶段的抵抗变形能力最强;随着改性剂掺量的增加,压实难度逐渐降低,但施工阶段所需要的能量逐渐增大;沥青混合料在145℃时,碾压成型较为容易,压实度较好。综上所述,后续北绕城高速路的施工,推荐采用掺量为3.5%~4.5%的中值级配的AC改性沥青混合料,在145℃时碾压成型。

沥青路面施工中沥青混合料离析及控制研究——以刚果(金)金沙萨马鲁古经济开发区建设项目为例

沥青混合料离析是沥青路面施工的常见问题,会对路面质量和使用寿命产生负面影响,须探索沥青混合料离析的原因,并提出有效的控制方法。文章以刚果(金)金沙萨马鲁古经济开发区建设项目为例,从沥青混合料运输、施工温度、摊铺质量等方面分析了产生离析现象的主要原因,并提出了相应的控制策略,如加强运输控制、加强施工温度控制、加强摊铺质量控制,旨在提升路面质量,延长道路使用寿命。

公路沥青路面离析原因及控制措施探讨

公路沥青路面施工中极易受到外界因素干扰,导致路面出现不同程度的离析问题,严重影响沥青路面施工质量。文中以某公路工程为例,分析沥青路面施工离析问题的影响因素,阐述材料离析、温度离析、碾压离析三方面相应的控制措施,以期为沥青路面工程提供参考。

混凝土路面加铺沥青混凝土面层改造技术研究

为提高交通行车质量,文中分析了市政混凝土路面加铺沥青混凝土面层改造技术,调查研究区域路面的强度与厚度、弯沉、接缝传荷能力和破损状况,确定研究区域内混凝土路面的反射裂缝是最常见的问题。在断裂力学的基础上,分析反射裂缝产生的原因,并根据分析结果,设计市政混凝土路面加铺沥青混凝土面层改造方案,同时通过马歇尔试验,验证了该技术可以改善路面的使用性能。

钢桥面铺装高弹沥青抗紫外老化措施及性能研究

为降低强紫外线对高弹沥青的老化作用,延缓钢桥面铺装层路用性能的衰减速率,通过模拟紫外老化试验研究紫外老化对高弹沥青性能的影响,对比3种抗紫外老化剂改善高弹沥青性能的效果,优选出最佳的抗紫外老化剂以及最佳掺量,并评价该抗紫外老化剂对高弹沥青混合料路用性能的影响。结果表明:1)紫外老化降低了高弹沥青的针入度、延度值和软化点,但抗车辙因子略有增大;2)3种抗紫外老化剂均能改善紫外老化对高弹沥青及其沥青混合料的不利影响,其中抗紫外老化剂UV-1改善效果最佳。建议采用抗紫外老化剂UV-1改性高弹沥青,它是延缓钢桥面铺装层紫外老化的有效措施,并能提高钢桥面铺装层的耐久性和服役寿命。

运用红外热像仪改善沥青混合料温度离析效果的研究

运用国外先进检测设备红外热像仪对安徽、江苏多条高速公路施工过程中运料车、摊铺机进料口、卸料斗、螺旋布料器轴后等不同离析位置进行定位,总结红外热像仪定性判断温度离析情况的效果。结合红外热像仪判断温差并与PQI(Pavement Quality Indicator)测量路面密实度共同研究温度离析对沥青路面压实度的影响,直观定性分析路面离析情况和找到离析的原因并定量评价路面离析程度及范围,从而为寻找有效解决沥青路面温度离析的方案,实现沥青路面质量全过程控制提供依据。

级配对沥青混合料集料离析的影响

为了比较不同级配类型的沥青混和料在施工过程中产生集料离析的差异程度,通过调整拌和楼热料仓比例生产出具有代表性的7种级配类型沥青混和料,分析了其摊铺后在横断面上不同位置的颗粒组成状况,混和料经碾压成型后,测定其在横断面上不同位置的构造深度,并评价其数值特征。研究结果表明:在相同条件下,产生集料离析程度由大到小的沥青混和料级配为:反S型、间断级配、最大密度曲线之上微弓型、S型、0.45次方最大密度曲线、含中间粒径较多的级配、最大密度曲线之下微弓型。

沥青路面温度场数值预估模型

为了准确预估在环境因素作用下沥青路面的温度分布状况,根据热传导基本理论,建立了沥青路面温度场数值预估模型,并使用有限差分方法对其求解.为了验证该模型的精度,在全国多个地区设立观测站,埋设温度传感器,实测沥青路面温度分布数据并收集与其相关的各种气象数据,如气温、太阳辐射、风速等.结果表明,模型可以较为准确地预估不同地区、不同季节沥青路面内的温度分布状况.

热沥青混合料碾压过程的离析现象

针对混合料不均匀导致路面早期损坏的问题,采用综合分析的方法,从碾压施工角度重点分析了热沥青混合料碾压过程的不均匀现象,通过分析可能造成沥青混合料碾压过程离析的多种原因,提出了碾压离析的概念。认为除热沥青混合料生产、摊铺和碾压可能造成碾压离析外,路面结构设计、施工工艺和压路机的设计与制造不合理也是造成碾压离析的3个重要原因。研究结果表明:造成混合料不均匀的原因很多,应该综合考虑混合料生产、摊铺和碾压,路面结构和施工工艺,以及压路机的设计等因素,才能进一步提高路面的质量。