基于关联性的玄武岩纤维沥青胶浆及其混合料性能研究

为全面提升玄武岩纤维沥青混合料性能,研究了纤维类型及玄武岩纤维长度、掺量等因素对沥青胶浆抗裂性能、抗剪性能及流变特性的影响规律;基于纤维胶浆与纤维沥青混合料性能的关联性分析,揭示了玄武岩纤维对沥青混合料性能的细观增强机制。结果表明:玄武岩纤维对沥青胶浆的抗裂性能及流变特性影响显著,其极限拉力和车辙因子分别达到原沥青胶浆的4.5倍及1.08倍;纤维沥青胶浆高温流变特性与其沥青混合料高温稳定性变化规律存在差异,而前者抗裂性能与后者低温抗裂性能关联性较强;玄武岩纤维与沥青胶结料、集料之间形成三维网状结构,有利于抑制裂缝扩展。     

沥青混合料动态模量预估模型研究进展

由于沥青路面结构受到车辆荷载、环境等因素的不断变化作用,它的实际工作状态与静态体系在材料性质等方面存在较大差距。因此,针对动态荷载作用下沥青路面结构的动态参数和动力特性的研究十分必要。沥青混合料动态模量是沥青路面设计的重要参数之一,通过室内试验测得沥青混合料不同温度、频率下的动态模量,然后绘制主曲线,可准确预测不同温度、频率及极端条件下沥青混合料的动态模量。然而,目前沥青混合料模量测试方法复杂、试验成本较高,因此寻求简便的方法获得或预估沥青混合料的模量成为近年来研究的热点。为此,已有众多学者针对沥青混合料动态模量预估模型进行了研究。典型的预估模型包括Witczak 1-37A模型、NCHRP 1-40D模型和Hirsch模型等,尽管这些模型是在大量试验数据的基础上拟合得到,但由于世界不同地区的材料、试验方法、环境条件等存在差异,致使三种经验预估模型在不同地区的适用性也不尽相同。与此同时,随着计算机技术的发展,研究人员逐渐从微观角度建立模型来预测混合料的动态模量,而在沥青混合料数值模拟方面,离散元法(DEM)具有其他数值模拟方法无可比拟的优势。在典型预估模型的适用性方面,国外针对沥青混合料动态模量的预估做了大量研究,对几种典型的动态模量预估模型的适用性进行了系统分析,并提出了具体的修正模型。但目前我国在预估模型方面的研究只集中于个别省份和地区,而全国范围内沥青混合料动态模量的综合测试较少,缺乏有效的预估模型基础数据,因此针对我国不同地区沥青混合料动态模量的预估模型有待进一步深入研究。在沥青混合料细观模型方面,基于CT图像处理技术的离散元仿真试验,可建立以真实试件为依据的虚拟几何模型,其中集料形状、分布以及空隙特征都可与实际情况一致,从而进行良好的虚拟仿真试验。本文归纳了沥青混合料动态模量预估模型的研究进展,分别对沥青混合料动态模量预估模型以及各预估模型在不同地区的适应性进行了分析,并介绍了基于DEM的动态模量预测方法。最后,分析了沥青混合料动态模量预估模型研究面临的问题并展望了其应用前景,以期为沥青混合料动态模量预估模型在我国沥青路面设计中的研究和应用提供参考。     

基于细观力学的纤维沥青混凝土有效松弛模量

为了研究纤维沥青混凝土的本构模型,将其视为以沥青混合料为粘弹性基体,纤维为弹性夹杂的两相复合材料。对基于复合材料细观力学理论建立的有效模量表达式进行了修正,提出了纤维沥青混凝土的割线有效松弛模量。以聚酯纤维沥青混凝土为例进行了有效松弛模量的解析分析和模拟蠕变实验的有限元分析,分析结果与试验数据的比较表明,该文提出的割线有效松弛模量模型对于纤维沥青混凝土粘弹性力学行为具有很好的预测能力。应用该模型对路面弯沉变形进行了有限元分析,结果表明:纤维的加入有效的改善了沥青混凝土路面的粘弹性性能。     

基于分数阶导数的沥青胶浆动态力学特性

通过对粉胶比为0.62、0.82、1.02、1.22和1.42的沥青胶浆在20℃、30℃、40℃和50℃条件下进行动态频率扫描试验,研究了不同粉胶比及试验温度条件下沥青胶浆复模量、抗车辙因子和相位角的变化规律。基于分数阶导数理论,建立了Nutting蠕变方程与经典分数阶导数Abel黏壶蠕变模型之间的关系,从而明确了Nutting蠕变方程各参数的物理意义。对分数阶Riemann-Liouville算子黏弹性蠕变本构模型的动态力学响应进行分析,提出了利用沥青胶浆动态频率扫描试验结果确定蠕变本构模型中参数A值和γ值的新方法。     

纤维复合材料粘弹性动态性能的细观力学分析

建立了纤维增强复合材料粘弹性动态性能的细观力学模型.首先建立了树脂基体相各向同性的粘弹性模型,模型参数由纯树脂基体材料的蠕变试验获取,在此基础上分别建立了针对单向和正交铺层复合材料的横观各相同性、正交各相异性的细观粘弹性模型.对单向、正交铺层复合材料进行了静态和动态试验,分别通过试验和上述理论模型得到了其阻尼比、动态储存模量、损耗模量和损耗因子,理论预测与试验结果吻合.     

回收沥青胶浆多尺度参数再生效果评价

为了研究不同再生剂掺量下再生沥青胶浆的再生效果、特征官能团和细观力学参数的演变及其对高温流变特性的影响,采用动态剪切流变试验(DSR)和傅里叶变换红外光谱(FTIR)技术,分别测试了KL90基质沥青及其压力老化(PAV)沥青、回收沥青胶浆、再生剂掺量为6%、9%、12%的再生沥青胶浆的特流变特性和征官能团,同时采用规划求解的方法得到了沥青胶浆细观力学参数,并对沥青胶浆的宏观流变特性参数与细观力学参数的关系进行了公式推导。结果表明,温度对沥青胶浆的流变特性有重要影响,再生剂的加入使得沥青胶浆的流变特性得到恢复,同时也降低其抗车辙能力,当再生剂掺量为9%时,回收沥青胶浆的高温流变特性恢复较好;相比KL90基质沥青,PAV老化沥青和回收沥青胶浆羰基指数(CI)增加;回收沥青胶浆在1 260 cm~(-1)处、1 018 cm~(-1)和1 089 cm~(-1)处出现了C-O-C键和Si-O-Si键的特征峰,再生沥青胶浆在1 744 cm~(-1)处和1 160 cm~(-1)处出现了饱和脂肪酸酯C=O键和直链C-C键的特征峰;回收沥青胶浆的细观力学参数E_1、η_1、E_2、η_2显著高于KL90基质沥青及再生沥青胶浆,随着再生剂掺量增加,E_1、η_1、E_2、η_2逐渐减小。     

基于单胞解析模型的单向复合材料强度预报方法

基于单胞解析模型,建立一种从复合材料细观组分到宏观单向板的强度预报方法。根据连续介质力学和均匀化方法构建细-宏观关联矩阵,通过该关联矩阵将细观组分材料的弹性和损伤性能传递到宏观单向板中。考虑复合材料细观损伤状态,当纤维和基体满足各自强度准则时失效,并通过失效因子折算成刚度的衰减。在此基础上,结合有限元分析,实现复合材料单向板纵横向拉伸模拟,从而预报单向板的拉伸强度。结果表明:该方法预报的模量和强度与实验值基本一致,验证了该方法的有效性与高效性。     

橡胶颗粒沥青混合料劈裂试验及其数值模拟研究

本研究构建的橡胶颗粒沥青混合料劈裂细观数值模型以裂缝数与劈裂强度为主要细观参数,与劈裂试验确定的宏观参数劈裂抗拉强度及劲度模量相互验证,从宏观与细观两个角度验证了橡胶颗粒的掺加将明显降低沥青混合料的力学强度。     

水泥对泡沫沥青冷再生混合料强度影响机理

采用扫描电镜对掺加水泥前后回收沥青路面材料(RAP)、新集料、泡沫沥青胶浆微观形貌的分布特征等进行对比研究,进而采用工业CT的无损检测技术定量揭示了水泥对泡沫沥青冷再生混合料马歇尔试件内部孔隙特征的影响。研究结果表明,泡沫沥青冷再生混合料中水泥水化产物显著改善了集料表面的棱角性,从而增加了沥青与集料的粘附性;水泥水化物与沥青形成的胶浆复合物所构成的空间立体网格结构在混合料中起到"加筋"、填充作用,且显著增强了泡沫沥青胶浆的整体稳定性,从而提高了混合料的强度;水泥水化产物起到次级结合料的同时,还改变了混合料内部孔隙分布特征,增加了微孔隙数量,降低了内部孔隙的平均孔径,从而提高了混合料的水稳定性。     

两种沥青胶浆的疲劳及自愈合性能试验

为了研究沥青胶浆的疲劳及自愈合特性,利用动态剪切流变仪（DSR）进行时间扫描及疲劳-愈合-再疲劳测试,并通过原子力显微镜（AFM）对细观结构进行观测,比较分析了不同粉胶比下基质沥青胶浆和苯乙烯-丁二烯-苯乙烯嵌段共聚物（SBS）改性沥青胶浆的疲劳性能,以及在常温（25℃）下3个不同间歇期的自愈合性能。试验发现：SBS沥青胶浆具有更好的疲劳和自愈合性能,两种沥青胶浆疲劳寿命均随粉胶比的增大而增加,同一粉胶比条件下,更长的间歇期有利于其自愈合,过大或者过小的粉胶比都会降低沥青胶浆的自愈合性能;AFM观测结果表明：基质沥青胶浆出现明显的"蜂状结构",粉胶比增加,矿粉吸附更多的沥青质,"蜂状结构"变多,与沥青界面内聚力作用增强,提高了抗疲劳性能,SBS改性剂与沥青相容性良好,改性沥青胶浆没有出现"蜂状结构",改性剂的加入增强了分子间内聚力,有助于提高抗疲劳性能,因此建议路面材料选用改性沥青胶浆。     

Dynamic modulus simulation of the asphalt concrete using the X-ray computed tomography images

The objective of this study is to predict the dynamic modulus of asphalt mixture using both two-dimensional (2D) and three-dimensional (3D) Distinct Element Method (DEM) generated from the X-ray computed tomography (X-ray CT) images. The 3D internal microstructure of the asphalt mixtures (i.e., spatial distribution of aggregate, sand mastic and air voids) was obtained using the X-ray CT. The X-ray CT images provided exact locations of aggregate, sand mastic and air voids to develop 2D and 3D models. An experimental program was developed with a uniaxial compression test to measure the dynamic modulus of sand mastic and asphalt mixtures at different temperatures and loading frequencies. In the DEM simulation, the mastic dynamic modulus and aggregate elastic modulus were used as input parameters to predict the asphalt mixture dynamic modulus. Three replicates of a 3D DEM and six replicates of a 2D DEM were used in the simulation. The strain response of the asphalt concrete under a compressive load was monitored, and the dynamic modulus was computed. The moduli of the 3D DEM and 2D DEM were then compared with both the experimental measurements results. It was revealed that the 3D discrete element models successfully predicted the asphalt mixture dynamic modulus over a range of temperatures and loading frequencies. It was found that 2D discrete element models under predicted the asphalt mixture dynamic modulus.     

A multiscale model for predicting the viscoelastic properties of asphalt concrete

It is well known that the accurate prediction of long term performance of asphalt concrete pavement requires modeling to account for viscoelasticity within the mastic. However, accounting for viscoelasticity can be costly when the material properties are measured at the scale of asphalt concrete. This is due to the fact that the material testing protocols must be performed recursively for each mixture considered for use in the final design.In this paper, a four level multiscale computational micromechanics methodology is utilized to determine the accuracy of micromechanics versus directly measured viscoelastic properties of asphalt concrete pavement. This is accomplished by first measuring the viscoelastic dynamic modulus of asphalt binder, as well as the elastic properties of the constituents, and this comprised the first scale analysis. In the second scale analysis, the finite element method is utilized to predict the effect of mineral fillers on the dynamic modulus. In the third scale analysis, the finite element method is again utilized to predict the effect of fine aggregates on the dynamic modulus. In the fourth and final scale analysis, the finite element method is utilized to predict the effect of large aggregates on the dynamic modulus of asphalt concrete. This final predicted result is then compared to the experimentally measured dynamic modulus of two different asphalt concretes for various volume fractions of the constituents. Results reveal that the errors in predictions are on the order of 60 %, while the ranking of the mixtures was consistent with experimental results. It should be noted that differences between the “final predicted results” and the experimental results can provide fruitful ground for understanding the effect of interactions not considered in the multiscale approach, most importantly, chemical interactions.     

Micromechanical finite element framework for predicting viscoelastic properties of asphalt mixtures

A micromechanical finite element (FE) framework was developed to predict the viscoelastic properties (complex modulus and creep stiffness) of the asphalt mixtures. The two-dimensional (2D) microstructure of an asphalt mixture was obtained from the scanned image. In the mixture microstructure, irregular aggregates and sand mastic were divided into different subdomains. The FE mesh was generated within each aggregate and mastic subdomain. The aggregate and mastic elements share nodes on the aggregate boundaries for deformation connectivity. Then the viscoelastic mastic with specified properties was incorporated with elastic aggregates to predict the viscoelastic properties of asphalt mixtures. The viscoelastic sand mastic and elastic aggregate properties were inputted into micromechanical FE models. The FE simulation was conducted on a computational sample to predict complex (dynamic) modulus and creep stiffness. The complex modulus predictions have good correlations with laboratory uniaxial compression test under a range of loading frequencies. The creep stiffness prediction over a period of reduced time yields favorable comparison with specimen test data. These comparison results indicate that this micromechanical model is capable of predicting the viscoelastic mixture behavior based on ingredient properties.     

Analytical modeling and experimental study of tensile strength of asphalt concrete composite at low temperatures

In this study, analytical modeling of the tensile strength of hot-mix asphalt (HMA) mixtures at low temperatures was developed. To do this, HMA mixtures were treated as a two-phase composite material with aggregates (coarse and fine) dispersed in an asphalt mastic matrix. A two-phase composite model, which was similar to Papanicolaou and Bakos's [J. Reinforced Plast. Compos. 11 (1992) 104] model with a particle embedded in an infinite matrix, was proposed. Unlike Papanicolaou and Bakos's model, an axial stress was introduced to the fiber end to consider the load transferred from the asphalt mastic the aggregate. Efforts were also made to consider the effect of aggregate gradation, asphalt mastic degradation, and interfacial damage between the aggregates and asphalt mastic matrix on the tensile strength of the HMA mixtures. Experimental investigations were conducted to validate the developed theoretical relations. A reasonable agreement was found between the predicted tensile strength and the experimental results at low temperatures. Parameters affecting the tensile strength of asphalt mixtures were discussed based on the calculated results.     

老化对水泥乳化沥青胶结料动态力学性能的影响

基于分数导数修正Burgers模型,建立了水泥乳化沥青胶结料（简称复合胶结料）的本构方程。结合不同材料配比的复合胶结料的老化试验及频率扫描试验,分析了老化时间及材料配比等因素对复合胶结料黏弹性力学参数的影响。研究表明,复合胶结料的存储模量与损耗模量均随老化时间的增加而增大,在老化时间为0~8 h时,存储模量及损耗模量增加较快,当老化时间超过8 h后,其增长趋势减缓。对于乳化沥青与水泥的质量比（m_A/m_C）为1.2和1.4的复合胶结料,在不同的加载频率下,其相位角均随老化时间的增加而减小。对于m_A/m_C为1.0的复合胶结料,其相位角随着老化时间的增加呈现先增加后减小的变化规律。随着老化时间的增加,复合胶结料趋向于弹性材料的力学性质。分数导数修正Burgers模型可以较好的描述老化后复合胶结料的黏弹性动态力学行为,模型参数弹性模量E₁、黏度η₁和分数导数r可以描述老化情况下材料黏弹特性的变化规律。     

Using the poker-chip test for determining the bulk modulus of asphalt binders

The properties of asphalt binders strongly influence the overall mechanical response of asphalt mixture composites. A thorough understanding of the mechanistic behavior of asphalt binders is important in order to fully and accurately characterize the behavior of the asphalt mixture. The mechanical properties of the asphalt binder, the matrix in the asphalt mixture composite, are time and temperature dependent and have a lower stiffness compared to the inclusions (aggregate particles). However, computational methods used to model the micromechanics of asphalt mixtures typically assume a constant bulk modulus or Poisson’s ratio for asphalt binders. This research investigates the time-dependence of the bulk modulus of asphalt binders. Several approaches for measuring the bulk modulus were explored and the poker-chip geometry was found to be the most suitable one. The boundary value problem for the poker-chip geometry was solved to determine the bulk modulus and Poisson’s ratio of asphalt binders as a function of time. The findings from this research improve our understanding of the viscoelastic behavior of asphaltic materials, and also guide important assumptions that are typically made during computational modeling of asphaltic materials.     

Heterogeneity effects on mixed‐mode I/II stress intensity factors and fracture path of laboratory asphalt mixtures in the shape of SCB specimen

Edge cracked semi‐circular shape specimen subjected to three point bend loading is a favourite test specimen for determining fracture toughness of asphalt mixtures. However, in the vast majority of previous experimental works, the homogeneous medium assumption has been considered for determining the stress intensity factor and geometry factors of asphalt mixtures tested with this test configuration. As a more realistic model and in order to consider the effects of heterogeneity on corresponding values of stress intensity factors, the asphalt mixture was modelled as a two‐phase aggregate/mastic heterogeneous mixture and its fracture behaviour was investigated using numerical models of asymmetric semi‐circular bend (ASCB) specimens. The generation and packing algorithm was employed to randomly distribute the aggregates with different shapes and sizes inside the mastic part. The effect of the mechanical properties of asphalt mixture (elastic modulus and the Poisson's ratios of aggregates and mastic), coarse aggregates distribution and crack length were studied on modes I and II geometry factors by means of extensive two‐dimensional finite element analyses. Moreover, the effect of the elastic modulus of asphalt mixture components was evaluated on the fracture path using the maximum tangential stress criterion. It was shown that crack tip location, elastic modulus of aggregates and mastic are the most important affecting parameters on the magnitude of modes I and II geometry factors. It was also shown that the geometry factors are not sensitive to the Poisson's ratios of aggregates and mastic. In addition, fracture cracking path is affected by the elastic modulus of the asphalt mixture components such that, depending on the difference between the stiffness of stiffer coarse aggregates and softer mastic part, the crack may propagate either through the aggregates, mastic or interface of aggregate/mastic.     

Micromechanical modelling of bituminous materials’ complex modulus at different length scales

The aim of this work is to establish a multi-scale modelling technique usable in the study of the complex viscoelastic properties of asphalt mixes. This technique is based on a biphasic approach. At each scale, the heterogeneous media is considered as a two-phase material composed of granular inclusions with linear elastic properties and a matrix of bituminous materials exhibiting linear viscoelastic behaviour at small strain values. In this approach, the homogeneous equivalent properties of biphasic composites are transferred from one scale of observation to the next, higher scale of observation. The viscoelastic properties of the matrix and the elastic properties of the aggregates serve as the input parameters for the numerical models. The generalised Maxwell rheological model is used to describe the viscoelastic behaviour of the matrix. Thanks to the rheological properties of bitumen and the elastic properties of the aggregates, the viscoelastic properties of mastic, mortar and hot mix asphalt (HMA) as bituminous composites can be, respectively, estimated using a micromechanical finite element model. Random inclusions of varying sizes and shapes are generated in order to construct the granular skeleton. A cyclic loading was imposed on the top layer of the digital model. The dynamic modulus of the pre-cited bituminous composites, obtained from the presented multi-scale modelling process while passing from the bitumen to the HMA scale, is validated by comparison with experimental measurements when possible. Concerning our results, we have found that at low temperature (?10 °C), the predicted dynamic modulus is satisfactorily comparable to the experimental measurements. On the other hand, an acceptable gap between predicted numerical results and experimental data takes place when the temperature increases.     

Prediction models of mixtures’ dynamic modulus using gene expression programming

The dynamic modulus (E*) among asphalt mixtures’ mechanical property parameters not only is important for asphalt mixtures’ pavement design but also in determining asphalt mixtures’ pavement performance associated with pavement response. Based on the principle of gene expression programming (GEP) algorithm, this paper explored two different GEP approach models, namely: GEP-I and GEP-II to predict the E* of hot mix asphalt (HMA) and mixtures containing recycled asphalt shingles, respectively. In this paper, The GEP-I was developed from a large database containing 2750 test data points from 205 unaged laboratory-blended HMA mixtures including 34 modified binders, and the GEP-II model was developed using the E* database containing 1701 sets of experimental data from 4 different demonstration projects. Both the GEP-I model and GEP-II model were compared with other E* prediction models. A sensitivity analysis of each model parameter was conducted by correlating these parameters with dynamic modulus. Both the GEP-I model and GEP-II model showed significantly higher prediction accuracy compared with the existing regression models and could easily be established. It is expected that these two GEP models could lead to more accurate characterisation of the asphalt mixtures’ E*, resulting in better performance prediction.     

Investigation into three-layered HMA mixtures

Hot-mix asphalt (HMA) mixtures consist of three phases: aggregate, asphalt binder (mastic) and air voids, of which the first two (aggregate and asphalt binder) provide the structure that withstands various kinds of loading.

Due to the nature of high inhomogeneity between aggregate and asphalt binder, significant stress and strain concentration occurs at the interface between the two phases, which causes adverse effect to HMA mixtures and potentially contributes to pavement distresses/failure.

This paper presents a novel idea to mitigate the stress and strain concentration by introducing an intermediate layer between aggregate and asphalt binder in HMA mixture. Microstructural analyses of layered system indicated that the three-layered composite HMA mixture would greatly improve the performance of asphalt mixture. The composite mixture showed more than 10% reduction in internal stress and strain and consequently its performance could be potentially improved. To validate the theoretical analyses, a laboratory experiment was conducted to compare the performance of a conventional mixture to that of a conceptual three-layered composite HMA mixture, which was formed by incorporating a stiff natural asphalt (gilsonite) as the intermediate layer. The results of the limited laboratory experiment confirmed the findings from the theoretical analyses.