Experimental evaluation on high temperature rheological properties of various fiber modified asphalt binders

High temperature rheological properties of fiber modified asphalt binders and impact of the type and content on such properties were studied.Three types of fiber,including polyester(PET),polyacrylonitrile(PAN) and cellulose(CEL),a control content(0%) and four levels of fiber content(2%,4%,6% and 8% by total asphalt binder mass) were used with asphalt binders.The high temperature rheological properties,consisting of complex modulus(G*) and phase angle δ,were measured using SHRP’s dynamic shear rheometer(DSR) between 46-82 ℃.Experimental results indicate that the changes of G* and tan δ of fiber modified asphalt binders with the increase of test temperature tend to slow down,and the temperature susceptibility is improved obviously compared to that of original asphalt binder.Fiber modification results in the increase of rutting parameter(G*/sin δ) at high temperatures,the decrease of temperature susceptibility,and further improved high temperature performance of asphalt binder.An excellent correlation exhibits between fiber content and high temperature performance of asphalt binder.Moreover,fiber type also has different influences on the improvement of G*/sin δ,G*/sin δ of PET and PAN fiber asphalt binders are both higher than that of CEL fiber,but G*/sin δ of CEL fiber is still higher than that of original asphalt.However,there is a critical fiber content when fibers start to interact with each other.Therefore,based on the critical fiber content and economic consideration,the optimum fiber contents for various fiber-modified asphalt binders are obtained.     

Influence of conductive additive on temperature susceptibility of asphalt binders

The effects of graphite on temperature susceptibility of asphalt binders were investigated by penetration test,Ring & Ball softening point test and viscosity test.And penetration index(IP),viscosity-temperature susceptibility(SVT),and penetration-viscosity numbers(NPV) were introduced to evaluate the effects.The results show that the penetration,softening point and viscosity of asphalt binder increase with the increase of content of graphite.This means that the addition of graphite makes asphalts stiffer.Th...     

沥青自愈合性能影响因素探究及CT扫描细观分析

为了直观研究沥青的自愈合性能,采用BBS(binder bond strength)拉拔实验探究温度、水分、老化及改性剂对沥青自愈合性能的影响,并利用CT(computed tomography)扫描实验,从细观角度观测沥青在不同条件下的自愈合进程.BBS实验结果表明:较高温度与干燥条件有利于沥青的自愈合,水分不利于沥...     

基于改性乳化沥青-水泥双胶结料的半柔性再生混合料性能研究

首先采用干燥条件和浸水条件下的劈裂试验研究了水泥加料顺序对半柔性再生混合料性能的影响,在此基础上提出击实试验法与修正的马歇尔试验法相结合,并基于性能评价的混合料配合比设计程序,包括材料选择、级配设计及性能评价。研究结果表明：先添加水泥的半柔性再生混合料具有密实的整体结构,且抗水损坏能力较强;半柔性再生混合料具有良好的高温抗车辙能力、低温抗开裂能力、抗水损害能力以及抗收缩能力。结合依托工程发现,基于改性乳化沥青-水泥双胶结料的半柔性再生技术是一种经济有效的路面大中修养护方式,有着良好的经济效益、社会效益和环境效益,具有重要的推广应用价值。     

Rheological characteristics of aged asphalt binder

Different aging levels(RTFOT,PAV-10h,PAV-20h and PAV-30 h) of asphalt binders with various mass ratios of mineral powder to asphalt(0,0.4,0.8,1.2,1.6,2.0) were used to investigate the rheological properties of aged asphalt binders with respect to their short and long terms aging characteristics.Viscosity test,dynamic shear test and creep test were conducted.The test results indicate that the viscosity of aged asphalt binder increases sharply with the extension of aging period.Complex shear modulus of aged asphalt increases,which indicates that the stiffness of asphalt binders can increase.The phase angle for aged asphalt binders reduces,which indicates that the elastic portion for viscoelastic property of asphalt binders increases.|G*|·sin δ increases after aging procedure which means that the fatigue resistance becomes poor.The creep test results show that creep strain curves varies remarkably for virgin and aged asphalt binders.The total strain during loading period and the permanent strain decreases significantly for aged asphalt binders,which implies that the elastic portion increases and the viscous portion decreases.     

沥青胶结料低温临界开裂温度计算的改进方法

针对当前沥青胶结料温度应力和低温临界开裂温度计算方法的局限性,为找寻一种更好的沥青胶结料温度应力及相应的低温临界开裂温度计算方法,选取4种不同产地的70^#基质沥青进行旋转薄膜老化（RTFO）和压力箱老化（PAV）展开研究. 利用BBR试验获得沥青胶结料的蠕变柔量,分别采用Hopkins & Hamming算法和CAM模型两步计算法以及Laplace变换一步计算法获得了沥青的温度应力,基于SAP理论计算相应的低温临界开裂温度. 通过统计学方法对计算结果进行比较和分析,采用相关性分析并结合实测路表温度数据对计算方法予以验证. 结果表明:Laplace变换一步计算法和Hopkins & Hamming算法两步计算法具有良好一致性,基于t检验法的低温临界开裂温度p值计算结果达0.90以上. Laplace变换一步计算法与BBR试验具有较强的相关性,临界开裂温度T_CR与S/m指标、Huet流变模型指标的相关系数分别可达0.84、0.94. 实测路表温度变化数据的计算结果证明了该方法不仅适用于匀速降温工况,也适用于任意降温速率下的现场连续变速降温工况.     

Shear resistance properties of TPS modified bitumen binders and asphalt mixtures

Shear resistance properties of the virgin bitumen and modified bitumen binders with Tafpack Super(TPS) modifier and SBS modified bitumen were discussed.Dynamic shear rheometer(DSR) was used to measure the laboratory creep data for these binders over a wide range of constant shear stresses at 20 ℃ to characterize the shear creep behaviors of all kinds of asphalt binders,and the rutting test system was used to investigate the permanent deformation of porous asphalt mixtures using the above bitumen binders for a fixed compressive stress.The shear strain rate and shear creep modulus were used to characterize the shear creep behavior of the TPS modified bitumen,and the rutting test results were used to show the consistency of porous asphalt mixtures with the bitumen binders.Results indicate that a distinction of shear creep strain can be made among different contents of TPS modified bitumen at the same stress level,where the shear creep strain-time response curve of the SBS modified bitumen binder is between the curves of the 8% TPS and 12% TPS modified bitumen binders.The shear strain rate and the shear creep modulus of the TPS modified bitumen binders are obtained to compare with those of the SBS modified bitumen binder which results in the same trend as the shear creep strain-time response curve.Permanent deformation results of all the porous asphalt mixtures from the rutting test show reasonable agreement with the findings of the shear strain rates and shear creep modulus over the range of shear stress levels.     

超硬质沥青改性结合料流变性能分析

为研究超硬质沥青(super hard asphalt,SHA)对超硬质沥青结合料的高、低温流变的影响效果,采用SHA作为改性剂对AH-90道路石油沥青进行改性,制备了不同质量分数（5%、6%、7%和8%）的SHA改性结合料,并进行动态剪切流变试验、多应力蠕变恢复试验及小梁弯曲蠕变试验. 试验结果表明:其适用于时温等效原理;SHA的掺入会有效提高沥青结合料的车辙因子G^*/sin δ,沥青混合料的高温性能得到明显改善;随着SHA掺量的增加,沥青结合料的平均应变恢复率R逐渐升高,不可恢复蠕变柔量J_nr逐渐降低,掺加SHA有利于提高沥青结合料高温抗变形能力与变形恢复能力;随着SHA的掺入,沥青结合料的蠕变劲度S与蠕变劲度变化率m变化幅度不大,对沥青结合料的低温抗裂性能影响不大. SHA改性沥青结合料高温抗车辙性能优异,低温性能相对于基质沥青PG分级保持不变.     

长寿命半刚性基层沥青路面的计算分析

选取半刚性基层沥青路面典型结构,对不同轴载下半刚性层底拉应力的分析发现,典型结构仅适合于超载不严重的交通状态.对混合式沥青路面结构沥青层底拉应变和半刚性层底拉应力进行了计算,得到同时满足沥青层和半刚性层不受疲劳破坏时的沥青层厚度,与国外长寿命路面设计软件PerRoad2.4的计算结果相比,混合式长寿命路面结构更具有经济性.     

Effect of ageing on fatigue properties of asphalt

The fatigue properties of asphalts were investigated after various laboratory simulation ageing tests and outdoor natural exposure ultraviolet radiation ageing,by dynamic shear rheometer(DSR) time sweep fatigue test in constant strain model and a new type of specimen which was introduced to avoid the problem of adhesion failure between rotor and asphalt binder.The results show that outdoor natural exposure ageing(NEA) causes the decrease of retained fatigue life distinctly,and photodegradation caused by outdoor NEA of 1 250 μm thin films asphalt for three months,is found to be severer than pressure ageing vessel(PAV) with respects to retained fatigue life.The effect of photodegradation increases as the time of outdoor NEA increases.DSR time sweep fatigue test in constant strain indicates that the aged styrene-butadiene-styrene(SBS) modified asphalt still displays better fatigue properties than the corresponding base asphalt after ageing.     

Long term performance of warm mix asphalt versus hot mix asphalt

The fatigue behavior, indirect tensile strength (ITS) and resilient modulus test results for warm mix asphalt (WMA) as well as hot mix asphalt (HMA) at different ageing levels were evaluated. Laboratory-prepared samples were aged artificially in the oven to simulate short-term and long term ageing in accordance with AASHTO R30 and then compared with unaged specimens. Beam fatigue testing was performed using beam specimens at 25℃ based on AASHTO T321 standard. Fatigue life, bending stiffness and dissipated energy for both unaged and aged mixtures were calculated using four-point beam fatigue test results. Three-point bending tests were performed using semi-circular bend (SCB) specimens at -10℃ and the critical mode I stress intensity factor K I was then calculated using the peak load obtained from the load-displacement curve. It is observed that Sasobit and Rheofalt warm mix asphalt additives have a significant effect on indirect tensile strength, resilient modulus, fatigue behavior and stress intensity factor of aged and unaged mixtures.     

The effect of cyclic hardening on fatigue properties of modified asphalt

The phenomenon of cyclic hardening is observed in fatigue tests of modified asphalt controlled by low strain/stress level and it is not clear how the phenomenon affects the fatigue properties of binders. The special time weep tests were performed to investigate the point. Tests results indicate that the cyclic hardening is caused by the rearrangement of molecules in binders, and it can make the inner structure of binders getting stable and increase the fatigue properties of asphalt binders. But fatigue damage occurs when fatigue tests start, no matter the phenomenon of cyclic hardening happens or not. If the controlled load is low, the effect of rearrangement of molecules on material is beyond the effect of fatigue damage so that the cyclic hardening can be observed. When the load conditions get worse, the effect of slight fatigue damages produced in hardening stage will show.     

交通量非均匀分布的沥青路面疲劳等效温度

针对现有沥青路面疲劳等效温度理论未考虑交通量非均匀分布和沥青路面温度取值不合理等问题,为更加准确科学地计算等效温度,提出沥青层当量温度和深度概念并推导其计算方法,建立大气日当量温度与沥青层当量温度的关系,采用沥青层当量深度处的当量温度作为沥青层代表温度并划分温度区间,开展沥青混合料动态模量和疲劳试验,统计各个温度区间内的交通量分布频率,基于Miner线性累积原理提出一种考虑交通量非均匀分布的沥青路面疲劳等效温度计算方法,计算两种交通量分布方式的等效温度值,最后与其他方法进行对比分析.结果表明:沥青层当量温度可作为沥青层代表温度来划分温度区间;考虑交通量非均匀分布的沥青路面疲劳等效温度计算方法在理论上改进了现有方法的不足,使等效温度的计算更加科学和可靠,两种交通量分布方式的等效温度实际计算结果相差1.6℃,与其他方法相比具有一定的优越性,后期应当加强观测,进一步完善计算方法的精确性.     

六盘山地区沥青气候适应性研究

为了给六盘山地区筑路施工选择合适的沥青品种和标号,在搜集、分析六盘山地区气象资料的基础上,借鉴美国SH RP沥青PG分级方法,采用SH RP公式将气温转换为位于路表以下20m m深处的平均最高温度作为高温设计温度;低温设计温度则采用路表温度,并根据六盘山地区的具体情况进行修正,然后提出了六盘山地区沥青路面气候分区、沥青路用性能PG分级及合理选择的沥青品种和标号,旨在为六盘山地区修筑沥青路面提供一定的技术支持.     

六盘山地区沥青结合料气候适应性研究

为了给六盘山地区筑路施工选择合适的沥青品种和标号,在搜集、分析六盘山地区气象资料的基础上,借鉴美国SHRP沥青PG分级方法,采用SHRP公式将气温转换为位于路表以下20mm深处的平均最高温度作为高温设计温度;低温设计温度则采用路表温度,并根据六盘山地区的具体情况进行修正,然后提出了六盘山地区沥青路面气候分区、沥青路用性能PG分级及合理选择的沥青品种和标号,旨在为六盘山地区修筑沥青路面提供一定的技术支持．     

考虑松弛的沥青混合料疲劳损伤累计模型研究

根据应变控制疲劳试验的受力特点,通过分解沥青混合料应变,控制疲劳试验输入和输出响应,分析沥青混合料应变控制疲劳试验过程中的松弛现象.基于损伤力学和粘弹理论,分析由应力松弛引起的疲劳损伤和演化规律,建立考虑应力松弛沥青混合料疲劳损伤累计模型.相同条件下一组大样本疲劳试验结果与模型计算结果的对比表明,提出的损伤演化模型不仅拟合效果良好,且揭示沥青混合料在重复载荷作用下初期模量衰减的粘弹非线性本质,有利于沥青混合料疲劳研究和寿命预测.     

黏弹性对沥青路面疲劳开裂的影响

建立了黏弹性三维有限元模型,对典型沥青路面结构路表及沥青层底的水平应力进行了计算,分析了荷载模式及温度对黏弹性响应的影响。结果表明:在循环荷载作用下,路表和沥青层底都经受水平压应力和拉应力的重复作用,且在路表和沥青层底分别产生少量的残余拉应力和残余压应力,这有可能是造成沥青路面从上到下或从下到上疲劳开裂的原因之一。随着温度的升高,残余应力减少,且路表产生的压应力幅值和沥青层底产生的拉应力幅值都降低。     

沥青混凝土路面温缩裂缝的研究

结合沈大高速公路沥青混凝土路面破损状况的实测资料,对高等级沥青混凝土路面温度收缩裂缝形成的力学机制和影响因素进行了研究.通过现场对沥青混凝土路面温缩裂缝发育规律的观测及沥青混合料室内试验的研究表明:低温变化速率对沥青混凝土路面内部产生温度应力的大小和性质起决定性作用.沥青的性质和矿料的性质及组成是决定沥青混凝土路面温缩裂缝发育状况的两个控制性因素;而环境因素如气温、路面结构、交通量及路龄则决定温缩裂缝的发育程度.     

粉胶比对橡胶沥青胶浆高温性能的影响研究

为了研究不同粉胶比对橡胶沥青胶浆高温性能的影响,选择石灰岩矿粉作为填料,粉胶比掺量为0.2、0.4、0.6、0.8。胶浆高温性能的评价指标选择Fail temperature和ZSV,通过DSR试验对不同胶浆进行研究。试验结果表明:随着粉胶比的增加,橡胶沥青胶浆的Fail temperature和ZSV值均逐渐变大,而且增大幅度较大,橡胶沥青胶浆的高温性能得到明显的改善;利用环境扫描电镜对胶浆进行扫描,发现添加矿粉的橡胶沥青胶浆光滑、细腻,矿粉被橡胶沥青裹覆均匀。     

动水作用下沥青混合料疲劳性能变化

为研究不同材料组成下沥青混合料抗疲劳性能受动水作用的影响,开发了模拟沥青路面受水、荷载、温度共同作用的室内试验设备并提出了试验方法.将6%、10%、14%3种空隙率,AC-16、SMA-16、SAC-16 3种级配,A-90、A-110、A-130 3种沥青组合成7种沥青混合料;对比分析其动水作用前后的应力疲劳方程参数变化.结果表明:7种沥青混合料动水作用后的疲劳性能均有不同程度衰减.疲劳荷载作用下,动水作用后的混合料沥青膜更易剥落.10%空隙率是AC类混合料的较不利空隙率;其疲劳寿命的衰减程度最大且应力敏感性增加.10%空隙率时,悬浮结构沥青混合料抗疲劳性能受动水作用影响要比骨架结构的大,高标号沥青混合料所受影响比低标号的大.