Pavement design with central plant hot-mix recycled asphalt mixes

Central plant hot mix recycling is one of the popular techniques adopted for recycling of asphalt pavement materials. Literature review reports varied levels of performances (laboratory as well as field) of recycled mix compared to the performances of corresponding virgin mixes. Thus, there is a need for conducting performance-related tests before finalizing any recycled mix design. The present paper discusses laboratory study conducted on recycled mix design of two different Reclaimed Asphalt Pavement (RAP) samples, and subsequently develops an integrated mix-design-structural-design approach for hot recycled mix. The total cost of the asphalt layer construction is estimated considering the constituent proportion and the pavement design thickness so that the designer can choose the best option.     

沥青路面再生利用试验分析

高级沥青路面的再生利用 ,在国内还是一个崭新的课题。经过多次反复试验 ,成功开发出了新型再生剂。以旧路改造工程为依托 ,对高等级沥青路面再生混合料的性能和设计方法进行了深入的试验和理论研究 ,大量的试验证明再生混合料的性能与旧料的掺配率和再生剂的用量有很大关系。提出了符合我国国情的再生混合料设计方法 ,为控制设计出的混合料的品质而增加了一些验证性试验     

沥青路面就地热再生工艺及实践

在厂拌冷再生、就地冷再生、厂拌热再生和就地热再生等沥青路面再生方法中,就地热再生工艺适用于沥青道路面层的维修养护,具有节省材料及运输费用,断路施工时间短等优点.介绍沥青路面就地热再生工艺的特点、发展及应用情况,以加拿大马泰克公司生产的AR2000型就地热再生机组的施工实践为例,对就地热再生设备的施工工艺及热再生路面的质量进行试验研究,对热再生路面的质量控制提出建议.     

Performance evaluation of high modulus asphalt mixtures for long life asphalt pavements

This paper describes the results of laboratory and full scale performance tests for a high modulus asphalt binder (HMAB) and mixes (HMAM) developed in this study for long life asphalt pavements. Various binder tests were first conducted on the HMAB and test results showed that the stiffness of the HMAB was significantly increased compared to the conventional binder without changing the low temperature properties of the binder. Laboratory tests for the mixes included dynamic modulus, moisture susceptibility, wheel tracking and fatigue tests.Dynamic modulus test results showed that the modulus of the HMAM was 50% higher than those of the conventional mix at the high temperatures. The results of performance test indicated that the resistances of the HMAM against moisture, rutting, and fatigue damage were better than those of the conventional mix. It was also found from the full scale test sections that the tensile strain values at the bottom of the asphalt layer for the HMAM sections were lower than those of the conventional mix sections although the asphalt layer thicknesses of the HMAM sections were thinner than those of the conventional sections. All the tensile strain values measured from the HMAM sections were within the fatigue endurance limit of 70 microstrain which is the fatigue criterion of a long life asphalt pavement. Similar to the wheel tracking test results, the rut depth occurred in the thick HMAM test section was two times smaller than the conventional pavement section.     

Characterization of warm mix asphalt binders containing artificially long-term aged binders

Reclaimed asphalt pavement (RAP) comprises one of the largest recycled materials, and warm mix asphalt (WMA) technologies become more commonly used due to their promising advantages in the United States and Europe. This paper addresses the laboratory investigation of performance properties of WMA binders containing aged binders. The recycled binders with the additives were produced using two (i.e., zeolite Aspha-min^® and wax Sasobit^®) of the available warm asphalt processes. The recycled WMA binders were artificially short-term and then long-term aged through the rolling thin film oven (RTFO) and pressure aging vessel (PAV) procedures. Superpave binder tests were carried out on the binders through the rotational viscometer, the dynamic shear rheometer (DSR), and the bending beam rheometer (BBR). In general, the results of this study indicated that (1) the additives and aged binders played an important role in determination of the binder properties; (2) the use of lower PG grade as a virgin binder (PG 58-28 in this study) was critical on offsetting the increase of binder stiffness caused by the addition of WMA additives and aged binders; and (3) even at the low recycling percentage of 15%, the lower PG grade was needed to get the results meeting current Superpave binder requirements.     

Laboratory evaluation of recycled construction and demolition waste for pavements

The wide production of construction and demolition waste and its illegal deposition are serious current problems in Brazil. This research proposes to evaluate the feasibility of using aggregate from recycled construction and demolition waste (RCDW) in pavement applications. A laboratory program was conducted by geotechnical characterization, bearing capacity and repeated load triaxial tests. The results show that the composition and the compactive effort influence on the physical characteristics of the RCDW aggregate. The compaction process has promoted a partial crushing and breakage of RCDW particles, changing the grain-size distribution and increasing the percentage of cubic grains. This physical change contributes to a better densification of the RCDW aggregate and consequently an improvement in bearing capacity, resilient modulus and resistance to permanent deformation. The results have shown that the RCDW aggregate may be utilized as coarse base and sub-base layer for low-volume roads.     

Effects of cross-anisotropy and stress-dependency of pavement layers on pavement responses under dynamic truck loading

Previous studies by the authors have determined pavement responses under dynamic loading considering cross-anisotropy in one layer only,either the cross-anisotropic viscoelastic asphalt concrete(AC)layer or the cross-anisotropic stress-dependent base layer,but not both.This study evaluates pavement stressestrain responses considering cross-anisotropy in all layers,i.e.AC,base and subbase,using finite element modeling(FEM) technique.An instrumented pavement section on Interstate I-40 near Albuquerque,New Mexico was used in ABAQUS framework as model geometry.Field asphalt cores were collected and tested in the laboratory to determine the cross-anisotropy(n-values) defined by horizontal to vertical modulus ratio,and other viscoelastic parameters as inputs of the model incorporated through user defined material interface(UMAT) functionality in ABAQUS.Field base and subbase materials were also collected and tested in the laboratory to determine stress-dependent nonlinear elastic model parameters,as inputs of the model,again incorporated through UMAT.The model validation task was carried out using field-measured deflections and strain values under falling weight deflectometer(FWD)loads at the instrumented section.The validated model was then subjected to an actual truck loading for studying cross-anisotropic effects.It was observed that horizontal tensile strain at the bottom of the AC layer and vertical strains in all layers decreased with an increase in n-value of the asphalt layer,from n1(anisotropy) to n=1(isotropy).This indicates that the increase in horizontal modulus caused the decrease in layer strains.It was also observed that if the base and subbase layers were considered stressdependent instead of linear elastic unbound layers,the horizontal tensile strain at the bottom of the asphalt layer increased and vertical strains on top of the base and subbase also increased.     

Crushed aggregate production from centralized combined and individual waste sources in Hong Kong

Owing to the comprehensive building redevelopment programmes in Hong Kong, there is a huge volume of concrete waste generated that will soon exhaust all the available landfill areas. As such, recycled aggregate is advocated. However, the use of recycled aggregate has been confined to lower-grade applications until now, such as the lower layers of a pavement structures, e.g., capping and sub-base. The main reason is the variable behaviour of recycled aggregates collected from different sources to be crushed in a centralized recycling plant. This paper applies some international standards to classify recycled aggregates. Aggregates were collected from twelve sources, including 10 from demolition sites (Samples 1–10), one from Tuen Mun Area 38 centralized recycling plant (Sample 11) and one from ordinary virgin aggregate (Sample 12). From test results, Sample 6, akin to Sample 12 (virgin aggregate), was found to be suitable for all types of construction applications, while Samples 2 and 9 were completely unsuitable as recycled concrete aggregates for any application grade. Sample 11 (Tuen Mun Area 38 centralized recycling plant) was found only suitable for non-structural applications, such as base course and fill. It is concluded that the different sources of recycled aggregate should preferably be separately crushed and classified rather than processed in a combined form centrally which will lower its overall quality and limit its application.     

高速公路大修工程厂拌热再生技术的应用

依托青银高速靖边至王圈梁段路面大修工程,研究了靖王高速公路回收沥青路面材料(RAP)的性能,厂拌热再生混合料的配合比及其路用性能。结果表明:路面回收沥青的25℃针入度为43.3(0.1 mm),软化点为62.2℃,RAP具备再生条件;经筛分0~10 mmRAP掺配10%,10~20 mmRAP掺配15%,再生混合料中新沥青用量为3%时,路用性能良好,其马歇尔残留稳定度为93.43%、冻融劈裂强度比86.5%、车辙试验动稳定度(5 cm厚)为7250次/mm。且经济效益明显,节能环保。     

Stabilizing blended calcium sulfate materials for roadway base construction

Blended calcium sulfate (BCS), a recycled fluorogypsum waste material, has been used in Louisiana as a pavement base layer for more than a decade. Without further chemical stabilization, the major concern of using raw BCS as a pavement structural layer is its moisture resistance. It could cause both short-term construction difficulties and long-term performance problems. In order to improve the moisture susceptibility of BCS, various cementitious agents were used in the laboratory for BCS stabilization. To further verify the efficiency of BCS stabilization schemes obtained from laboratory and assess the field performance for stabilized BCS materials as well as potential cost-benefits, three pavement test sections were constructed and tested using the accelerated loading facility (ALF) device. Both laboratory and field test results indicated that a grade 120 granulated ground blast furnace slag (GGBFS) of 10 vol.% stabilized BCS material possessed a superior performance over raw BCS in terms of water resistance, durability, and good long-term performance. Field test results further demonstrated that the GGBFS stabilized BCS base outperformed both a regular crushed stone base and a fly ash stabilized BCS base by a significantly large margin.A life-cycle cost analysis proved that, besides its outstanding laboratory and field performance, using the GGBFS stabilized BCS can provide a substantial long-term savings over regular crushed stone and fly ash stabilized BCS bases in a 30-year pavement design life period.     

多次再生沥青混合料沥青组分迁移及其性能

通过室内试验模拟沥青混合料的多次再生过程,探讨了多次再生沥青的物理性质变化特征和组分迁移规律;通过马歇尔试验确定多次再生沥青混合料的配合比,利用单轴贯入强度试验、半圆弯拉试验和冻融劈裂试验对其使用性能进行了评价,并通过沥青混合料性能试验仪(AMPT)分析了其相位角在温度和加载频率同步耦合作用下的变化规律.结果表明:沥青经历多次再生后流变性能变差,高温性能提升,低温性能衰减显著;再生剂在旧沥青中的增溶作用随着其掺量的提高而增强,随着再生次数的增加呈指数规律衰减;再生沥青混合料的高温稳定性随再生次数增加呈对数规律增长,水稳定性对再生次数的敏感度较低,3次再生后其马歇尔体积指标均可满足规范要求;1次再生沥青混合料的动态黏弹特性与全新料较为接近,2次再生后,其弹性效应增强,低温抗裂性能劣化加速.综上所述,沥青混合料经多次再生后,应重点关注其低温性能的恢复情况.     

临长高速公路沥青路面就地热再生应用研究

以临长高速公路就地热再生工程为依托,简述了就地热再生技术的施工流程,阐述了原沥青路面混合料试验、沥青掺加再生剂试验要点,并通过再生混合料施工配合比设计,总结了施工过程中的质量控制措施。     

就地热再生沥青混合料配合比优化设计及性能研究

为了避免在沥青路面就地热再生中由于级配设计不良导致的沥青混合料出现离析、松散、粘接性能不佳和路 用性能等问题。通过对原路面材料进行调查,掌握原材料级配及老化程度,根据调查结果对沥青路面就地热再生材料进行 级配优化设计,控制再生剂用量、级配和最佳油石比,得到室内配合比。在此基础上对再生沥青混合料进行水稳定性和高 温稳定性能检测。试验结果表明通过对原有沥青路面情况调查和就地热再生沥青混合料配合比优化设计,可以得到路用性 能优良的再生沥青混凝土路面。     

预应力再生混凝土叠合梁受弯性能试验研究

为研究无黏结预应力再生混凝土叠合梁构件的受弯性能,以再生混凝土在叠合梁中的位置、叠合层高度、构件的配筋率为参数,对1根预应力普通混凝土整浇梁、1根预应力再生混凝土整浇梁和6根预应力再生混凝土叠合梁构件进行弯曲加载试验,分析了试验梁构件的受力过程和破坏形态,探讨了各参数对试验梁构件极限承载力的影响.基于试验数据,对承载力...     

钢纤维再生混凝土在路面工程中的应用研究

本文通过上海市某道路改建工程实例,对含50％再生粗集料的钢纤维混凝土路面进行了较为系统的研究。首先在室内对再生粗集料的密度、洛杉矶磨耗、压碎指标等基本性能进行了测试。然后针对拟定的三组不同配合比的钢纤维再生混凝土试件,在室内进行了抗折强度、抗压强度等试验,最后根据试验结果并结合工程经验,选取了一组较为理想的钢纤维再生混凝土配合比,完成了钢纤维再生混凝土路面的施工。同时对试验路段进行了全面的现场检测,结果证明钢纤雏再生混凝土在普通路面上的应用是安全可行的,而且会有很好的发展前景。     

沥青路面就地热再生施工机械设备选型与配套

结合沥青混凝土路面就地热再生工艺在国内的应用,根据海南东线高速公路府城—十八坡段左幅大修工程热再生段施工的实际情况,对机械设备的采购、使用、改进等进行探讨,以推广就地热再生工艺的应用。     

不同来源再生骨料的基本性能及其对混凝土抗压强度的影响

针对实际工程中废弃混凝土种类和性能复杂多变的特点,系统测试了由4类不同来源(拆除的废旧建筑物、预制构件厂不合格构件、废弃马路路面和试验室废弃试件)废弃混凝土破碎加工而成的共6种再生骨料的基本性能。试验结果表明,不同来源再生骨料的基本性能存在一定差异。研究利用不同再生骨料配制再生混凝土,并测试了不同来源再生骨料对再生混凝土抗压强度的影响。     

沥青混合料铺装层现场模量探究-以钢桥面铺装为例

沥青混合料铺装层在荷载作用下的力学响应为铺装体系的设计提供必要的指导,在铺装层力学响应的计算中,各层模量是一个重要的输入参数。过往研究中,研究人员主要通过室内试验的方法确定铺装层混合料的模量值,但忽略了混合料的室内试验模量值与其现场模量值可能存在的偏差。针对以上问题,文章以一处钢桥面铺装工程为例,介绍一种确定沥青混合料铺装层现场模量主曲线的方法：基于不同加载工况下铺装层底部的应变实测数据,利用有限元模型对铺装层混合料的现场模量进行反算,拟合得到相应的混合料现场模量主曲线并验证其适用性。此外,将反算得到的混合料现场模量与其室内试验模量进行对比,分析两类模量之间的差异性。研究结果表明,反算得到的铺装层混合料的现场模量在不同加载工况下变化显著,其数值随加载温度的增加而减小,随加载频率的增加而增大,表现出黏弹性的特征;利用不同加载工况下的混合料现场模量值可以较好地拟合得到混合料的现场模量主曲线,且该模量主曲线经过验证后证明有效。对比铺装层混合料的单轴压缩试验模量与现场模量发现：混合料的室内模量值与现场模量值在不同加载工况下并不完全匹配,其现场模量值普遍要小于对应的室内压缩模量值;两类模量对应的模量主曲线之间也有较大偏差,在加载频率较高或较低时,主曲线间的偏差更为显著;可采用幂函数对两类混合料的室内模量进行修正,使修正后的室内模量能够反映铺装层混合料的现场模量特征。     

Laboratory evaluation of fatigue characteristics of recycled asphalt mixture

This paper presents the results of a laboratory study of evaluating the fatigue characteristics of hot-mix asphalt (HMA) mixtures using different testing methods. In this study, the fatigue performance of HMA mixtures was evaluated with the Superpave indirect tension (IDT) tests and beam fatigue test. The HMA mixtures containing 0%, 10%, 20%, and 30% of recycled asphalt pavement (RAP) were plant prepared with one source of aggregate, limestone, and one type of binder, PG 64–22. The fatigue properties tested included indirect tensile strength (ITS), failure strain, toughness index (TI), resilient modulus, DCSE_f, energy ratio, plateau value, and load cycles to failure. The results from this study indicated that both Superpave IDT and beam fatigue tests agreed with each other in ranking the fatigue resistance of mixtures when proper procedures were followed.     

旧水泥混凝土路面碎石化再生利用研究

目前,旧水泥混凝土路面的再生利用得到越来越广泛的重视和应用。论述了碎石化技术的概况,分析了旧水泥混凝土路面面板经过破碎碾压的碎石化层特性、碎石化分层及强度形成机制。最后针对这些特点结合实践经验,总结提出碎石化后沥青加铺层结构组合设计原则。