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 K1 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.

Reducing the Compaction Segregation of Hot Mix Asphalt

This paper presented the methods of reducing the compaction segregation of asphalt layer by improving the operating characteristics of roller and paver. The fit formula, which expresses the compaction rule of the paving layer after passing different rolling passes of the steel wheel roller, was also put forward. The measured results of test road show that when some technical methods are adopted, the compaction segregation can be controlled.

The Compaction Characteristics of Hot Mixed Asphalt Mixtures

The quality of compaction is important to the performance of hot mixed asphalt （HMA） pavement. Most premature failures of asphalt pavement are concerned with poor compaction. Compaction characteristic of lIMA mixtures were studied. Compaction tests were done with typical widely used HMA mixtures, including dense gradation asphalt mixtures with different nominal maximum aggregate size （AC13,AC20,AC25）, and mixtures with different gradation （AC13, SMA13,Supl3 and OGFC13）. HMA mixtures were sampled at different compaction temperature and Marshall blow numbers, varying between 60 and 175 ~C and between 15 and 75 lows, respectively. The compaction characteristics of these mixtures were evaluated. The results showed that the Marshall stability and volumetric properties were significantly affected by the compaction temperature. Mixtures with the same NMAS but different type of gradation need different compaction energy to get the designed density.

Addressing the Fuel Resistance of Hot Mix Asphalt by an Enhanced Test Method

In areas where hot mix asphalt(HMA)is likely to be exposed by any form of mineral oil the layer has to withstand the attack of these substances in order not to damage the construction.The European Standard EN 12697-43 provides a test procedure to determine the resistance of HMA to fuel.The paper reviews this method thoroughly.A completely revised and simplified test device for the brush test was developed meeting the requirements of the standard and creating results with a high repeatability at the same time.The test conditions given by the standard such as the exposure to fuel,cleaning of the specimen after exposure or the contact pressure of the brush were varied to isolate those test conditions with a substantial influence on the result.The research revealed that in the standard some conditions with a rather small influence are set quite strictly while other conditions with a distinct influence on the result are not defined with the required accuracy to obtain comparable and repeatable results.The paper presents suggestions for the improvement of the test method and the standard itself in respect to the layout of the test device and the definition of important test conditions to enhance the outcome of the EN 12697-43.

Application of nano silica to improve self-healing of asphalt mixes

Nano silica due to its spherical shape, tiny size and higher density compared to bitumen, may have an inherent potential to improve hot mix asphalt(HMA) self-healing. In this research scanning electron microscopy(SEM) images were used to investigate size, morphology and dispersion of nano silica particles. Additionally, HMA self-healing mechanism was also examined by SEM. Furthermore, dynamic indirect tensile test(IDT) was used to evaluate HMA self-healing index. The SEM results indicated that bitumen mortar flowing into micro cracks may be one of the most important mechanisms of HMA self-healing. The experiment results also showed that modification of bitumen by nano silica promotes the ability of the HMA self-healing.

Relationship between fatigue life of asphalt concrete and polypropylene/polyester fibers using artificial neural network and genetic algorithm

While various kinds of fibers are used to improve the hot mix asphalt(HMA) performance, a few works have been undertaken on the hybrid fiber-reinforced HMA. Therefore, the fatigue life of modified HMA samples using polypropylene and polyester fibers was evaluated and two models namely regression and artificial neural network(ANN) were used to predict the fatigue life based on the fibers parameters. As ANN contains many parameters such as the number of hidden layers which directly influence the prediction accuracy, genetic algorithm(GA) was used to solve optimization problem for ANN. Moreover, the trial and error method was used to optimize the GA parameters such as the population size. The comparison of the results obtained from regression and optimized ANN with GA shows that the two-hidden-layer ANN with two and five neurons in the first and second hidden layers, respectively, can predict the fatigue life of fiber-reinforced HMA with high accuracy(correlation coefficient of 0.96).

Measuring crack propagation in reinforced asphalt concretes

Two different reinforcing methodologies are applied：modification of the overlay characteristics by adding chopped glass fibers to the hot mixture asphalt （HMA） and reinforcing asphalt overlay with glass grids.Theory of fracture mechanics （FM） is employed to determine crack growth rates for the suggested anti-cracking overlay systems.Asphalt mixture designing tests,three point bending tests and fatigue crack propagation tests were carried out.The critical stress intensity factors KIC are determined for plain and reinforced asphalt concrete.Depending on the fatigue crack propagation,the crack growth rate is determined for each type of anti-cracking system and the cracking process is also analyzed.One of the significant points in this study is the attempt to give better understanding of the crack propagation for multilayer asphaltic overlay or what are suggested herein to be called composite structure anti-cracking overlay system.The results indicate that the reinforcing materials improve anti-cracking characteristics of the asphalt concrete.Composite structure anti-cracking overlay gives a good solution for the reflective cracking phenomenon over old cracked pavements.

Estimation of the Fatigue Endurance Limit of HMAC for Perpetual Pavements

A simplified procedure was described to estimate the FEL of three kinds of hot-mix asphalt concrete （HMAC） without doing any fatigue tests. The procedure required two fundamental properties of HMAC, tensile strength under different temperatures and strain rates, and flexural stiffness under different stain levels. This information can reliably be obtained in simple tests, which are the monotonic uniaxial tensile test （MUTT） and the four-point bending test （FPBT）. A new parameter, the initial stress ratio Rinitial, was introduced to connect these two tests, which was defined as the ratio of applied initial stress and tensile strength of the specimen. At last the FEL can be expressed as a function of the initial flexural stiffness, frequency and temperature. Obviously, this procedure has the potential to be very useful in view of long-life pavement design and time consuming traditional fatigue tests.

热拌沥青混合料(HMA)生产控制要点探讨

针对热拌沥青混合料生产的过程控制,结合工程实践,论述了生产过程中沥青混合料的均匀性和配合比准确性等应注意的问题和采取的措施。

不同RAP掺量下热再生沥青混合料性能衰变规律

本文采用自主研发的全寿命分析仪对沥青混合料分别进行0、4、8、12个月的模拟老化,采用冻融劈裂试验、动态蠕变试验和半圆弯曲试验,研究不同RAP掺量下热再生沥青混合料长期老化后各项性能的衰变规律.结果表明:在12个月模拟老化后,RAP掺量为30%时沥青混合料的流变次数达到最大,RAP掺量的提高使得TSR衰减幅度变大且断裂能下降.50%RAP掺量时再生料TSR衰减幅度比新拌料大7.9%,流变次数和断裂能较新拌料分别减少38.6%和61.7%.长期老化作用下RAP掺量对沥青混合料疲劳寿命衰减的影响不明显,但会降低其应力敏感性.

热拌极薄抗滑磨耗层在高速公路抗滑性能提升中的应用

为研究热拌极薄抗滑磨耗层在高速公路养护中的应用,提升路面抗滑性能,论文结合实际工程,介绍了热拌极薄抗滑磨耗层工程特性,详细阐述了热拌极薄抗滑磨耗层原材料及配合比设计,重点对热拌极薄抗滑磨耗层施工技术要点进行研究。结果表明:公路养护中采取热拌极薄磨耗层技术进行处理,其路面抗滑性能得到有效提高,并节约养护成本。

热拌沥青混合料拌和和易性的评价方法

基于沥青混合料的材料组成及分布,采用扫描电镜(SEM)测定热拌沥青混合料中集料表面裹附的沥青膜厚度,并提出一种拌和和易性评价指标.采用集料分布均匀性和压实度测试结果进一步验证和分析不同热拌沥青混合料拌和和易性的变化规律.结果表明:沥青种类、级配类型及拌和温度对热拌沥青混合料拌和和易性影响作用不同;沥青膜在集料表面裹附得越均匀,热拌沥青混合料的拌和和易性就越好,集料分布的离散性越小,热拌沥青混合料成型的压实度越大.

基于响应曲面法确定玄武岩纤维热再生沥青混合料最佳配合比

在进行沥青混合料配合比设计时,由于掺加两种或两种以上掺合物时,采用马歇尔试验法或正交试验法进行沥青混合料配合比存在不足,为了确定沥青混合料最佳配合比,通过基于响应曲面法中的BBD(Box-Behnken design)法对级配类型AC-13掺加玄武岩纤维、RAP的热再生沥青混合料进行级配优化设计。结果表明,计算优化得出最佳油石比为5.17%、旧料掺量RAP为31.89%及玄武岩纤维掺量0.26%。并通过试验对预测模型进行验证,预测值与实测值模型之间相对误差较小(小于3%),可见BBD法建立的二阶模型具有较好的拟合效果,对再生沥青混合料各掺量配合比设计能进行有效优化,并且最佳各掺量下的玄武岩纤维热再生沥青混合料具有良好的路用性能。

Development of high stability hot mix asphalt concrete with hybrid binder

Cost reduction of public works projects has been desired due to severe financial circumstances. Therefore, asphalt pavement has been requested to extend its life. Semi-flexible pavement or epoxy asphalt pavement, which has high rutting resistance and oil resistance, may be applied to the place where these performances are demanded. However, special technique is required in manufacturing and construction. In addition, these materials have also raised a problem that they cannot be recycled. Meanwhile, conventional asphalt pavement has several drawbacks. It is vulnerable to rutting caused by traffic load and damage caused by petroleum oils such as gasoline or motor oil. The materials used in asphalt mixtures were studied for improving the durability of asphalt mixture. A high stability asphalt concrete was developed which has equal or superior performance to semi-flexible pavement and epoxy asphalt pavement. In this paper, the process of selecting the substance and the characteristics evaluation of the developed mixtures are described. Furthermore, an inspection result as well as follow- up survey of the performance of the developed mixtures obtained from trial and actual construction is shown.

基于沥青混凝土搅拌站的配合比设计与实践

针对当前沥青混合料目标配合比与生产配合比相互独立、脱节的情况,提出基于沥青混凝土搅拌站的配合比设计理念。弱化目标配合比设计流程,强调以目标配合比在沥青混凝土搅拌站进行试生产,从而得出各档热料比例,以此作为生产配比进行配合比设计。然后以此设计结果在沥青混凝土搅拌站进行联调联试,最终通过微调目标配合比来实现目标配合比与生产配合比在沥青混凝土搅拌站上的协调统一。

厂拌热再生AC-20沥青混合料配合比设计研究

根据《公路沥青路面再生技术规范》对厂拌热再生AC-20沥青混合料配比进行设计研究,本文依托黑龙江省交通投资集团有限公司权属高速公路质量提升(二期)A2-1标段,对厂拌热再生AC-20沥青混合料进行配合比设计,通过马歇尔实验获得相应数据最终确定最佳沥青用量为4.5%时抗水损害性能、高温稳定性能等路用性能满足要求。结果表明:该厂拌热再生AC-20沥青混合料性能符合规范要求,能够有效节约沥青与石料材料,路面性能良好。

Graphene sandwiched crumb rubber dispersed hot mix asphalt

The crumb rubber obtained from discarded vehicle tires and graphene oxide prepared by oxidation of graphite powder in laboratory were used to modify virgin bitumen. Four different hot mix asphalt matrices prepared using virgin bitumen, crumb rubber modified bitumen, graphene oxide modified bitumen and combination of crumb rubber-graphene oxide modified bitumen are compared. The modified bitumen matrices are characterised by Fourier transform infrared spectroscopy and scanning electron microscopy for structural and morphological analysis. Marshall properties along with indirect tensile test and tensile strength ratio tests were carried out to check the resistance towards cracking and moisture susceptibility of matrices. The results show that, crumb rubber and graphene oxide are completely compatible with bitumen. 9.8% crumb rubber content in crumb rubber modified bitumen hot mix asphalt exhibits the optimum result. The performance of graphene oxide modified bitumen hot mix asphalt exhibits superior performance in comparison to control mix and crumb rubber modified bitumen hot mix asphalt samples.The enhanced properties of modified bitumen hot mix asphalt with the combining effect of graphene oxide and crumb rubber, are suitable for road construction.

Investigation of material composition,design,and performance of open-graded asphalt mixtures for semi-flexible pavement:A comprehensive experimental study

The primary goal of this study is the design and construction of semi-flexible pavement(SFP)mixture in accordance with the engineering and mechanical criteria.This study involves the use of a range of gradation curves,air void contents,cellulose and synthesized fibers,and neat and modified asphalt binders to prepare the open-graded asphalt(OGA)mixtures.To analyze the characteristics of these mixtures,a variety of test,namely binder drainage,semi-circular bending(SCB),Cantabro,wheel tracking,indirect tensile strength(ITS),and permeability tests were conducted.Additionally,to analyze the prepared grouting material,flexural strength,compressive strength,and fluidity tests were conducted.In the final stage,SFP was compared to HMA in terms of engineering characteristics and performance.According to the results,SFP was more resistant to skid,rutting,fire,and moisture damage,while HMA had a better performance in fracture tests,including SCB test.According to the results of the mechanical performance tests conducted on OGA mixtures,the highest and lowest values for air void content to achieve the highest mechanical performance level were 30%-35%and 25%,respectively.Also,based on the laboratory results,it was determined that the required void ratio for constructing OGA mixtures was 24%-26%based on the bitumen type and fibers amount in the mixture.Finally,SFP mixture can be regarded as a viable alternative to common pavements thanks to its high resistance to rutting and moisture damage,long freezing-thawing fatigue life,and adequate fire and skid resistance.

Mix design,development,production and policies of recycled hot mix asphalt:A review

Worldwide,flexible pavements are the paramount type of pavements.These national assets can be recycled to serve the next design life without the need to dispose of them in landfill.The old/distressed,flexible pavement material is called,reclaimed asphalt pavement(RAP)material.In view of the sustainable development practice,100%RAP should be recycled.However,the practical range of RAP incorporation in a drum mix plant ranges from 10%to 50%whereas in a batch mix plant,it is 10%-35%.In a batch mix plant,incorporation of the hot dried RAP(instead of cold RAP feeding)can increase the RAP incorporation level by 20%.Studies recommended that the rejuvenator should be added over the RAP material instead adding with the base binder.The addition of rejuvenator on the RAP conveyor belt(to the pug mill),provided sufficient time for rejuvenating the aged binder coating over RAP aggregates.Further,a thorough knowledge of the mix design process of recycled hot mix asphalt(RAP-HMA)is essential to produce a durable mix.For high RAP content(>20%),the RAP binder properties are important for the mix design process.However,very limited studies discussed(in detail)the recovery process of the RAP binder.The review article through light on the binder recovery process,method of RAP gradation,specific gravity determination for RAP material,minimum desirable properties of the RAP material etc.This review paper also provides a narrative review of the historical development of RAP-HMA technology,technical aspects related to the procurement of RAP material,mix design and production of the recycled mix.Moreover,the international&national policies/laws for construction and demolition waste are discussed.

Addressing the permanent deformation behavior of hot mix asphalt by triaxial cyclic compression testing with cyclic confining pressure

Rutting or permanent deformation is one of the major distress modes of hot mix asphalt in the field. Triaxial cycle compression testing （TCCT） is a standardized and scientifically accepted test method to address this distress mode in the lab and to characterize the resistance to permanent deformation. In most labs and according to EN 12697-25, standard TGCTs are carried out with cyclic axial loading and a constant confining pressure. In road pavements on the other hand, dynamic traffic loading due to passing wheels leads to cyclic confining pressure. In order to bring the TCCT closer to reality, the radial reaction and its phase lag to axial loading in standard TCCTs are analyzed and an enhanced TCCT with cyclic confining pressure is introduced. The cyclic confining pressure takes into account the viscoelastic material response by the radial phase lag to axial phase loading. In a subsequent test program, TCCTs with different confining pressure amplitudes were carried out on two hot mix asphalts. Results from standard and enhanced TCCTs were analyzed, compared and discussed. It is shown that the resistance to permanent deformation in- creases significantly when the viscoelastic material response is taken into account in the TCCT by introducing cyclic confining pressure.