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.

Construction Technology of Warm Mix Asphalt Pavement in Cold High-Altitude Areas

With the continuous development of domestic highway construction,highway civil engineering and service level quality have attracted much attention.Good pavement quality and high-quality service make people feel comfortable and smooth when traveling.High-quality pavement can significantly reduce the probability of traffic accidents.At present,there is a direct relationship between pavement quality and pavement construction operations.Carrying out pavement construction operations in cold high-altitude areas requires a reasonable selection of construction equipment and methods.The application of warm-mix asphalt pavement construction technology can ensure pavement quality.Therefore,this paper analyzes the advantages of warm-mix technology,the environmental characteristics of cold high-altitude areas,and construction preparations,and discusses the construction technology of warm-mix asphalt pavement in cold high-altitude areas in detail,to improve the overall road quality of cold high-altitude areas.

Rheological properties of warm mix asphalt binder by DSR test at medium temperature

The rheological properties including the complex modulus G＊ and the phase angle δof matrix and warm mix asphalt （WMA）binders were measured by using the dynamic shear rheometer （DSR ） test at the medium temperature ranging from 16 to 40 ℃,and the relationships between the fatigue factor G＊ sinδand the matrix binder property,WMA additive and test temperature were established.It is found that G＊ decreases with the increasing temperature while δincreases inversely,and G＊ of the asphalt binder with high WMA additive dosage is large,and δis small.G＊sinδexponentially decreases with the increasing temperature and linearly increases with the increase in additive dosage,and the amplitudes of variation are large at low temperatures and high additive dosages.The effect of WMA additive on the rheological property is more remarkable for the matrix asphalt binder with low G＊.Besides,aging has a great effect on the property of matrix asphalt binder,and a slight effect on the interaction between asphalt and additive.The high additive dosage can increase the fatigue cracking potential of the asphalt binder.

Performance evaluation and chemical property analysis of RWMA binders with 100% artificial reclaimed asphalt

The performance evaluation and chemical property analysis of the recycled warm mix asphalt （RWMA） binders containing 100% artificial reclaimed asphalt （ RA） are presented, and the combined effects of different percentages of the rejuvenator and warm mix additive （WMA） additives on RWMA binders are analyzed through laboratory tests. Three types of WMA additives ad one commercial rejuvenator named GST were selected to restore the artificial RA. The laboratory performace tests including the penetration test, softening test ad rotary, viscosity （RV） test were carried out. In addition, the Fourier transform infrared spectroscopy （FTIR） test was performed to explore the chemical property of RWMA binders. The results of the performance tests indicate that the rejuvenator GST has the ability to restore the artificial RA; choosing the optimum content of WMA additives and rejuvenator is the key to restoring 100% artificial RA, since the combined effects of them play an important role in determining the basic laboratory performance of RWMA binders. The FTIR tests show that the process of recycling mainly adjusts the chemical component of aged asphalt and no remarkable change is observed in the FTI1R spectra of RWMA binders in terms of chemical functional groups with the introduction of WMA additives.

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.

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).

Warm asphalt rubber:A sustainable way for waste tire rubber recycling

Recycling end-of-life tire rubber as asphalt modifier is known as a sustainable paving technology with merits including enhanced pavement durability,waste tire consumption and noise reduction.However,the criticisms on the high construction emissions of asphalt rubber(AR)have limited its application.Warm mix asphalt(WMA)effectively reduces the mixing and compaction temperatures of conventional hot mix asphalt mixtures.The combination of AR and WMA,called warm asphalt rubber(WAR),is a promising paving material which achieves pavement sustainability from principles to practices.Many studies have demonstrated that WMA technologies work effectively with AR pavement in different ways,alleviating the concerns of potential higher emissions of AR by decreasing mixing and paving temperatures.A comprehensive literature review about WAR brings a better understanding of this promising paving technology.The findings of 165 publications were summarized in this review.It summarized the recent developments of WAR in various aspects,including rheological properties,mix design,mixture mechanical performance,field application,construction emission,and asphalt-rubber-WMA additive interaction.It is expected that this review is able to provide extensive information to explore further research development and application of WAR.

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.

The Influence of Material Related Parameters on the Mechanical Properties of Foamed Asphalt Mix

By indirect tensile strength （ITS） test and unconfined compressive strength （UCS） test, the influence of various material related parameters, including asphalt foamability, aggregate temperature, mixing moisture content （MMC） and foamed asphalt （FA） content, on the mechanical properties of FA mixes was studied. The results indicated that both asphalt foamability and aggregate temperature greatly affected ITS of FA mixes. Too low aggregate temperature was unfavorable for mechanical properties of FA mixes. Foamed index alone was unfit for the evaluation of asphalt foamability. Compared with half-life, expansion ratio had more prominent influence on ITS of FA mixes. MMC had significant impact on the mechanical properties of FA mixes and should be optimized by trial and test in FA mix design. The mechanical properties of FA mix were sensitive to the change of FA content. Compared with the ITS determined with standard Marshall specimens, both the ITS and UCS determined with static compressed specimens by 15 cm diameter were more effective in terms of choosing the optimal asphalt content for FA mixes.

Evaluation of environmental factors to fatigue performance of asphalt mixes

This paper studies the effect of different environmental factors, including the axle load weight, environmental temperature, vehicle speed, and the aging level of asphalt, on the fatigue performance of asphalt mixes based on four-point bending beam fatigue tests. A fractional factorial design method named ＂uniform design＂ was applied in experimental design. The relations of the environmental factors to initial stiffness, fatigue life, phase angle and cumulative dissipated energy were established with the general linear modeling method. It is found that there exists very good correlativity between the environmental factors and the fatigue performance indices of asphalt mixes. The coefficients of total correlation are mainly beyond 0. 95. The results indicate that the consideration of the effect of environmental factors is necessary in the fatigue performance evaluation on real asphalt pavement.

Investigation on Microcrystalline Wax Doped Asphalts by Temperature Control Mode of Atomic Force Microscopy

Because of its economical and environmentally friendly characteristics, the warm mix asphalt(WMA) is widely used in pavement engineering. However, the lack of microscopic study of WMA brings difficulties in understanding of its mechanical behavior and mechanisms at macroscopic scale which finally hinders the enhancement of WMA's performance. Therefore, this article aims to use atomic force microscopy(AFM), a promising microscopic technique, to investigate the effects of wax-based warm mix agents on asphalt microstructures and micromechanical properties at different temperatures. For simplicity's sake, microcrystalline waxes are selected as an alternative of these wax-based additives. It is shown that the sample preparation method has a vital impact on the morphology of asphalt samples. The effects of microcrystalline wax on asphalt's mechanical properties can be well captured by AFM tests. Results show that the blending of #70, #80 and #90 microcrystalline waxes lowers the modulus(20—60 MPa) of Pen70 asphalt at 25 ℃ while increasing its adhesion force(5—20 n N). The results of this study may shed some light on the comprehension of the effects of wax-based additives on asphalt materials at macroscopic level which can help estimate and predict its actual performance.

Experimental Study on Fatigue Performance of Gussasphalt Mixture

Four-point flexural fatigue test for Gussasphalt mixture specimen was carried out at a straincontrolled mode system. The results showed that the development of the tested stiffness modulus and phase angle of the mixtures with increasing load cycles exhibited three periods, initial generation, slow development and failure period. The fatigue crack generation zone formed in the third period, in which the macro mechanical properties were signifi cantly decreased. Moreover, we also analyzed the effects of asphalt content and mixing temperature on the fatigue life of the mixture. The results showed that the fi rst period when the specimen＇s initial stiffness modulus was reduced to 80% accounted for 5%-10% of the total fatigue life; the second period in which the reduction became slow and demonstrated a liner relationship with load cycles occupied 70%-85% of the fatigue life; and the third period was about 5%-10%. The results indicated that the lower the mixing temperature, the longer the fatigue life of Gussasphalt mixture. Besides, the increasing of asphalt content has a minor effect on the fatigue life of Gussasphalt mixture

Experimental Alternative to the Determination of the Thermal Dependence of the Complex Modulus of Asphalt Mixes in Dry Tropical Areas

Current pavement design methods do not allow for the reduction of early deformation of the surface layers of bituminous pavements in the city of Ouagadougou. Weather conditions combined with traffic, particularly during heat waves, are factors. The temperature at the surface of the bituminous pavement can reach 62˚C but the complex modulus associated with this temperature is not taken into account in the design, hence the interest in proposing laws of dependence of the complex moduli is taken into account in the maximum temperatures of the pavement surface. The objective of this paper is to propose an experimental method to determine the temperature dependence of the complex moduli of asphalt mixes for temperatures between 40˚C and 70˚C. This experimental method consists of performing axial compression tests on cylindrical asphalt specimens. It was applied to three different formulas of bituminous mixes, intended for the wearing course, obtained from mixes of crushed granites, granular classes 6/10, 4/6 and 0/4, pure bitumens of grade 50/70, 35/50 and modified bitumen of grade 10/65. The comparative study of the experimental results obtained with the results of a semi-empirical methodology revealed a root mean square deviation from the mean of between 6.58% and 14.8% of the norms of the complex moduli (modulus of rigidity) of the asphalt mixes for a fixed frequency of solicitations of 10 Hz. The consistency of these results with data from the literature led to the initial conclusion that asphalt mixes formulated with 35/50 and 10/65 bitumen would have better compressive strength than those formulated with 50/70 bitumen, for exposure temperatures between 40˚C and 70˚C. This experimental approach could be an alternative to the complex modulus test for determining the modulus of rigidity for design purposes under real pavement exposure conditions in the city of Ouagadougou during heat waves.

Mechanical performance of cold mix asphalt containing cup lump rubber as a sustainable bio-modifier

The road construction industry aims to contribute to the protection of already compromised environment.Cold mix asphalt(CMA)is a measure initiated by the road industry to protect the environment and preserve energy.Despite having additional benefits,CMA has attracted little attention due to its inferior performance.CMA's performance is enhanced using a sustainable binder bio-modifier,natural cup lump rubber(CLR)is one of them.This study evaluated the tensile properties,rutting,moisture susceptibility,and adhesion properties of CLR-modified CMA(CMA-CR).The tensile property was enhanced by 26%due to CLR modification.CMA-CR had excellent rutting resistance of less than 2 mm rut depth at 10,000 load cycles,showing 70%improvement compared with conventional CMA.Moisture susceptibility evaluation indicated that CMA-CR had tensile strength ratio(TSR)value of 104%,satisfying the minimum 80%requirement of AASHTO T283.It also retained more than 96%bitumen coating.The moisture damage resistance was improved by 12%and 10%in terms of TSR and stripping,respectively.The durability results revealed that the CMA-CR mixture prevented higher mass loss,representing 14%improvement compared with conventional CMA.

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.

Automated,economical,and environmentally-friendly asphalt mix design based on machine learning and multi-objective grey wolf optimization

The increasing impact of the greenhouse effect on ecosystems is prompting transportation agencies to seek methods for reducing CO_(2)emissions during pavement construction and maintenance.Additionally,the laboratory mix design process,which involves selecting aggregate gradation and binder content,is time-consuming and labor-intensive.To accelerate the traditional mix design procedure,this study presented a mix design procedure that can automatically determine gradation and binder content based on machine learning(ML)and a meta-heuristic algorithm.Specifically,ML approaches were employed to model the relationship between volumetric properties(mixture bulk specific gravity(Gmb)and air void(VV))and both mixture component properties and mixture proportion,based on a dataset collected from literature with 660 mixture designs.Integrated with the prediction of ML models and the modified multi-objective grey wolf optimization(MOGWO)algorithm,an automatic asphalt mix design was proposed to pursue three goals,including VV,cost,and CO_(2)emission.The results indicated that least squares support vector regression(LSSVR)and e Xtreme gradient boosting(XGBoost)achieved the highest prediction accuracies(correlation coefficient:0.92 for VV and 0.96 for Gmb).The MOGWO algorithm successfully found the 26 optimal mix designs for the case of VV vs.cost vs.CO_(2)emission.Compared to the traditional laboratory design,the optimal mixture with VV of4%achieves a cost saving of 2.46%and a reduction of 4.03%in carbon emission.The volumetric properties of the mixtures output by the approach also align closely with values measured in a laboratory.

Influence of the Temperature on Coated Bituminous of Road Structures in Senegal (West Africa)

The Senegalese road network is strongly influenced in the long term by seasonal variations in climate and weather conditions. Indeed, much of the damage is due to these environmental factors. The objective of this paper is to study the behaviour of bituminous structures under the effect of high temperatures. Material samples were taken for a physico-mechanical characterization of the coated components. The results show that Marshall creep (2.87, 3.39, 5, 5.5 mm) and the bitumen penetrability increase with the increasing of temperatures respectively from 34°C to 45°C and from 20°C to 50°C. Marshall Stability drops from 15.81 kN to 11.31 kN for temperatures between 34°C and 45°C. The simulation carried out on Alize-LCPC shows an increase in distortions of traction at the basis of the rolling layer and at the top of the platform if temperatures vary between 34°C and 45°C. This work makes it possible to conform that the bituminous concrete is thermally sensitive and the hypothesis of fixing the constant modulus of the bituminous layers in Senegal for all projects remains unsuitable for a good dimensioning of sustainable road structures. The knowledge of the equivalent regional temperature will make it possible to produce quality pavements with a long lifespan.

Estimation of the Equivalent Design Temperature of a Pavement in Burkina Faso

The bituminous pavements of the city of Ouagadougou(Burkina Faso)are made using old design methods which take into account the climate from the notion of equivalent temperature.Thus an equivalent temperature of 30°C is often used for the design of bituminous pavements.The observation that has been made is that this temperature does not currently make it possible to reduce the problems of early degradation of the pavements linked to meteorological fluctuations.The objective of this article is to propose a numerical approach for determining the equivalent temperature from temperature measurements taken at the surface of the pavement.This approach consists in jointly using the Alizé-Lcpc sizing software and the Comsol Multiphysics software using the finite element method.For a four-layer bituminous pavement,located at 12.38°North and 1.48°West,in Ouagadougou,consisting of a surface course of bituminous concrete of 8 cm and a base course of gravel bitumen of 16 cm,an equivalent temperature of 35°C was obtained.

Caltrans use of scrap tires in asphalt rubber products:a comprehensive review

The California Department of Transportation （Caltrans） has been using scrap tire rubber in asphalt pavements since the 1970s in chip seals and the 1980s in rubberized hot mix asphalt（RHMA）. Both the wet （field blend） and dry processes were used in early trials. Caltrans has also used rubber modified binders containing both crumb rubber modifier and polymer modifier that could be manufactured at a refinery facility, a terminal blend wet process. Since the beginning of this century, Caltrans increased the use of scrap tire rubber in paving projects and invested considerable resources in developing technically sound, cost effective, and environmentally friendly strategies for using scrap tire rubber in roadway applications. By the end of year 2010, approximately 31% of all hot mix asphalt （HMA） placed by Caltrans was rubberized HMA, roughly 1.2 million tons. Caltrans efforts in using asphalt rubber products were also demonstrated in its research and technology development. These included the construction of two full-scale field experiments, five warranty projects, and an accelerated pavement study using a heavy vehicle simulator. Additionally, terminal blend asphalt rubber and rubberized warm mix asphalts began to be experimented on trial basis. This paper provides a comprehensive review of Caltrans experience over four decades with asphalt rubber products. Current practices and future outlook are also discussed.