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.

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.

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).

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.

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.

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.

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.

Recycling of reclaimed fibers from end-of-life tires in hot mix asphalt

Nowadays, the disposal of end-of-life tires(ELT) is worldwide one of the major concerns for the environment as well as for public health. Crumb rubber and steel wires, the main byproducts(in terms of weight) deriving from the ELT processing, can be recycled in several ways. However, the textile fiber, representing about 10% of the waste by weight, is typically not reused and ends up in landfills or incinerators. The present paper deals with the use of reclaimed fibers from ELT in hot mix asphalt(HMA), with the aim to improve its performance. The study included the preliminary characterization of the fiber through microscope observation and Fourier trans form infrared(FTIR) spectroscopy and then the investigation of the mechanical properties of HMA containing ELT fibers, in comparison with an ordinary HMA with no fibers. In particular, indirect tensile strength(ITS), indirect tensile stiffness modulus(ITSM), semi-circular bending(SCB), three point bending(3PB)and indirect tensile fatigue(ITF) tests were carried out. The results showed that the use of ELT fibers does not reflect in a significant improvement in terms of strength and stiffness properties. However, the ELT fibers determine a noticeable increase of the HMA resistance to fatigue, probably related to the ability of the fibers in sewing the micro-crack edges and contrasting the macro-crack opening.

Numerical visco-elastoplastic constitutive modelization of creep recovery tests on hot mix asphalt

This paper discusses a visco-elastoplastic constitutive model to analyze the creep deformability of asphalt concretes at high service temperatures, finalized to improve the interpretation of permanent deformation phenomenon and performance design of road pavements. A three dimensional constitutive visco-elastoplastic model is introduced, in tensor as well as in numerical form. The associated uniaxial model is used to arrange a plastic element in series with the viscoelastic component. The latter is defined by an elastic spring placed in parallel with three Maxwell elements. Three different hardening laws, namely isotropic, kinematic and mixed hardening, are included in the constitutive model to compare the creep deformability. The proposed constitutive model has been calibrated and validated on the basis of uniaxial creep-recovery test results at 40℃. This is performed with a high performance hot mix asphalt concrete （HP-HMA） at different stresses and loading times. Depending on the hardening law considered, permanent deformation data predicted by the proposed model results are reasonably consistent with the experimental creep-recovery data. A rational constitutive model that is physically congruent with the creep phenomenon of asphalt concretes was developed and calibrated to achieve a deeper understanding of the stress-strain response of such materials. The fundamental relevance of an appropriate plastic response modeling, in the study of the creep behavior of asphalt concretes for highway and road pavements.

An empirical method for estimating surface area of aggregates in hot mix asphalt

Bitumen requirement in hot mix asphalt （HMA） is directly dependent on the surface area of the aggregates in the mix, which in turn has effect on the asphalt film thickness and the flow characteristics. The surface area of aggregate blend in HMA is calculated using the specific surface area factors assigned to percentage passing through some specific standard sieve sizes and the imaging techniques. The first process is less capital intensive, but purely manual and labour intensive and prone to human errors. Imaging techniques though eliminating the human errors, still have limited use due to capital intensiveness and requirement of well-established ]aboratories with qualified technicians. Most of the developing countries like India are shortage of well-equipped laboratories and qualified technicians. To overcome these difficulties, the present mathematical model has been developed to estimate the surface area of aggregate blend of HMA from physical properties of aggregates evaluated using simple laboratory equipment. This model has been validated compared with the existing established methods of calculations and can be used as one of the tools in different developing and under developed countries for proper design of HMA.

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.

Thermal segregation of asphalt material in road repair

This paper presents results from a field study of asphaltic pavement patching operations performed by three different contractors working in a total of ten sites. It forms part of an ongoing research programme towards improving the performance of pothole repairs. Thermal imaging technology was used to record temperatures of the patching material throughout the entire exercise, from the stage of material collection, through transportation to repair site, patch forming, and compaction. Practical complications occurring during patch repairs were also identified. It was found that depending on the weather conditions, duration of the travel and poor insulation of the transported hot asphalt mix, its temperature can drop as high as 116.6 ℃ over the period that the reinstatement team travel to the site and prepare the patch. This impacting is on the durability and perfor- mance of the executed repairs. Cold spots on the asphalt mat and temperature differentials between the new hot-fill asphalt mix and existing pavement were also identified as poorly compacted areas that were prone to premature failure. For example, over the five-minute period, the temperature at one point reduced by 33% whereas the temperatures of nearby areas decreased by 65% and 71%. A return visit to the repair sites, three months later, revealed that locations where thermal segregation was noted, during the patching opera- tion, had failed prematurely.

Water flow simulation and analysis in HMA microstructure

This paper introduces a new method for reconstructing virtual two-dimensional （2-D） micro- structure of hot mix asphalt （HMA）. Based on the method, the gradation of coarse aggregates and the film thickness of the asphalt binder can be defined by the user. The HMA microstructure then serves as the input to the computational fluid dynamic （CFD） software （ANSYS-FLUENT） to investigate the water flow pattern through it. It is found that the realistic flow fields can be simulated in the 2-D micro- structure and the flow patterns in some typical air void structures can be identified. These flow patterns can be used to explain the mechanism that could result in moisture damage in HMA pavement. The one-dimensional numerical permeability values are also derived from the flow fields of the 2-D HMA microstructure and compared with the measured values obtained by the Karol-Warner permeameter. Be- cause the interconnected air voids channels in actual HMA samples cannot be fully represented in a 2-D model, some poor agreements need to be improved.