Long-term performance of recycled asphalt mixtures containing high RAP and RAS

The application of reclaimed asphalt pavement(RAP)and reclaimed asphalt shingles(RAS)on asphalt pavement can reduce the asphalt paving cost,conserve energy and protect the environment.However,the use of high contents of RAP and RAS in asphalt pavement may lead to durability issues,especially the fatigue cracking and thermal cracking.It is necessary to conduct a series of analyses on asphalt mixtures containing high RAP and RAS,and seek methods to enhance their long-term performance.This paper provides a comprehensive over-view of the long-term performance of recycled asphalt mixtures containing high contents of RAP and RAS.The findings in this research show that rutting resistance of high recycled asphalt mixtures is not a concern,whereas their resistance to fatigue and thermal cracking is not conclusive.Recycling agents can be used to improve the thermal cracking resistance of high recycled asphalt mixtures.An optimum decision on recycling agents will improve the durability properties of high recycled asphalt mixtures.It is recommended that to use a balanced mixture design approach with testing of the blended asphalt binders will provide better understanding of long-term performance of recycled asphalt mixtures containing high RAP and RAS.

Design Method and Performance for Large Stone Porous Asphalt Mixtures

Design method for large stone porous asphalt mixtures （LSPM） was analyzed to avoid the early distresses of semi-rigid asphalt pavements. Based on stone-to-stone skeleton structure concept, processes of LSPM gradation design was given. The gradation composite design for LSPM shows that the LSPM nominal maximum size （ N MS） should be larger than 26.5 mm, and the NMS sieve passing percentage should be greater than 50%. Through experiments and calculations on the volume properties of the aggregate, the range of aggregate gradation curve of LSPM was given. In terms of asphalt binder＇s normalized test results, MAC-70 and SBS modified asphalt were selected as the asphalt binders. The applicability of large scale Marshall Method and gyratory compaction method to shape specimens was investigated. Based on the asphalt mixture performance evaluation, the optimum asphalt content range （3.1%-3.6%）, the bitumen film＇s thickness range （13-16 μm） and the air void range （13%-18 %） were recommended. Finally, LSPM was tested by the laboratory performance tests including rutting resistance test, fatigue test and water stability test. The theoretic and practical analysis shows that LSPM has a good performance on water permeability, rutting resistance and reflection crack resistance.

Effects of Temperature on the Dynamic Properties of Asphalt Mixtures

By using the falling weight deflectometer（FWD）,the dynamic loading tests on different thickness of asphalt mixture pavement in different temperature were performed.The experimental results show that the effects of temperature on dynamic properties of asphalt mixture are significant,and the thickness of asphalt mixture is also another important influence factor.The comparisons indicate that effect of temperature on the behaviors of dynamic loading properties and static loading properties of asphalt mixture were quite different.

Effect of Loading Condition and Temperature on Dynamic Properties of Asphalt Mixtures

In order to study the effects of loading condition and temperature on the dynamic properties of asphalt mixtures, the dynamic loading tests on different loading condition （various speeds and loads under a certain roughness） and temperature conditions were performed. The experimental result show that the dynamic properties of asphalt mixtures are influenced by vehicle load and speed, besides, the effects of temperature on dynamic properties of asphalt mixture are significant.

Parameter Characterisation of Asphalt Mixtures for Visco-Elastoplastic Analysis

Asphalt mixtures exhibit strong viscous properties under repetitive loads. This phenomenon can be simulated in creep and recovery tests. By applying the visco elastoplastic model proposed, data recorded in the tests are interpreted. It is emphasised that applicability of the visco elastoplastic model depends on the proper method of characterising parameters involved in the constitutive equations. Since two or more strain components of elasticity and viscosity coexist during the loading or unloading, a measuring system of two loggers is introduced to decouple these components. Test data are analysed in three steps as elastic, visco elastic and visco plastic evaluations, using the records collected at the moment of unloading, during the periods of recovery and creep respectively. Factors that may influence the accuracy of data analysis are also discussed.

Effects of Fibers on the Dynamic Properties of Asphalt Mixtures

The dynamic characteristics of fiber-modified asphalt mixture were investigated. Cellulose fiber, polyester fiber and mineral fiber were used as additives for asphalt mixture, and the dosage was 0.3%, 0.3%, 0.4%, respectively. Dynamic modulus test using SuperPave simple performance tester （SPT） was conducted to study the dynamic modulus （E＇） and phase angle （δ） for the control asphalt mixture and fiber-modified ones at various temperatures and frequencies. Experimental results show that all fiber-modified asphalt mixtures have higher dynamic modulus compared with control mixture. The dynamic modulus master curves of each type of asphalt mixtures are determined based on nonlinear least square regression in accordance with the time- temperature superposition theory at a control temperature （21.1℃）. The fatigue parameter E^＊×sinδ and rutting parameter E^＊/sinδ of asphalt mixture are adopted to study the fatigue and rutting-resistance properties, and experimental results indicate that such properties can be improved by fiber additives.

Investigation of Micro-mechanical Response of Asphalt Mixtures by a Three-dimensional Discrete Element Model

The micro-mechanical response of asphalt mixtures was studied using the discrete element method. The discrete element sample of stone mastic asphalt was generated first and the vehicle load was applied to the sample. A user-written program was coded with the FISH language in PFC3 D to extract the contact forces within the sample and the displacements of the particles. Then, the contact forces within the whole sample, in asphalt mastic, in coarse aggregates and between asphalt mastic and coarse aggregates were investigated. Finally, the movement of the particles in the sample was analyzed. The sample was divided into 15 areas and a figure was drawn to show how the balls move in each area according to the displacements of the balls in each area. The displacements of asphalt mastic balls and coarse aggregates were also analyzed. The experimental results explain how the asphalt mixture bears vehicle load and the potential reasons why the rutting forms from a micro-mechanical view.

Statistical Analysis of the Asphalt Mixtures Volumetric Properties

Based on statistics principle,random error and systematic error were considered and the volumetric properties of the two mixtures types,namely A and B,were statistically analyzed using different distribution methods.Seventy-two samples of mixture A and fifty-two of mixture B were fabricated using the Marshall method.The probability distributions were compared on the basis of goodness of fit.Weibull model was found to be most appropriate model for describing the asphalt mixtures volumetric properties distribution.The two-parameter Weibull distribution function applied well to model the bulk specific gravity and voids filled with asphalt data,whereas,the three-parameter Weibull distribution appeared to be more appropriate in the discussing of air voids and voids in mineral aggregate.The experimetal results is revealed that compared with the mean value,the peak value of Weibull distribution was suggested as an alternative and more powerful parameter for describing the test data distribution characteristic.The analysis of test results also revealed that there were significant differences in the volumetric properties of the two tested mixtures for the same confidence level.The confidence interval decreased with the decreasing in reliability.

Numerical Investigation into the Effect of Air Voids on the Anisotropy of Asphalt Mixtures

The aim of this study is to investigate the asphalt mixture anisotropy of both the modulus and Poisson＇s ratio due to air voids using a discrete element modeling simulation method. Three three-dimensional cubic digital samples of asphalt mixture with different shapes of single air void were built using discrete element software PFC^（3D）. The aggregate gradation, air voids and mastic included in the digital samples were modeled using different contact models, with due consideration of the volumetric fractions of the different phases. Laboratory uniaxial complex modulus test and indirect tensile strength test were conducted to obtain material input parameters for numerical modeling. Simulation of the uniaxial cyclic compressive tests was performed on the three cubic samples loaded in three different directions. Dynamic modulus in three directions and Poisson＇s ratio in six directions were calculated from the compression stress-strain responses. Results show that both the modulus and Poisson＇s ratio are dependent on the preferential orientation of air voids. The anisotropy of the modulus and Poisson＇s ratio increases as the pressure loading on the asphalt mixture increases. Compared to the modulus, Poisson＇s ratio due to air voids has been shown to be more anisotropic. The maximum of Poisson＇s ratio and modulus is shown to be up to 80% and 11% higher than the minimum, respectively.

Application and Research on Plant-Mixed Thermal Regeneration Technology of RAP Asphalt Mixtures

When the plant-mixed thermal regeneration technology is adopted for the waste asphalt pavement mixtures,its performance can basically reach the level of freshly-mixed asphalt concrete,which can be used for paving the middle and lower layers of road pavements of various grades.Through the research and application of plant-mixed thermal regeneration technology based on China's Kunming-Yuxi Expressway Pavement Overhaul Project,this paper summarizes relevant technical points and effectively advocates the promotion and application of this technology in highway maintenance.

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.

Effects of diluted methanol and water as foaming agents on the performance of latex foamed warm asphalt mixtures

Latex as an asphalt modifier has gained popularity in the asphalt industry as it improves the durability of asphalt pavement.However,the elastomeric properties of latex stiffen the asphalt binders,resulting in additional energy consumption during the production of asphalt mixtures,which may cause a higher emission of greenhouse gases.This is undesirable for sustainable development and the environment.In this study,the applicability of diluted methanol and water was comparatively evaluated as foaming agents in the production of warm mix asphalt(WMA)mixtures incorporating latex.Diluted methanol was used because it has a lower boiling point and latent heat than water,allowing the asphalt mixture to be produced at a lower temperature and thus consuming less energy.The performance of the foamed asphalt mixture was investigated through service characteristics,mechanical performance,and moisture susceptibility of mixtures.The service characteristics,on the other hand,were measured in a laboratory while preparing and compacting the asphalt mixture,which refers to the amount of energy required during the production and construction stages in the asphalt plant and on the construction site,respectively.The degree of energy required was assessed based on the workability index,coatability index,and the compaction energy index.The mechanical performance of asphalt mixtures was characterized by indirect tensile strength,resilient modulus,and dynamic creep tests.The resistance to moisture damage was evaluated based on the common parameter,indirect tensile strength ratio.The findings revealed that the use of diluted methanol foaming agent helped improve the workability of latex modified asphalt mixtures.The foamed latex-modified WMA demonstrated better performance compared to asphalt mixtures prepared using water as the foaming agent.

Analytical Study on the Effect of Electric Arc Furnace Dust(EAFD)on the Rutting of Asphalt Concrete Mixtures

As a byproduct of the steelmaking process,significant amounts of hazardous electric arc furnace dust(EAFD)are produced.Utilizing the solidification/stabilization technology with asphalt mix is one way to safeguard the environment from its negative effects.Rutting was used as an indicator to assess the asphalt mixture with EAFD since it is an important factor in pavement design.This study’s major goal is to ascertain how EAFD affects the rutting of asphalt-concrete mixtures.To evaluate the ideal asphalt content,the Marshall test method was applied to asphalt-concrete mixtures.EAFD was added to the asphalt cement in four different volume percentages as a binder addition.Then,using the Universal Testing Machine,participants were exposed to a replica of the rutting test(UTM).Experiments were conducted at 25℃,40℃ and 55℃,and at frequencies of 1 Hz,4 Hz and 8 Hz.Rutting was measured for each specimen.Test results showed that rut depth has a negative correlation with EAFD%and a positive correlation with temperature.The use of EAFD has dual advantages,protecting the environment from the adverse impact of EAFD and reducing the cost of asphalt mix without jeopardizing pavement performance.

Multiscale Study on Low Temperature Crack Resistance Mechanism of Steel Slag Asphalt Mixture

The objective of this paper was to study low temperature crack resistance mechanism of steel slag asphalt mixture(SAM).Thermal stress restrained specimen test(TSRST)and three-point bending test were carried out to evaluate the low-temperature crack resistance of SAM and basalt asphalt mixture(BAM).Based on the digital image correlation technique(DIC),the strain field distribution and crack propagation of SAM were analyzed from the microscopic point of view,and a new index,crack length factor(C),was proposed to evaluate the crack resistance of the asphalt mixture.The crystal phase composition and microstructure of steel slag aggregate(SA)and basalt aggregate(BA)were studied by X-ray diffraction(XRD)and scanning electron microscopy(SEM)to explore the low-temperature crack resistance mechanism of SAM.Results show that the low-temperature crack resistance of SAM is better than that of BAM;SAM has good integrity and persistent elastic deformation,and its bending failure mode is a hysteretic quasi-brittle failure;The SA surface is evenly distributed with pores and has surface roughness.SA has the composition phase of alkaline aggregate-calcite(CaCO3),so it has good adhesion to asphalt,which reveals the mechanism of excellent low-temperature crack resistance of SAM.

Effect of aggregate gradation on low temperature performance of asphalt paving mixtures

Low temperature cracking has become one of the important factors that diminish asphalt pavement's ride quality and service life.Especially in cold region,cracking caused by low temperature is the main distress form.This paper discussed the effect of aggregate gradation on the low temperature performance in asphalt paving mixtures.A total of 11 asphalt mixtures with 11 different aggregate gradations and one asphalt binder content were studied.Volumetric properties of the coarse aggregate and asphalt mixtures showed aggregate grading has a significant impact on the degree of aggregate interlock in asphalt mixtures.A trend is existed in the low temperature performance with the change of gradation.With the aid of mathematic statistics,it indicates gradation affects the low temperature performance significantly.The findings also indicate the relationship between the degree of aggregate interlock in asphalt mixtures and the low temperature performance:With the stone-to-stone contact developed,the mixture has a high energy to resist contract and deformation at low temperature.The properties of fine aggregate and asphalt play an important part in resisting low temperature cracking in floating structure.But it provides lower energy to resist low temperature cracking compared to the skeleton structure.

Use of recycled concrete aggregates in asphalt mixtures for pavements:A review

Large quantities of natural aggregates(NA)are required in the manufacturing of asphalt mixtures for pavements.The extraction of NA generates high environmental impacts that negatively affect environmental preservation and conservation.Diverse alternative materials obtained in construction and demolition processes in civil construction worked have been studies as possible replacements for NA,with the purpose of reducing these environmental impacts.The foregoing study presents a state of knowledge review referring to the use of recycled concrete aggregates(RCA)when these are used in the manufacturing of asphalt mixtures(mainly hot-mix asphalt HMA type).Environmental aspects are presented,as well as possible benefits and limitations of using RCA as replacements for NA in asphalt mixtures.However,it is not possible to establish a behavior pattern,since the characteristics of the RCA are very heterogeneous and vary from the original source of the concrete.It is highlighted from the literature that RCA has a wide potential for use in the manufacture of asphalt mixtures,since in most studies,the mixtures with these materials comply the quality requirements contemplated by the construction specifications,mainly in low-volume roads.Additionally,based on the literature review,some recommendations and suggestions are presented for future research.

Laboratory investigation on the properties of asphalt mixtures modified with double-adding admixtures and sensitivity analysis

In order to improve the high temperature stability and low temperature cracking resistance of asphalt mixtures, two varieties of admixtures （anti-rutting agent and lignin fiber） were selected and then combined. This is called double-mixture technology. A series of tests about pavement performance of base asphalt mixtures and asphalt mixtures with admixture of anti-rutting agent or lignin fiber were conducted. Meanwhile sensitivity an- alyses were used to study the influence of three factors （i.e., asphalt grade, aggregate type and gradation） on the high and low temperature performance and water stability of said asphalt mixtures. Test results indicated that the dynamic stability, residual stability, TSR and low temperature failure strain of asphalt mixtures have increased significantly with the additions of 0.40% anti-rutting agent and 0.36% lignin fiber. These results show that the high and low temperature and water stabilities of asphalt mixtures improve obviously. This supports the beneficial comprehensive effect of the double admixture. The problem of improving the asphalt mixtures performance with a single admixture is solved, in addition to also improving other pavement performance. Based on the sensitivity analysis, the most influential factors of dynamic stability, low temperature failure strain and TSR are the gradation, followed by asphalt grade and aggregate type.

Effects of moisture damage on asphalt mixtures

The reduction in the ability of bitumen to bond with the aggregate surface due to the infiltration of moisture has been recognised for years, and this deterioration phenomenon is called moisture damage. In general, the loss of bonding between bitumen and aggregate shortens the service life of the top layer of the pavement. Many investigations have been conducted to understand the mechanisms of moisture damage due to the loss of bonding strength between bitumen and aggregate and to find ways to improve and strengthen the bond to mitigate the effect of moisture. This paper reviews the extensive literature on the loss of bitumen-aggregate bonding strength due to moisture damage in asphalt mixtures.The general description of the theories and mechanisms that explain the effect of the thermodynamic, chemical, physical and mechanical characteristics of the bitumen and aggregate on the bonding phenomenon are discussed in this paper. In addition, the causes of and contributing factors to moisture damage and methods to improve the bond between bitumen and aggregates are also discussed. Moreover, a description of the test methods that can be used to evaluate moisture damage in poorly bonded and compacted mixtures are also presented. Special attention is given to a well-known method, known as the pulloff test, which has been successfully used to evaluate aggregate-binder bond strength, both for laboratory and in-situ tests. This includes the test methods, the factors that affect the bonding strength results and their correlation with other test method. A review of the failure mode of bitumen under the pull-off loading test is discussed in the final section of this paper.

Evaluation of the cracking and aging susceptibility of asphalt mixtures using viscoelastic properties and master curve parameters

Aging can significantly affect the performance of asphalt mixtures, causing increase in stiffness, reduction in relaxation capability and increase in cracking susceptibility. It is also well known that fundamental viscoelastic properties are used for design and modelling of asphalt mixtures and pavement structures to addressing rutting, fatigue and thermal cracking concerns. The objective of this paper is to study how the viscoelastic properties of asphalt mixture change over time, and evaluate and identify the cracking and aging susceptibility of asphalt mixtures with different mix variables during material selection and mixture design. Ten mixtures are evaluated using different laboratory conditioning protocols to simulate a range of aging levels in the field. The complex modulus test is then conducted on the lab aged mixtures to measure the viscoelastic properties in order to construct the dynamic modulus and phase angle master curves. The mixture Glover-Rowe(G-Rm) parameter and the shape parameters of the dynamic modulus and phase angle master curves, including inflection point frequency(-β/γ), difference between the glassy modulus and the inflection point modulus(γ), peak value of phase angle(a) and the horizontal position(frequency) of the peak phase angle value(c), are determined and evaluated for the mixtures with different aging conditions and mix variables. The study indicates the ability of the G-Rmparameter and all the master curve shape parameters to capture the effect of different aging conditions on linear viscoelastic mixture properties, as well as the cracking and aging susceptibility of asphalt mixtures.

Normalized fatigue properties of asphalt mixture at various temperatures

This study normalized the mixture's fatigue behavior at various temperatures,and the strength and fatigue tests of the mixture were conducted.The stress state of the asphalt mixture includes direct tensile,uniaxial compression,and indirect tensile.The Desai yield surface and fatigue path were proposed.And a normalized fatigue characteristics model of the mixture was established.The following conclusions were obtained.With the increases in the loading rate,the strength of the asphalt mixture increased.As the temperature increases,the strength of the mixture is reduced.At various temperatures and rates,the strength forms a closed curved surface.The Desai strength yield surface was established,which forms a closed curved surface.When the loading rate and temperature are below a certain critical line,the asphalt mixture will not undergo strength damage.At a fixed stress state,the fatigue damage path of the mixture was determined.The stress ratio was determined considering the influence of the loading rate.In this way,a normalized model can be described to express the asphalt mixture fatigue properties at various temperatures and stress levels.For the asphalt mixture in an indirect tensile state,the normalized fatigue equation parameter is 4.09.This model is more suitable for reflecting the viscous-elastic behavior of the mixtures than the fatigue equation determined by the notional stress ratio.