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The loss of performance against fatigue is evident for situations of poor execution of the surface layer, quantified in this research by the parameter in-field air voids. This loss of performance has a direct impact on highways operating costs. To analyse the loss of fatigue performance, eight field-applied asphalt mixes were evaluated, comparing laboratory compaction (5.50% air voids) with as-built in-field core samples (random variable air voids). The impact of increased air voids on LVE behaviour, fatigue life, and costs were investigated. Decrease in stiffness was observed for in-field air voids greater than 7.00%. Through the S-VECD model and FlexPAVETM software, a significant decrease in fatigue life was observed for in-field air voids greater than 8.00%. Costs, defined as costs per traffic request (N) (US$/N) were significantly affected for in-field air voids greater than this value (8.00%). Based on that, a Payment reduction factor (PRF) was proposed. In this way, it is concluded that the framework demonstrated throughout the paper, based on a mechanistic approach and using the FlexPAVETM, allows the evaluation of the construction quality impact on asphalt pavement cost. [ABSTRACT FROM AUTHOR]

The measured strain during a creep-recovery (CR) test comprises both reversible and irreversible strains; therefore, adequate treatment is required to accurately separate them. In this paper, a generalised version of the CR test was proposed to investigate the permanent deformation behaviour of asphalt mixtures exerted by a variety of loading patterns in the time domain. The companion back-calculation algorithm was also proposed to separate with improved accuracy and repeatability the pure viscoelastic (VE) and viscoplastic (VP) strains. First, the creep compliance (CC) was back-calculated based only on the recovery data by using an approximate analytical creep compliance function of the Huet-Sayegh model as the solution function in the optimisation process. Then, the pure VE and VP strains were determined. The results show that the proposed method attains a good level of reliability although relatively short durations of the recovery period have been used. [ABSTRACT FROM AUTHOR]

This paper presents a new energy-based failure criterion that is based on the simplified viscoelastic continuum damage model. This study found that the average reduction in pseudo stiffness up to failure, referred to here as DR, is a material constant that is independent of mode of loading, temperature, and stress/strain amplitude. Twenty different asphalt mixtures were used to validate the proposed method. This paper presents typical values of DR and shows that the DR changes with the mixture characteristics. The advantages of the DR failure criterion over a previous failure criterion (known as the GR criterion) are that it: (1) allows the prediction of fatigue failure in arithmetic scale, which reduces possible errors due to extrapolation of the accelerated laboratory fatigue test data to realistic traffic volumes encountered in the field and (2) reduces the number of tests required to characterise the failure criterion. Statistical analysis was performed in this study and the results show confidence levels that can be obtained from two or three fatigue tests. [ABSTRACT FROM AUTHOR]

Usually, aggregates used for asphalt mixtures consist mainly of natural aggregates. Sometimes the natural aggregates are substituted with limited amounts of industrial and construction wastes. The current paper deals with evaluating the mechanical performance of new developed hot asphalt mixtures made of up to 98% industrial and construction by products. In this project, different types of industrial by-products, namely, RAP, foundry sand, and steel slag in addition to biobased rejuvenators have been used to find the composition of the best asphalt mixtures made mainly of wastes that can substitute the asphalt mixtures made of natural aggregates. Fourteen selected asphalt mixtures have been evaluated using the circular road simulator test at VTI. The CRS testing program has been set up to allow different measurements, e.g. surface deterioration and wear, friction, and visual inspection. The test results demonstrated that it is possible to obtain paving mixtures with high content of recycled materials. [ABSTRACT FROM AUTHOR]

The present paper presents the rutting evaluation of different asphalt mixtures in use in the state of Rio Grande do Sul, Brazil's southernmost-region, through the uniaxial repeated load test and the monitoring of mixtures performance in field, culminating in a criteria proposal for the parameter Flow Number depending on traffic. For this, five distinct asphalt binders were studied, five grain size distributions, three warm mixtures and 21 hot mixes, with different mineralogical types of aggregates, and 15 monitored test sites distributed geographically throughout the state. The results indicated that the binder modifications were the most influential characteristics in the asphalt mixtures rutting. Also, it was verified that the Flow Number criteria proposed so far in the country present significant differences. In this way, a new criterion was suggested, and it is possible to infer a good applicability for asphalt concretes, except for warm mixes and those with rubber binder. [ABSTRACT FROM AUTHOR]

This paper addresses the measurement and modelling of the damaged properties of asphalt mixtures including the fracture, healing and viscoplastic deformation of the asphalt mixtures in both tensile and compressive loading as being affected by their composition and conditioning with ageing and exposure to temperature and moisture. An energy-based mechanics is applied to obtain the material fundamental properties such as surface energies, bond energies, anisotropy, yield functions and plastic potential functions that are valid for actual asphalt mixtures, viscoelastic crack growth criteria under both tensile and compressive loading, a simple mechanics-based method of determining the fatigue endurance limit, and the measurement and prediction of healing in restoring the damage done by fracture. Healing is antifracture and cracking is the net result of the interplay of these two complimentary mechanisms. Because fracture in asphalt mixtures is not the growth of a single crack but the simultaneous growth of multiple cracks that start out as air voids, this fact leads to the use of the growth of damage density to characterise fracture in an asphalt mixture. It was discovered that the form of Paris' law applies to the growth of damage density of asphalt mixtures in both tensile and compressive loadings. The importance of this fact lies in many developments from this discovery, e.g. compressive monotonic loading of cylindrical test samples permits a direct determination of the Paris' Law coefficient and exponent. In all cases, measured material properties are presented as they vary with mixture composition and with conditioning such as moisture and ageing, both in the lab and in the field. The measurements of these properties are made simply, quickly and accurately by the use of mechanics so that an entire characterisation of the properties of an asphalt mixture in tension and compression can be completed in the space of one day. The net effect is to reduce the efforts expended in the lab and the systematic error due to the assumptions made by the existing models and simultaneously to increase the efficiency and cost-effectiveness of materials testing and raise the reliability of the design of mixtures, pavement structures and specifications and the prediction of the life cycles in as-built pavements. [ABSTRACT FROM AUTHOR]

Moisture damage in asphalt pavements is the degradation of the mechanical properties of the asphalt composite due to the action of water. In a companion paper the mechanisms of moisture damage were discussed. It was established that in order to characterise moisture damage in asphalt mixtures, it is important to comprehensively describe and model the effect of thermodynamic, chemical, physical, and mechanical processes. This paper discusses existing tests and analytical methods that can be used to assess and quantify moisture damage potential in asphalt mixtures. These methods range from visual qualification of asphalt binder stripped from the aggregate, to analytical-based models that include multiple material properties derived using fracture mechanics, continuum mechanics, thermodynamics, and/or micromechanics. In addition, this paper presents a new approach for classifying moisture damage, which emphasises recent analytical developments. Finally, advances in the mathematical modelling of moisture damage are summarised and future research efforts in this area are identified. [ABSTRACT FROM AUTHOR]

Moisture-induced damage in asphaltic mixes is a complex problem which needs to be approached 'from the inside out'. It is of essence to determine the fundamental physical and mechanical processes which contribute to moisture-induced damage. Once these processes are determined, the controlling parameters need to be defined and measured. The research described in this and the previous paper is focusing on the development of an energy-based computational framework which incorporates moisture-induced damage by integrating the physical and mechanical moisture-induced damage processes within the (dry) elasto-visco-plastic constitutive model. In the previous paper, the moisture infiltration processes and their formulations were derived and verified. In this paper, focus is placed on the determination of the moisture susceptibility parameters of the computational model. Determination of moisture diffusion coefficients of the mastic is discussed and a computational study is performed to show the effect of filler concentration in the mastic. A computational-experimental procedure to determine the moisture susceptibility of the aggregate-mastic bond is shown and demonstrated. Finally, an extensive parametric analyses is performed which shows the impact of moisture damage on the asphalt mix response by varying the moisture susceptibility parameters. It is concluded, among others, that to avoid moisture-induced damage, bitumen should have as low as possible moisture diffusion properties; the amount of filler in the mastic should be decided upon, on the basis of a combination of the mechanical properties of the mastic, the diffusion coefficients of the filler and the bitumen and the mastic moisture damage parameters. Furthermore, the aggregate-mastic bond strength should be maximised by keeping the moisture susceptibility parameters as low as possible; combinations of mastics with low moisture diffusion coefficients and low moisture susceptible aggregate-mastic bonds should be preferred, and it should be avoided at all times to introduce moisture into the mix before and during the time of mixing. Above all, the research in this paper shows the importance of determining the fundamental moisture susceptibility parameters and the effect they may have on the lifetime performance of asphaltic pavements. [ABSTRACT FROM AUTHOR]

The ground-penetrating radar (GPR) is a proven technology that is used typically to determine the thicknesses of pavement layers. This paper explores the applicability of the GPR to assess the density of the asphalt layer in pavements. The measurements were conducted on three test sections that were constructed using different asphalt mixtures. Each of the test sections was divided into sub-test sections that were compacted using different compaction methods and number of roller passes in order to achieve a range of asphalt mixture densities. The results showed that there was very good correlation between the GPR results and density of extracted field cores. Consequently, the paper examines the correlation between density and mechanical properties of asphalt mixtures. The results of the mechanical tests provided valuable information on the effect of density on performance. [ABSTRACT FROM AUTHOR]

This paper presents the theoretical background for the development of a constitutive model that is used in the simulation of the compaction of asphalt mixtures. The constitutive model is developed to comply with the principles of thermodynamics, and is derived to represent the macroscopic behaviour of an asphalt mixture as a highly compressible viscoelastic material. The paper presents the details of the mathematical formulation and the computational implementation of the model in the finite element package computer-aided pavement analysis 3D. The capabilities of the compaction model and its sensitivity to changes in model's parameters are illustrated using simple numerical applications. In a companion publication, (Masad et al., Finite element modelling of field compaction of hot mix asphalt. Part II: Application,International Journal of Pavement Engineering, Accepted, 2014), the model is verified against field compaction measurements which demonstrate the ability of the model to capture the general trends of the compaction observed in the field. [ABSTRACT FROM AUTHOR]

The National Cooperative Highway Research Program (NCHRP) 1-37A mechanistic-empirical pavement design guide (MEPDG) utilises the dynamic modulus of asphalt concrete in a multilayered elastic analysis to determine the primary responses in asphalt pavements. The dynamic modulus depends on temperature and loading frequency. In the MEPDG, the pulse time is used to determine the loading frequency. This methodology has been under scrutiny due to the large modulus it estimates. This paper evaluates several approximation methods, including the current MEPDG analysis, for the calculation of stresses and strains in linear viscoelastic materials by comparing analysis results with the solutions from the exact linear viscoelastic analysis. Sources of the errors that result from various approximation methods are discussed. Also, an alternative method to that of the MEPDG is proposed for determining the appropriate representative elastic modulus of asphalt concrete. [ABSTRACT FROM AUTHOR]

The detrimental effects of water in asphalt mixtures and its manifestation as distresses in asphalt pavements were first recognised in the 1930s and have been studied extensively during the last 35 years. This deterioration process, referred to as moisture damage, is generally defined as the degradation of the mechanical properties of the material due to the presence of moisture in its microstructure. Moisture damage is a complex phenomenon that involves thermodynamic, chemical, physical and mechanical processes. This paper describes the processes by which moisture damage affects asphalt mixtures. A critique of various moisture damage mechanisms is presented, followed by a review of recent work on modes of moisture transport (i.e. water permeability, capillary rise and vapour diffusion) and their relationship to moisture damage. Special attention is given to the characterisation of void structures of asphalt mixtures, which is an important factor that influences moisture transport. Finally, the paper presents a review of existing theories on the adhesive bond between aggregates and asphalt binders and the effect of the presence of moisture at the interface. The mechanisms described in the paper are complemented by a second paper that presents recent advances in moisture damage characterisation using experimental methods, analytical-based approaches (i.e. fracture mechanics, continuum mechanics, thermodynamics and micromechanics), and numerical modelling. [ABSTRACT FROM AUTHOR]

With the implementation of the Superpave mix design method, some state highway agencies have experienced significant problems in durability of hot mix asphalt (HMA) mixtures due to lower binder content. With the adoption of revised HMA specifications for the state of Maryland, it was desired to evaluate the potential risks to both agency and contractors. This was achieved by calculating the α and β risks through the construction of operating characteristic curves. Furthermore, simulation analyses were conducted for assessing the impact of the current HMA production quality on the specification tolerances percent within specification limits and mixture pay factor. The findings of this study are based on a large set of quality control and quality acceptance data since the analyses were based on 7 consecutive years of production and paving of Superpave mixtures in the state. The risk analysis indicated that the agency bears a significant risk on accepting low-quality material, and thus changes in the current State Highway Administration specification are needed and discussed in this paper. The simulation analysis illustrated that the correlation among mixture parameters had minimal impact on pay factors. Furthermore, it was concluded that the asphalt content has a more pronounced impact on the pay factor than any other mixture property. Overall, the analysis indicated that significant changes in the acceptance specifications are needed in order to reduce the risks of accepting lower quality, or rejecting good quality, HMA mixtures. Furthermore, changes of the order of 10%, 20% even 50% in specification tolerances represent feasible and currently achievable levels of production quality by the paving industry, and thus no increase in the production cost of HMA is expected. Such change in the specification tolerances is expected to promote an overall improvement in quality of Superpave mixtures in the state and the region. The approach used in this study can be used by highway agencies and the pavement industry to evaluate risks related to the acceptance of hot asphalt mixtures. The pay factor analysis can aid in adjusting pay schedules and specification tolerances for accepting higher quality materials. [ABSTRACT FROM AUTHOR]

This paper investigates the effects of Acrylonitrile Butadiene Styrene (ABS) polymer as an asphalt binder modifier on reducing the moisture susceptibility of hot asphalt mixtures. In order to recognise the efficiency of ABS polymer, repeated load tests in dry and wet conditions along with the thermodynamic parameters calculated through measuring the surface free energy (SFE) components of asphalt binders and aggregates were used. The results showed that ABS polymer caused an increase in the cohesion free energy and a reduction in the released energy of the system during stripping, indicating the reduced tendency of the system toward stripping. The results of repeated load tests supported the results obtained from the SFE method, demonstrating an improvement in moisture susceptibility of modified mixtures, especially the samples constructed by acidic aggregates. In addition, moisture sensitivity index was calculated using the thermodynamic parameters and asphalt mixtures modulus from cyclic loading tests. The results were similar to those of wet-to-dry modulus ratio and showed that ABS significantly reduced the stripping percentage of modified mixtures. [ABSTRACT FROM AUTHOR]

This paper provides a test protocol for performing creep tests on asphalt mixture beam specimens using the bending beam rheometer, and addresses the issues related to performing this test. First, a detailed sample preparation procedure is presented and the experimental data are provided to assess the consistency of this method. Then, three loading methods are investigated, and results are analysed and compared using statistical tools. Finally, a preliminary investigation on the representative volume element of asphalt mixtures at low temperatures is performed by testing beams of different sizes. [ABSTRACT FROM AUTHOR]

This study is sponsored by the Regional Transportation Commission of Washoe County to assess the impact of lime treatment on the moisture damage of hot-mixture asphalt (HMA) mixtures near Reno, Nevada. This paper presents the laboratory evaluation of lime application in HMA mixtures, mechanistic analyses of those results and an evaluation of plant-produced HMA mixtures to evaluate the variability of moisture susceptibility. The laboratory evaluation based upon resilient modulus testing detected moisture sensitivity benefits with the use of lime over multiple freeze-thaw cycles, but could not distinguish between the marinated and non-marinated laboratory mixtures. The mechanistic analysis based upon laboratory mixtures indicated similar results in terms of the presence of lime and showed slight signs of improvement with the marination process. The field variability based on tensile strength ratios (TSR) indicated that the marination process does reduce the variability of the benefits of lime treatment on moisture sensitivity. [ABSTRACT FROM AUTHOR]

The findings of an extensive literature review on bitumen and asphalt mixture ageing test methods are presented in the paper. The primary factors affecting the durability of bituminous paving mixtures, assuming they are constructed correctly, are age hardening and moisture damage. Ageing of the bituminous binder is manifested as an increase in its stiffness (or viscosity). Water damage is generally manifested as a loss of cohesion in the mixture and/or loss of adhesion between the bitumen and aggregate interface (stripping). Short-term ageing is primarily due to volatilisation of the bitumen within the asphalt mixture during mixing and construction, while long-term ageing is due to oxidation and some steric hardening in the field. Of the tests used to simulate short-term ageing, the extended heating procedures of the thin film oven test (TFOT) and the rolling thin film oven test (RTFOT) are the most frequently used binder methods. In regard to long-term binder ageing, the oxidative pressure ageing vessel (PAV) test and the rotating cylinder ageing test (RCAT) have shown the greatest potential. Asphalt mixture ageing is primarily limited to extended heating methods for loose bituminous material prior to compaction and combinations of extended oven ageing, high and low pressure oxidation and ultraviolet and infrared light treatments. [ABSTRACT FROM AUTHOR]

The high-content waste rubber powder (WRP)-modified asphalt (WRMA) has poor storage stability and tends to produce many volatile organic compounds (VOCs). This study aimed to research the influence of incorporating high-content WRP on the performance enhancement and VOCs emission of asphalt and its mixtures. The storage stability, rheological properties and cracking resistance of WRMA were tested. Further, the high and low-temperature properties of WRMA mixtures were evaluated. Additionally, the VOCs emission characteristics of WRMA mixtures were analysed. The results indicate that activated WRP has good compatibility with asphalt. The high-content of WRP can significantly enhance the high-temperature rheological properties and low temperature cracking resistance of asphalt binder, and the addition of nanometre calcium carbonate (B3) adsorbent can further enhance the physicochemical properties of asphalt binder. Moreover, compared with 70# asphalt mixture, the dynamic stability of WRMA mixture increases by about 50%, and the immersion residual stability and freeze–thaw splitting strength values increase by 6.34% and 5.98%, respectively. In addition, the B3 adsorbent can significantly reduce the VOCs emission from WRMA mixtures. The corresponding conclusions could provide guidance for the large-scale application of high-content WRMA mixtures and promote cleaner and greener products. [ABSTRACT FROM AUTHOR]

The field density of as-constructed asphalt pavements usually exhibits considerable variability. Understanding and quantifying this variability is of crucial importance for building more reliable and durable pavements. This study investigates the probability distribution of the field density based on an analytical model of gyratory compaction. The model is derived from mass balance and the transition state theory for the process of aggregate rearrangement. Meanwhile, the variability in the compaction effort is also taken into account. The model is first calibrated by the laboratory gyratory compaction experiments, and is then used to predict the probability distribution of the field density, which is compared with field measurements. It is shown that the probabilistic model can capture the left-skewed and leptokurtic features of the field density distribution. The present model surpasses the commonly used Gaussian distribution for characterising the field density distribution. A parametric study is performed to investigate the effects of the compaction properties of mixture and field compaction effort on the probability distribution of the field density. The model can potentially be used to guide the asphalt mix design for achieving the desired field density. [ABSTRACT FROM AUTHOR]

Climate change and the depletion of natural resources are causing society to adopt more environmentally sustainable approaches. In areas such as construction and civil engineering, waste and by-product valorisation could help in the fight against climate change, reducing the consumption of raw materials. Thus, the use of residues or by-products in asphalt mixture manufacturing as road pavement layers has great potential due to their characteristics. This study aimed to characterise a flotation sterile (low-grade magnesium carbonate; LG-MC) generated in the beneficiation process of natural magnesite and to analyse its potential as a filler in asphalt mixture manufacturing. The physical, chemical, and microscopic properties of LG-MC were characterised and its potential use as a filler for asphalt mixtures was evaluated using the UCL (Universal de Caracterización de Ligantes) method. The optimum filler/bitumen ratio for LG-MC was 1.49, higher than the 1.33 of calcium carbonate. Results showed a protective effect of LG-MC against ageing both in the short and long- term, reducing losses from abrasion. [ABSTRACT FROM AUTHOR]

In the present study, stress sensitivity of modified binders in the multiple stress creep and recovery (MSCR) test and its relationship with rutting resistance of the asphalt mixtures are investigated. For this purpose, different groups of styrene butadiene styrene (SBS), polyphosphoric acid (PPA) and SBS + PPA modified binders were produced; in each of which, the binders have the same continuous high temperature performance gradings (PGs) and linear viscoelastic (LVE) properties. The MSCR tests were performed at 40°C, 55°C, and at the PG temperatures of the modified binders to consider a wide range of high pavement temperatures. To depict the stress sensitivity, stress levels of 12.8, 25.6, and 40 kPa were added to the MSCR standard procedure and the non-recoverable compliance (Jnr) and percent recovery (R) parameters were obtained at all the stress levels applied. To study the rutting resistance of asphalt mixtures prepared with the same asphalt binders, the flow number (FN) and |E*| parameters were determined at 40°C and 55°C, through the dynamic creep and dynamic modulus performance tests, respectively. Results of the MSCR test show that at the temperature range considered, the standard stresses are not sufficient to enter the modified binders into nonlinear region, thus higher stress levels should be applied to assess the nonlinearity and address the true rutting potential. Results of the mixtures performance tests show great correlations with the results of the MSCR of the modified binders at the nonlinear stress levels, especially with the Jnr parameter, regardless of the test temperatures. [ABSTRACT FROM AUTHOR]

In this study, a phase change material microcapsule was produced by using cenospheres as the microcapsule shell, polyethylene glycol 2000 as the phase change material, and silica sol as the sealing material. The produced CenoPCM microcapsule was analyzed using scanning electronic microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR). The thermal properties and stability of the CenoPCM were evaluated using differential scanning calorimetry (DSC), thermogravimetric analysis (TG), and a thermal cycling test. The results showed that the phase change temperature and enthalpy of the CenoPCM were 55.7°C and 101.4 J/g, respectively, with a mass loss of 2.35% at 200°C. After 200 thermal cycles, the mass change remained stable at 2.05%. An outdoor test was conducted to assess the impact of CenoPCM on the thermal performance of asphalt mixtures. In comparison with conventional asphalt mixture specimens, the maximum temperature differences at depths of 2, 5, and 8 cm below the surface of the phase change asphalt mixture specimens were 4.9°C, 6.4°C, and 5.9°C, respectively. Finally, the influence of CenoPCM on the performance of asphalt mixtures was evaluated, revealing a promising future for its use in asphalt pavements. [ABSTRACT FROM AUTHOR]

In this study, permanent deformation potential of different asphalt mixtures subjected to the same aging condition was assessed, based on viscoelastic characteristics from the dynamic modulus (DM) test. First it was shown that the HWTT and RLPD test results were not well correlated, which might be due to the differences in the boundary condition and the impacts of moisture damage and stripping in the HWTT. The analysis results suggested that the shape parameter (γ) of the DM master-curves could be utilized to assess the rutting resistance potential of the asphalt mixtures from the RLPD test, compared to other rheological parameters such as the inflection point frequency and β. The |E*| at the RLPD test condition was well correlated to the rutting performance compared to the asphalt mixture's rutting parameter |E*|/sinδ and the |E*| at the inflection point frequency. A novel rutting parameter (VERIndex) was developed to assess the rutting resistance potential of the asphalt mixtures, which simultaneously accounts for the |E*| and slope of the DM master-curves. Thereafter, the cracking and rutting performance thresholds were proposed, and, correspondingly used in the performance space diagram to aid with implementing the balanced mix design approach using the viscoelastic characteristics of asphalt mixtures. [ABSTRACT FROM AUTHOR]

Erosion of the base layers in rigid pavements is a complex hydro-mechanical process that rapidly reduces the structural integrity of these structures. This research revisits a vertical shaking table testing method to characterise the erosion susceptibility of the materials used on base layers in rigid pavements. The procedure consists of applying a vertical vibration to a cylindrical sample of the material under evaluation, which is partially immersed in water in a cylindrical metallic container with a high-strength concrete base. The vertical movement of the sample causes a radial flow of water on its base, which induces high shear forces that eventually erode the bottom of the sample. The volumetric loss of material from the testing sample under different water velocities and pressure conditions is used to quantify its susceptibility to erosion. After presenting the theoretical principles and the numerical formulation of the hydro-mechanical erosion processes occurring in this test, the experimental method was applied to characterise the erosion susceptibility of five different materials. The results suggest that the vertical shaking experimental technique is more versatile and accurate in quantifying the erosion susceptibility of base materials than available standardised tests. [ABSTRACT FROM AUTHOR]

The tire-pavement interaction has become an important research topic in recent years as the road transportation system and automobile industry develop. The distribution of contact stress between tires and asphalt pavement caused by traffic load is nonuniform. Furthermore, the asphalt mixture is a typical heterogeneous composite material, consisting at the microscale of aggregates, asphalt binder and air voids. However, much of the previous research has tended to focus on uniform-loaded pavement structure, which is comprised of homogeneous asphalt mixture. In this study, the inhomogeneous contact stress was applied on the macroscale finite element pavement model to study the influence of footprint on the mechanical properties of the asphalt pavement. The effect of tire contact stress on asphalt mixtures was investigated using a coupling method between the pavement model and a microscale model of asphalt mixture. This proposed algorithm is capable of simulating the impact of traffic load on the pavement structure and the asphalt mixture in real situations. It is useful for gaining a better understanding of the deformation processes that occur within the asphalt mixture under the real traffic load, which cannot be derived from the conventional laboratory tests and thus is beneficial to the pavement design. [ABSTRACT FROM AUTHOR]

The use of un-conventional materials in asphalt pavements is becoming popular as DOTs in many countries started to legislate their in the paving industry. The motive behind this is to get rid of available waste while maintaining or improving the pavement performance Fly ash is among those recycled materials that can be used as a substitute for virgin aggregates inbituminous mixtures. This study investigates the effect of using Municipal Solid Waste Incineration Fly Ash (MSWI-FA) as partial or full replacement of fine aggregates and mineral filler on the performance of asphalt mixtures.. The purpose of the experimental testing program is to determine the optimal MSWI-FA replacement type and percentage to be used in asphalt mixtures. This is done through a series of dynamic modulus tests with different MSWI-FA replacement percentages. The different mixes are then ranked based on their rutting and fatigue cracking potential using simple performance indicators. [ABSTRACT FROM AUTHOR]

The high-resolution X-ray CT was applied to investigate the fatigue damage evolution of asphalt mixtures. The detailed Xray CT images in the centre of the samples were used to characterise the fatigue cracking and air voids increase at different vertical deformations. Air void content and surface area distribution before and after loading were also analysed. The results show that the main failure mode of asphalt mixtures at low temperature is debonding at the interface between aggregates and mastic, which is an adhesive failure. The maximum change of air void content due to fatigue damage often occurs near the middle of the sample. Cracks were observed in and around flat and elongated aggregates and on aggregates with insufficient fracture faces, demonstrating the effects of aggregate angularity and shape on fatigue cracking. The microcracks develop continuously throughout the entire fatigue process. [ABSTRACT FROM AUTHOR]

The permanent deformation of asphalt pavement under similar traffic conditions depends on a number of factors. The factors considered in this study are bitumen source, aggregate source, aggregate gradation, bulk specific gravity of aggregates (Gsb), percentage of aggregates passing #4 sieve, air voids (Va), optimum bitumen content, binder grade, load repetitions, temperature, and Marshall stability. Asphalt pavement analyzer (APA) test, Cooper wheel tracking test (CWTT), and repeated load axial test (RLAT) were performed on thirteen different types of hot mixed asphalt (HMA) mixtures. Three artificial neural network (ANN) algorithms, namely Backpropagation (BP), Conjugate gradient (CG), and Broyden-Fletcher Goldfarb-Shanno (BFGS) were used to analyse the data. The best fit ANN algorithm for each of the laboratory tests (APA, CWTT, RLAT) was selected, based on the coefficient of determination (R-squared), root-mean-square error (RMSE), mean bias error (MBE) and the mean square error (MSE) closest to the gamma statistic Г. The results showed no single ANN algorithm is suitable for predicting all HMA rutting susceptibility tests data. The BP algorithm most appropriately predicts APA test data, the BFGS algorithm precisely fits CWTT results, and the CG algorithm seems most suitable to predict RLAT data. However, further, differentiating testing is required for a more precise comparison of rutting predicting ability of various ANN algorithms. [ABSTRACT FROM AUTHOR]

This research recommends a mathematical modelling approach to determine flow time (FT). The scope of the work includes the collection and analysis of the static creep test data for asphalt mixtures produced using two different nominal maximum aggregate size (NMAS) values and two base binder grades. Modifiers of styrene butadiene styrene (SBS), polyphosphoric acid (PPA) and combination of them are selected to consider a wide range of testing times from 120 to 30,000 s. The FTs of the mixtures are determined using three techniques: the method developed in national cooperative highway research programme (NCHRP) Report 465, the Francken model, and the proposed mathematical model which is based on the ordinary tangent function. The results show that the NCHRP method is sensitive to the user-selected size of logarithmic scale unit of time, causing difficulties in the FT computation. It is also shown that the Francken model, often used to fit the dynamic creep curves, cannot completely fit the static creep test data, and so is not capable of estimating FT, properly. However, based on the limited data available in this study, the proposed tangent model performs very well in characterising all the three stages of the static creep curve and estimates the accurate value of FT in a reasonable time. Because of the simplicity, computational speed and accuracy of the proposed tangent model, it can be considered as an alternative to the NCHRP method to determine FT. [ABSTRACT FROM AUTHOR]

Skid resistance is a key factor in road safety. Surface friction characteristics of roads are dependent on the microtexture and macrotexture of the surface. The decay of skid resistance with time is a function of traffic level and aggregate characteristics. This study developed predictive models for skid resistance of asphalt pavements and seal coat surfaces. The researchers examined the surface friction characteristics of 35 asphalt pavement test sections and 35 seal coat test sections. The skid number was measured using a skid trailer, while the microtexture and macrotexture of the test sections were measured using a dynamic friction tester and a circular texture meter, respectively. The Aggregate Image Measurement System (AIMS) and Micro-Deval test were also used to evaluate the aggregate shape properties and its resistance to polishing and abrasion. The developed skid prediction models express the skid number over time as a function of aggregate gradation, aggregate resistance to abrasion and polishing, and traffic level. The models showed good correlations with skid numbers measured in the field. These models can be used to optimise the mix design to provide adequate level of friction and estimate the skid number of asphalt pavements and seal coat surfaces over time. [ABSTRACT FROM AUTHOR]

Asphalt aging is recognised as one of the important factors causing cracking related failures in asphalt pavements. Asphalt aging occurs during production, construction, and service life of the asphalt surfaced pavements. Since constituents of asphalt mixtures are continuously increasing (increased recycled asphalt pavement (RAP), rejuvenators, compaction aids, warm-mix additives, fibres, etc.) and interactions between these constituents are complicating the mixture design process, relying solely on the volumetric mixture design is usually not resulting in asphalt mixtures with the highest possible performance. Thus, asphalt mixture test methods for rutting and cracking should be improved and incorporated into current mixture design methods to be able to develop more durable asphalt mixtures that last for their intended service lives. In this study, the most effective asphalt mixture long-term aging protocol was determined to achieve reliable semi-circular bend (SCB) test parameters that are correlated with in-situ cracking performance. The selected aging protocol will be integrated into the balanced mix design procedures that are currently being developed. Developed asphalt mixture design methods are expected to improve the longevity of asphalt materials, reduce life-cycle costs for agencies, and improve long-term road users' comfort. [ABSTRACT FROM AUTHOR]

Flow number (FN) test, which evaluates permanent deformation (PD) of asphalt concrete (AC) mixtures, contains data noise that leads to a false representation of the tertiary stage of flow. Most studies, however, ignore this aspect and have not quantified the amount of noise in the data. This, in turn, leads to unrealistic characterisation, ranking of AC mixtures and correlation of FN with other factors such as mix volumetric, aggregate parameters and dynamic modulus. As such, this study quantifies the extent of noise in the FN data and its consequent impact on characterisation of PD behaviour of AC mixtures. Twelve AC mixtures were prepared with different aggregate gradations and binder grades, and FN test was performed at a single temperature. Statistical analysis confirms that the corrected FNs and the original FNs are statistically different from each other. Moreover, all of the AC mixtures are characterised with and without data noise, and it is concluded that noise in the data has a significant influence on the ranking of AC mixtures. Furthermore, the results indicate data noise either reverses the expected sign or reduces coefficient of determination of correlation. The results of this study would have insightful implications on findings of earlier studies. [ABSTRACT FROM AUTHOR]

Asphalt mixtures exhibit deterioration in properties due to several factors; one of these factors is the moisture damage. Many kinds of research have focused on this matter in Iraq; however, up to now, the pavement is suffering from moisture failure due to the penetration of surface water. Asphalt concrete is modified in this research by adding anti-stripping agent and polymer to withstand the moisture damage that occurs in the pavements. Key factors to enhance the mixtures to withstand the damages due to moisture are aggregate–binder cohesion and adhesion. Therefore, the aim of this research is to evaluate the effect of the addition of the anti-stripping agent and the polymer on the moisture susceptibility of asphalt concrete mixtures before and after conditioning. Indirect tensile strength test, Marshall test, and double punching shear test are used to satisfy the evaluation of the mixture properties. The anti-stripping agents that are used were WetFix with styrene butadiene styrene (SBS) polymer with different percentages. It is found that the modified asphalt mixture has good mixture properties in terms of Marshall stability, retained Marshall stability, and better resistance of moisture and stripping. It has been found that the addition of 0.5% WetFix and 3% SBS polymer maximizes the properties among other percentages. It is also observed that the mixing technique of modifiers is important to the resulting performance of asphalt mixtures. [ABSTRACT FROM AUTHOR]

Cracking in asphalt pavements is the net result of fracture and healing. The ability to accurately measure and predict the appearance of cracking depends on being able to determine the material properties that govern the rate of development of these two contrary aspects of cracking. This study is devoted to identifying the datum material properties in undamaged samples. It will make use of viscoelastic formulations and of well-known mechanics concepts the way in which these properties are altered by the composition of the mixture. Also introduced in this study is a process that makes extensive use of the pseudo-strain concept in decomposing the strain components. One of the many benefits of this approach is the ability to measure the fatigue endurance limit of an asphalt mixture with a simple test that requires only half an hour. The study begins with a detailed discussion of these concepts and properties and the test methods that simply and accurately measure them. One of the great advantages of using mechanics is that it provides a rapid and efficient way to predict the rate of appearance of the two aspects of pavement cracking, fracture and healing. Mechanics requires the use of material properties. An accurate and efficient determination of undamaged material properties is fundamental and important to the prediction of the performance of asphalt mixtures. It is found that the undamaged properties of an asphalt mixture are different when they are loaded in tension or in compression and this distinction is important. This study addresses the efficiency of the laboratory testing methods, and the effects of the volumetric material components and environmental factors such as temperature and ageing on the undamaged material properties. It also introduces the non-destructive tests that must be made in order, subsequently, to measure the damaged properties of the same materials. [ABSTRACT FROM AUTHOR]

The response and degradation of the hot mix asphalt (HMA) materials used in pavement structures are affected by their inherent heterogeneity. The objective of this work is to study the impact of two different sources of HMA heterogeneity in the uncertainty of the mechanical moisture degradation of HMA. The first source of heterogeneity is the spatial variability of the properties of the bulk fine aggregate matrix (FAM) of the mixture, and the second is the location and shape of the coarse aggregate particles. The heterogeneity of the bulk FAM phase was modelled using a random field technique, while that of the coarse aggregates was accounted for by randomly generating realistic probable sets of aggregate particles. Thus, ‘computational replicates’ of HMA microstructures were generated and subjected to moisture diffusion and mechanical loading using a finite element approach. In the mechanical simulations, a non-linear viscoelastic moisture damage constitutive relationship based on continuum damage mechanics theory was selected to characterise the response of the bulk FAM phase. The results show that conducting computational simulations with realistic HMA microstructures that properly capture the heterogeneity of the material is useful to quantify the mean values and dispersion (i.e. uncertainty) associated with the response and degradation of the mixture. This information, which cannot be easily obtained in the field or in the laboratory due to the difficulty of acquiring a sufficient amount of data, is useful to conduct structural reliability analysis and to predict the life cycle behaviour of the material. [ABSTRACT FROM AUTHOR]

To improve the uniformity of the temperature and electromagnetic fields of asphalt mixtures heated by microwaves, the structure of a horn antenna is examined. The length and width of the feed waveguide are calculated as 85 mm and 55 mm, respectively, according to waveguide theory. The height of the antenna only slightly influences gain distribution according to the radiated electromagnetic field. The length-width ratio of the aperture plane of the antenna affects the uniformity of distribution of the electromagnetic field. When the ratio is the same as that of the feed waveguide, the gain of the electromagnetic field is the most evenly distributed. The farther the ratio deviates from that of the feed waveguide, the more intensively the electromagnetic field transmits. However, the simulation result indicates that the antenna with the most uniform distribution of electromagnetic field reflects the most energy. [ABSTRACT FROM AUTHOR]

The saturation ageing tensile stiffness (SATS) procedure is the first laboratory asphalt mixture durability protocol to combine moisture damage and oxidative ageing during the conditioning of asphalt mixtures prior to mechanical testing. However, the application of the SATS procedure has tended to be predominantly targeted at base materials with relatively ‘hard’ binders and overall high stiffness modulus requirements and is considered potentially too severe for more standard asphalt mixtures. This research study focused on understanding the effect of changes to the SATS conditioning parameters on the relative moisture damage assessment performance of asphalt mixtures, particularly ‘softer’ binder, high binder content and, finally, low air void content mixtures. Using four different aggregate types, together with ‘hard’ 10/20 pen and ‘softer’ 40/60 pen bitumen, the parameters of pressure, temperature and duration were altered, either one at a time or in combination, to arrive at a suitable combination for testing more commonly used 40/60 pen material. The optimum combination of parameters to allow the SATS procedure to be used for a wide range of typically used asphalt mixtures was found to be 0.5 MPa pressure, 85°C temperature and 24 h duration. The revised SATS durability conditioning protocol was still able to successfully discriminate between ‘poor’ moisture susceptible aggregate and ‘good’ material. [ABSTRACT FROM AUTHOR]

A recent study at Arizona State University has shown that the phase angle, φ, was a good laboratory parameter to distinguish the asphalt mixture's tyre/pavement noise characteristics in the field. The phase angle is obtained simultaneously from the E* dynamic complex modulus test (AASHTO TP 62-03). In particular, the peak or maximum phase angle obtained from the range of the E* test frequencies provided the best indication of the mixture's noise-dampening response. The objective of this study was to utilise the φ-E* relationships to develop appropriate master curves for the phase angle parameter. In addition, the objective was to develop predictive phase angle models so that they can be used to assess the dampening response, and therefore the tyre/pavement noise characteristics of the different asphalt mixtures. E*-φ results from 217 conventional and crumb rubber-modified asphalt mixtures were used in the analysis. The beta distribution was found to best fit the phase angle master curve relationship and the statistical goodness-of-fit parameters were found to be excellent. Phase angle predictive equations were modelled with combinations of mixture properties such as aggregate gradations, binder viscosity-temperature susceptibility parameters, asphalt content, mixture air voids, temperature and loading frequency. Over 6510 data points were included in the development of the phase angle predictive equations. They included equations for both conventional and crumb rubber-modified mixtures. The predictive equations had very good to excellent goodness-of-fit statistics. [ABSTRACT FROM AUTHOR]