Paving Materials and Pavement Analysis

This paper presents a newly developed accelerated polishing device used in the laboratory as a screening tool for selecting high polishing-resistant and high-friction aggregates and for optimizing the mix design to ensure satisfactory field performance in terms of preventing premature loss of friction due to vehicle tire-pavement surface polishing and wearing actions. The accelerated polishing equipment can test two types of Hot Mix Asphalt (HMA) specimen sizes: one is the 15.24 cm diameter gyratory compacted specimen, and the other one is the 45.72 cm by 45.72 cm by 5.08 cm slab specimen made by a roller compactor. The repeatability of the test results was confirmed through a series of testing and statistical analysis. Also, the polishing and friction performance of HMA specimens made by different aggregates and compaction methods (gyratory vs. roller compaction) was compared.

When designing pavement, engineers must optimize some requirements such as user safety (skid resistance), environmental impact (noise, rolling resistance...)... However, this skid resistance evolves during the entire pavement life. So it is a common practice to perform laboratory tests to forecast the evolution of skid resistance. Previous works done in the French Laboratory of Bridges and Roads (Laboratoire Central des Ponts et Chaussées, LCPC) have identified phenomena such as binder removal, aggregate polishing and seasonnal variations to be responsible of these variations. This paper focuses on the polished stone values of aggregates and the aging of asphalt on the evolution of pavement skid resistance. Skid resistance of different specimens of nude aggregates and asphalt mixes that are submitted to polishing and aging was studied. On skid resistance point of view, aging of aggregates can be neglected in comparison to those of asphalt. Rocks with high polishing resistance offer less variation of skid resistance. Aging of asphalt tends to increase skid resistance until 12 month and remains this latter constant after.

The presence of excess pore water in the bitumen stabilized materials (BSMs) can result in a rapid deterioration due to moisture damage. The process associated with moisture ingress and damage is complex and can occur over an extended period in-service. In the absence of a research method that realistically simulates the possible mechanisms of moisture damage, a surrogate, laboratory-based moisture conditioning method was developed. This method aims to accelerate the ingress of moisture into the mix so that the evaluation of its effect on mixture stiffness (Mr) and shear parameters (C & φ) can be made. This paper presents the results of an experiment aimed at determining whether cyclic pulses of water under pressure into BSMs induce sufficient, measurable damage to a triaxial specimen that will distinguish between BSMs with different levels of resistance to moisture damage. An additional constraint for the simulation procedure was the allowable time and cost, i.e. the conditioning has to be accomplished within a reasonable length of time with simple, cost effective laboratory equipment. The evaluation of moisture damage in this experiment was carried out using the newly developed "Moisture Induction Simulation Test" (MIST) device and triaxial testing. Mix compositions of aggregate blends with and without RAP, with different bitumen binder types (foamed bitumen or bitumen emulsion) and active filler types (cement or lime) and contents, were investigated. The findings presented in this paper show that cyclic water pressure can be used to simulate accelerated moisture damage on triaxial specimen enough to distinguish between the mixture of high resistance and high susceptibility to moisture damage. Importantly, validation of MIST device using the known laboratory Model Mobile Load Simulator (MMLS3), a one-third scale accelerated pavement tester (APT) device, shows agreeable ranking of BSMs for MMLS3 and the MIST-triaxial combination, in terms of moisture resistance.

This paper presents a method for identifying a practical dynamic modulus testing procedure. The currently well adopted method of calculating the dynamic method is discussed and a more fundamental dynamic modulus calculation method is proposed in this research. A comprehensive shakedown test was performed the dynamic modulus test on one asphalt mixture. The analysis results show no permanent damage was found on tested specimens for all three test temperatures. Comparison of the master curves built by different temperature and frequency combination shakedowns the redundant test temperature and frequency. A more practical dynamic modulus test procedure is developed using this shakedown method. This research shows that three test temperatures, 4.4, 21.1 and 37.8°C, and six frequencies, 25, 10, 5, 1, 0.5 and 0.1Hz are adequate to build a smooth master curve for asphalt mixtures.

In the highway tunnel, the asphalt pavement will be used more and more common, and the corresponding fire-retardant asphalt technology research and application is still lacking. In the future, the study should be focused on the special asphalt flame retardant and the processing technology research. Using flash point and ignition point could not distinguish the combustion ability between different types of asphalt with different amount of flame retardant. The oxygen index method could evaluate the sustained combustion performance of asphalt. Based on the oxygen index method used in textiles, put forward a primary oxygen index test method for asphalt. The asphalt flame-retardant evaluation method and standard also should be further refined and adjusted in the future research and application. From the performance test results, it could be found that the addition of fire-retardant is benefit for the pavement-performance of asphalt. For the Magnesium hydroxide agent, the amount of 8% could result in compositive optimal performance of asphalt.

Utilization of reclaimed asphalt pavement (RAP) aggregate in highway projects has become common practice in the United States because it has considerable environmental and economical advantages. This study evaluates the resilient modulus (M_r) of a crushed RAP on its own, a basaltic virgin aggregate (VA) on its own as well as when the two are bended for use in pavement base and subbase courses. A series of laboratory tests were conducted to assess their fundamental properties including M_r. Test results show that under the same stress conditions, the resilient modulus of pure RAP is higher than that of VA. The factors influencing M_r are discussed and a model that captures the variation of M_r with stress level, water content and density is proposed. This model is capable of incorporating the effect of percent RAP on M_r. This M_r model will help engineers design roads using recycled materials more expediently, thereby aiding the profession's march towards greener highways.

This paper introduced fractal theory to the description of gradation of asphalt mixture. The feasibility of description of RAP gradation by fractal theory was firstly discussed. The fractal dimension calculated by Least Square Method (LSM) was employed to evaluate gradation of RAP. Compaction tests, surface-dry condition method tests and indirect tensile strength tests were then employed to evaluate physical and mechanical performance of RAP mixtures stabilized by foamed asphalt. Relationships between fractal dimension and test results were studied. It seems that the fractal dimensions are of relevance to the performance of cold-recycling asphalt mixture. And this points out a new direction of RAP research field.

The objective of this laboratory study is to utilize the semi-circular bending (SCB) test to evaluate the effect of reclaimed asphalt pavement (RAP) on the cracking resistance of asphalt mixtures. Two type of SCB test, the tensile strength and the fracture test, were conducted on a gravel mixture containing four percentages of RAP. The results show that RAP generally increased the SCB tensile strength but significantly decreased the post-failure tenacity of asphalt mixtures. RAP also decreased the J-integral of asphalt mixture and therefore its cracking resistance. Both short-term and long-term aged asphalt mixtures exhibited similar trend in evaluating the effect of RAP.

A series of unconventional unconfined uniaxial compression tests were performed on cylindrical specimens of compacted hot-mix asphaltic concrete. Not only continuous monotonic loading tests at different constant strain or load rates but also sustained loading tests and minute cycles of unload/reload during otherwise monotonic loading were performed. Axial and radial strains were measured locally respectively by a pair of local deformation transducers (LDTs) and a set of three clip gauges. Therefore, it becomes possible to precisely evaluate: 1) initial Young's moduli (E_o) and Poisson's ratios (V_o); 2) equivalent elastic Young's moduli (E_eq) and Poisson's ratios (V_eq) for different axial stress values; and 3) tangential stiffness values (E_tan) and Poisson's ratios (V_tan) which vary with an increase in the axial stress. Then, it becomes possible to predict the deformation of HMA from a given loading history based on the elastic theory when all parameters above can be determined.

The objective of this paper is to capture variability from different extraction and recovery procedures. In recent years, state agencies emphasize on grading plants depending upon their RAP stockpile variability. Depending upon this grading of the plants, maximum allowable percentage of RAP for the plants will be determined. The recent NCHRP 9-33 manual "Mix design manual for Hot Mix Asphalt" gives procedure to determine RAP stockpile variability. The different extraction and recovery methods give different allowable percentage of RAP. This paper evaluates impact of different extraction recovery procedure on RAP binder property and allowable percentage of RAP which is determined by considering RAP aggregate gradation and RAP binder content. Selection of appropriate combination of extraction recovery method will not only grade the plant on uniform basis but also lead to more precise determination of allowable percentage of RAP.

Asphalt mixtures are granular composite materials stabilized by the presence of asphalt binder, compaction of which is one of the most important factors affecting the performance of asphalt pavement. And the quality level of compacted asphalt mixtures relies greatly on the compaction temperature determined roughly by the viscosity test of asphalt binder. So, the method for determining compaction temperature can not consider interaction between viscosity of asphalt binder and aggregate properties, such as gradation. Based on the test results of two kinds of asphalt mixtures with different combined aggregate gradations and same binder, the effects of aggregate gradation on compaction temperature are investigating in this paper.

Due to the limitation of traffic condition and paving equipment, longitudinal joint is an unavoidable and common problem in hot mix asphalt (HMA) pavement construction. These longitudinal joints between lanes of HMA pavements are generally susceptible to moisture and other failures and have been one of the major problems for HMA pavements. Joint heater is one of the common techniques to improve the quality of longitudinal joint construction. This paper presents the results of a laboratory study of evaluating effects of joint heater on longitudinal joints. A test field project was conducted to evaluate the effect of joint heater on longitudinal joints and specimen cores along the longitudinal joints were taken in both conventional section and heat-treated section. Air voids, permeability tests and indirect tensile test were conducted on those field specimens. The test results showed that, with proper temperature control, the joint heater can significantly improve the behavior of pavement around longitudinal joints and is a very useful technique in improving longitudinal construction quality.

Warm mix asphalt (WMA) technologies have been developed to mix, transport, pave, and compact asphalt mixture at temperatures up to 40°C lower than the conventional hot-mix asphalt (HMA). The benefits of WMA include energy savings, lower CO₂ emissions, and reduced workers' exposure to fumes, reduced binder ageing, and faster release of pavement to traffic due to shorter cooling time. Since it was introduced into Shanghai, China in 2006, WMA has been successfully used in more than 10 projects, including expressways and viaducts. The WMA in these projects performs well so far. This paper presents some of these WMA projects in Shanghai.

Bituminous mixture is generally considered as isotropic. Nevertheless, its compaction on roads or in laboratory induces anisotropic properties. Anisotropic properties of bituminous mixtures compacted with a French LPC wheel compactor are highlighted in this paper, in the linear viscoelastic domain. Tension-compression complex modulus tests have been performed on parallelepipedic specimens in two directions, i) direction of compactor wheel movement (direction I) and ii) direction of compaction (direction II). These tests consist in measuring sinusoidal axial and lateral strains as well as sinusoidal axial stress, when sinusoidal axial loading is applied on the specimen. Two parameters are investigated, loading frequency and temperature. Two complex moduli, E_I* and E_II*, and four Poisson's ratios, ν_{II I}*, ν_{III I}*, ν_{I II}* and ν_{III II}*, can be obtained. The vertical direction appears softer than the other one for the highest frequencies. There are few differences between the two directions I and II for parameters concerning viscous effects (phases angles φ(E_I) and φ(E_II), and shift factors). The four Poisson's ratios reveal anisotropic properties. In addition modeling using anisotropic version of the "2S2P1D" model developed in our laboratory at ENTPE fits well the data.

The deformation of asphalt mixtures can be well described by a generalized Maxwell viscoelastic model, which Prony series coefficients are obtained via static creep tests of AC-13C unmodified and modified asphalt mixtures. A half-sinusoidal load with 0.1s loading duration and 0.9s unloading duration is used to simulate the dynamic vehicle load, and the strain of AC-13C unmodified and modified asphalt mixtures under repeated load is analyzed by viscoelastic finite element method, then we obtain an excellent correlation with the measured strain. The results shows that the viscoelastic finite element method together with the parameters determined by the static creep test could well predict strain of asphalt mixtures under repeated load, and these analysis could be used in permanent deformation prediction of asphalt pavement under moving loads.

Asphalt mixtures are a composite material consisting of asphalt binder, coarse and fine aggregates, mineral filler, and air voids. The overall behavior of an asphalt mixture is dependent on the properties and volumetric fractions of its individual constituents and their interactions, which is predictable with micromechanical models. This study evaluates the applicability of four different micromechanical models for predicting dynamic modulus of asphalt mixtures. The four models included a 3-D two-layered model, a differential model, the Composite Sphere model, and the Generalized Self-Consistent (GSC) model. The evaluation shows that the predicted dynamic modulus from the differential model were reasonably close to the measured value whereas the other three models under-predicted to some degree the dynamic modulus of asphalt mixture.

This study presents an approach to formulize asphalt concrete stiffness for specific microstructures. An asphalt concrete was designed on the basis of the Superpave mix design method. Its images were obtained from X-ray Computed Tomography (X-ray CT). Through processing those X-ray CT images, two-microstructure-based models, namely the Model-I and the Model-II were rebuilt on the basis of the discrete element (DE) method. In Model-I, no air void was included, while in Model-II, the air void level was 3.1%. The DE simulation of the asphalt concrete was conducted with those two models whose primary inputs were the stiffness values of both coarse aggregate and asphalt sand mastic. The asphalt sand mastic was defined as a sub-mix of fines, fine aggregate (less than 2.36mm), and asphalt binder. Through regression analysis of the DE simulation results, the asphalt concrete stiffness values were formulized into two analytical equations for Model-I and Model-II, respectively. A potential application of those two equations is to predict effective stiffness values of the asphalt concrete at various temperatures and different loading conditions. At the end of this study, an application example is provided. It was found that compared with the measured data, the formulized equation of Model-II could more precisely predict the asphalt concrete dynamic moduli at various temperatures and different frequencies than other models.

This study developed micromechanical finite element (FE) models for simulating the viscoelastic behavior of asphalt mixtures. The two-dimensional (2D) microstructure of asphalt mixtures was captured by optically scanning the surface image of sectioned specimens. FE mesh of image samples was generated within each aggregate and asphalt mastic. Along the aggregate boundary, the FEs share the nodes to connect the deformation. The micromechanical FE model was accomplished by incorporating specimen microstructure and ingredient properties (viscoelastic asphalt mastic and elastic aggregates). The generalized Maxwell model was applied for viscoelastic asphalt mastic with calibrated parameters from nonlinear regression analysis of the mastic test data on dynamic modulus and phase angle. The displacement-based FE simulations were conducted on the digital sample under sinusoidal cyclic loadings. The predicted dynamic modulus and phase angle were compared favorably with the mixture test data over a frequency range. The simulation results of the asphalt mixture samples have good correlations with the numerical calibration of asphalt mastic specimens. These results indicate that the developed micromechanical FE model can provide a computational tool for predicting the global viscoelastic properties of asphalt mixtures with captured microstructure and ingredient properties.

The properties of recycled aggregate concrete (RAC) incorporating mineral admixture including fly ash and slag were studied through laboratory tests and practical project. The test results indicated that by adding fly ash, the apparent density of RAC reduced significantly, and the workability of RAC improved observably. The ratio of tension strength to compression strength and the ratio of splitting tensile strength to compressive strength of RAC both increased, so the tensile capability were improved and the frangibility reduced, which were helpful to improve the crack resistance and volume stability of road RAC. The abrasion resisting property of RAC was improved. The project application of RAC showed that the compression strength of the concrete adding 80~100% recycled concrete coarse aggregate could reach C35 (35MPa~40MPa) and the flexural strength could be higher than 5.0 MPa at 28 d, both of which satisfied the requirement in the heavy and special heavy traffic road, and could open to traffic at 3 d. The overall performance of RAC pavement were excellent, and without dehiscence after working one year.

The present research was designed to study the mechanical properties of typical portland cement concrete (PCC) used in Iowa pavements. These properties are required as input values by the AASHTO Mechanistic-Empirical Pavement Design Guide (MEPDG). In this research, over 20,000 data were collected, compiled, and statistically analyzed. The typical input values of Iowa pavement concrete, such as 28-day compressive strength (f' _c), elastic modulus (E_c), modulus of rupture (MOR), and splitting tensile strength (f' _sp), were obtained and compared with the MEPDG default values. The relationships among Iowa concrete material properties were established through nonlinear regression analyses. The results of the study indicated that Iowa has a good documentation on the compressive strength of pavement concrete produced during the last few decades, but there were severe shortage of complete sets of concrete test data on the properties that are required by the current MEPDG. As a result, appropriately documenting complete sets of concrete properties, including MOR, E_c, and information on concrete mix design, is essential for updating the typical material input values and providing rational prediction equations for concrete pavement design in future.

A laboratory investigation was conducted to determine the coefficient of thermal expansion (CTE) of typical concrete paving mixtures made with coarse aggregate from eight different sources in the state of Michigan, USA. The primary aggregate class included limestone, dolomite, slag, gravel and trap rock. The Three replicate test specimens were fabricated for each mixture-age combination. The test specimens were moist cured for 3, 7, 14, 28, 90, 180, and 365 days prior to testing. CTE was determined using two methods: 1) The provisional AASHTO TP60 protocol and 2) A revised test procedure based on AASHTO TP60 developed at the University of Texas at Austin. The average measured 28-day CTE values ranged from 8.11 μ∊/°C to 10.65 μ∊/°C based on AASHTO TP60 method and 8.12 μ∊/°C to 10.80 μ∊/°C based on the revised method. In this paper, the CTE results based on the two aforementioned test procedures are compared using statistical methods and analyses. Furthermore, the paper discusses the practical impact of the statistical results by investigating the transverse cracking performance of jointed plain concrete pavements. The Mechanistic-Empirical Design Guide (M-E PDG) software developed by National Highway Cooperative Research Program (NCHRP) was employed for this investigation.

Cement-stabilized recycled aggregate base course material was prepared with lower quantities of ordinary Portland cement (only 4% and 5% by weight) and recycled aggregate replacing 30%,40%,50%,60%,75%,80%,90% and 100% of crushed stone. Compaction, un-confined compressive strength and dry shrinkage of mixture were tested. The effects of recycled aggregate replacing levels and cement dosage were analyzed based on compaction test. The results showed that the use of 100% recycled concrete aggregates increased the optimum moisture content and decreased the maximum dry density of base course materials compared to those of natural base materials. The effect of recycled aggregate replacement on un-confined compressive strength was discussed at 7, 28 and 90 days. The relational model between recycled aggregate replacement and un-confined compressive strength were established. The results of dry shrinkage tests showed that the ratio of dry shrinkage of the base materials prepared with recycled concrete aggregates increased with the increase of replacement levels of recycled concrete aggregates. The primary mix proportion parameters were determined with maximum replacement of recycled aggregates, meeting the requirements of base course road performance and lower costs.

Because of some drawbacks including low strength, poor dimensional stability, low abrasion resistance, easy to crack and other shortcomings, Portland cement concrete has been limited in its use as a dominant pavement material in highway construction. This paper studied the feasibility of making high performance pavement concrete by adding 20~40% of high-quality composite ultra-fine fly ash (CUFA) technology to achieve high-performance of concrete roads. The test results indicated that, with cementitious material content of 360~400 kg/m³ and CUFA content of 20%~40%, adding CUFA improved the workability of concrete significantly; in the meantime, the 28d compressive strength was as high as 50 MPa, and the later strength of concrete continued growing. The designed concrete satisfied the requirements of opening to traffic 3 days after construction and heavy and extra heavy traffic in 28 days. The durability, especially the abrasion resistance, and the crack-resistance were improved significantly.

The particle size distributions of the mixture of fly ash, slag and cement were studied. The micro gradation of the mixture of fly ash and slag, also named as Ultra Fly ash and Slag (UFS), was analyzed and optimized. The properties of cement mortar containing fly ash, slag and UFS were studied through laboratory tests. The hydration of UFS when adding the activator was also analyzed. Test results indicated that best ratio of fly ash to slag was 4:1, which would achieve the best filling effect, much better micro gradation and the highest density for UFS, and thus improve the early strength. Both the early and late stage strength of cement mortar containing fly ash was lower than those of the cement mortar containing slag or UFS. At the environment provided by the activator, the strength performance of cement mortar would be highly improved because of the secondary hydration of the cementitious material due to the water reducing and densifying effect of the UFS.

An improved solution algorithm based on Finite Element Method is adopted to analyze rigid pavements under moving vehicular or aircraft loads. Analysis is based on the classical theory of thick plates resting on two-parameter elastic soil medium. The pavement is discretized by four node thick plate elements that account for the transverse shear deformation and bending. The underlying soil medium is modeled by Pasternak shear layer and linear elastic spring and dashpot systems. The dynamic interaction between the moving load and the pavement is considered by modeling the vehicle by spring-dashpot unit. The pavement-vehicle interaction force is modeled with Dirac-delta function. It has been observed that the dynamic interaction between the moving load and the pavement has significant effect on pavement response.

The CSIR Built-Environment, in conjunction with the University of Pretoria and the Cement and Concrete Institute of South Africa, developed a low cost option for the upgrading of unsurfaced (gravel) roads. The proposed solution is the placing of a thin layer of normal concrete reinforced with 5.6mm diameter steel with a mesh grid size of 200mm. This thin layer is placed on top of the existing unsurfaced road with minimal preparation to the existing road surface using labour-intensive construction methods. Through full-scale trials this type of upgrading proved to be adequate for low-volume traffic applications (e.g. residential streets) as well as for higher-volume applications (e.g. bus routes). During the trials test sections were subjected to a total of over 700,000 ESALs over a period of 5 years without showing any deterioration. In order to determine the structural capacity of this type of overlay full-scale Heavy Vehicle Simulator (HVS) tests were conducted. This paper summarizes the first results from the accelerated pavement testing (APT) tests and is aimed at building confidence in the use of Ultra Thin-layer Reinforced Concrete Pavement (UTRCP), with cognizance being taken of the pavement structure, support conditions, construction, climate and traffic.

Voids beneath slab is one of the common distresses of cement concrete pavement, which seriously influences the service ability and the tired life-span of the cement concrete pavement, and the Falling Weight Deflectometer(FWD) gets more and more applications on identifing the voids beneath the cement concrete slab because of its advantages such as speediness, nondestructiveness, etc. The formula for calculating the stresses, strains and deflections of the PCC pavement slab are deduced for different void shapes, and the displacement calculation models of the slab are established for winkler foundation, then the displacements for different void size and position are solved, and also the deflection basin curves are simulated. Through contrasting the deflection curves with voids and without voids beneath slab, the comparison analysis method for identifying the voids beneath slab is put forward based on the FWD measured deflection data. By applying this method in engineering, it is showed that it is a brief and effective method for evaluating the voids for PCC pavement. The achievements of this paper offer a new method and theoretic support for identifying the voids of concrete pavement.

Slab void is one of the most serious diseases. Maintenance workers need to repair them in time otherwise the whole slab will be damaged. It is very important to ensure the engineering quantity in maintenance. The pavement diseases analysis model relating to void have been established and the weight are calculated by FAHP. Heavy traffic loads have an effect on void, thus the traffic grade affection coefficient ξ to modify the calculation model has been introduced in order to meet the practice. Damage blocks are multiplied by corresponding weight and traffic grade affection coefficient, and then the void ratio is the sum blocks calculated divided by the whole blocks. The results of test section in Hunan expressway show that void ratio estimation by FAHP is contiguous to that by FWD (Falling Weight Deflectometer). In view of this, the method has good practical significance in void slab treatment plan.

This paper summarizes the results of a study that was conducted to compare the performance of new generation asphalt treated base (ATB) mixtures to unbound granular materials (UGM) currently used in construction of base layers. A laboratory testing program was initially conducted on two types of ATB and UGM materials. The program included performing permanent deformation and resilient modulus repeated loading triaxial on the UGM materials. The dynamic modulus and flow number tests were used to examine the intermediate and high temperature response of the ATB mixtures under cyclic loading. In addition, the new Mechanistic Empirical Design Guide (MEPDG) software was used to compare the performance of pavement sections with ATB mixtures to existing pavement sections. The results of the laboratory testing program showed that the asphalt treated base mixtures have several folds improvement of UGM in terms of stiffness and permanent deformation resistance. In addition, the MEPDG analysis showed that pavement sections with ATB mixtures exhibited much lower rutting and fatigue cracking than the conventional pavement section.

Six asphalt pavement test sections with five base materials (i.e. four chemically stabilized base materials and a crushed stone) were tested under accelerated loading. The performance of test sections was analyzed based on the instrument responses, field non-destructive tests as well as forensic investigation. Among four chemically stabilized base materials, both slag and fly ash stabilized Blended Calcium Sulfate (BCS) bases performed significantly better than a crushed stone base course. However, two foamed asphalt (FA) treated base materials exhibited an inferior field performance than the stone base studied. Field measurements indicated that the majority of test sections failed due to rutting. To predict the rutting development, a modified plastic model was introduced in this study and subsequently implemented into a finite element (FE) simulation analysis. The FE simulation results indicated that the predicted rutting development on selected test sections agreed reasonably well with the measured deformation results.

In many states, the use of RAP in surface, base, and sub-base courses is limited and large quantities of RAP aggregate remain unused. To explore the possibility of more or complete use of milled RAPs, it is necessary to study physical and mechanical properties of RAPs. In this study, RAPs from two sources were selected. Binder contents and properties of coarse and fine aggregates after removing asphalt binders were determined. RAPs were also tested for their maximum densities and California Bearing Ratios (CBRs). The influence of binder contents and aggregate properties on the physical and mechanical properties of RAPs was discussed. The binder content of RAPs was found to be higher than that in the original mix designs. The coarse aggregate angularity (CAA) of the RAPs was increased compared to that of the original mixes. The combined bulk specific gravities of aggregates from RAPs decreased slightly as compared with those in the original mixes. The percentage of fine particles in the RAPs was increased from that in the original mixes. The RAP with a higher binder content and a lower fine aggregate angularity had a higher optimum moisture content, a higher maximum dry density, and lower CBR values. The aggregates from the RAPs were not of uniform hardness based on the LA abrasion tests.

In-place recycling of asphalt pavement is an inexpensive and sustainable pavement rehabilitation method. Existing Hot Mix Asphalt (HMA) layer is pulverized and blended with some of or the entire base course to form a broadly graded material referred to as recycled pavement material (RPM). RPM can be compacted as the new base course and overlaid by a new layer of HMA. Additives may be added to improve the properties of RPM base course, such as cement or fly ash. In this study, three flexible pavement sections with different base materials were constructed at MnROAD test facility to evaluate the RPM with and without fly ash additive and to compare them with conventional crushed aggregate base course, Minnesota Department of Transportation Class 6 aggregates. The fly ash used was a high carbon and high calcium content off-specification self-cementitious fly ash. Various field tests were conducted, using dynamic cone penetrometer, lightweight deflectometer, soil stiffness gauge, and falling weight deflectometer. The backcalculated modulus of base materials from these field tests were compared with each other and with the resilient modulus from laboratory tests. It was found that there are significant differences in the moduli from different test methods. It is believed that this is due to the stress and strain dependence of these materials. However, in any case, the fly ash stabilized RPM has higher modulus than RPM, followed by Class 6.

In Alaska, granular base course materials, typically known as D-1 aggregate materials, undergo significant changes in resilient properties due to seasonal conditions. In the springtime, saturated base course materials are weakened due to thawing, resulting in reduced resilient properties. This paper investigates seasonal effects on the resilient modulus (M_R) of a D-l material from southeast Alaska. Experimental work was performed on a granular material to investigate the impact of fines content, moisture and temperature on its resilient modulus. A frost heave/freezing cell was designed to condition soil specimens prior to resilient modulus testing. Depending on its thermal state, two separate prediction models were used to estimate M_R of the D-l material.

This paper presents the application of Analysis of Variance (ANOVA) approach to study effects of different aggregate properties on the resilient modulus behavior of unbound aggregates. In a recent research project at the University of Illinois, stress-dependent resilient modulus characterization models, in the form proposed for use by the Mechanistic Empirical Pavement Design Guide (MEPDG), were established for three different aggregate types (dolomite, limestone, and uncrushed gravel) using a statistically well-formulated laboratory test matrix. Such a consistent database enabled the evaluation of the model parameter dependence on different aggregate properties, such as particle shape, type and amount of fines, and moisture condition, using the Analysis of Variance (ANOVA) approach. From the statistical analyses, aggregate particle type or angularity was found to have a significant effect on the resilient moduli. At low fines content, the type of fines and moisture state in relation to optimum moisture condition were found to be somewhat insignificant as far as the regression parameter values are concerned. The effect of amount of fines became quite significant especially when the amount of fines was increased.

Aggregates used in asphalt concrete should be tough and durable to withstand HMA production, transportation, construction, traffic loads and environmental effects. Aggregate morphology not only plays an important role in aggregates' mechanical properties but also influences the asphalt pavement skid resistance. The Micro-Deval apparatus, which can evaluate aggregates' hardness or wear resistance, was used for assessing the polishing resistance of aggregates. The abrasion testing in conjunction with image analysis for aggregate shape, angularity and texture, is the focus of this study. Aggregates from ten Virginia sources were used for the Micro-Deval abrasion and digital images of twenty five particles chosen from each source were captured with a regular camera and analyzed with the MATLAB-based program to characterize the particle morphology. Due to time constraints and material availability the aggregates that were analyzed before and after abrasion were not the same aggregates. With one exception (Nolichucky quartzite), all of the aggregates exhibited very good abrasion resistance after being tested in the Micro-Deval. Also, because some of the aggregates abraded differently their morphological parameters after abrasion were larger or equal to the parameters before abrasion.

The packing of aggregate skeleton directly affects the capability of a mixture to transmit and distribute loads. It has significant impact on the performance hot mix asphalt (HMA) mixtures. This paper conducted an analysis of aggregate packing characteristics using a Discrete Element Modeling (DEM) simulation. A Washington typical HMA gradation is used as an example for the analysis. By using the PFC^3D DEM simulation to relate the gradation parameter to the volumetric properties of the structure, this paper theoretically demonstrated the different roles of aggregate particles in an HMA mixture. A new criterion to differentiate "coarse" and "fine" aggregates is developed, which is consistent with the Bailey's method definition. Aggregate contacts and contact force are also studied in this paper to evaluate the capability of the aggregate structure to transmit stresses through aggregate skeleton, and thereby, to resist permanent deformation. It is suggested that the method described in this paper based on the analysis of aggregate packing and DEM simulation provide a promising direction to theoretically understand the characteristics of a packed aggregate structure, as well as to guide the aggregate gradation design.

Fouling refers to the condition of railroad ballast when voids in this unbound aggregate layer are filled with relatively finer materials or fouling agents commonly from the ballast aggregate breakdown, outside contamination, or from subgrade soil intrusion. When ballast gets fouled, this unbound layer may not adequately serve its primary functions to provide drainage and structural support under the repeated loading applied by trains. Coal dust fouling has been identified as one of the most critical fouling scenarios as it significantly decreases the strength and stability of railroad ballast. A Discrete Element Modeling (DEM) approach was adopted in this study to investigate the coal dust fouled ballast performances. A DEM program BLOKS3D was used to employ realistic three-dimensional polyhedrons as discrete elements generated through digital imaging of aggregate particles. An appropriate DEM model parameter calibration process was carried out to predict both the clean ballast condition and the partially to fully coal dust fouled ballast behavior as obtained from laboratory shear box tests, which properly validated the BLOKS3D DEM simulations.

Geogrids have been widely used as an effective reinforcement in constructions, such as slopes and pavement bases. The mechanism of reinforcement action of geogrids is mainly achieved through the interlocking actions between aggregates and the grids. Different geogrids products and aggregates combinations would significantly affect the effects of interlocking. Accordingly, it is necessary to evaluate the effects of different geogrids on aggregates commonly used in potential engineering projects. In this study, laboratory experimental and analytical investigations were conducted to evaluate the performance of pavement base materials with or without geogrids reinforcement by using cyclic loading system, Loaded Wheel Tester (LWT). Meanwhile, rut depth (vertical deformation) of pavement base was considered to evaluate the effect of improvement.

The objective of this study is to demonstrate that a waste material can be used as reinforcement and for this purpose a series of experimental study was carried out to investigate the CBR behavior of waste plastic strip reinforced soil. The effect of waste plastic strip content (0.25% to 4.0%) and strip length on the CBR and secant modulus of strip reinforced soil was investigated. The study reveals that addition of waste plastic strips of appropriate size and proportions in soil results in an appreciable increase in both the CBR and secant modulus. The waste plastic strip reinforced soil can be used in low cost embankment/road construction leading to significant cost advantage as well as safe disposal of these waste materials in an environment friendly manner.

Significant work has been done by the International Center for Aggregate Research (ICAR) to identify the effects of the anisotropic nature of compacted base courses on the stress, strain, and permanent deformation characteristics of pavement foundations. As continuation to this effort, current paper presents a mechanistic approach for determination of the variation of pore water pressure under a moving wheel load. This paper also presents a methodology as to evaluate the effect of pore water pressure on the anisotropic response of aggregate layers. Sixty-two aggregate systems were tested with varying fine contents and water contents. The aggregate blends were molded according to AASHTO T-180 and tested using state of the art equipment called the Rapid Triaxial Tester (RaTT) at three saturation levels to capture the moisture susceptibility of the aggregate systems. Variable Dynamic Confining Pressure (VDCP) stress paths were in turn used to determine the anisotropic material properties for each aggregate system. This approach shows that the external pressure applied on the surface of the pavement results in a reduction of the initial negative pore water pressure. The change in pore water pressure induced by traffic load for high fines content specimens at elevated saturation levels results in positive pore water pressure which is synonymous with more critical conditions for plastic deformation. Further analysis on the results shows the agreement between the proposed approach and the principle of change in pore water pressure presented by Henkel. Mohr-Coulomb yield function was employed as a performance indicator in this study. The stress sensitive and anisotropic material model showed that the hardening component of the stiffness in vertical direction at the centerline of the load and at the top of the aggregate base layer is approximately 20% smaller when the influence of pore water pressure is considered in the formulations.

Large amount of sediments are dredged from rivers and lakes as a result of environmental dredging in China. These dredged materials (DM) have poor geotechnical properties and are normally treated as wastes. On the other hand, there is a huge demand of sub-grade materials due to the increasing number of highway construction projects in the eastern China. Thus the reuse of the DM as sub-grade material may be considered as an environmental-friendly and economical option. In this study a dredged material taken from Tai-hu lake was modified by adding fine sand, quicklime and Portland cement. Water content, Atterberg limits, and California bearing ratio (CBR) of the modified soil were determined. Test results show that fine sand significantly decreases the plasticity of the modified soil and increases its workability. However, a great amount of sand is required to meet the standard for a highway sub-grade material, which increases substantially the volume of the modified soil and the cost. Quicklime evidently decreases the water content and plasticity of the modified soil, and improved significantly its mechanical behavior. When the amount of quicklime and cement are equal, cement modified soil has larger CBR strength than that of quicklime modified soil. Test results also indicate that less amount of cement is required to meet the highway standard than that of using quicklime.

Temporal and spatial relationships between air and soil temperature are relevant to many applications in geotechnical and geo-environmental engineering. However, such data are not often available for a given site-specific project, so it remains attractive to develop practical models that do not require extensive and esoteric parameters. The impetus for the work presented herein is the common use of lime and cement to stabilize soils in road construction. While these additives have been used successfully to increase shear strength and reduce moisture susceptibility, their performance is temperature dependent. This manuscript presents soil temperature data for lime and cement-stabilized sub-grades from four sites. In general, each site was instrumented for air temperature, sub-grade temperature and moisture content. For the soils tested, estimated thermal diffusivity values range between 5.7 x 10^–7 and 7.8 x 10^–7 m²/s. These results are incorporated into a sinusoidal approximation of diurnal temperature fluctuations for purposes of preliminary modeling. Limitations in this approach are discussed, along with recommendations for model refinement. This work is part of a larger effort to predict subsurface temperatures and the corresponding strength of lime or cement stabilized sub-grades with little more than a standard weather forecast.

Several non-nuclear and portable tools for structural properties assessment of pavement materials have been currently introduced to the market. They are capable of directly measure in-place stiffness and strength of compacted pavement materials, which are the fundamental properties for mechanistic design and performance evaluation of the pavement system. This paper presents stiffness and strength based methods for rapid in-place monitoring compaction quality control during highway construction in Thailand. Results indicated that these methods exhibited good potential for construction quality control as well as the development of performance-based specifications in Thailand.

Because repeated load triaxial testing is cumbersome and not readily available, especially in developing countries, characterization of unbound granular road base and subbase materials is still done using empirical methods such as California Bearing Ratio (CBR) testing. Although widely applicable and useful, the CBR does not provide information on the mechanical behavior such as the resilient and permanent deformation characteristics of the material. A relatively simple testing technique, a repeated load CBR test, is developed to characterize the mechanical behavior of unbound base and subbase materials, which can be used as an input in mechanistic design analyses. The repeated load CBR test is quite useful to estimate the mechanical behavior of unbound granular materials, especially the resilient modulus. Furthermore, big scale cyclic triaxial tests are carried out to measure the resilient modulus which is then compared with the repeated load CBR results.

A frost-resistant earth fill was proposed by mixing waste foundry sand (WFS), fly ash (FA), expandable polystyrene (EPS) beads, Portland cement and water in proportions, which was known as WFS-FA-EPS fill. This study examined the unconfined compressive strength (UCS) weakening susceptibility of a range of WFS-FA-EPS specimens prepared at designated compositions which were exposed to freeze-thaw (F-T) cycling from 20 °C to –15 °C and up to 5 times. It was found that the inclusion of EPS reduced the unit weight of the fill materials by 20–40%. The majority of UCS loss was found suffered in the first F-T impact. Cement component clearly enhanced the anti-frost capability of materials. Components of EPS and FA also improved the F-T resistance of materials. Water was the main factor leading to F-T impairment, and should be prudentially added into the mixture. Inclusion of EPS beads was able to mitigate the frost impact by the means of reducing UCS loss. The optimal contents were 1.08% for EPS bead and 30% for FA.

The mechanical characteristics of the lightweight fill using hydraulic sand mixing with expanded polystyrene (EPS) beads were investigated in this paper. Unconfined compression tests, CBR tests and tri-axial shear tests were performed for the presented lightweight fill. The numerical study using a simple model in PLAXIS manual was conducted to verify the performance of embankments filling with the proposed material. Compared with the general lime stabilized soil embankments, the proposed material can significantly reduce the settlement which is beneficial for the highway serviceability. The research results show that the mixing lightweight soil is adequate to be used as the filling material of highway embankments to decrease the damage potential of the bridge-head jumping and to control the post-construction settlement. It is a new kind of filling conception for highway embankment projects.

The bearing capacity of subgrade soils, which is a critical parameter for assessing pavement conditions and guiding the type and extent of maintenance and rehabilitation (M&R), is greatly influenced by soil water content. In this study, a case of long-term spatial distribution of moisture content in existing cohesive subgrade in Shanghai was investigated. The in-situ testing data revealed significant variations in the water content of the sub-asphalt soils layers in both the horizontal and vertical directions. The equilibrium moisture contents (EMC) beneath pavement were calculated based on unsaturated soil theory and Fredlund & Xing equation was chosen as the soil-water characteristic curve (SWCC). Comparison of water content estimates from investigation and from prediction shows that, the relative elevation of groundwater table (GWT) is an influential factor controlling moisture distribution in subgrade, but areas with high water content immediately beneath pavement mainly reflect the inefficacy of pavement drainage systems.

Due to rapid development in the industrial sectors, huge quantities of waste materials are being produced as by-product and such wastes are to be located over dumping zones near the plants. These wastes not only need depositional land, but also create accumulation hazard and pollute environment around the plants. On the other hand procurement of conventional materials in huge quantity required for construction of subgrade of road is becoming very difficult in many locations due to various problems. So need has arisen for proper disposal of the waste materials. Utilizing these materials in the area of road construction after improving their characteristics suitably can provide useful solution of this problem. So keeping this in view, an experimental study was undertaken to explore the possibility of utilization of the alternative materials like pond ash, rice husk ash (RHA) by mixing with local alluvial soil by adding small percentage of lime for the construction of road subgrade as cost effective mix.

This paper used dynamic FEM model instead of continuum elastic layered system to simulate whole or broken semi-rigid base asphalt pavement response under FWD. Calculating results indicated that the sublayer strength can be evaluated by special FWD deflection basin parameter. Subgrade modulus (Esg) can be well evaluated by Curvature Index CI₇ and Shape Factor F₈ and the estimated results were not affected by pavement structure cracking condition. Whether Esg greater than 170MPa or not is defined as pavement subgrade failure criteria. Curvature Index CI₃ can use to indicate the semi-rigid base layer structural condition and its criteria is CI₃ value greater than 60um. This method have been applied and validated successfully in Jialiu Expressway rehabilitation project in Shanghai. It can more precisely distinguish weak sections for pavement rehabilitation design.

The paper presents a method based on deflection basin parameters to evaluate the subgrade modulus. The paper develops 2-D and 3-D dynamic FEM to simulate semi-rigid asphalt pavement deflection basin response under FWD loading pulse. It is discovered that the relationship between Curvature Index CI₆ and Shape Factor F₆ may be used to determine the subgrade modulus. The moduli, thicknesses and cracked condition of upper layers have minimal effect on the relationship between CI₆ and F₆. Based on the calculation and analysis, the nomograph of subgrade modulus is presented.

This paper deals with the implementation and comparison of the falling weight deflectometer (FWD) and Benkelman Beam (BB) for pavement evaluation. Field measurements were made at an in-service pavement A30 in Shanghai, China. Based on the deflections measured by FWD and BB, the exact relation between the results of FWD and BB was established. The modulus of the subgrade was back-calculated with MODULUS, and the ratio of E_(sta) and M_R(dyn) was consistent with the suggestion of AASHTO 1993. Due to the fact that FWD test is very convenient and rapid, it indicates that FWD is an appropriate device for the pavement structural evaluation and the selection of optimal pavement rehabilitation strategy. It is believed that the dynamic modulus back-calculated from FWD test results can be used as a stiffness modulus for the subgrade of new pavement construction in China.

Ground Penetrating Radar (GPR) has been using in the pavement engineering since almost twenty years. The traditional and mostly diffused application is the evaluation of the thicknesses of pavement layers. Such a measure can be done at traffic velocity with no impact on safety and operability of the roads. The actual frontier is the evaluation of the thickness in the case of thin layers. More recently GPR has been used to evaluate the pavement conditions. In the paper we present the methods for the electronic detection of pavement singularities as for moisture and bulk densities evaluation. At this regards a novel approach in the frequency domain that has been recently developed and validated is presented in the paper.

Moisture content is an important parameter due to its important influence on the serviceability of the pavement. Drainage is considered as one of most important factors in pavement projects. When water is trapped inside a flexible surface structure layer, it deteriorates surface layer and causes stripping, raveling and potholes in Hot Mixing Asphalt (HMA). Traditional methods to evaluate the pavement, for example, core-drilling can not meet the requirement to estimate the pavement moisture content effectively, because there are many disadvantages in this method such as low efficiency, bad representation, especially destruction to the pavement. Based on the above analysis, a new rapid, high efficient and nondestructive technology was proposed in this study. Ground Penetrating Radar (GPR) was developed recently, which is used widely for the pavement thickness detection. In this study, GPR was conducted to detect the moisture content of flexible surface, and the results demonstrate the effectiveness of the new kind.

Pavement preservation can extend a pavement's effective service life, improve safety and pavement service condition, and is a cost-effective approach. There are many benefits of adding pavement preservation into pavement management system. Pavement management system (PMS) can identify pavement preservation needs and help program pavement preservation projects. Pavement preservation increases the effectiveness of pavement management system, which can allocate available funding more cost-effectively. Although integrating pavement preservation into pavement management system is not a new thing, 9 out of 41 state agencies still utilized "worst first" approaches in their project prioritization based on a survey results in 2008. It is a challenging task to add the pavement preservation component to a PMS. An example of integration of pavement preservation with pavement management system is provided. This paper also provides guidance on how to add the pavement preservation components to pavement management system using a stepwise method.

The cost-effectiveness of different maintenance treatments including micro surfacing, HMA overlay and mill & fill were evaluated by using OPTime. The treatment effectiveness was calculated as the difference in computed areas associated with the post-treatment performance indicator curve and the do-nothing curve. It was found that mill & fill had the highest unit costs, followed by HMA overlay and micro surfacing. HMA overlay had the highest effectiveness, followed by mill & fill and micro surfacing. Micro surfacing was found to be the most cost-effective treatment due to its low cost.

The relationship between surface friction and roadway safety has long been recognized by transportation agencies and concern with the number of accidents occurring in wet pavement conditions has grown. For this reason it is imperative for road safety and road asset management divisions to undertake pavement wet skid resistance survey on a routine and regular basis. Many kinds of equipment are available to measure skid resistance on road surface, such as side force tester, Lock Wheel Tester, Fix-Skip Tester and Variable Slip Tester. In this paper, Norsemeter ROAR MkII, a new kind of variable slip tester, is introduced. Norsemeter ROAR MkII can be operated on both fix slip mode and variable slip mode. It will be demonstrated in this paper that the testing results from Norsemeter ROAR MkII are useful for both road network condition monitoring and safety investigation of black spot area through stopping distance analysis and lose-of-controlled analysis. Therefore, it is believed that the application of Norsemeter ROAR MkII variable slip skid resistance testing can help various road controlling authorities to make better decision on road maintenance programs and road safety improvement programs.

The Maryland State Highway Administration (MDSHA) conducts periodical friction surveys on the pavement network to monitor its overall skid resistance condition. It was found from the survey data that pavement friction could be affected by numerous variables: rehabilitation activities, traffic patterns, traffic volumes, survey vehicle test speeds, weather-related factors, and etc. Those variables affect pavement friction condition simultaneously by different mechanisms and in different degrees. It is of importance to investigate the relative significance of those variables in affecting pavement friction so it can be used for friction data interpretation and engineering decision making. This paper applies a multivariate analysis on the friction data using stepwise regression. The stepwise regression provides a measure to assess the relative importance of those variables based on the order of their entry into the model. Cross-validation is then used to examine the effectiveness and generality of the developed model. The engineering implications of the developed model are discussed. The advantages and limitations of using stepwise regression and feasible alternatives for analysis are also discussed.

This paper presents long-term (six-year in duration) field monitoring results of moisture in six completely rehabilitated highway pavement sections on Interstate I-90 in Ashtabula county, Ohio. There were a total of six monitoring sections for six different drainable base materials used in construction. The Time Domain Reflectometery (TDR) was used to measure moisture contents in different pavement layers and cohesive subgrade soils (up to 1.829 m below the pavement surface). Statistical analysis was performed to exam the time history of moisture variations at different pavement layers as well as seasonal variations of moisture profile with depth. The comparative effectiveness of six different drainable base materials in alleviating excess moisture in the pavement system was also evaluated based on statistical analysis of moisture data.

A method for improving the design of drainage layer in pavement was presented. Based on the percolation theory, the mathematical physics model for calculating the water exchanges were established, involving drainage layer with a constant cross-width thickness and drainage layer with a varying cross-width thickness. Then, the analytical solutions of flux distribution in drainage layer with a constant cross-width thickness and drainage layer with a varying cross-width thickness were obtained to verify the improvement of discharge capacity of proposed drainage layer. Then, the models were calculated and analyzed. The analysis results showed that the drainage layer with a varying cross-width thickness can improve the water drainage capacity well. Additionally, through the parameter analysis, it demonstrated that the parameters of n and H' play a significant role in improving the discharge capacity of drainage layer.

Subgrade resilient modulus (E_R) is a crucial parameter for pavement design and evaluation with a mechanistic-empirical method. To existing pavement overlaying and reconstruction, E_R is difficult to determine because it is a function of both water content and stress level. In this paper, a 3-stage method to determine E_R considering moisture condition coupled with stress is presented. Firstly, the equilibrium moisture of every sublayer of an existing subgrade was predicted by soil water characteristic curve and validated by in-situ water content tests. Secondly, a constitutive model of resilient modulus (M_R) was established for the subgrade soil on the basis of triaxial repeated loading tests. Its parameters related to water content were regressed as well. Finally, according to the equivalent principle of deflection at the top of pavement structure, a prediction function of subgrade E_R was proposed based on moisture-stress coupling condition and KENLAYER pavement analysis program. Its validity was verified by Falling Weight Deflectometer (FWD) tests. The presented 3-stage method has successfully been applied to predict E_R of the existing subgrade in widening engineering of Shanghai A11 Expressway.

In the Netherlands Blast Furnace Slags (BFS) are used as a self-cementing road base material on a wide scale for many decades. An example is the motorway A32 which was built in the years 1986–1988. Some 10 years after construction the first transversal heaves occurred at the asphalt pavement surface. Since then the number of heaves has considerably increased and the heaves kept on growing in height. Finally the pavement was fully reconstructed in 2008 and 2009. In 2007 an extensive research was initiated into the performance of the BFS base material on the motorway A32. This research included: (1) Inventory of the number, length and height of the transversal heaves at the pavement surface. (2) Falling Weight Deflection measurements at some heaves, but also in between some heaves, from which the modulus value of the BFS road base was backcalculated. The modulus values show an extreme variation. (3) Materials research on bound BFS base material obtained by taking cores. The modulus of elasticity, compressive strength, tensile strength and coefficient of linear thermal expansion has been investigated. (4) Development of a mechanical model which describes the birth and growth of the heaves. The model enables to quantify the effects of the magnitude of the mechanical properties of the BFS road base and the season of construction of the base on the development of the pattern of transversal heaves. (5) Chemical and mineralogical analyses of the BFS road base material. This research is intended to indicate possible deleterious reactions and their effects on the long-term performance of BFS.

The National Airport Pavement Test Facility (NAPTF) is a fully enclosed instrumented test track 274.3 m (900 ft) long by 18.3 m (60 ft) wide. In construction cycle three (CC3), four new flexible pavement test items (LFC1 through LFC4) were constructed. The pavement structures were of conventional construction with 127-mm (5-in) asphalt surface, 203-mm (8-in) crushed stone base, varying subbase thickness, and a silty clay subgrade of 3 to 4 CBR. The test items were named LFC1 (thinnest subbase) through LFC4 (thickest subbase). Traffic tests were performed with 6-wheel loading in one wheel track and 4-wheel loading in the other wheel track. Rut depth and profile measurements were made on the asphalt surface during traffic testing. A fixed wander pattern was applied to the traffic during the tests. The wander pattern consisted of 66 repetitions, 33 traveling east and 33 traveling west. Sensors were embedded into the pavement layers to measure the pavement response to applied loads and included asphalt strain gages (ASG), multiple depth deflectometers (MDD), and soil pressure cells (PC). Subgrade pressure cells (2 inches, Kulite) were placed only in test item LFC4 and were placed 10 cm (4 inches) and 43 cm (17 inches) below the subgrade surface. This paper summarizes the subgrade vertical stress measurements under 6-wheel and 4-wheel landing gears at 245 kN (55,000 lb) and 289 kN (65,000 lb) wheel loads at different wander positions. There was no evidence of structural failure in LFC4 at the end of traffic testing.

The Federal Aviation Administration (FAA) National Airport Pavement Test Facility (NAPTF) is located at the William J. Hughes Technical Center, Atlantic City International Airport, New Jersey. The primary objective of the tests performed at the NAPTF is to generate full-scale pavement performance and response data for development and verification of airport pavement design criteria. Four construction cycles (CC1, CC2-OL, CC3, CC5-TS) for testing flexible pavements under heavy aircraft loading have been completed and the fifth one is under way. In both CC1 and CC3, deformation of the aggregate base and aggregate subbase due to densification was noted and contributed to the rutting of the asphalt pavement test sections. This paper will discuss if the Total Void (TV) calculation based upon historic data of CC1 and CC3 can be used to predict the total deformation of the aggregate base and subbase layers in flexible pavements, as well as, to investigate whether the FAA gradation specifications for subbase and base courses are susceptible to deformation based upon the total void calculation.

This paper describes the economic analyses of using thick granular base design in cold regions. The use of thick granular bases is believed to lead to higher and uniform structural support. For regions in freeze-thaw zones, the use of thick granular base helps to move the weaker and frost susceptible subgrade material further down in the pavement structure where stress, strain, and frost penetration are lower. To implement such design in cold regions, the performance benefits must overcome the initial high investment and results in longer term economic benefits. This paper discusses results of analyses on the design, economic and performance of pavements of different granular base thickness. The effects of local environmental conditions such as freeze-thaw are assessed. Recommendations are provided on the use of thick granular base for flexible pavement design in cold regions.

Based on the typical highways widening approaches used in the process of expressway extension in China, the differential settlement and cracking mechanism in the pavement while widening unilaterally and bilaterally were studied using the FEM software RFPA. The results showed that the cracks initially appeared from the toe of side slope of the new foundation. As time went on, the settlement increased and cracks arised from the toe of side slope of the old foundation. Then these cracks propagated gradually and eventually formed a clear sliding surface, leading to glides along the interfaces between the old and new foundations. The interfaces were apt to be the potential gliding planes. If the embankment was higher, the global stability would be worse and the differential settlement would be larger. While the differential settlement and glide increased, the generated additional flexural-tensile stress and shear stress also increased progressively. The consequences were that the longitudinal cracks would appear in the foundation and further brought about the cracking of the asphalt pavement.

China has developed her expressway system after 10 years' intensive construction with most of its expressway systems concentrated in the coastal areas. In the central and western parts a majority of the highway system is comprised of rural roads with low volume traffic. The objective of this article is to display the current rural roads situation in China, the existing problems in the rural road system, and some of the main factors impacting rural road infrastructures, and dedicate the rural road development strategies to preserve China's extensive rural road system. This paper also focuses on the main problems and the development objectives of rural roads in different areas of China. Base on the study, the solutions to typical rural roads of each area are organized and strategies for rural roads are also recommended.

QC/QA (Quality Control/ Quality Assurance) tests on asphalt binder may assess that the as-constructed pavement has characteristics different from the ones set out in the contract for the as-designed pavement due to the insufficient quality of the bitumen. Therefore, a Pay Adjustment (PA) is needed. In the light of the above facts, the objective of this paper was the assessment of a quantitative relationship between asphalt binder quality and the consequent Pay Adjustment, for a given class of boundary conditions. Once the problem was modelled, experiments and simulations were carried out through the use of M-E PDG (Mechanistic-Empirical Pavement Design Guide, 2007). Consequences in terms of pavement life cycle cost analysis (LCCA) and contractor's expectations were derived. Results demonstrated how bitumen quality and cost influence Pay Adjustment and contractor's strategy.

Some 85% of Australia's sealed road network is comprised of unbound granular pavements with a wearing surface treatment of stone aggregate embedded in a thin bituminous binder seal. Experimental pavement deterioration data gathered by means of accelerated load testing (ALT) on various forms of binder seal and stone aggregate over separate test pavements was used to estimate relative performance factors for cumulative rutting and roughness deterioration under these surface treatments. The ALT experiments were under controlled environmental conditions that were either continuously wet or continuously dry to allow modification of these relative performance factors for other environmental conditions. These relative performance factors have been applied to the observed deterioration of given surface treatments to develop road network deterioration (RD) models that allow prediction of the influence of various surface treatments on pavement deterioration. This paper demonstrates that when the relative performance factors are applied to the observed pavement deterioration under a given surface treatment to predict pavement deterioration under other forms of surface treatment, selection of a surface treatment option with the lowest pavement life-cycle cost is possible for a given traffic load and environmental condition.

The Mechanistic-Empirical Pavement Design Guide (M-E PDG) requires detailed traffic data to characterize the axle loads and their repetitions, and subsequently predict pavement performance. For level 1, the M-E PDG requires, at 95% confidence level, 84 days of coverage for traffic data i.e., one week per month (OWPM). The data coverage can produce 1 to 2% errors in axle load and truck traffic distributions, as well as 5 to 10% error in AADTT values. In preliminary analyses of five WIM sites in Michigan, it was found that OWPM data produced significant variation in monthly distribution factors and AADTT, especially for sites with AADTT less than 1000 vehicles. Subsequent M-E PDG analyses using OWPM versus continuous traffic data yielded significant variation in predicted pavement performance. Therefore, the objective of this paper is to investigate whether using OWPM WIM data is equivalent to continuous WIM data when determining traffic characteristics—truck traffic classification (TTC), axle load distribution, monthly distribution factors (MDFs), hourly distribution factors (HDFs), axle groups per vehicle (AGPV) and AADTT. To accomplish the study objective, traffic characterizations from one week and continuous data coverage from 34 WIM sites in Michigan were obtained and compared in order to provide confidence intervals in terms of traffic characterization and pavement performance differences between OWPM and continuous data.

Superposition effects of runway asphalt pavement under multiple aircraft tires load are discussed in this paper. 30 x 20 x 10 m (Full Size Model), 15 x 20 x 10 m (1/2 Model) and 15 x 15 x 10m (1/4 Model) size models are established on ABAQUS 3D numerical analysis platform. Using those models, asphalt pavement responses under single tire, double tires, single tandem, dual tandem, dual triple, and compound landing gear are studied. Results show that multiple superposition effects are apparent. The pavement surface deflection under full landing gear is larger than any other tire groups; the maximum vertical strain on the top of the sub-grade and the horizontal stress at the bottom of the base appear in 6 tires group for A 380 and rear 8 tires group for B-777; the largest strain or stress can reach 1.15 times of the full landing gear's value. Based on the pavement responses under multiple tires load, the fatigue life of pavement is analyzed. Functions developed by LEDFAA, APSDSR and UC Berkeley are used in the fatigue analysis. The results of flexible and semi-rigid pavements show that the allowed load repetitions of runway asphalt pavement under full landing gear are 20~30% higher than 6 or 4 tires group. Therefore, the full landing gear is recommended to be used in asphalt pavement structure design.

A simplified three-dimensional model is established to analyze the responses in asphalt overlay (AC) paved on existing concrete pavements (PCC) slabs under vehicle loads, by using the finite element method, through some examples, the convergence of loading stresses in AC nearby the joint of PCC slabs and interface forces are discussed, the expressions of the nominal maximum tensile stress σ_1max in AC are then formulated, and the influences of load position x, structural parameters (E₁, h₁, h₂, k₀, δ), interlayer stiffness and void underneath PCC slabs on the stresses σ_1max, τ_1max in AC and the internal forces q_2max, τ_2max are analyzed, in the end, the damage modes of AC on PCC structure are issued based on the strength theory. The study indicated that the sectional internal forces (axial force N and momentM) can be taken as convergence criteria to reasonably determine the model meshing density. The stress σ_1max can be calculated upon corresponding sectional internal forces N, M and a stress concentration factor ξ_p; the stresses σ_1max, τ_1max may reach peak values when the load position x not exceeding ±0.2m; the influences of structural parameters E₁, h₁ on the stresses σ_1max, τ_1max and the interface forces q_2max, τ_2max are much significant; eliminating the void underneath PCC slabs will have a disadvantageous effect on the stress σ_1max but an active effect on the interface forces q_2max, τ_2max; a higher joint spring stiffness C_w will considerably reduce the stresses σ_1max, τ_1max and the interface forces q_2max, τ_2max; the placing width of soft interlayer over the joint should be 0.3~0.4m; the soft interlayer with higher stiffness will reduce the stress σ_1max, but raise the interface force q_2max, therefore increase the risk of interface damage.

In this paper, liner Drucker-Prager creep model was used to simulate the visco-elastoplastic response of flexible pavement under traffic loads. The effect of asphalt layer thickness, asphalt stiffness, interactive properties between the asphalt and base layers, base and sub-grade modulus, and the traffic loads level were considered in parametric study.

Rut is always serious when asphalt pavements sustain heavy loading and slow moving vehicles. This indicates that traditional asphalt pavements structural combination design methods can not offer sufficient rutting resistance performance for the special section. In this study, full-thickness rutting tests under heavy load and slow speed were developed for many surface course combinations. The contribution rate of each surface layers to the whole surface course's rutting resistance performance was studied. Test results show that the rutting resistance performance of top surface layer, middle surface layer and bottom surface layer should be improved simultaneously to prevent rut in the continuous uphill expressway; the use of modified bituminous or anti-rut agents is an effective way to improve the rutting resistance performance of asphalt mixture. Finally, a suitable asphalt surface course was recommended for a 13km continuous uphill asphalt pavement maintenance project.