HMA Layer Research Articles

Revisiting Field Performance of Cold Central-Plant Recycled Test Sections at MnROAD Low-Volume Road

In 2017 four test sections (test sections 133, 233, 135, and 235) containing a cold central-plant recycled (CCPR) layer underneath a surface treatment were constructed on the MnROAD low-volume road (LVR). Two types of CCPR mix designs were constructed: test sections 133 and 235 contained an emulsified asphalt; test sections 135 and 233 contained a foamed asphalt. Each CCPR mix design (foamed asphalt and emulsified asphalt) had two types of wearing surface layers (double chip seal and 1.5 in. HMA [hot-mix asphalt] overlay—thinlay) to create the four test sections. The rest of the pavement structure beneath the newly constructed CCPR was left in place and consistent throughout all four test sections with the remaining granular base over the existing clay subgrade. This paper presents a revisiting of the field performance of the CCPR test sections at the MnROAD LVR. To do this extensive field data was collected over approximately 3 years through visual distress surveys, and ride quality, rutting, and falling-weight deflectometer testing. Field study determined that both CCPR mix designs (foam and emulsion) performed similarly and the thinlay HMA layer outperformed the double chip seal in respect of rutting; but both surfaces are considered valid alternatives for future applications depending on the traffic volumes expected.

Effect of Repeated Traffic Loads on Most Significant Distresses of Flexible Pavement

Early fatigue and rutting are among the most common types of road damage due to their main relationship with pavement performance. These damages occur due to excessive loads on the axles of the vehicles or improper design of the mixture in addition to the traditional design methods used in paving designs. Therefore, these premature damages must be avoided for the proper performance and service of the road. In order to overcome some traditional design weaknesses, mechanical-empirical design techniques using software like the ABAQUS program are essential. This program determines the exact stresses, strains, and displacement in asphalt pavement, which is then used to predict rutting and fatigue failures. HMA layers behave like viscoelastic materials in actual field conditions, and temperature variations and loading period influence their mechanical response. This study aims to investigate the ABAQUS software's problem-simulation capabilities and compare the findings to experimental work using the mechanical-empirical approach (E-M) to investigate the most valuable features during temperature change and optimize the design of paving constructions. The results highlighted the significance of the impact that increased loads and temperature changes might have on the performance service life of flexible paving with flexible-viscous layers, where life decreases with increasing loads applied to the pavement surface, where life reduces to 50% of age when the loads are increased to twice the standard load. At the same time, both the vertical stress and the percentage of damage increase with both the change in temperature and with the Temperature increases also result in higher tensile and compressive strain values, which might have an impact on the cost of the paving life cycle. Therefore its impact on future maintenance requirements must be verified.

A 3D-FE Model for the Rutting Prediction in Geogrid Reinforced Flexible Pavements

Permanent deformation (rutting) is an important disturbing failure on flexible road pavements. This phenomenon appears on the flexible pavement as longitudinal depressions, and it is a consequence of the degradation of materials under high traffic loading based on consolidation/densification, surface wear, plastic/shear flow, and mechanical deformation. Hence, the rutting phenomenon depends on the accumulation of permanent deformations on pavement surfaces subjected to repeated wheel loads. In recent years, several studies have confirmed that the service life of asphalt pavements can be increased by using geosynthetics between or within layers because of the improved mechanical properties. The aim of this paper is to present the results of the 3D-finite element (FE) simulations and the development of the rutting phenomenon in a traditional flexible pavement and a reinforced one, both subjected to a cyclic load. Through Abaqus/CAE software, a road section reinforced by a geogrid was analyzed and compared with a traditional road section to investigate the advantages given by the geosynthetic completely embedded at two-thirds of the asphalt concrete layer (AC) in terms of permanent deformations. The results show the capability of the proposed FE study, that uses the plasticity model of Drucker-Prager for unbound materials combined with the simple creep law to model HMA layers to predict the permanent deformation distribution.

Seasonal and diurnal variations of back-calculated layer moduli in flexible pavement and FWD testing guidelines

Seasonal and diurnal variations can significantly impact falling weight deflectometer (FWD) measurements and, thus, deflection-based parameters such as back-calculated layer moduli. Therefore, it is necessary to evaluate and quantify these effects. The back-calculated layer moduli data from the Long-Term Pavement Performance Seasonal Monitoring Program study were analyzed within each climatic region. The effects of seasonal and diurnal changes were quantified and related to ambient temperatures were related to the development of general measurement guidelines. The HMA layer moduli showed minimal variation during the spring and fall seasons in every climatic region and were consistently higher based on the deflections measured before noon. However, temperature correction, generally applied to the HMA layer moduli, can eliminate the temperature impacts of the FWD measurements. Because the unbound layer moduli are back-calculated from the single measured deflection basins on the surface, temperature and moisture conditions at the time of measurements can affect the material properties. The base and subgrade moduli showed minimal variation within the temperature ranges of the spring and fall seasons. Therefore, such temperature within each climatic region may result in layer moduli values closest to their representative in-field conditions. In addition, the unbound layer showed no effect of time within a day, suggesting that FWD testing can be conducted at any time during the day. Based on the results, the preferred temperature ranges for FWD measurements are 55–70 °F and 65–75 °F in the freeze and non-freeze regions, respectively. FWD measurements can be conducted at any time during the day. The preferred seasons for testing are spring and fall in all climatic regions.

A synthesis of the first full-scale experiment in Central America

ABSTRACT The initial full-scale experiment in Costa Rica began in 2012 under a program that has been identified as PaveLab. The main purposes were to identify the effect of typical construction practices in the country: use of granular vs. cement-treated bases (CTB), and thin vs. thick HMA layers. The effect of moisture was also considered: sections under optimal moisture conditions were compared to sections where the water table was raised to approximately the middle of the subbase. The recorded information includes: stress and strain measurements for the top layers of the structure, vertical pressure in supporting layers, surface roughness and deflection data. Preliminary results show the importance of considering the effect of water on the stability of pavement structures. It was noted that even though the CTB layer showed higher initial stiffness as compared to a granular base, the loss of stiffness associated to load-induced damage occurred at a significantly higher rate than that observed at the other layers. Similarly, the results showed that an increase in HMA layer thickness results in higher overall structural capacity, independent of the supporting layers. The data is currently being used to calibrate fatigue, permanent deformation and surface roughness transfer functions.

An alternative approach to testing of moisture susceptibility of recycled pavement materials

Recycling is one of the most sustainable methods of pavement construction. However, moisture entering through thin HMA surface layer(s) overlying recycled pavements has often caused their premature deterioration. This study was conducted to develop an alternative laboratory moisture conditioning and testing procedure for recycled layers, and recommend tests and structure to enhance the resistance against moisture damage. The study developed a unique way to utilize a dynamic moisture conditioning process to obtain a more realistic evaluation of the moisture resistance of recycled layers than the currently used static immersion tests. Instead of using samples of only recycled (Full Depth Reclaimed, FDR, with asphalt emulsion) layers, the study evaluated composite samples that are more representative of actual pavement structures. Composite samples were prepared by attaching HMA samples on top of FDR samples with tack coat. The samples were tested for permeability and modulus using Ultrasonic Pulse Velocity test, a nondestructive test (NDT) test. The samples were subjected to 2,000 cycles of the Moisture Induced Stress Test (MiST) and then retested for modulus. The conditioning process was able to simulate moisture damage in the composite samples, and the nondestructive test was able to detect moisture-induced damage. The samples with two HMA layers showed significantly lower loss (28%) in modulus than those with only one HMA layer with the same thickness (72%). Two layers of tack coat for the samples with the two HMA layers were more effective in reducing the ingress of water through the HMA layers into the FDR layer than the one layer of tack coat for one HMA layer samples. Use of composite samples and NDT, and the dynamic moisture conditioning process (MiST) are recommended for the design of recycled layers. The use of two separate HMA layers with intervening two tack coat layers instead of a single HMA layer with a single tack coat is recommended for the enhancement of moisture resistance of recycled pavements.

3D-FEM Analysis on Geogrid Reinforced Flexible Pavement Roads

Nowadays, the need to increase pavement service life, guarantee high performance, reduce service and maintenance costs has been turned a greater attention on the use of reinforcements. This paper presents findings of a numerical investigation on geogrid reinforced flexible pavement roads, under wheel traffic loads, using a three-dimensional Finite Element Method (FEM). The results obtained show the effectiveness of glass fibre grids as reinforcement which, with appropriate design and correct installation, by improving interface shear resistance, can be used to expand the performance of flexible pavements in different ways: by increasing the road service life providing a relevant contribution against superficial rutting or by decreasing the construction costs due to the reduction in the reinforced HMA layer thickness and thus of mineral aggregate required for its construction.

Evaluation of the effective parameters on shear resistance of interface in a geocomposite-reinforced pavement

Application of geosynthetics is known as an important way to reduce and delay emergence of reflective cracks. However, reliance on these materials can have some disadvantages, including reduction of shear resistance in the interface between two HMA layers, along with emergence of some defects in areas on which vehicles brake, accelerate or turn. A large number of parameters affect the interlayer shear resistance. In this research activity, a double-shear device has been developed and evaluated in order to measure shear resistance between layers in the interface zone. The device is equipped by a system for application and control of normal compressive and tensile loading. In this research, using the L16 (2 × 2–4 × 4) orthogonal array, the factors that are most influential on the shear resistance of the interlayer zone reinforced by geocomposite are evaluated. Temperature, with effectiveness 2.4 times greater than that of the other parameters, the effect of which is relatively uniform, is found to be the most relevant parameter, followed by the tack-coat application rate. The findings indicate that the shear loading rate and geocomposite grid size have the next most significant contribution to the maximum shear resistance, both with and without application of normal load.

RETRACTED: Effect of segregation on rutting resistance of asphalt pavement

Mix segregation is generally described as localized non-uniform zones of mix that do not conform to the original Job Mix Formula in gradation or asphalt content. Segregation may cause field performance issue such as rutting but no good trend between segregation and field/laboratory rut depth is observed. In this paper, a field road with segregation was monitored and those reported parameters used to detect segregation were collected. The segregated areas and the control non-segregated areas were identified by visual assessment. Rut depth were measured within one year after the road was opened to traffic. Rut depth from segregated areas and non-segregated areas are compared to evaluate the effect of segregation on rutting performance. The possibility of using different parameters such as pavement texture and construction temperature to detect segregation is also analyzed. Acknowledging that the rut depth may be affected by multiple parameters, a statistical Partial Least Squares (PLS) regression method is applied to select predictor variables that have the most significant effect on rut depth, and to develop rut depth prediction model. Results indicate that rut depth from segregated areas (visual) are statistically higher than rut depth from the non-segregated areas (visual). It is also found that pavement texture and construction temperature are the potential factors to detect segregation since they are correlated well with both visual assessment and rut depth. The developed rut depth prediction model shows good predictability and is well validated by considering segregation (mean texture depth), climatic effect (aging days), material property (HMA layer moduli), and pavement structure (entire HMA thickness).

PREDICTED DESIGN THICKNESS OF MODIFIED HMA LAYER FOR FLEXIBLE HIGHWAY PAVEMENT

The major reason for using asphalt mixture modifiers is to improve the performance of asphalt pavement to meet the requirement under prevailing stresses from traffic loading and environment effects and to reduce the pavement thickness. Structural thickness design of asphalt pavement layers is a function of many factors; one of the most important of them is the elastic modulus (E) of the asphalt mix. E values may be estimated directly in a laboratory by test, or indirectly by correlation with other tests like Marshall Stability. Additionally, E of hot mixture asphalt is used to estimate the layer relative strength coefficient (a) that is used to estimate the Structural Number parameter (SN), which allows for determining the required layer thickness. The major objective of this research is to predate a statically model to estimate the effect of asphalt modification on the layer thickness. 75 specimens of control and modified HMA for surface are designed and tested according to Marshall Method with optimum asphalt cement content (4.8%) and different types and contents of available modifiers.

Detection of Delamination in the HMA Layer of Runway Pavement Structure Using Asphalt Strain Gauges

AbstractAsphalt pavement distresses like surface shoving and slippage cracking can be found at airports in areas where aircraft brake and turn, such as high-speed exits, as a result of the high surface-shear forces. Slippage failure is typically caused by the deterioration of bonding between asphalt layers (delamination), or a lack of shear resistivity within the surface-layer asphalt mix. High pavement temperatures have also been shown to contribute to slippage failures in asphalt concrete pavements. At the intersection of Runway 4 R-22 L and High-Speed Taxiway N (HST-N) at Newark Liberty International Airport (EWR), interlayer delamination was determined to be the cause of shoving and slippage cracking on the pavement surface. In 2012, asphalt strain gauges were installed during a scheduled repaving of the runway and taxiway. This paper details the components of an asphalt strain gauge instrumentation system, and analyzes the strain responses collected from the gauges installed at EWR. By identifying la...

Full-scale field testing on a highway composite pavement dynamic responses

A series of full-scale field tests were conducted to observe the composite pavement’s dynamic responses subjected to heavy traffic load. The tire contact pressure beneficially influences the dynamic strains and the dynamic stresses of pavement. A typical “M” shape is observed for the distribution of dynamic responses cross lane. The range of dynamic soil stress on roadbed ranges at 20–50kPa, and a non-linear model is presented for the dynamic stress attenuation along subgrade depth. Furthermore, the increasing of truck speed decreases the dynamic responses of composite pavement. This is owing to the viscoelastic property of HMA layer and the resonant frequency. At a lower moving speed, the dominant frequency of heavy truck loading is close to the dominant frequency of HMA layer. This would amplify the vibrations of pavements and consequently result in larger mechanical responses. The experimental findings would be helpful to understand the dynamic performance of composite pavement subjected to heavy traffic load.

타이어 종류 (Wide Base Tire and Dual Tire Assembly)에 따른 아스팔트 포장 반응 평가

PURPOSES : The first generation of wide base tires introduced in the early 1980s was found to cause a significant increase in pavement damage compared to dual-tire assemblies. However, wide base tires have evolved considerably, and a new generation of wide base tire is thought to be comparable to conventional dual tires for pavement damage. A challenge associated with using wide base tires is the accurate quantification of pavement damage induced by these tires. The objective of this study was to investigate the responses of flexible pavement to continuously moving vehicular loading under various tire configurations. METHODS : The comparison of the strain/stress responses of full-depth pavement caused by conventional dual tire assembly and new generation of wide-base tires was performed. The FE model incorporates linear viscoelasticity of asphalt material and continuous moving load using implicit dynamic analysis. RESULTS AND CONCLUSIONS : The result demonstrates that the new wide-base tires caused slightly more fatigue damage and less primary rutting damage in HMA layer than a dual-tire assembly, but caused more secondary rutting damage in subgrade than a dual tire assembly.

비접착식 콘크리트 덧씌우기 포장에서의 아스팔트와 Geotextile 중간층에 대한 영향 평가

PURPOSES : The objective of this study is to investigate the effect of asphalt and geotextile interlayer on the fracture behavior of unbonded concrete overlay through a laboratory composite beam test. METHODS : In order to evaluate the effect of interlayer materials on the fracture behavior of unbonded concrete overlay, a laboratory test of composite beam was conducted with different types of interlayer. The test results of the composite beam using two types of geotextile interlayer with different thicknesses were compared to the test results of the composite beam using the tradition type of asphalt interlayer. The unbonded concrete overlay on the existing concrete pavement without interlayer was set for the control condition. RESULTS AND CONCLUSION : Overall, the laboratory composite beam test results did show the effect of asphalt and geotextile interlayer on the fracture behavior of composite concrete beams. The three-layer geotextile interlayer and HMA layer both increase the peak load when the first macrocrack occurs in the top concrete beam, while the HMA interlayer causes the smallest load drop percentage after the first macrocrack. The three-layer geotextile did show better performance than the single-layer geotextile through the greater peak load and smaller load drop percentage. It indicates that the thickness of geotextile interlayer will affect the fracture behavior of unbonded concrete overlay and the thicker geotextile interlayer is recommended.

Simulation of unbound material resilient modulus effects on mechanistic-empirical pavement designs

The variability of resilient modulus (M R) of unbound materials and subgrade due to laboratory test conditions affect pavement performance and designs. The performance-based mechanistic-empirical pavement design guide (MEPDG) is gaining more popularity in recent years for pavement design use. However, limited research efforts have quantitatively studied M R effects based on ME models. This research targets to evaluate the influences of M R variability on pavement performance and designs based on the MEPDG performance models. With a normal-distribution of M R seed values, pavement responses were computed with a layer-elastic analysis model, pavement performance was then predicted using MEPDG models, and design variability was studied via Monte Carlo simulation. Results indicate that the relationship between layer design thickness and M R varies from almost linear to nonlinear, which is highly dependent on the pavement structure and material properties. For the evaluated specific pavement structure and range of M R values, the least susceptible is the HMA design thickness as a function of M R under fatigue with a design Coefficient of Variance (CV) of 7.51 %, while the most susceptible is the base design thickness as a function of M R also under fatigue with a CV of 54.32 %. The combined effect of both rut depth and fatigue life considering the variability of both base and subgrade results in a design CV of 22.58 % for asphalt layer and 26.08 % for base layer. When using a weaker base layer or a thinner HMA layer, the modeled thickness design CV has changed −4.19 to 1.14 %.

Dynamic Response in ALF Aggregate Base Asphalt Pavement

In order to evaluate pavement dynamic responses accurately under truck loading, the full-scale asphalt pavement accelerated loading facility (ALF) was used. 10 strain gauges and 2 soil pressure cells were installed; temperature sensors were also installed in the different depth of the HMA layer. Pavement response was measured under real traffic load with ALF. The measured pavement responses are compared between the pavement sections to evaluate the effects of various experimental factors, such as axle load, speed, et al. Dynamic strain at the bottom of HMA layer and vertical compressive stress on the top of the subgrade were examined in the full-scale testing road, the regression models between dynamic response and axle load, dynamic response and speed were put forward respectively. Studies show that there is not only tensile strain but also compressive strain in the dynamic response, and the strain response is in the station of tension and compression alternation. Under the intermediate temperature, the strain response at the bottom of the asphalt layer is increased linearly with the increase of axle load and the vertical compressive stresses at the top of the subgrade is also increased with the increase of axle load. Speed has a great effect on strain response at the bottom of HMA layer, and has little effect on vertical compressive stress, it affects the loading duration of stress only. The destroy for the pavement by low speed and heavy load is more serious than that is normal.

Recalibration of the Asphalt Layer Coefficient

While there is an increasing interest in mechanistic-empirical flexible pavement design, this methodology will likely not be implemented by the majority of transportation agencies for several more years. Therefore, there is a need for optimization of the current design methodology, which for many agencies, is the 1993 AASHTO design guide. This approach contains a flexible pavement design equation with inputs of soil modulus, traffic, structural number, reliability, variability, and change in serviceability. A sensitivity analysis conducted on the inputs to this equation showed that the HMA layer coefficient (a 1 ) is the most influential on the resulting HMA thickness. A recalibration of a 1 was performed using data from the National Center for Asphalt Technology Test Track. A least-squares regression was performed to minimize the error between predicted and actual equivalent single axle loadings applied to the test sections. The resulting average a 1 was 0.54 with a standard deviation of 0.08. Using 0.54 instead of the AASHTO recommended coefficient (0.44) results in a HMA thickness savings of approximately 18%.

Modelling Tensile Strain Response in Asphalt Pavements

ABSTRACT Traditionally, HMA pavement designs and modeling methods have historically been based on the fundamental assumption that fatigue cracking generally initiates at the bottom of the HMA layer due to excessive tensile stresses/strains, and then propagates upwards to the surface. However, fatigue cracking can either be bottom-up or top-down initiated depending on the location of the maximum horizontal tensile stresses and strains in the HMA layer. Various factors such as the pavement structure and wheel/tire loading configurations influence both the location and magnitude of the fatigue crack-related tensile strains that are induced in the HMA layer. In this study, the influence of these factors on the tensile strains responses and potential location of fatigue crack initiation in HMA pavements was investigated. To address the non-uniformity distribution of the tire-pavement contact pressure (TPCP), including the vertical tire-pavement contact pressure and horizontal tire-pavement stress, a three-dimensional finite element program was utilized for the computational simulations and numerical analyses. Specifically, the actual TPCP of different tire types and tread patterns measured under variable load levels and tire inflation pressures were utilized to evaluate and analyze the potential locations of maximum tensile strains in terms of fatigue crack initiation. The results showed that the longitudinal and low latitudinal tire-pavement stress hardly influence the maximum tensile strains in the HMA layer; and that the maximum tensile strains can occur either at the top or bottom (or both) of the HMA layer, thus inducing top-down and/or bottom-up fatigue crack initiation. Just like heavy-truck tire loading, the study also demonstrated that light-truck tire loading can induce excessive fatigue crack-related tensile strains in the pavement.

Non-Destructive Testing Technologies

ABSTRACT In this study, the application of the Ground Penetrating Radar (GPR) as a nondestructive testing (NDT) tool was investigated for evaluating perpetual pavements. In total, eight in-service Texas perpetual pavement sections were evaluated and are discussed in this paper. Based on this study, the GPR was found to be an ideal NDT tool for structurally evaluating perpetual pavements. Concerns were raised in this paper about the uniformity and permeability of the 1-inch Stone Filled HMA layer, which is the main structural layer in the Texas perpetual pavement structure. The results obtained indicated that the GPR has great potential for determining pavement layer thickness, assessing compaction uniformity, locating areas of moisture retention, and identifying low density areas in the upper asphalt layers. Additionally, TTI's GPR system has the advantage of rapidly and continuously collecting pavement data up to a depth of 610 mm, together with integrated video images, over any desired highway length while travelling at a speed of about 113 km/hr. Overall, the GPR was found to be a highly beneficial and effective NDT tool for forensic and structural evaluation of perpetual pavement structures. Based on the findings of this study and subsequent validation of the GPR results through coring, the Texas DOT has modified its recommendations for future perpetual pavement designs.

A study of temperature and traffic load related response in different layers in an instrumented flexible pavement

The first fully instrumented flexible pavement test section in Maine was constructed in Fall, 2005. Temperature data were collected for a period of 5 months and stress–strain data were collected by running a truck at different speeds. The temperature data were analysed to develop models to predict these temperatures on the basis of ambient temperature and solar radiation. The haversine equation was found to be suitable for modelling the strain response in HMA layers, whereas slight variations were used for modelling the responses in the subbase and subgrade layers. The strain in the HMA layer shows a lag when compared to the fitted model. The HMA tensile strains matched well with the predicted strains at lower time of loading and lower temperatures. Subbase stresses were greater than predicted values. The subbase strains matched well with the predicted ones. The measured subgrade stresses were greater than predicted stress values.