Evaluation Method for Transverse Cracking in Asphalt Pavements on Freeways

With the growing awareness of sustainable construction practices and because warm-mix asphalt (WMA) is environmentally friendly, WMA is gaining popularity for pavement construction in the United States. Currently, it is generally believed that rutting and moisture damage are two major concerns for WMA pavements, but because WMA requires less aging, its cracking resistance is expected to be improved. One of the primary cracking distresses of concern is transverse cracking, which could be thermal cracking in asphalt pavement or reflective cracking in asphalt overlay caused by underlying thermal cracking. Thus, transverse cracking is another primary distress. This study investigated the long-term field transverse cracking of 28 pavement projects, including WMA pavements and corresponding hot-mix asphalt (HMA) control pavements across the United States, covering different climate zones, WMA technologies, service years, pavement structures, and traffic volume levels. Two distress surveys were conducted at an interval of 2 years, and the material properties of the asphalt mixtures and binders were determined with field cores and extracted binders. The long-term field performance of the WMA and HMA pavements were compared for transverse cracking. The study found that HMA and WMA pavements exhibited comparable transverse cracking. Fracture work density obtained from indirect tensile testing at 14°F was found to be the significant determinant for transverse cracking. Significant mix design parameters were identified that can affect the resistance of mixtures to transverse cracking and that can be employed to guide the development of a well-performing mix design.

Thermal fatigue and cracking behaviors of asphalt mixtures under different temperature variations

While machine learning (ML) provides a powerful tool for correlating various factors and asphalt pavement cracking, its poor interpretability hinders a deeper mechanistic analysis of how these factors contribute to crack development. In this regard, this study proposed an interpretation framework for ML models, which consists of feature importance based on the SHapley Additive exPlanations (SHAP) method, factor influence analysis based on Accumulated Local Effects (ALE) and local conditional effects (LCE), and feature interaction analysis based on H-statistic and second-order ALE. Using the U.S. long-term pavement performance (LTPP) database, a gradient boosting regression tree (GBR) model was developed with maintenance, design, traffic, and climate factors as inputs and transverse, longitudinal, and alligator cracking as outputs. The generalization performance of all three cracking models exceeded 82%. Results indicated that transverse cracking is primarily triggered by low-temperature events, while longitudinal and alligator cracking are mainly caused by fatigue damage induced by traffic loads. Feature interaction analysis further revealed significant interactions in transverse cracking between the cumulative freezing index (CFI) and traffic load (CESAL) and in fatigue cracking between freeze‒thaw cycles (CFT) and precipitation (CTP). The outcome of this study is expected to bridge the gap between data-driven predictions and mechanistic understanding, providing interpretable insights for the design of durable asphalt pavements and the optimization of maintenance strategies.

Asphalt complex cracks' sensitivity to temperature and crack depth and adjustment of the composite stress intensity factor

Dynamic response of temperature-seepage-stress coupling in asphalt pavement

Asphalt pavements often suffer reflective cracking phenomena. Crack appearance at the road surface leads to several detrimental effects, including the loss of watertightness. Geocomposites, such as grid-reinforced bituminous membranes, represent an efficient method against reflective cracking since they combine improved tensile properties of grids and stress-relieving effects of membranes. Moreover, membranes allow pavement waterproofing. This paper presents laboratory and field studies carried out to investigate the reflective cracking resistance of geocomposite-reinforced asphalt systems. The study is based on a real-scale field trial constructed along an in-service motorway. Five geocomposites were taken into account and the possible use of a tack coat and application on a milled surface were also evaluated. Interface shear tests were carried out both on field cores and on laboratory-made samples. Moreover, pre-notched laboratory specimens were subjected to specifically developed simulative tests through the Wheel Tracking equipment. Experimental results clearly showed that a proper selection and application of optimised grid-reinforced bituminous membranes can significantly enhance reflective cracking resistance of asphalt pavements.

Crack sealing prevents the ingress of water in the pavement structure, thus preventing the weakening of the pavement and delaying its deterioration. Earlier studies indicate that sealing pavements in areas with a high ground water table (GWT) may prevent moisture from escaping upwards through cracks in asphalt pavements, therefore, accelerating stripping. The objective of this study was to provide guidelines for using crack sealing to minimize moisture entrapment under cracks, thus reducing stripping on low volume roadways. To achieve this, a calibrated Finite Element (FE) model was used to model a field experiment consisting of cracked and crack-sealed asphalt pavement sections. Sensitivity analysis was then conducted to compare crack-sealed and unsealed sections under different GWT levels, air relative humidity, air temperatures, rain intensities, and asphalt hydraulic conductivities. Results indicate that crack sealing could be applied under common rain intensities in Louisiana and any GWT depth without potential for stripping because of moisture entrapment if the hydraulic conductivity of the original pavement does not exceed 2 × 10–6 m/s. Yet, crack sealing should be applied after a dry period to ensure that the existing moisture in the original pavement is minimal. A non-linear regression model was developed for use in the Southern United States to help determine whether crack sealing should be used to avoid moisture damage in a cracked pavement at a given site based on the GWT and air relative humidity without the need for FE simulations. This can be a useful tool when planning maintenance activities.

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

Fatigue cracking in asphalt pavements results in decreased ride quality, decreased fuel economy, and provides an avenue for intrusion of water. Since the current asphalt mixture design relies primarily on proportioning of component materials, performance is not considered directly. An advancement in technology is to design through direct material property assessment and correlations to field performance, a performance-based mixture design. The objectives of this paper are to: (1) relate mixture stiffness, fatigue, and pavement system characteristics together for use in the performance-based mixture design; (2) identify a Simplified-Viscoelastic Continuum Damage (S-VECD) model output parameter which produces the most separation between poorly and satisfactorily performing structures when combined with dynamic modulus and phase angle information; and (3) evaluate the impact of reclaimed asphalt pavement on the performance of the indicator. A pavement response model was coupled with the S-VECD analysis to determine the fatigue life using a representative pavement structure. Results show a relationship exists between the fatigue life of the pavement system, the dynamic modulus and phase angle, as well as an energy-based index. This approach holds promise because of its reliance on material attributes that can be derived on one testing machine. The model parameters from dynamic modulus and direct tension cyclic fatigue testing can also be incorporated into performance prediction software, further enhancing the appeal of a performance specification using the approach described in this study.

Report on the Prediction of SurfaceInitiated Longitudinal Wheel Path Cracking in Asphalt Pavements

A prediction model for top-down cracking in asphalt pavements with open-graded friction course

In this paper, structural performance of a flexible pavement is evaluated using the finite element analysis considering the effect of tire pressure, axle load variations of vehicles. The pavement structure is modeled as three-dimensional four-layer system using finite element software of ANSYS. The pavement model is subjected to traffic loadings to simulate truck wheel loads at three different tire inflation pressures. Results from the model are verified using in laboratory test data. Model comparisons with measured laboratory test data are in good agreement. Therefore, finite element method could be used to estimate the potential distress efficiently. Analysis results show that peak maximum shear stress are very high and locates at the same magnitude level of the shear intensity of HMA, while maximum tension stress in direction of X, Y and Z are small. Hence, shear stress is an important factor that could result in top-down cracking in asphalt pavements.

The phenomenon of top-down cracking in asphalt pavements has drawn increased attention in recent years, yet the asphalt pavement field still lacks an effective top-down crack initiation model. Many factors contribute to the initiation and propagation of top-down cracking. This study developed a phenomenological top-down crack initiation model for mechanistic–empirical pavement design. Pavements at FHWA's accelerated loading facility were used to develop a top-down crack initiation model based on the failure strain of asphalt mixtures, as obtained from indirect tensile testing. It was found that the current Mechanistic– Empirical Pavement Design Guide top-down cracking model failed to predict top-down cracking in the wheelpath in the field accurately, whereas the proposed failure strain–based top-down cracking model was effective in predicting top-down cracking in the field. In addition, the Level 2 prediction of failure strain is developed here; it is based on binder failure shear strain, air void content, asphalt content, and percentage of aggregate passing U.S. Number 4 and Number 200 sieves. Further studies are needed to validate this new top-down cracking model and to develop an effective crack propagation model.

In this paper, a machine process to repair cracks in asphalt pavements by filling them with hot bitumen is demonstrated for the first time. We have characterized the quality of these fillings. Furthermore, the paper examines how the filling speed, temperature, bitumen type, crack width, crack irregularity, and the flow of hot bitumen affect the crack filling quality by the machine. In the laboratory we have used a 3D-printer as the machine to fill the cracks due to its simplicity. We have characterized the quality of the repaired cracks in terms of their porosity and shear and tensile strength. We have demonstrated that the bitumen flow, filling speed, and width and depth of cracks determine the quality of the filling and will need to be carefully controlled in a future autonomous crack filling device. The complex interaction between these parameters will need to be underpinned in future research.

Low temperature performance grading currently relies solely on Bending Beam Rheometer (BBR) for determining low temperature creep stiffness (S) and rate of modulus relaxation (m-value) at 60 s, both determined at low stress-strain levels, in the pre-failure zones. This aspect raises questions with regard to applicability of properties derived from the linear viscoelastic range for prediction of asphalt binder thermal cracking behavior. Furthermore, many researchers have reported a discrepancy between field cracking severity and predictions based on asphalt binder properties since the asphalt binder-aggregate interaction is non-existent in asphalt binder testing. Therefore evaluation of asphalt mastics properties which could save a considerable amount of time and equipment in comparison to mixture testing should be prioritized. These challenges indicate that considering fracture properties of asphalt mastics could be a better approach for prediction of thermal cracking in asphalt pavements. It is believed that development of failure master curves for the damage characterization of asphalt mastics at different temperatures and loading rates would be beneficial for better characterization of resistance to thermal cracking. Therefore, this study presents framework and preliminary results on the development of such asphalt mastic failure master curves using the new BBR-SENB test for damage resistance characterization. The complexity of the visco-elastic behavior of asphalt mastics in terms of time and temperature dependency is also recognized by the sensitivity of the failure properties to changes in loading time and temperature.