Distress Modes Research Articles

Mechanistic Model for Transition Probabilities

One important input in a pavement-management system is the matrix of transition probabilities. A methodology is proposed that employees mechanistic distress submodels for evaluating pavement distresses in terms of fundamental material behavior and structural response to environment and traffic factors. This approach allows the distress modes to be modeled individually so that the appropriate measures for correcting deficiencies can be readily identified. The performance submodels are formulated within a stochastic framework for determining the transition probabilities. The formulation is based on state-of-the-art structural reliability methods, specifically, the first-order reliability method (FORM), and is applicable to individual and combined modes of distresses. It is able to handle numerous variables with various distribution types and correlations. The multimode distress case is an extension of the individual distress modes incorporating the concept of cut-sets and directional simulation. With the proposed methodology, the assumption of a time-invariance matrix of transition probabilities, as adopted in existing pavement-management systems, is no longer necessary.

Effect of Roughness and Sliding Friction on Contact Stresses

The stress distributions associated with smooth surfaces in contact are rarely experienced in practice. Factors such as surface roughness, lubricant films, and third body particulates are known to influence the state of stress and the resulting rolling contact fatigue life. This paper describes a numerical technique for evaluating the complete subsurface field of stress resulting from the elastic contact of nonconforming rough bodies, based on measurements of their profile. The effect of sliding friction is included. The presence of asperities within the contact region gives rise to high shear stresses near the surface. Realistic coefficients of friction for lubricated sliding contacts (i.e., μ ≈ 0.1) causes the “smooth body” shear stresses to interact with the asperity stresses to produce a large, highly stressed region exposed to the surface. The significance of these near-surface stresses is discussed in relation to modes of surface distress which lead to eventual failure of the contacting surfaces.

Asphalt Concrete Creep as Related to Rutting

Rutting is one of the major modes of distress in flexible pavements. It is caused by plastic deformation that can occur in any of pavement layers. Historically, rutting of asphalt concrete has been considered a mix design and/or construction problem. Furthermore, current methods of mix design are independent from pavement thickness design procedures. The focus of this paper is on permanent deformation of asphalt concrete layer. The primary objective is to develop a methodology for characterization of rutting potential of asphalt mixtures that can be easily implementable at state highway agencies. Permanent deformation characterization procedures are to be based upon parameters that can be integrated into mechanistic pavement design procedures. A mechanistic methodology is developed for permanent deformation characterization of asphalt paving materials. Rheological properties of hot mix asphalt (HMA) are thoroughly studied by means of a simple creep test that is originally developed by Shell researchers. Procedures are developed in order to account for nonlinear, viscoelastic, and viscoplastic deformation components of HMA. Results indicate that structural arrangement of pavement layers has a significant influence on rutting performance of the HMA layer. Findings of this study can be easily implemented in an integrated mix-thickness design procedure.

Structural Deterioration Model for Rigid Airfield Pavements

Corps of Engineers accelerated traffic tests were reanalyzed to develop a structural deterioration model for airfield pavements. Test‐back performance was measured in terms of structural condition index varying from zero to 100. This index is derived from the pavement‐condition index. Pavement performance is predicted in terms of a structural condition index from the pavement's layered elastic stresses, flexural strength, and number of traffic loads. This model was compared to other design criteria, unfailed test sections, and three failed airfield pavements and gave reasonable agreement. This model only accounts for damage from fatigue loading, and there are a number of other potential pavement‐distress modes that it does not include. Each of these distress modes needs to be evaluated separately.

Elastic Stresses Below Asperities in Lubricated Contacts

The presence of contacting asperities in lubricated rolling bearings modifies the subsurface stress field strongly in the neighborhood of the surface and, to a lesser extent, at larger depths where the maxima of the shear or von Mises stress of a smooth Hertzian contact normally exist. The near surface stresses are of importance because they may result in micropitting, a mode of surface distress which leads to the eventual fatigue failure of the contacting surfaces. A mathematical method is presented in this paper which allows the statistical calculation of important parameters (maximum von Mises stress or maximum shear stress amplitude) of the stress fields generated under elastically deforming asperities during their passage through a lubricated contact. The asperities themselves are modelled using estimates of the surface spectral moments obtained from single-profile trace measurements. The method is applicable to both isotropic and anisotropic rough surfaces. Moreover, the important effect of the shear surface tractions, including tractions over the asperities, is contained in the analysis. Computed examples are presented for different surface textures and film thicknesses in the case of a deep groove ball bearing. Finally, a qualitative attempt is made to correlate features of these stress fields with the presence of surface pitting, and the limitations of the analysis are discussed.

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Permanent deformation, mainly referring to rutting, is one of the main distress modes of asphalt pavement. Exploring effective methods to mitigate the rutting distress is of great significance for providing a long-life and safe road. The rutting solutions were first reviewed. It was found that the efforts from academic and engineering industries focused on enhancing the rheological properties of asphalt binder by adding modifying powder, fiber or mixture into binder or mixture, as well as strengthening aggregate interlock and applying novel pavement structure. Semi-flexible asphalt pavement was suggested to be a promising method to fight the rutting distress, because it has a high mechanical property without scarifying the flexibility of asphalt pavement. In order to consider the influence of temperature on rutting occurrence, cool asphalt pavements, especially heat-transfer induced structures, were reviewed and deemed to be a new strategy for reducing rutting susceptibility of asphalt pavement. In order to evaluate the effectiveness of above rutting solutions, many tests, such as multi-stress creep recovery test for asphalt binder and wheel tracking test for asphalt mixture, were reviewed. By linking the reported results of wheel tracking test with high-temperature rutting mechanism it was advised to develop a test method that could reproduce the real field pavement environment, including multiple stress mode, temperature gradient control system and pavement structure, to assess the rutting response of asphalt mixture. This review is expected to provide an overall insight on the existing rutting solutions and test methods, and recommend future studying areas relevant to rutting distress.

Structural Design of Cemented Pavement Layers

A mechanistic structural design procedure for pavements containing cement- and lime-treated layers is outlined. The procedure includes provision for use of a range in traffic wheel loadings, fundamental material properties, and failure criteria, including fatigue. Layered elastic theory is utilized to calculate stresses and strains at critical positions in the pavement components, and these are compared with allowable values to minimize specific distress modes. Use of standard designs resulting from the more detailed analyses are discussed and explained. Reasonable agreement between predicted and actual response and behavior of several trial pavements are noted. Three design examples illustrating the procedure are included.