Top-down cracks (TDCs) in flexible and rubblized pavements constitute a distress that has been reported in the United States and other countries. Researchers have reached different conclusions regarding the causes of TDCs. In this study, field and laboratory investigations were conducted on conventional flexible and rubblized pavements exhibiting TDCs. The engineering characteristics of the pavement layers were obtained from the analysis of field data and laboratory test results. Detailed mechanistic analyses were then conducted using these characteristics to determine the potential for TDCs. The results of such analyses were compared with field data and are presented and discussed in this paper. The results and field data show that ( a) surface radial tensile stress induced by wheel loads and enhanced by differential stiffness due to construction, temperature, and aging can cause TDCs, ( b) aging of the asphalt binder decreases the tensile strength and the tensile strain at failure of the asphalt mix, and ( c) the locations of the maximum surface tensile stress predicted by the mechanistic analysis correspond very well to the locations of the TDCs observed in the field.
The degradation and the damage state of a flexible pavement section may be attributed to several factors. These include environmental factors, traffic loading factors, and material interaction and variability factors. The collective conditions of a pavement section in a particular damage state may be called pavement damage index (PDI). Such a damage index is related to the pavement deflection output. This paper discusses the characteristic parameters of the pavement time-dependent deflection response and their relationship to the damage done to the flexible pavement section in question. Further, a case study is presented where a full-depth asphaltic highway pavement section was tested after construction and before it was subjected to any traffic loading. The calculated characteristic parameters of the time-dependent deflection response indicated, at the time, that a severe damage in the form of permanent deformations (rut depth) should be expected when the pavement section is opened to traffic. The highway section in this case study experienced a rut depth of up to 25.4 mm (1 in.) after only six months of mixed traffic (trucks and cars).
“Louisiana–Vision 2020” serves as a benchmark for improving highway pavements over a 20-year period. Cost-effective pavement preservation is emphasized in current Louisiana state law and federal law. The Louisiana Department of Transportation and Development (LADOTD) and the FHWA strategic plans also emphasize cost-effective pavement preservation. In an effort to improve the pavement management system (PMS), the Louisiana Transportation Research Center initiated a two-phase research study to evaluate the overall performance and effectiveness of the system. This paper focuses on the Phase I study and addresses the state-of-the-art practice of LADOTD's PMS and the results of a departmental survey to assess the needs of the various districts. The use of various location reference systems by different units in the department makes linking to different database sets difficult. Although many of the districts’ engineers have no concerns about all the referencing systems, most would prefer to have a unified reference location system. All the districts have access to the PMS data and most of them use it; however, the degree of use varies from one district to another. This paper also discusses the types of PMS output and reports, the degree to which the outputs are analyzed, the accuracy of the information currently available, and the degree to which the current PMS data track and differentiate between different preservation actions.
A large research program sponsored by the Michigan Department of Transportation was designed and completed to evaluate the effect of polymer modification on the various properties of asphalt mixtures. These include the micro-and macrostructural, morphological, chemical, and engineering properties. Some of the engineering properties of the styrenebutadiene-styrene and styrene-etylene-butylene-styrene polymer-modified asphalt mixtures are presented and discussed. The elastic, fatigue, tensile, and permanent deformation properties were investigated at 60, 25, and −5°C. It was found that, for some polymer systems, the fatigue life and the indirect tensile strength increased considerably at 25°C while the elastic properties at −5°C were not affected by the addition of polymer. The implication of this is that the use of some polymer systems in asphalt mixtures enhances their fatigue cracking and rutting resistance without affecting the low temperature cracking potential.Some polymer systems are being increasingly used in asphalt concrete pavements because of their role in reducing several types of pavement distress and enhancing pavement performance. Pavement performance is affected by the properties and behaviors of the roadbed soil, the granular subbase and base layers, and the asphalt concrete layer. Several properties of the asphalt concrete layer affect pavement performance. These include fatigue cracking, rutting, hardening of the asphalt binder, and temperature cracking potentials.Based on their functions and behaviors, polymers can be divided into three types (1): dispersed thermoplastics such as polyethylene; network thermoplastics such as styrene-butadiene-styrene (SBS), styrene-etylene-butylene-styrene (SEBS), and styrene-butadienerubber; and reacting polymers such as Elvaloy AM. In general, the addition of polymers to asphalt concrete mixtures enhances the resistance of the asphalt concrete (AC) to fatigue cracking, rutting, temperature cracking, and stripping (2,3). With regard to fatigue and tensile strength properties, studies have shown that the addition of polymers to asphalt mixtures results in a substantial improvement in these properties. Shuler et al. (4) conducted indirect tensile tests using AC-5 binder and SBS polymer system as one of the modifiers. They reported that, for AC-5 modified with 6 percent SBS polymer, tensile strength increased significantly over that of the straight AC-5 at −21, 25, and 41°C. Button et al. (5), on the basis of a stresscontrolled fatigue testing and a fracture mechanics evaluation, reported that AC-5 modified with SBS polymer exhibited superior fatigue properties compared to those of straight AC-5 at 20 and 0°C.In 1994, a three-phase research study was initiated at Michigan State University (MSU) to characterize the properties and possible benefits of polymer-modified asphalt (PMA) mixtures under low and high temperatures. The study was funded by the Michigan Department of Transportation (MDOT). The three phases cover (a) the fundamental physical, chemical, and ther...
For the past 2 decades, significant research has been conducted on polymer-modified asphalt (PMA) mixtures. Polymers can successfully improve the performance of asphalt pavements at low, intermediate, and high temperatures by increasing mixture resistance to fatigue cracking, thermal cracking, and permanent deformation. Most of the research has been concentrated on the characterization and relative comparison of neat and PMA mixtures, and little work has been done toward the development of fatigue and permanent deformation models for PMA mixtures. A 3-year study that was sponsored by the Michigan Department of Transportation was conducted at Michigan State University to characterize PMA mixtures. It was found that the rheological and engineering properties of PMA mixtures largely depend on the polymer type and content. The improvements in the fatigue lives and resistance to permanent deformation are mainly due to the improvements in the rheological properties of the binders. Fatigue life and permanent deformation models were developed. These models show that the laboratory fatigue life and permanent deformation are strongly related to the rheological properties of binders and the engineering properties of PMA mixtures.
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