Browsing by Subject "Low temperature"

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    Cracking of Asphalt Concrete at Low Temperatures
    (Center for Transportation Studies, University of Minnesota, 1994-10) Labuz, Joseph; Dai, Shongtao
    The objectives of this research are (1) to characterize the fracture resistance of asphalt concrete at low temperatures and (2) to develop a simple test method for laboratory testing. Cracking of asphalt concrete at low temperatures is a major problem in the Upper Midwest. The cold temperatures in the winter months impart a brittle behavior to an otherwise ductile (viscous) material. The formation of cracks in the pavement provides a pathway for the migration of water, which may refreeze and cause more damage. The conventional three-point-bend (3PB) load configuration is proposed for conducting fracture tests. The entire 3PB fixture is placed in an environmental chamber, where the temperature is controlled and maintained at -18° (0°) and -34°C (-30°F). The experimental apparatus and test procedure are described in detail, and the corresponding formulae are derived. Following linear fracture mechanics, the fracture toughness of a particular asphalt concrete at 10% air voids is about 0.5 MPa-m° s at both temperatures, although the nonlinear response is more pronounced at -18"C. This means that less energy is needed to initiate a crack at -34°C compared to -18"C. Furthermore, it appears that the toughness of the asphalt concrete is increased with an increase in compactive energy, which is indicated by a decrease in air voids content.
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    Impact of asphalt mixture design parameters on transverse cracking performance and laboratory testing results
    (2015-04) Helmer, Benjamin William
    In cold climate regions, thermal cracking of asphalt pavements is a primary pavement distress. Cold climates cause thermal contraction within the pavement. When combined with the brittle behavior of asphalt at low temperatures, the thermally induced stresses are relieved by transverse cracks forming in the pavement. This cracking facilitates poor ride quality and premature failure of the pavement. There is currently no asphalt mixture performance test required by a majority of Department of Transportations (DOTs) in the United States to address the issue of thermal cracking. Previous research has indicated that fracture energy of asphalt mixtures is a reliable predictor of transverse cracking performance. This mechanistic property of asphalt mixtures can be found using the disk-shaped compact tension (DCT) test. On basis of previous research, a low-temperature cracking performance specification that uses DCT fracture energy has been developed. This project focused on eighteen highways containing twenty-six separate study sections. The projects encompassed different construction techniques, material compositions and climatic zones. The results from field studies, analysis of the mix parameters for each section and laboratory testing for sections are presented in this document. The results provide validation for previous research that suggests the use a performance test is vital to accurate projection of roadway transverse cracking performance. Other findings include reaffirmation of common knowledge about various mix parameters that suggest increasing or decreasing values will have positive and negative effects on both cracking amounts and performance testing. In nearly all instances, sections with an overlay construction type performed inferior to reclaimed construction types. For example, reclaimed sections exhibited roughly one-third the average transverse cracking amount of overlay sections. This phenomenon will be monitored in future studies.
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    Optimizing Asphalt Mixtures for Low-volume Roads in Minnesota
    (Minnesota Department of Transportation, 2023-08) Barman, Manik; Dhasmana, Heena; Manickavasagan, Vishruthi; Marasteanu, Mihai
    Minnesota has a large number of low-volume asphalt roads. These roads typically fail because of environmental factors, such as frigid temperatures, freeze-thaw cycles, and seasonal and daily temperature variations. The goal of this study was to suggest modifications to asphalt mixture designs currently used for low-volume roads in Minnesota to improve the resistance of the mixes against the environmentally driven distresses. The study was conducted by accomplishing multiple tasks, such as a literature review, online survey, fieldwork studying the cause of the asphalt pavement distresses, laboratory work comparing asphalt mixtures designed with Superpave-4, Superpave-5, and regressed air voids methods, and studying the field compaction of Superpave-5 mixes. The mechanical performance of the asphalt mixes was studied by conducting Disc-Shaped Compact Tension (DCT), Indirect Tensile Strength (ITS), and Dynamic Modulus (DM) tests. The study included both laboratory- and plant-produced mixes. The study found that asphalt layers for the low-volume roads did not get enough densification, which augments environmentally driven distresses, such as thermal cracks, and longitudinal joint cracks. The Superpave-5 method holds considerable promise for the design of asphalt mixtures for low-volume roads in Minnesota, which may likely increase the asphalt layer densification and mitigate some of the common distresses.