Browsing by Subject "Creep test"

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    Investigation of asphalt binder and asphalt mixture low temperature properties using analogical models
    (2012-09) Moon, Ki Hoon
    In very cold climates, thermal cracking is the main distress that affects asphalt pavements. At these temperatures, asphalt materials become very stiff and reach stress values higher than their strength, and cracks form and propagate. Asphalt pavements are built with asphalt mixtures, which are composite materials that contain coarse and fine aggregates of specific sizes bound together with asphalt binder, a highly temperature susceptible viscoelastic material. In past years, micromechanical composite material models were used to explain the relationship between asphalt binder and asphalt mixture stiffness properties. Asphalt mixtures were assumed as two-phase materials or as three-phase material. Due to low order microstructural information (volume fractions) used in these models, the asphalt mixture stiffness was significantly under predicted. Recently, a semi-empirical model called Hirsch model and a transformation based on mechanically analog models, called ENTPE (École Nationale des Travaux Publics de l'État) transformation, were successfully used to predict asphalt mixture creep stiffness from asphalt binders creep stiffness and vice-versa, at low temperatures. In this thesis, these two models are further investigated to understand the physical meaning of the models parameters and to establish a link between the microstructure of mixtures and these parameters. This will be accomplished by analyzing digital images of the mixtures to obtain extensive information on their aggregate structure and by performing extensive three point bending creep tests on asphalt mixtures and their component asphalt binders. It is expected these results will significantly improve the design of asphalt mixture with good thermal cracking resistance.
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    Reassessment of Diametral Compression Test on Asphalt Concrete
    (Minnesota Department of Transportation, 1996-12) Drescher, Andrew; Newcomb, David; Zhang, Wei
    This report examines the diametral compression test, as described in ASTM D4123-82 (1987) and SHRP Protocol P07 (1993) procedures. The test helps determine the resilient modulus of asphalt concrete, and less frequently its Poisson's ratio, both mechanical parameters of an ideally elastic material. However, the actual behavior of asphalt concrete is not elastic, but viscoelastic. The viscoelastic behavior of asphalt concrete under traffic-induced loads can be described by the phase angle and the magnitude of the complex compliance or complex modulus. These can be determined from the diametral compression tests that subject the specimen to haversine load history, and from the viscoelastic data interpretation algorithms derived in the current research. To avoid inaccuracies in the data interpretation, the vertical deformation should be measured over a 1/4 diameter central sector of the cylinder by means, for example, of the in-house developed displacement gage. A series of tests on specimens with various asphalt binder viscosity verified the validity of the viscoelastic data interpretation. Specimens from Mn/ROAD materials showed the presence of viscoelastic properties even at temperatures well below freezing.