Browsing by Subject "Asphalt concrete"
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Item Cracking of Asphalt Concrete at Low Temperatures(Center for Transportation Studies, University of Minnesota, 1994-10) Labuz, Joseph; Dai, ShongtaoThe 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.Item Influence of Roofing Shingles on Asphalt Concrete Mixture Properties(1993-06) Newcomb, David; Stroup-Gardiner, Mary; Weikle, Brian; Drescher, AndrewIt is estimated that the production of new roofing shingles generates approximately 1,000,000 tons of waste annually in the U.S., and about 36,000 tons of this waste is in the Twin Cities Metro Area of Minnesota. With another 8.5 million tons of waste materials which are similar to those used in asphalt concrete, it seems viable that their use in hot-mix would be an attractive alternative to disposing of them in landfills. This report presents the results of an effort to evaluate the use of roofing waste generated by manufacturers and from reconstruction projects. It was shown that up to 5%, by weight of mixture, manufacturing waste roofing shingles could be used in asphalt concrete with a minimum impact on the properties of the mixture. At a level of 7.5%, a noticeable softening of the mixture occurs, and this might be detrimental to pavement performance. The use of shingles from roof reconstruction projects resulted in the embrittlement of the mixture which may be undesirable for low temperature cracking of pavements. The manufactured shingle waste seems to work well in stone mastic asphalt mixtures.Item Low-temperature fracture behavior of asphalt concrete in semi-circular bend test.(2012-06) Zegeye Teshale, EyoabAsphalt concrete mixtures behave as quasi-brittle materials at temperatures close to the glass transition of the component asphalt binder. A salient feature of structures that consists of quasi-brittle materials is that there exists an intricate size effect on the structural strength. The existence of such size effect is mainly attributed to the presence and the stable growth of a relatively large fracture process zone (FPZ) that develops ahead of the crack tip prior to failure (maximum load) of the structure. This inelastic region is characterized by non-linear material deformation and fracture energy dissipation that ultimately generate stress redistribution and govern the strain-softening of the material. Understanding this size effect is crucial for two purposes: a) extrapolation of small-scale laboratory testing results to full-scale design, and b) identification of material fracture properties. In this research work, laboratory experiments and numerical simulations were conducted to investigate the size effect of asphalt concrete tested in semi-circular bend (SCB) test at low temperature. Geometrically similar specimens of different sizes and with different notch lengths were tested. The experimental results were analyzed with the energetic-size effect theory, and were used to develop type I and II strength scaling laws, respectively, for the notchless and deep notched specimens. The validity of the scaling laws at large sizes was evaluated through finite element simulations of mode I crack growth in the SCB test. A cohesive zone model (CZM) was successfully calibrated by experimental data, and implemented to predict the nominal strength in large SCB specimens. The strengths predicted from the numerical models were in good agreement with the scaling laws' strength prediction. Based on the analyses of the strength scaling laws derived, important conclusions on the fracture behavior of asphalt concrete at low temperature, as well as size of FPZ were drawn.Item Reassessment of Diametral Compression Test on Asphalt Concrete(Minnesota Department of Transportation, 1996-12) Drescher, Andrew; Newcomb, David; Zhang, WeiThis 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.