Browsing by Subject "Bending Beam Rheometer"

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    Determining the flexural strength of asphalt mixtures using the Bending Beam Rheometer.
    (2010-12) Turos, Mugurel Ioan
    Asphalt mixture creep stiffness and strength are needed in the AASHTO Mechanistic Empirical Pavement Design Guide low temperature algorithm to predict low temperature performance. A procedure for obtaining creep stiffness by testing thin mixture beams using a Bending Beam Rheometer was previously developed at University of Minnesota. The possibility of performing strength tests on thin mixtures beams using a slightly modified Bending Beam Rheometer is investigated in this thesis. First, standardized strength tests, such as Indiredt Tension Test, Thermal Stress Restrained Specimen Test, and Direct Tension Test are performed on a group of eleven mixtures. Then, on the same eleven mixtures, three sets of tests are performed using the proposed method called Bending Beam Strength (BBS).  The first set of tests is performed to investigate the reliability and reproducibility of BBS testing method, and the validity of the measuring concept. Weibull modulus is calculated as part of the analysis.  The second set of tests is used to investigate the joint effect of temperature, conditioning time and loading rate, on the measured strength of three different mixtures, by using a 23 factorial design  The third set consists in tests performed on a second group of eight mixtures tested at three temperatures. The different test results are then compared. Initially the measured values were put side by side. Promising results were obtained but the values were statistically different. The measured values are transformed taking into account the size of the samples and the testing method difference. The statistical analysis performed on the corrected values show that the BBS strength values are similar to the values obtained with other test methods.
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    Experimental Investigation of Bio-sealants Used for Pavement Preservation and Development of a New Strength Test for Asphalt Binders at Low Temperature
    (2017-10) Ghosh, Debaroti
    Surface treatment using sealants as a mean of pavement preservation is an important tool for cost-effectively extending service life of pavement. Sealants have become an important tool for cost-effectively extending the service life pavements. Due to the combined negative effects of asphalt aging and thermal cracking, it is always more challenging to choose an appropriate preservation technique for pavements built in cold-regions. Asphalt aging and thermal cracking negatively affect pavements built in cold climates. Therefore, it is important to evaluate the effects of sealants in laboratory conditions before application in the field to ensure effective performance. However, preservation activities cannot effectively address major distresses, such as low-temperature cracking, that can occur when the pavement was built from the very beginning with less durable materials. Therefore, an essential requirement to mitigate low-temperature cracking of pavements for asphalt materials used in the construction of pavement built in cold- regions is ensuring proper fracture properties of the asphalt materials used in construction. This study has two parts. In the first part, a laboratory evaluation of the effects of adding bio-sealants to both asphalt binder and mixture is performed. The goal is to obtain relevant properties of treated asphalt materials to understand the mechanism by which sealants improve pavement performance. For asphalt binders, a dynamic shear rheometer and a bending beam rheometer were used to obtain rheological properties of treated and untreated asphalt binders. For asphalt mixtures, field cores from both untreated and treated sections were collected and thin beam specimens were prepared from the cores to compare the creep and strength properties of the field-treated and laboratory-treated mixture. It is observed that the oil-based sealants have a significant softening effect on the control binder compared to the water-based sealant and traditional emulsion. Oil-based sealants increased rutting and fatigue potential of the binder and helped the low-temperature cracking resistance. For asphalt mixtures, different trends are observed for the field samples compared to the laboratory prepared samples. Similar to binder results, significant differences are observed between the asphalt mixtures treated with oil-based and water-based sealants, respectively. Additional analyses were performed to better understand the sealant effects. Fourier transform infrared spectroscopy (FTIR) analysis showed that the sealant products could not be detected in mixture samples collected from the surface of the treated section. Semi-empirical Hirsch model was able to predict asphalt mixture creep stiffness from binder stiffness. The results of a distress survey of the test sections correlated well with the laboratory findings. In the second part, a news binder strength testing method is proposed with the goal to provide an effective tool for selecting asphalt binders that are crack resistant. A modified Bending Beam Rheometer (BBR) is used to perform three-point bending strength tests, at constant loading rate, on asphalt binder beams at low temperature. Based on the results, a protocol for selecting the most crack resistant material from binders with similar rheological properties is proposed.