Determining the flexural strength of asphalt mixtures using the Bending Beam Rheometer.

Abstract

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.