The Flexural Strength of Asphalt Mixtures Using the Bending Beam Rheometer

Asphalt mixture creep stiffness and strength are needed in the low temperature temperature algorithm of the AASHTO Mechanistic Empirical Pavement Design Guide to predict low temperature performance. A procedure for obtaining creep stiffness by testing thin mixture beams with a Bending Beam Rheometer was previously developed at University of Minnesota. Preliminary work investigating the possibility of also obtaining bending strength by testing thin mixtures beams is presented in this paper. Indirect Tensile (IDT), and Direct Tension (DT) strength tests are performed on eleven mixtures. The same eleven mixtures are used to perform three sets of tests using the proposed method named Bending Beam Strength (BBS). First set 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. Second set of tests is done to investigate the effect of temperature, conditioning time and loading rate on the measured strength of three I1l1xtu:es. Third set consists of tests performed at three different temperatures on eight mixtures. IDT, DT and BBS experimental determined strengths are first compared without using any transformation, and results are found to be statistically different. The results are then transformed to take into account the size of the samples and the testing configuration. The statistical analysis indicates that BBS strength values are similar to the values obtained with IDT test method.