Investigation on asphalt binder strength at low temperatures

A new strength test method for asphalt binders at low temperatures is investigated in this paper. A modified Bending Beam Rheometer (BBR), capable of applying loads at different rates, is used to obtain asphalt binder flexural strength. Strength values obtained from the BBR test are compared with strength values obtained from the Direct Tension Tester (DTT) test and significant differences are found between the two tests. Additional BBR strength tests are run on asphalt binder beams after replacing the ethanol used in the cooling bath with potassium acetate, similar to DTT testing conditions, and flexural strengths significantly larger than those obtained with ethanol are obtained. Weakest link theory is used to convert three-point bending strength to direct tension strength and to perform volume correction of DTT values. Based on the corrected values, the BBR and DTT strength measurements are similar, when the same cooling medium is used. The effect of the cooling medium on BBR creep stiffness is also evaluated. From the limited experimental tests, it appears that there are no significant differences in stiffness and m-value after 1 h of isothermal storage.