Temperature Dependent Tensile Strength of Asphalt Mixtures in Relation to Field Cracking Data

The relative performance of conventional and polymer modified asphalt mixtures was evaluated in the laboratory and in the field. Homogeneous beams of several mixtures were tested in four-point-flexion tests at controlled temperature. The test results enabled a fast and accurate determination of how the tensile strength and apparent modulus decrease when the temperature increases. The three polymer modified mixtures had significantly higher tensile strength and modulus than the conventional mixture at any temperature. A method was developed for quantitative evaluation of the field cracking degree and its evolution with time (position, length, orientation, evolution of damage condition). Surveys were performed on several rigid base and flexible pavements of various ages. Usually, new overlays with polymer bitumen were less fissured (by a factor of 2 after three years) than overlays with conventional bitumen. It was also observed that flexible pavements with polymer bitumen show practically no cracks after three years of service. These results are encouraging for the polymer bitumen, but three years is too short for a rigourous comparison of performance.