Durability and stiffness of mastic asphalt on steel bridge deck plates loaded in flexure

The objective of this work was to improve both the durability and stiffness of mastic asphalt - the preferred surfacing material for steel deck bridges in the United Kingdom and overseas - by varying the binder viscosity and binder content to obtain the optimum mix. A mix design similar to that adopted for the Humber Bridge was chosen as the standard mix with which to compare the modified mixes. The method of testing involved repeated loading of composite steel/asphalt plates in 3 point bending until fatigue cracking occurred. Dynamic load pulses were applied to simulate the force/time variation occurring under real traffic. Single pulse tests were carried out to determine the stiffness of all the mixes. All of the tests were conducted at controlled temperature. The results showed that fatigue endurance was improved at temperatures above 15 degrees C by reducing binder viscosity. However, the performance was reduced at lower temperatures. A similar result was achieved by increasing the binder content. Finally, an optimum performance for both endurance and stiffness was obtained by reducing both the viscosity and the binder content.