Fundamental Characterization of Engineering Properties of Gussasphalt Mixtures

Surfacing the deck of a steel bridge is costly and technically challenging and an improvement on the life of the surfacing would be of economic benefit to the bridge industry. The objective of this work was to improve both the durability and stiffness of the Gussasphalt mixture, one of the preferred surfacing materials for steel deck bridges around the world, by varying the binder types and binder and filler content to obtain the optimum mix. A three-stage characterization process was proposed for the Gussasphalt mix in this study. Fundamental characterization started with evaluation of the viscoelastic properties of binders, extended to the rheological behavior of asphalt-mineral filler mastics, and ended with investigation of the engineering properties of Gussasphalt mixture. The degree of stiffening was found to vary significantly with different types of mineral filler and bitumen. The addition of Trinidad Lake asphalt (TLA) to bitumen caused an increase in stiffness, and the stiffening effect was more pronounced at lower temperatures than at higher temperatures. The suitable concentration of TLA was found to be in the range of 20-30% by weight of the binder. The optimum filler content was determined according to the rheological properties and the formation of the critical network. The increase in moduli resulting from the addition of mineral fillers had the potential benefit of improving the resistance to rutting of the Gussasphalt mixture. This indicated the possible presence of physicochemical reinforcement between the binder and filler. Fillers that produced very significant stiffening effects, however, could result in brittle mixtures and difficulty in construction. The engineering properties of a Gussasphalt mix could be characterized by Lueer fluidity, indentation, bending, and wheel-tracking tests.