Filler Reinforcement Mechanisms in Asphalt Mastics

This dissertation proposes two mechanisms by which mineral filler changes the mechanical and thermo-volumetric properties of the asphalt binder: (a) physico-chemical interaction that results in an overall softening of the continuous phase of the mastic (i.e., binder) and (b) a mechanical reinforcement due to volume replacement and particle to particle interaction that results in an increase of stiffness of the mastic.;The experimental results collected in this study indicate that the physico-chemical interaction effect is the result of adsorption of asphaltenes and resins (i.e., polar groups in asphalt) on the surface of the filler particles. This adsorption is partially responsible for the changes in the mechanical properties (e.g., stiffness, viscosity) and thermo-volumetric properties (e.g., coefficients of thermal contraction and glass transition temperature-Tg) of the mastic. The amount of polar groups adsorbed was found to depend on the Braunauer-Emmett-Teller (BET) surface area of the filler but not on the chemical composition of the filler or the asphalt. The higher the BET surface area, the greater the amount of polar groups adsorbed, and the lower the glass transition temperature.;The mechanical reinforcement was verified with micromechanical models for a wide variety of mastics using the Finite Element Method (FEM). Simulations at high and low temperatures were used to show the importance of filler gradation on estimating the mechanical reinforcement due to particle to particle interaction.;Experimental measurements for mastics prepared with different fillers, combined with two asphalts, at concentration ranging from 10 to 40 % filler by volume of asphalt confirmed that the mechanical and thermo-volumetric properties of mastics are the result of two competing effects: a softening of the viscoelastic matrix due to adsorption of polar components on the filler surface and a stiffening effect due to volume reinforcement of the mineral filler and particle to particle interactions.