Experimental study on the enhancement of mechanical properties of bituminous mastics at high strains

The paper presents the results of a laboratory investigation aimed at evaluating the effects of filler on the rheological properties of bituminous mastics. More specifically, the mechanical behaviour of mixtures made with bitumen and inorganic aggregate is analyzed: selected fines from Municipal Solid Waste Incinerator (MSWI) ashes were used. The interaction between binder and aggregate determines a change in the rheological behaviour. Experimental data show a viscoelastic behaviour in the usual operating temperatures range and in a dynamic stress configuration characterized by high strains. It can also be observed that the thermal susceptibility of the mastic markedly depends on the content of filler, which is responsible for the variations of stiffness and resilience, measured in terms of complex modulus and phase angle. In order to examine the rheological effect of inorganic filler, tests were performed with the objective of checking the mastic behaviour at the edge of the linear viscoelastic region. Above the linear viscoelastic threshold, the bituminous mastic is significantly sensitive to the presence of filler and a statistically robust protocol is required. The experimental data were obtained by means of a dynamic shear rheometer (DSR) and synthesized with a viscoelastic model. For the interpretation of the results, master curves of the main performance indices were calculated, being related to the filler content. As expected, the results confirm that artificial aggregate from MSW incinerators can be used in order to improve mastic properties.