Effect of Softening Additives on the Moisture Susceptibility of Recycled Bituminous Materials Using Chemical-Mechanical-Imaging Methods

This study examined the effects of softening additives on the moisture susceptibility of recycled bituminous materials using chemical, mechanical, and imaging laboratory investigation methods. Two chemically different rejuvenators, one petroleum-tech (aromatic extracts) and one green-tech (tall oil), and an amine-based warm mix additive were selected as such softening additives. For chemical investigation, the two rejuvenators were examined using saturates-aromatics-resins-asphaltenes (SARA) analysis, Fourier-transform infrared (FT-IR) spectroscopy, thermogravimetric analysis coupled with FT-IR (TGA-IR), and nuclear magnetic resonance (NMR). Mechanically, a semicircular bending (SCB) fracture test was conducted to evaluate the moisture damage resistance of the recycled bituminous mixtures treated with the different rejuvenators and the warm mix additive. Laser scanning microscopy (LSM) was also used to acquire noncontact microscale topographical images to evaluate the effect of lower temperatures on aggregate-matrix interaction in the production of mixtures with the warm mix additive. The test-analysis results were then investigated to identify relationships between different features (i.e., chemical, mechanical, and topographical) of the mixtures associated with the different rejuvenators and the warm mix additive. Although additional data and investigations are still necessary to reach more definite conclusions, it appears that specific chemical functional groups in the rejuvenating agents are associated with the rejuvenated mixtures' moisture sensitivity, and the lower production temperatures used in warm mixtures may lead to a somewhat more porous region between the aggregates and the matrix phase of recycled-rejuvenated bituminous mixtures.