Effect of moisture susceptibility on different bituminous mastics

Moisture or water damage in asphalt mixtures can be defined as the loss of strength and durability, and an increase in stiffness leading to a more brittle behavior of materials and cause the adhesive failure at the binder-aggregate surface and/or cohesive failure within the binder or mastics. The performance and behaviour of asphalt mixtures are strictly dependent on the response of bituminous binders and mastics. The scope of this research is to acquire information on how moisture may affect rheological and chemical properties of different mastics made by different fillers. A neat bitumen and four mastics were prepared and tested, each of which combined with a specific filler. The conditioning procedure consisted in repeating wetting and drying cycles for three times. After each conditioning phase, couple of samples were tested by means of Dynamic Shear Rheometer (DSR) and Fourier Transfer Infrared spectrometer (FTIR). DSR was employed to determine the rheological properties of materials, such as the complex shear modulus (G*) and the phase angle (δ) at different temperatures and frequencies. FTIR has been used to investigate the chemical composition of bitumen and mastics after its reaction with water, in particular a specific range of wavelength was investigated to determine the absorption of the water and to combine data coming from rheological analysis. At high frequency and/or low temperature all materials behave as a solid; both rheological parameters (complex shear modulus and phase angle) tend to an asymptotic value throughout all the conditioning processes, whereas at low frequency and/or high temperatures is evident an increase of the complex shear modulus, due to water intrusion. Differences between mastics and neat bitumen are present in the intermediate frequency region. FTIR spectra for all mastics confirmed their rheological behavior.