Moisture-induced strength degradation of aggregate–asphalt mastic bonds

A common manifestation of moisture-induced damage in asphalt mixtures is the loss of adhesion at the aggregate–asphalt mastic interface and/or cohesion within the bulk mastic. This paper investigates the effects of moisture on the aggregate–mastic interfacial adhesive strength as well as the bulk mastic cohesive strength. Physical adsorption concepts were used to characterise the thermodynamic work of adhesion and debonding of the aggregate–mastic bonds using dynamic vapour sorption and contact angle measurements. Moisture diffusion in the aggregate substrates and in the bulk mastics was determined using gravimetric techniques. Mineral composition of the aggregates was characterised by a technique based on the combination of a scanning electron microscope and multiple energy dispersive X-ray detectors. Aggregate–mastic bond strength was determined using moisture-conditioned butt-jointed tensile test specimens, while mastic cohesive strength was determined using dog bone-shaped tensile specimens. Aggregate–mastic bonds comprising granite mastics performed worse in terms of moisture resistance than limestone mastic bonds. The effect of moisture on the aggregate–mastic interfacial bond appears to be more detrimental than the effect of moisture on the bulk mastic

Temporary Networks in Polymer Modified Asphalts

The viscosity functions of several polymer-modified asphalts (PMAs) were studied at different temperatures in steady-state rate sweep tests. The materials were obtained by mixing different base asphalts with either styrene-butadiene-styrene (SBS), ethylenevinylacetate (EVA) or reactive ethylene terpolymers (RET). The first two polymers form a physical network that is swollen by the asphalt, while the latter is functionalized with glycidylmethacrylate (GMA) and can crosslink and/or chemically bond with the molecules of asphaltenes. In the presence of SBS or EVA, at certain temperatures, the viscosity curves exhibit a Newtonian behavior at low shear rates, followed by two distinct shear-thinning phenomena. In some cases, the first shear-thinning is preceded by a small shear-thickening region. Similar phenomena are not present in the viscosity curves of the RET-modified asphalts and can be related to a temporary nature of the physical polymer network

Rheology of Asphalts Modified with Glycidylmethacrylate Functionalized Polymers

Asphalt is known to be a colloidal suspension in which asphaltenes are covered by a stabilizing phase of polar resins and form complex micelles that are dispersed in the oily maltenic phase. In order to enhance its mechanical properties (e.g., in road paving), asphalts are often loaded with polymeric materials, thereby obtaining blends that can have different physical or chemical structures, depending on the composition of the added polymer. Asphalts modified by the addition of reactive ethylene terpolymers were prepared and their dielectric and rheological properties were measured both before and after a cure at high temperature. Even if it is not possible to determine the exact nature of the chemical interactions between asphalt and polymer, master curves obtained from dynamic data clearly show that during the cure the material tends to the behavior of a cross-linked network