Measure of asphalt emulsions stability by oscillatory rheology

A new methodology to monitoring an asphalt emulsion destabilization process is proposed. This method is based on the evolution of some rheological properties along time such as the viscosity, the Cross-rate constant and the elastic and viscous modulus of the emulsion. Two concentrated asphalt emulsions (70% of asphalt) have been formulated to study their stability using cationic emulsifiers. Results suggest that emulsions viscosity and consequently the Cross-rate constant decrease over time. The rheological behavior of emulsions evolves from shear-thinning to Newtonian as coalescence takes place. Coalescence was verified by the measure of the droplets size distribution against time using a laser light scattering equipment. This parameter evolves during time and reaches values of about 400 and 900% of increase in the emulsions studied. The elastic and viscous modulus of the emulsions tend also to decrease as long as coalescence occurs and were followed-up in time. In our systems, a drop of about 90% has been calculated as soon as emulsions become unstable. Results of this methodology were compared to those of traditional methods used in industry. Finally, the applicability of this test is conditioned to viscoelastic asphalt emulsions. The minimal requirements of asphalt content were found for one of the emulsions. However, the viscoelasticity of the testing emulsion must be the first parameter to be checked out, and this factor depends on many formulation parameters.