Physical and rheological characterization of carbonated bitumen for paving applications

In the paving industry, current attempts aimed at reducing greenhouse gas emissions have focused on the development of technologies that decrease bitumen viscosity so that asphalt mixtures can be produced at temperatures that are lower than conventional mixing temperature for hot-mix asphalt. This study focuses on the feasibility of producing new lower energy asphalt mixtures using CO2-modified bitumen. Gravimetric sorption techniques were used to establish the kinetics of CO2 diffusion in bitumen at multiple pressures. The rheological properties of the carbonated bitumen were characterized at multiple temperatures and loading frequencies using a dynamic shear rheometer.

The results showed that CO2, at concentrations of up to about 0.3% w/w, caused significant (up to 3-folds) reduction in bitumen viscosity. A 10-fold increase in equilibrium CO2 uptake was observed when binders were conditioned in CO2 at 300 psi versus at 40 psi. The carbonated bitumen developed in this study has potential application in the production of lower energy asphalt mixtures. The work presents a novel application of CO2 at subcritical conditions, to reducing bitumen viscosity so that asphalt can be produced at lower temperature for paving applications. The work represents the first time such as attempt has been in the asphalt paving industry.