Ageing and moisture effects on the morphology and adhesion properties of polyurethane modified bitumen with cecabase

The number of studies on using polyurethane as bitumen modifier has been increasing in recent years. With the increase in the demand for more durable and sustainable road paving materials it is crucial to understand the short and long-term behaviour of modified bitumens. This study employs the Atomic Force Microscopy tests to examine how ageing affects the morphological and adhesion properties of Polyurethane Modified Bitumen enhanced with a chemical Warm Mix Asphalt (Cecabase). The ageing and moisture effects were quantified using Atomic Force Microscopy to gain detailed insights into the microscale topographical changes and conduct spectroscopy analysis of the modified bitumen. The Atomic Force Microscopy analysis revealed that ageing and moisture reduce the bee-structure through 2D and 3D topography images. The presence of moisture has been seen to modify the surface roughness with the incorporation of Cecabase. Despite the overall trend of roughness decreasing in long-term aged conditions, there is an increase of 4.0% for bitumen with polyurethane, 12.4% for bitumen combined with polyurethane and cecabase, and 35.4% for bitumen augmented with cecabase, in comparison to base bitumen in unaged conditions. The tip deflection ratio which examined the sensitivity of the sample to the presence of water from the spectroscopy analysis showed that incorporating Cecabase decreased by 9.8% and 4.7% respectively after short term and long term aged conditions that proved the characteristic of Cecabase reducing the viscosity of the bitumen. The smaller tip deflection value also indicates that the ageing process stiffened the bitumen. The adhesive force analysis revealed that ageing has a considerable detrimental effect on the bitumens’ adhesive force where during short term condition, the most reduction value of 21nN was recorded for sample incorporating with Polyurethane and Cecabase. Moisture also affected the adhesive force by lowering the adhesive force values of all samples when compared to dry conditions. However, incorporating Polyurethane and Cecabase improved the aggregate-bitumen adhesion, as indicated by the higher adhesive force values observed in dry and wet conditions as well after ageing when compared to the base bitumen. These findings proved the benefits of adding Polyurethane with Cecabase to bitumen as a modifier for Warm Mix Asphalt application.