Investigating physical and rheological properties of foamed bitumen

Foamed asphalt mixes are gaining ground as effective alternatives to asphalt base and sub-base standard layers in Europe and in other countries worldwide. As a significant amount of research is being conducted to advance sustainable practices for road pavements, foaming asphalt mixes have become a valid option to common asphalt paving technologies. Several advantages and the environmental benefits of foamed asphalt mixes have been debated and assessed. The present study aimed to evaluate: (1) the foaming characteristics of several bitumens sourced from different refineries with the same classification grade; (2) the physical, rheological, and chemical properties of bitumens before and after foaming; and (3) the effectiveness of a foaming additive in the enhancement of final product performance. Results showed that the same penetration-grade bitumen can provide very different results in terms of foaming properties (expansion ratio and half-life) depending on its chemical composition (differential scanning calorimetry and optical microscope analysis). The experimental program also assessed how the foaming process affected the physical and rheological behavior of bitumens (penetration, Ring and Ball test, dynamic viscosity, complex modulus, and phase angle).