# Resonant Acoustic Spectroscopy for Measuring Complex Modulus of Bitumen

## TL;DR

Resonant Acoustic Spectroscopy (RAS) can measure bitumen stiffness at low temperatures, matching traditional methods, but is less effective at higher temperatures.

## Contribution

RAS is applied for the first time to bitumen to measure its complex modulus, showing promise for quality control at low temperatures.

## Key findings

- RAS-derived complex modulus values agree well with DSR measurements at −20 °C and −30 °C.
- RAS is effective for assessing stiffness and aging effects in bitumen but fails to generate full master curves at high temperatures.

## Abstract

What are the main findings?
Resonant Acoustic Spectroscopy (RAS) was successfully applied to bitumen for the first time and can determine the complex modulus of bitumen in a temperature range from −30 °C to 20 °C.At low temperatures, RAS-derived complex modulus values show good agreement with Dynamic Shear Rheometer (DSR) measurements, especially at −20 °C and −30 °C.

Resonant Acoustic Spectroscopy (RAS) was successfully applied to bitumen for the first time and can determine the complex modulus of bitumen in a temperature range from −30 °C to 20 °C.

At low temperatures, RAS-derived complex modulus values show good agreement with Dynamic Shear Rheometer (DSR) measurements, especially at −20 °C and −30 °C.

What are the implications of the main findings?
RAS provides a fast, cost-effective, and non-destructive method for assessing stiffness and ageing effects in bitumen, offering potential for quality control and routine material evaluation.Due to the determination and use of natural resonant frequencies, RAS alone cannot generate a full master curve of bitumen and is not suitable for characterizing bitumen behaviour at high temperatures or low loading frequencies.

RAS provides a fast, cost-effective, and non-destructive method for assessing stiffness and ageing effects in bitumen, offering potential for quality control and routine material evaluation.

Due to the determination and use of natural resonant frequencies, RAS alone cannot generate a full master curve of bitumen and is not suitable for characterizing bitumen behaviour at high temperatures or low loading frequencies.

The complex modulus is one of the intrinsic properties of bituminous materials, and, hence, is of importance for their rheological characterization. It was shown by various authors that the complex modulus of asphalt mixtures can be calculated from dynamic modulus measurements using the Resonant Acoustic Spectroscopy (RAS). This paper extends the RAS technique to bitumen. For the purpose of validation, rheological data for the same bitumen are also derived from standard Dynamic Shear Rheometer (DSR) tests, and the master curves resulting from both methods are compared. The laboratory programme comprised a temperature range from −30 °C to 20 °C, and four different bitumens in unaged and aged condition, resulting in 36 different test variants. RAS successfully characterizes the complex modulus of bitumen and reflects temperature and ageing effects, with good agreement to DSR results at low temperatures. At higher temperatures, viscosity and damping introduce deviations, indicating that RAS is effective for modulus evaluation but not sufficient for complete master curve development.