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Stiffening Effect of Fillers Based on Rheology and Micromechanics Models

Rahim, Abdur; Milad, Abdalrhman; Yusoff, Nur Izzi Md; Airey, Gordon; Thom, Nick

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Abdur Rahim

Abdalrhman Milad

Nur Izzi Md Yusoff

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Professor of Pavement Engineering Materials

Assistant Professor


The aggregate in an asphalt mixture is coated with mastic consisting of bitumen (dilute phase) and filler (particulates phase). The interaction of bitumen and filler and packing of filler plays an important role in the properties of mastics. The micromechanics models from composite rheology can be used to predict the stiffening effect of a suspension. In this research, the stiffening effect of fillers was investigated based on the rheology of mastic. The frequency sweep tests in a dynamic shear rheometer at different temperatures were performed within a linear viscoelastic range to construct the master curves. The volume fractions were expressed as compositional volumes of filler in mastic. The particle shape and surface texture are determined through microscopy. We used six micromechanics-based models to predict the stiffening potential of fillers in mastics. The models include Maron–Pierce, Lewis Nielsen, Mooney, Krieger–Dougherty, Chong, Robinson, and Hashin Models. The results show that the same volume content of filler has a different effective volume. The fillers increase the stiffening effect of the composite, especially at high temperatures. The behaviour of fillers with similar effective volume and packing is identical. The filler type affects the stiffening of mastics. Micromechanics modelling results show that most models show an accurate stiffening effect at lower concentrations with the exception of the Chong Model. The Maron–Pierce Model under-estimates the stiffening potential for granite mastic at higher concentrations beyond the 30% filler content fraction. The value of maximum packing fraction (ϕm) and Einstien coefficient (KE) in the Mooney model are significantly different from other models for limestone and granite, respectively. The line of equality graph shows good agreement of measured and predicted stiffness. It is difficult to precisely model the mastic data with any single model due to the presence of complex stiffening effects beyond volume filling.


Rahim, A., Milad, A., Yusoff, N. I. M., Airey, G., & Thom, N. (2021). Stiffening Effect of Fillers Based on Rheology and Micromechanics Models. Applied Sciences, 11(14), Article 6521.

Journal Article Type Article
Acceptance Date Jul 2, 2021
Online Publication Date Jul 15, 2021
Publication Date Jul 2, 2021
Deposit Date Jul 19, 2021
Publicly Available Date Jul 20, 2021
Journal Applied Sciences
Electronic ISSN 2076-3417
Publisher MDPI
Peer Reviewed Peer Reviewed
Volume 11
Issue 14
Article Number 6521
Keywords Fluid Flow and Transfer Processes; Computer Science Applications; Process Chemistry and Technology; General Engineering; Instrumentation; General Materials Science
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