# Effects of Synthetic Fibers and Rubber Powder from ELTs on the Rheology of Mineral Filler–Bitumen Compositions

## TL;DR

Adding materials from old tires improves the performance of asphalt mixtures at high temperatures while maintaining flexibility at lower temperatures.

## Contribution

The study shows that ELT-derived additives can actively enhance asphalt mastic performance beyond traditional stabilizing roles.

## Key findings

- ELT-derived additives increase high-temperature stiffness and elasticity of asphalt mastics.
- Balanced fiber–rubber ratios maintain mid-temperature flexibility and improve recovery under load.
- Thermal stability tests confirm performance gains after initial heating.

## Abstract

What are the main findings?
End-of-life tire (ELT) fibers and rubber powder enhance asphalt mastic rheology.Combined use of ELT fiber and rubber increases high-temperature stiffness and elasticity.ELT-derived additives improve recovery and reduce creep under load.Balanced fiber–rubber ratios maintain mid-temp flexibility of asphalt mastics.

End-of-life tire (ELT) fibers and rubber powder enhance asphalt mastic rheology.

Combined use of ELT fiber and rubber increases high-temperature stiffness and elasticity.

ELT-derived additives improve recovery and reduce creep under load.

Balanced fiber–rubber ratios maintain mid-temp flexibility of asphalt mastics.

What is the implication of the main finding?
ELT-derived additives may improve sustainability of pavement materials.Improved durability and deformation resistance of asphalt mixtures.Possibility for reduction in need for polymer-modified binders and support for circular economy.

ELT-derived additives may improve sustainability of pavement materials.

Improved durability and deformation resistance of asphalt mixtures.

Possibility for reduction in need for polymer-modified binders and support for circular economy.

This study investigates the influence of synthetic fibers and rubber powder derived from end-of-life tires (ELTs) on the rheological behavior of asphalt mastics composed of paving-grade bitumen and mineral filler. Nine asphalt mastic formulations were prepared with varying fiber and rubber contents, reflecting the composition of stone mastic asphalt mixtures. Dynamic shear rheometer tests were conducted to assess dynamic stiffness modulus, phase angle, non-recoverable creep compliance, and elastic recovery. The results demonstrated that ELT-derived additives significantly enhanced high-temperature stiffness and elasticity, while maintaining satisfactory viscoelastic balance at lower temperatures. Synergistic effects between fibers and rubber were observed, improving both non-recoverable compliance and percent recovery, particularly at elevated shear stresses. Prolonged exposure to production temperatures (175 °C) confirmed the thermal stability of the modified mastics, with the most notable performance gains occurring during the first hour of heating. Based on the findings, it was concluded that ELT-based fiber–rubber additives can improve high-temperature performance of asphalt mastics without negative effects in intermediate and, possibly, also low service temperatures. This permits expanding the use cases for these kinds of additives beyond the role of inert stabilizers in stone mastic asphalt to an active modifier for extending asphalt mix performance.