This article is a condensed version of the comparative study of the behavior of Fortifix® and other asphalt interlayers. Read the full story
Asphalt is the universally preferred material for road construction due to its excellent cost and performance. However, it’s not impervious to damage. Rutting, settlement, distortion or cracking can cause asphalt roads to deteriorate over time. A common cause of damage to renovated asphalt overlays is reflective cracking, a phenomenon in which old cracks in the underlying layer resurface. There are different anti-cracking interface systems that can be used to prevent this issue. Possible solutions include steel meshes, non-woven geotextiles, geogrids or combigrids. Which solution is chosen depends on whether the renovation is structural or non-structural. For non-structural renovation, the performance of various interlayers has been thoroughly evaluated in both laboratory and field tests (Norambuena-Contreras & Gonzalez-Torre 2015, Pasquini et al. 2013, Vervaecke & Maeck 2008). This research revealed two important facts:
- The correct installation of the interlayer plays a key role in achieving good anti-reflective cracking behavior.
- Steel-based interlayers are the most efficient solution to prevent reflective cracking.
Steel features excellent anti-cracking properties thanks to its high Young’s modulus (=E-modulus) and good anchorage in the asphalt matrix. The current steel reinforcement products for road renovation are either welded steel mesh or hexagonal meshes that feature transversal placed reinforcement bars. While these meshes provide an excellent solution for structural renovations, they can be too excessive for non-structural renovations. The meshes are very rigid and need extra fixation with nails or, preferably, a slurry seal. They need at least 5 cm overlay to be completely covered and removing them at the end of the road life is arduous and time-consuming since they cannot be ground with traditional grinding machines. In 2012, Bekaert, a leading producer of hexagonal steel mesh, initiated a project to develop a new steel-based interlayer for non-structural road renovations. Through extensive research and close partnerships with highway and road engineers, Bekaert developed Fortifix®, a unique steel cord structure that offers specific advantages compared to traditional steel meshes or geo-synthetics:
- Fast and correct installation: The flexible steel cords of the interlayer can be easily rolled out, either manually or automatically, on both rough and smooth surfaces, without needing fixation or protection.
- Lifelong road stability: The steel structure remains stable during the installation process and its properties are not reduced by mechanical or thermal interaction with the asphalt.
- 100% recyclable: The structure includes strategically located brittle spots. While these spots do not affect the strength of the structure during the service-life of the overlay, it makes it possible to ground grid and asphalt together once the road has reached its end-of-life. The magnetic properties of steel ensure a perfect separation of steel and asphalt making both materials 100% recyclable.
- Excellent anti-reflective cracking properties: Different tests showed that Fortifix® increases the fatigue life-time of the roadway significantly compared to glass-based interlayers with a similar EA and a higher tensile strength. This is due to the excellent interlocking properties of the 3D cord structure.
- Conforms to the industry norms: The galvanized steel cord structure meets the EN10244-2 norms for Class D material. The lifetime of the product in the application matches that of the road surface.
Read the full study on the behavior of Fortifix® and other types of asphalt interlayers. Don’t hesitate to contact me at Frederik.Vervaecke@bekaert.com should you have any questions and requests.