3D printing asphalt for road repairs enhances its toughness
Work by the Self-Repairing Cities team at UCL on developing a 3D printer for asphalt has now been published as an open access article in the journal Materials and Design. We believe this is the first time that 3D printing for asphalt has been demonstrated.
The developed system is able to scan a crack and then 3D print asphalt into it as a repair. This means the technique has the potential to be used on autonomous vehicles or drones to autonomously repair roads and complex infrastructure.
Unexpectedly, it was found that the 3D printed asphalt is up to 9 times more ductile than cast asphalt, with similar fracture strengths. Upon examination of the fracture surface of the printed asphalt it is possible to see a crack bridging component, thought to be composed of a lighter saturated fraction of the asphalt. The 3D printing process seems to create a composite structure with the softer elements of asphalt coalescing in much larger concentrations than in the cast asphalt, giving the printed material a higher toughness.
As cracks on roads are often areas of increased stress or wear, using this technique to deposit asphalt with enhanced ductility and toughness could prolong the life of the repair. In addition, the mechanical properties of 3D printed asphalt can be altered depending on the process conditions, raising the possibility of allowing toughness to be tailored to the repair.
The asphalt extruder is an innovative design, which was developed in order to overcome the difficulties presented by asphalt behaving as a non-Newtonian liquid when moving through the extruder. The extruder design enables the 3D printing of asphalt at a variety of temperatures and process conditions, allowing for modification of the asphalt properties as described above. In addition, the feed and pellet system makes it relatively straight forward to add other materials such as small micro-aggregates or nanomaterials, and then vary the composition of the feedstock during printing to create more complex, functionally graded infrastructure materials with a wider range of properties.
This flexible and tunable asphalt printing system offers a new approach for the maintenance of road infrastructure. The extruder can also be mounted on a drone (as previously demonstrated), which opens up a new way to repair hard to access structures such as flat roofs of buildings. Other repair methods often require the erection of scaffolding and closure of infrastructure for safe access, meaning this new approach could both cut costs and improve safety. In addition, rather than waiting for roads to disintegrate into potholes, this technique could be used to intervene at a much earlier stage and repair cracks as they appear, preserving the road surface for far longer and avoiding the disruption and cost of major roadworks.
This article is based on the following paper:
Richard J. Jackson, Adam Wojcik, Mark Miodownik (2018) 3D printing of asphalt and its effect on mechanical properties. Materials & Design. 160, 468-474. Doi:10.1016/j.matdes.2018.09.030