Empa researchers are exploring new ways to reinforce roads through simple techniques and to recycle them easily after use. The researchers’ tools include a few meters of string and a robot.
A robotic arm places a string in a mandala-like pattern on a gravel bed. But what seems to be a modern art performance is a fundamental research work that investigates new ways to construct roads.
While robot-assisted construction methods for road construction purposes are being tested, these techniques have only been applied to structural engineering, to date. But a new kind of mechanical reinforcement is intended to alter the usual structure of the surface of the road and to save useful resources in the days to come, or even to recycle the surfaces of roads collectively.
An Idea from Structural Engineering
The concept emerged from a study performed by the Gramazio Kohler Research laboratory at ETH Zurich. The study was designed as an art and research project. In this analysis, pillars stacked on one another purely from gravel and strings showed that remarkable stability can be obtained by merely interlocking the gravel with a thread without using any cement as a binder.
Laboratory tests have demonstrated that gravel pillars measuring 80 cm in height and 33 cm in diameter can tolerate a pressure of 200 kN, which is equivalent to a load of 20 tons.
Moreover, asphalt contains a binder, bitumen, and different sizes of rocks. Therefore, Martin Arraigada and Saeed Abbasion from the Concrete & Asphalt laboratory of Empa applied this idea to construct roads.
We want to find out how a recyclable pavement could be produced in the future. To do this, we are using digitalized construction methods in road construction for the first time.
Martin Arraigada, Concrete & Asphalt, Empa
A string-reinforced road surface that prevents the need for bitumen can provide several benefits. Bitumen is obtained from crude oil and, as a result, air pollutants are discharged at the time of production and also afterward during use.
Moreover, bitumen makes asphalt prone to deformation and cracking and also makes it impermeable to rainwater—a concern that could be resolved. According to the investigators, rock could perhaps be used that is otherwise not appropriate for constructing roads, but this method is quite rare. Finally, the process results in a pavement that can be rolled and recycled.
A String and Loose Gravel
The two investigators from Empa are utilizing different experimental setups to validate solutions for the above-stated aspects. In this context, the robotic arm has a crucial role to play. It lays out the string in a programmed mandala-like pattern on the layers of gravel piled on top of one another.
To perform the mechanical tests, five of these layers of thread and gravel are positioned on top of one another in a test box, and the bottom of the box is encased with a rubber mat that attaches the entire package to the ground. The package replicates the deformable bed on which the pavement is used.
The fact that the string is precisely the same as the one utilized by all Swiss citizens for bundling wastepaper demonstrates that the Empa team has pioneered a new and low-cost approach.
Mechanical Tests and Computer Modeling
This gravel-thread package is subsequently loaded with pressure and a rotating plate. The load test demonstrated that when the individual gravel stones are entangled with the thread, the package can tolerate a pressure of 5 kN (half a ton) without the stones moving considerably. Generally, the binder bitumen carries out this process in asphalt.
Dynamic load tests with rolling pressure—analogous to adverse conditions tolerated by road pavements—will soon be performed.
Along with their laboratory experiments, the team has also used the Discrete Element Method (DEM) to model everything in 3D on the computer. This should expose the tensile forces acting on the thread and the displacement of individual stones—something that cannot be analyzed in laboratory settings. Besides this, the researchers will completely examine the various patterns and mesh widths and their impacts on pavement stability.
The study performed by Arraigada and Abbasion has not resulted in an ultimate product that can be readily used for constructing roads. But their study offers plenty of innovative prospects to reach closer to a recyclable and potentially rollable road pavement through easy methods.
Video Credit: Empa.