How can simulating ballast materials in roads reduce environmental impact and societal costs?
Swedish roads are and will remain for the foreseeable future the core of Swedish infrastructure. Normally, roads are built of several bound and unbound layers of aggregate, which are subject to requirements regarding desired functionality, lifespan and surrounding soil types. Previous research at Chalmers and other universities studied ballast material as a system of particles compacted to a bed with specific properties. These properties can be adjusted by changing the character of the aggregate material and how compaction is done, but it is extremely difficult to experimentally determine how individual particles move or otherwise contribute to the rigidity of the ballast bed. Thus, the research has been limited to what is physically measurable.
In an interdisciplinary research project in the framework of the Building Futures and Production Areas of Advance, researchers at the Chalmers departments of Product and Production Development, Mathematical Sciences and Civil and Environmental Engineering collaborated with
the Fraunhofer-Chalmers Centre for Industrial Mathematics (FCC) and NCC to develop and use a simulation technology called Discrete Element Modelling (DEM) to study key processes in handling ballast materials for road construction. Loading and unloading from trucks was one process step studied, and preliminary results show that significant segregation effects occur during unloading. In addition, the study simulated the compaction of the ballast bed and preliminary results show that when comparing two cases with the upper and lower limit values for the particle size distribution, the resulting rigidity of the bed differs by a factor of two in the first compaction cycle. If the rigidity of the road body varies, it can lead to fatigue fractures and reduced lifespan, resulting in expensive maintenance measures. (Pictured left to right from above, Johannes Quist PPU, Fredrik Edelvik, FCC)What is the next step with this simulation technology?
The project plans to go into its second phase, in which the entire process from loading, hauling, unloading, spreading and compacting will be studied as a process chain. If the sources of variation can be identified throughout the process chain, we hope that these insights can lead to measures to reduce the effects of variation, and eventually lead to roads with a longer lifespan and higher quality.