On the automated fabrication of graded concrete elements
On 8 January 2025, Boris Blagojevic presented the outcome of his doctoral research titled "On the automated fabrication of graded concrete elements" in front of the doctoral committee. The doctoral committee consisted of the chairman Prof. Dr.-Ing. André Casal Kulzer (IFS), the supervisor Prof. Dr.-Ing. Dr. h.c. Oliver Sawodny (ISYS), and Prof. Dr.-Ing. Alexander Verl (ISW) as the second examiner.
Congratulations to Boris Blagojevic on his great achievement.
Post defense quiz – earning the cap the hard way. © Boris Blagojevic
Abstract Doctoral Research
As a significant sector in the global economy, the construction industry is increasingly in the focus of research. This is due to the high consumption of resources, increasing urbanisation and the resulting high demand for living space as well as relatively low productivity, offering significant potential for new technologies. A particularly interesting technology is the concept of graded concrete, as the use of hollow concrete spheres enables mass savings of up to 50% without any loss of load-bearing capacity. The spheres remain in the component as a lost mould, which increases recyclability.
The aim of this work is to develop a prototype production system for graded concrete elements that enables automated production - not only in a factory environment but also on the construction site. For this purpose, a hydraulic manipulator is used, inherently offering the desired flexibility with regard to the working environment. Two different end effectors were developed for the fabrication. One is a vacuum gripper with a camera system for recognising and placing the hollow spheres, the other is an extrusion unit for concreting. A conventional hydraulic concrete pump is used to pump the concrete, the control and sensor systems of which have been adapted accordingly.
The gripping process is automated with collision-free trajectory generation via optimal control and pose control for the picking and placing. Working in unknown environments is made possible by an environment model that uses the depth image of the stereo camera and is built up step by step through exploration. The hollow concrete spheres are recognised by a neural network and the manipulator poses for gripping and placing of the spheres are calculated based on optimisation.
The automation of the concreting process first requires modelling of the dynamics of the concrete delivery process, modelling and control of the hydraulic concrete pump and a filling state control for the extruder. The reference path for the extruder position is planned using a graph-based approach, so that the concrete flow avoids the fragile hollow spheres. The synchronisation of extruder movement and volume discharge respects input constraints and path deviations, for which a novel approach was developed.
Concrete conveying system for on-site application. © Boris Blagojevic
Papers of which the dissertation consisted
- Modeling and Volume Flow Control of a Hydraulic Concrete Piston Pump, DOI:10.1109/CCTA60707.2024.10666564
- Trajectory Planning for Concrete Element Fabrication with Optimal Control, DOI:10.1109/IECON48115.2021.9589695
- Path planning for graded concrete element fabrication, DOI:10.1007/s41693-023-00096-5
- Dynamics of Path Following and Constrained Path Synchronization Applied to Graded Concrete Element Fabrication, DOI:10.1109/CASE56687.2023.10260681
- Modeling and Volume Flow Control of a Hydraulic Concrete Piston Pump, DOI:10.1109/CCTA60707.2024.10666564