The world of 3D printing has opened up limitless possibilities in recent times, and researchers at Cambridge have now used the technology to create a concrete wall that could help make our infrastructure safer, smarter, and more sustainable.
The collaboration between the Cambridge team and industry has resulted in the creation of a retaining wall known as a headwall which can provide real-time information, courtesy of the sensors embedded in its structure.
The sensors offer current data on temperature, strain, and pressure. The metrics help researchers to detect and correct flaws before they develop. "Making the wall digital means it can speak for itself, and we can use our sensors to understand these 3D-printed structures better and accelerate their acceptance in the industry," said Professor Abir Al-Tabbaa, from the Department of Engineering at Cambridge, in a media release by the university.
The structure has been currently installed on the A30 roadway in Cornwall, England.
The strength is provided by its geometry
Precast concrete headwall constructions are often built in constrained forms. The team says that such conventional methods of construction necessitate formwork and considerable steel reinforcing.
However, using 3D printing, they designed and built a curved hollow wall with no formwork and no steel reinforcement. The wall's strength is derived from geometry rather than steel.
The wall is approximately two metres high and three and a half metres wide, taking one hour to print. It was created in Gloucestershire utilising a robot arm-based concrete printer. According to the team, making the wall with 3D printing saves money, materials, and carbon emissions.
Prof Al-Tabbaa's team in the Department of Engineering have been developing novel sensor technologies and investigating the usefulness of current commercial sensors to extract higher-quality information from infrastructure over the past six years. They provided sensors to detect temperature throughout the printing process for this project.
Temperature fluctuations at various levels of the 3D printed wall were continually monitored for possible hotspots, thermal gradients, or abnormalities. To understand the thermal behaviour of the 3D printed wall, the temperature data will be connected with the matching thermal imaging profile.
Researchers also used the sensors to assess relative humidity, pressure, strain, electrical resistivity, and electrochemical potential in addition to temperature.
The measurements give useful information about the sensors' dependability, robustness, precision, and lifetime. "A LiDAR system also was used to scan the wall as it was being printed to create a 3D point cloud and generate a digital twin of the wall."
The critical role of sensors
The Cambridge team created a PZT (Piezoceramic Lead-Zirconate-Titanate) sensor, which measures electromechanical impedance response and tracks changes in these data over time to identify potential damage. These smart sensors can illustrate how 3D printed mortar hardens over time while also monitoring the health of the host structure.
"Eight PZT sensors were embedded within the wall layers at different positions during the 3D printing process to capture the presence of loading and strain, both during the construction process and service life after field installation."
The team, which includes people specialised in smart materials, automation and robotics, and data science, also created a custom wireless data-gathering system. This allowed the embedded sensors' multifrequency electromechanical response data to be collected remotely from Cambridge.
“The sensor data and ‘digital twin’ will help infrastructure professionals better understand how 3D printing can be used and tailored to print larger and more complex cement-based materials for the strategic road network," said Prof Al-Tabbaa.