University of Cambridge
University of Cambridge researchers, working in partnership with industry, have developed what they say is the first 3D printed piece of concrete infrastructure to be used on a National Highways project. The structure, which is a type of retaining wall known as a headwall, has been installed on the A30 in Cornwall, where it is providing real-time information thanks to Cambridge-designed sensors embedded in its structure.
The sensors in the structure provide up-to-date measurements including temperature, strain, and pressure. The “digital twin” of the wall could help spot and correct faults before they occur according to the researchers.
According to the university, headwall structures are usually made in limited shapes from precast concrete, which requires formwork and extensive steel reinforcement. With the use of 3D printing, the team, which included specialists from Costain, Jacobs and Versarien, could design and construct a curved, hollow wall with no formwork and no steel reinforcement. The wall gets its strength from geometry instead of steel.
The wall took one hour to print according to the university, and is roughly two metres high and three and a half metres across. The researchers printed the wall in Gloucestershire at the headquarters of the advanced engineering company Versarien, using a robot arm-based concrete 3D printer.
For six years, Professor Abir Al-Tabbaa’s team in the Department of Engineering has been working on new sensor technologies and exploring the effectiveness of existing commercial sensors to get better-quality information out of infrastructure. Her team has also developed “smart self healing” concretes. Prof. Al-Tabbaa’s team supplied sensors to measure temperature during the printing process.
“Since you need an extremely fast-setting cement for 3D printing, it also generates an enormous amount of heat,” said Al-Tabbaa. “We embedded our sensors in the wall to measure temperature during construction, and now we’re getting data from them while the wall is on site.”
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As well as temperature, these sensors also measure relative humidity, pressure, strain, electrical resistivity, and electrochemical potential. The measurements provide valuable insights into the reliability, robustness, accuracy and longevity of the sensors according to the team. A LiDAR system was also used to scan the wall as it was being printed, in order to generate a 3D point cloud and a digital twin of the wall.
Al-Tabbaa added: “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 industry.”
The Cambridge team developed a type of sensor known as a Piezoceramic Lead-Zirconate-Titanate (PZT) sensor, which measures electromechanical impedance response and monitors changes in these measurements over time to detect any possible damage. Eight PZT sensors were embedded in the wall at different points during the 3D printing process to capture the presence of loading and strain.
A bespoke wireless data acquisition system was also developed by the team, which enabled the collection of the multifrequency electromechanical response data of the embedded sensors remotely from Cambridge.
“This project will serve as a living laboratory, generating valuable data over its lifespan,” added Al-Tabbaa. “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.”
The team included Dr. Sripriya Rengaraju, Dr. Christos Vlachakis, Dr. Yen-Fang Su, Dr. Damian Palin, Dr. Hussam Taha, Dr. Richard Anvo and Dr. Lilia Potseluyko from Cambridge; as well as Costain’s Head of Materials Bhavika Ramrakhyani, a part-time PhD student in the Department of Engineering, and Ben Harries, Architectural Innovation Lead at Versarien, who is also starting a part-time PhD in the Department of Engineering in October.
