Concrete Insight: From Site to Laboratory

Jonathan Leu is a laboratory technician in the concrete laboratory of the Institute for Building Materials at ETH Zurich. His path there took him through mechanical engineering studies at ETH Zurich, which he left behind in favour of the trades, an apprenticeship as a bricklayer, and years of work on building sites. He is the man researchers turn to when theory meets the concrete mixer – and the one who bridges the laboratory and industry.

Jonathan Leu works in the concrete laboratory of the Institute for Building Materials at ETH Zurich. Photo by Lea Keller

Jonathan Leu's path is anything but linear. He began his studies in Mechanical Engineering at ETH – but the heavy emphasis on theory with little practical application led him to switch to an Economics degree at the university. Office life and academic pursuits didn't fill him. His desire for activity and physical work took precedence: he worked as a bicycle courier. Eventually, he decided on a fresh start and became a bricklayer’s apprentice. Following that, he worked on construction sites, advanced his skills to become a site supervisor and foreman, and later, he found employment as a laboratory technician at the NCCR DFAB at ETH Zurich, where he continued to develop his expertise as a construction materials tester and a specialist in concrete engineering.

From the Construction Site to the Laboratory

When he took up his new role at ETH Zurich, he struggled to find the words to describe the feeling: “For me, it was like driving a train into a wall.” The contrast with the construction site could not have been greater. There, every day was clearly defined, every hour of work visible – you were either building something or you weren’t. “I had to get used to not being able to see so clearly in the evening what I had achieved,” he says. Nevertheless, he brought a decisive advantage with him: the environment at ETH was not unfamiliar to him thanks to his studies. He was familiar with the academic language and tone. So Jonathan takes on a mediating role: “I can speak to a site manager on the phone, and we understand each other when we discuss the research project, because he knows I used to be a site manager and understands me,” he says.

All about Concrete

‘When I came to ETH, I thought: I'm coming to ETH, this is all about concrete. The people here surely know how to mix concrete.’ Things turned out differently. Researchers came to Jonathan and asked him how to mix concrete. A recipe for concrete was quickly found, says Jonathan. However, he wanted to understand how to mix concrete from scratch. So he trained as a building materials tester to understand the raw materials and principles of concrete production. Because not all concrete is the same. His colleague Heinz Richner sums it up as follows: "Anyone can mix concrete. But not everyone can mix good concrete.‘ Researchers mixing concrete for the first time often underestimate how many parameters influence it – workability, flow behaviour, strength and durability. The newly acquired knowledge had a direct impact on his work with the researchers: ’The more knowledge I have, the more confident I am in giving practical advice." The decision-making power always lies with the researchers, Jonathan explains his advisory role.

Jonathan is supporting the concrete casting on site the ETH Zurich Campus Hönggerberg. Photo by Mike Lyrenmann.

The Chemistry of Concrete

What fascinates him about concrete is the incredible depth of the subject: ‘You can learn so much when you study concrete.’ He was familiar with the practical side from construction sites, but it was only here that he discovered the theory – how many factors influence the quality of concrete production: from grain size distribution to numerous chemical and physical processes that interact with each other. One common misconception about concrete, for example, is that it dries. Concrete does not dry. ‘What happens during the hardening process is a chemical reaction between cement and water – hydration. New hydrate phases are formed and the water is chemically bound. That's why concrete hardens even under water,’ he explains. Jonathan recently developed a concrete for a project that turned out exactly as he had imagined it. ‘This proves that he not only knows the parameters, but also masters them,’ he says with satisfaction.

Transfer into Industry thanks to Network

"There's always been a certain tension when pouring concrete – you only know if it's worked out once you've removed the formwork," says Jonathan. He vividly remembers that thrill on the building site: the suspense of waiting, the satisfaction when everything comes together. What drives him hasn't changed – just the setting. As a foreman, there would have been limited room for new ideas. He found them at ETH Zurich. And that thrill of removing the formwork? He still feels it here too. Over the past few years, Jonathan has built up a network that directly benefits research within the NCCR DFAB. Through ongoing training and daily interaction with both academia and industry, he knows the right people to talk to – in the cement industry, among formwork manufacturers, and among concrete producers. "If we need something for a project, I can draw on this network and speak to the right people," he says. This way, laboratory research flows directly into practice – and vice versa.