After experiencing the tragic first days of the war in the suburbs of Kyiv, Viacheslav Troian, a professor at the Kyiv National University of Construction and Architecture, left with his family to Western Europe. As a father of four children, he was allowed to leave Ukraine. Coincidence played no small role in how he ultimately ended up in Switzerland and then at ETH Zurich. “We were standing at the train station in Budapest, and my wife and I were trying to decide where we should go,” Troian says. At that time, Ukrainian refugees didn’t have to pay for train travel. The only cost was 3 euros for the seat reservation, regardless of destination. One train for which Troian was able to reserve seats had Zurich as its terminus. And so it happened that he and his family went to Switzerland. “At that time, we were hoping the war would end soon and we would return home.” But things turned out differently.
As a chemical engineer specialised in concrete, Troian has 20 years of experience in the development of various types of concrete. Among other projects, he had a hand in developing the concrete mixtures for the sleepers for the Ukrainian railway and in the foundation of the safety confinement built around the damaged nuclear reactor in Chernobyl. Troian is currently working as a visiting researcher at ETH Zurich with Professors Ueli Angst and Robert Flatt, both of whom are also concrete specialists.
Troian has just published a scientific paper on concrete recycling with coauthors from ETH Zurich and Gustave Eiffel University in Paris. For some time now, building materials engineers have been crushing concrete demolition waste and using it to produce fresh concrete. This can replace up to 50 percent of the gravel or crushed stone required, according to the current standards. Troian sees huge potential in the use of recycled concrete for the reconstruction of destroyed buildings and infrastructure in Ukraine. In the new study, he outlines the concept behind the role recycled concrete can play.
Concrete is known for being a building material with a notable carbon footprint due to cement production. Recycled concrete requires the same amount of cement as conventional concrete. Accordingly, the focus with recycled concrete is not on reducing the carbon footprint, but rather on optimising material flows. “When we demolish buildings, the demolished materials end up in construction waste landfills; when we build new buildings with conventional concrete, we have to quarry a lot of new crushed stone. If we could reuse at least some of the demolition waste, we would take up less landfill capacity and reduce crushed stone mining,” Troian says.
Moreover, managing in a reasonably short time to rebuild the infrastructure of a war-torn country is a huge challenge for the crushed stone supply chain. “If we can recycle and reuse demolition waste on site, we can minimise logistic expenses,” Troian says.
In the new study, Troian also shows how to reduce certain disadvantages of recycled concrete with relatively little additional effort. Civil engineers know that concrete with too much recycled content has lower load-bearing capacity and is less resistant to water, salts and the atmosphere. That means it has a shorter service life. In addition, recycled concrete has a higher tendency to crack than conventional concrete, which makes using it more of a challenge. These disadvantages are due first and foremost to the fact that the surface of the crushed recycled material consists of old cement mortar, which absorbs liquid.
To counter this problem, several methods have been developed in recent years to pretreat the demolition waste, including prewetting it with water or treating it with heat, acid or microwaves. Troian emphasizes in the study that simply prewetting the demolition waste with water already brings great benefits. For reconstruction in Ukraine, this is an efficient and viable solution that can mitigate the immense resource requirements of the other approaches.
Currently, practically no recycled concrete is used in Ukraine. Switzerland, on the other hand, is considered the European leader with 18 percent of the concrete used containing recycled material.
Troian’s employment at ETH Zurich was made possible by the commitment of the Institute for Building Materials and the Department of Civil, Environmental and Geomatic Engineering (D-BAUG) as well as the Executive Board of ETH Zurich. As part of the ETH solidarity campaign with researchers from Ukraine, it was agreed at short notice to host visiting researchers from Ukraine like Troian and to split the funding between the relevant institute, the department and the university as a whole. In addition, companies from the construction sector are supporting Troian’s stay via the ETH Foundation’s partnership council for sustainable construction and digital fabrication.
Not only has Troian advanced research on recycled concrete at ETH, he has also translated existing educational videos for students into Ukrainian. “I hope these videos will be helpful to students in Ukraine, as well as to industry,” he says, adding that he wants to help Ukrainians interested in this field to increase their knowledge, lowering barriers for them to contribute to an efficient and durable reconstruction.
This is also in the spirit of his hosts at ETH, Professors Angst and Flatt, who are coauthors of the concrete recycling study. “When the war in Ukraine started, we asked ourselves how we could help the people of Ukraine,” says Flatt. “Making knowledge that is relevant to them easily accessible is a modest way we can contribute.”
Repair what can be repaired
Troian says it won’t be possible to demolish and fast rebuild all old and the damaged buildings: “We can’t rebuild in just a few years what it took decades to create.” Instead, what can be repaired should be repaired. With this in mind, over the coming months he will be devoting his attention to the question of forecasting the remaining service life of old concrete buildings. Models developed at ETH Zurich could be used for this. This will help urban planners prioritise when it comes to reconstruction.
Troian hopes that his children will experience many positive things in Switzerland and that this will outshine their memories of the first days of the war in Ukraine. However, he is aware that many people are currently fighting or enduring extreme hardship in Ukraine, and that many children have also remained there. With his expertise and his research, he would like to make his contribution to a hopefully speedy reconstruction of his home country.