Several cubic kilometres of concrete are used worldwide every year, and the production of cement is responsible for around 8% of anthropogenic CO2 emissions. This is set to change. That is why research is being conducted worldwide into new kinds of concrete that use less cement. Future types of concrete will differ from today's concrete in their atomic composition.

These new types of concrete will be used to build large structures that can withstand frequently recurring loads – from railway bridges to wind turbines. This poses a highly complex scientific question: How can the atomic scale be linked to the scale of large buildings? Which intermediate steps have to be taken into account? How can knowledge from the nano and micro world be utilised to achieve results that can be implemented in the construction industry?

Such questions are now to be answered in a newly launched ERC Synergy Grant. Synergy Grants are highly remunerated research projects, funded by the European Research Council ERC, in which several research groups work together. One of the Principal Investigators of the new large-scale project is Prof Bernhard Pichler from the Institute of Mechanics of Materials and Structures at TU Wien. In addition to his research group, two research teams from RWTH Aachen University and a team from TU Brno are also involved. They are led by Professors Miroslav Vořechovský, Thomas Matschei and Rostislav Chudoba.

Material fatigue as the main risk

“To make cement more environmentally friendly, suitable substitute materials are added,” says Bernhard Pichler. “The proportion of cement in the cement bag should be reduced. But it makes little sense to transport substitute materials all over the world. In the future, we will use whatever is available locally in the right quantity and quality – from ground rock to heat-treated clays. We will therefore be dealing with very different types of cement, with great chemical diversity.”

However, it is not only the composition of cement and concrete that is changing, but also the material requirements in the construction industry. An important key figure for concrete is its compressive strength: which weight can be loaded onto a piece of concrete before it breaks? However, this is not necessarily the decisive factor for concrete structures such as railway bridges or wind power towers. The challenge does not lie in extreme compressive loads. Instead, one has to deal with vibrations, with recurring load cycles that lead to material fatigue – until the structure is so damaged that it is no longer fit for use.

This becomes particularly important when the goal is to save resources and build structures that are as light as possible. With a lower dead weight, the static load on the material is not a major problem, but in comparison, time-variable loads play an increasingly important role. “As a result, fatigue will often become a key design criterion in the future,” says Bernhard Pichler.

Understanding fatigue - down to the nanostructure

The causes of fatigue phenomena are still not sufficiently understood, which is why the current legal standards are mainly based on empirical knowledge. This is a problem for the use of new cement mixtures. After all, people want to use them immediately, without having to observe them for decades first.

“We are convinced that the causes and mechanisms of concrete fatigue can be found in the nanostructure of the material,” says Bernhard Pichler. “We therefore need to build a bridge from the material science of the smallest scales of cement-bound building materials to the fatigue science of large reinforced concrete structures.”

This bridge can only be created via several intermediate steps: The load-bearing strength of a concrete structure depends on the concrete mix. The properties of the concrete mix depend on the rock and cement from which it is made. How well the cement holds the material together depends on its microstructure: it is not homogeneous, but consists of tiny crystalline structures, pores and cracks. And the properties of this microstructure can only be understood if the ingredients are analysed at an atomic level.

No research group in the world can investigate all these different levels at the same time - and that is why an ERC Synergy Grant is exactly the right funding instrument for such a question, says Bernhard Pichler: “We at TU Wien specialise in predicting the relationship between the microstructure of cementitious building materials and their macroscopic material properties. Our three project partners in Aachen and Brno work on size scales below and above this.” These perspectives are now to be combined. The methods used are also diverse; experiments are just as necessary as mathematical models and computer simulations.

ERC Synergy Grants

With Synergy Grants, the European Research Council (ERC) supports teams of two to four senior scientists. These grants support projects that lead to progress at the frontiers of knowledge through interdisciplinary collaboration. The funding for the new project ‘Concrete matrices for high-cycle-fatigue resistant, eco-efficient infrastructure’ amounts to 10 million euros over a period of six years, of which 2.43 million euros will go to TU Wien.

Bernhard Pichler

Bernhard Pichler studied civil engineering at TU Wien, where he graduated with honours in 2003. In 2006 and 2008, two research visits took him to the École Nationale des Ponts et Chaussées in France. In 2009, he was awarded the Venia Docendi for the specialism ‘Strength of Materials and Structural Analysis’ at TU Wien. In 2010, he was appointed Head of the Laboratory for Macroscopic Materials Testing at the Institute of Mechanics of Materials and Structures. One year later, he was awarded a tenure-track position on the subject of ‘Mechanics of cementitious materials’. He has been a university professor at TU Wien since 2020.

Contact:

Prof. Bernhard Pichler
Institute of Mechanics of Materials and Structures
TU Wien
43 1 58801 20230
bernhard.pichler@tuwien.ac.at