If paradise were made of concrete

Zunino picks up a smooth grey concrete cube. It is made of only a few simple ingredients: cement, sand, gravel, additives and water. Limestone and clay are first heated in a kiln and ground into powder together. The result is cement, a binder that lay people often confuse with actual concrete. Adding water produces a paste that then hardens. Properly formulated concrete is reliable, safe, robust and undemanding – the ideal choice for foundations and columns.

Except for that one problem. The cement-firing process not only consumes energy, but also releases significant amounts of CO2 from the limestone. Consequently, the concrete industry is a major emitter of greenhouse gases and responsible for up to 9 per cent of artificial greenhouse gas emissions worldwide. That corresponds to about four times the contribution of all air traffic. Nonetheless, these figures should be put into perspective. “Compared to other building materials such as steel, aluminium and glass,” says Zunino, “concrete has a relatively small carbon footprint. The sheer quantity of the material is what makes its footprint seem so immense.” Even timber is an impractical replacement as a building material because far too much of it would be needed: to replace even half of the concrete with timber, you’d probably have to plant a forest the size of India and wait 30 years... “Further improving concrete, this great building material, would be a significant advancement for the industry. The upside is huge.”

For this reason, Zunino and his team want to develop a new family of concrete – ultra-green concrete. The researchers estimate that this could save up to 800 million tonnes of CO2 worldwide per year, corresponding to 2 per cent of the carbon emissions generated by humans globally or 20 times Switzerland’s carbon emissions. To achieve this, Zunino will rely on a two-fold strategy. First, the proportion of cement (the particularly CO2-intensive component) will be reduced by around 60–70 per cent by replacing it with mineral additives. The goal is for these mineral additives, and not the cement, to shape the interactions in the concrete. That will require new types of chemical additives, in particular so-called polymer dispersants, which are a key focus of research. Second, the proportion of binder in concrete – i.e. cement plus water – will also be reduced. The big challenge now is to understand down to the smallest detail the complex balance between flow behaviour and strength development so as to retain the same properties despite the changed formulation.

No alternative to concrete

“The human and economic aspects are just as important as the technical ones,” says Zunino. “The material has to cater for everyday demands. If it takes a week to harden, for example, instead of a day or so as is currently the case, it will not find acceptance.” Thus, the research team is working closely with a large cement manufacturer. “If we are successful, industry will have a solution at hand for meeting CO2 targets and saving on carbon taxes,” he says. Might a completely new building material be a solution? Hardly: “On the streets of Nigeria, where people may sometimes mix concrete with their bare hands, a rocket science solution would have no chance.”

Zunino dreams of having all concrete everywhere replaced overnight by its ultra-sustainable variant, without anyone noticing the difference. He says, laughing: “This would be a transformation as magical as that of the material itself.”

This news article is a slightly edited version of an external media release of the external page SNSF