SIA: Mrs Stürwald, when we hear “concrete”, we almost always think of landscapes of gray walls. Why did you choose this material as a research subject?
Simone Stürwald: Before getting into building materials design, I worked as a structural engineer. It was a bit of chance that led me to materials, when I took charge of the construction materials testing center at the OST. Since then, I have dedicated my time to researching new sustainable concrete mixes – a construction material used in construction, infrastructure projects and the construction of bridges and tunnels.
What do we mean by sustainable concrete?
Sustainability can be considered as a whole or through the prism of ecological aspects. In building materials research, we focus on ecological criteria, such as resource conservation, circular economy and reduction of CO emissions.2 during manufacturing.
Cement production would be responsible for nearly 8% of CO emissions2 of human origin in the world. Why not just reduce the share of cement?
This is what we are already doing. But we can’t go below a certain limit, because we need the cement as a binder to ensure structural integrity. In the early days of concrete construction, the share of cement was lower, for cost reasons. But given the defects that affected concrete in the 1970s, we subsequently returned to higher quantities of cement.
You are conducting research on Klark concrete. What is it exactly?
Klark concrete offsets CO2 rejected during production thanks to the addition of vegetable charcoal, in other words biogenic carbon. It is therefore climate neutral. Klark concrete was developed for and with Logbau AG, a concrete manufacturer from Graubünden who wanted to incorporate locally produced charcoal into the building material. Our specialized university, for its part, conducts applied research programs and contributes to making this innovation marketable.
Can Klark concrete be used in civil engineering?
As things currently stand and given its characteristics, Klark concrete is less suited to the particularly high demands of civil engineering. But we are currently working to improve its durability against exogenous influences, such as de-icing salts. In the building sector, which represents more than 70% of concrete consumed by volume, Klark concrete is already usable and can make a significant contribution to reducing CO emissions.2.
The high consumption of concrete in Switzerland could require enormous quantities of charcoal, and therefore wood. Isn’t this an example of greenwashing?
That’s not how I see things. According to the guidelines of the European Biochar Certificate (EBC)1the vegetable charcoal used for concrete must come from wood or plant residues, such as ashes from regional cogeneration plants. If they were not used for concrete, this “waste” would simply be thrown away. But we must keep in mind the fact that concrete is the second most used material after water. Switzerland produces nearly 15 million cubic meters of concrete each year. We must therefore control its use. And in addition, the compensation of CO emissions2 remains a wise transition solution.
How do you judge the carbonation of concrete, which allows CO to be chemically fixed?2 and therefore store it sustainably?
This method is suitable for old concrete and operates mainly on the surface. It is less sought after for existing reinforced concrete structures, to the extent that carbonation reduces protection against corrosion and therefore the lifespan of the construction. Not to mention the fact that mixing concrete with recycled concrete aggregates requires more cement, which ultimately limits CO savings2. Carbonation helps reduce CO2 about five to ten percent per cubic meter of recycled concrete. Therefore, it has limited potential.
Are there other promising approaches for more durable concrete?
The upcoming abandonment of the minimum quantity of cement in the normative arsenal has opened the way to the development of different formulations. Within the strict framework of the regulations governing the constituents of concrete, it is now possible to certify the additives available at regional level. This helps promote closed circuits.
What role does digital play in the design of new concrete formulas?
We are currently working on the development of a tool called OptimiX in partnership with a control software supplier. Machine learning allows concrete manufacturers to better control the many parameters that influence concrete and to develop formulas containing less cement. The deployment of this tool should, in our opinion, allow cement savings of at least twenty percent.
Even in a more durable version, isn’t concrete doomed to disappear?
Rather than targeting specific building materials, we need to broaden our thinking, because it’s not just about which materials are more or less sustainable. Indeed, it is just as important to have efficient supporting structures adapted to the materials, with a lower environmental impact per unit of use. This is what prompted me to create the SIA “Sustainable Supporting Structures” working group. This develops approaches for sustainable supporting structures, all materials combined, and prepares SIA guidelines on the subject. Ultimately, we need comprehensive planning and design processes that integrate the issue of sustainability as early as possible.
How much does durable concrete cost?
On the one hand, by reducing the quantity of cement, we reduce costs. On the other hand, chemical admixtures and higher requirements for the preparation of concrete mixes lead to additional costs. In addition, durable concrete must remain in the formwork longer, which leads to longer lead times. All of this results in a higher final bill, which is not a bad thing. Indeed, we must stop considering concrete as a mass product. I prefer that we have a quality technical solution that is durable and works well. We should limit the use of concrete to applications where other materials do not perform as well. I expect slight additional costs for materials. On the other hand, the construction aspect has potential for savings, provided it is subject to judicious planning.
What’s next for sustainable concrete?
Basic research is important, but we cannot rely entirely on pilot projects. We need to generalize the adoption of sustainable solutions in the construction sector and that is what we are working on. It is indeed the only way to reduce CO emissions.2 significantly.
To write to the authors: Christer Joho, Communication and public affairs specialist at SIA, christer.joho [at] sia.ch (christ[dot]cloak[at]is[dot]ch) and Hana Buterin, Communication intern at SIA, hana.buterin [at] sia.ch (hana[dot]buterin[at]is[dot]ch)
Note
1. The European Charcoal Certificate (EBC) has been developed since 2010 under the leadership of the Ithaka Institute before becoming a voluntary industry standard.
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