Making concrete more sustainable saves raw materials and CO2

Construction plays an important role in achieving the climate goals. The sector consumes half of all raw materials in our country, accounts for 40 percent of energy consumption and a third of total CO2 emissions. Because half of all building materials are concrete, a lot can be gained by making it more sustainable. TNO has developed a new approach to this, which is also closely in line with the latest initiatives from the sector, Material-driven Multi-criteria Design Optimization or MIMO.

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“Save space for more sustainable concrete”

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Significant CO2 reduction

‘This approach mainly consists of the much smarter and greater use of secondary material flows that are becoming available locally, such as construction and demolition waste. They make up a third of the waste that our country produces each year. We have calculated that the construction can easily recycle ten times as much of the material in concrete, and that at least half of the primary raw materials must be used to make concrete. Recycling also results in a significant CO2 reduction. “Complete recycling of elements from existing concrete structures and rubble means an estimated 0.75 to 1.25 million tonnes less CO2 per year,” says Siska Valcke from TNO, an expert in circular concrete.

Recycle much more

The MIMO method, in full material-driven Multi-criteria Design Optimization, is an approach to more sustainable concrete that provides benefits for all parties involved: customers, construction companies, recycling companies, constructors / designers and concrete suppliers,. Information on locally available raw materials and materials is central to MIMO.

Siska: ‘In this approach, we take as our starting point the properties of the materials that make up the construction and demolition waste. From there, we can recycle much more than we do now. Every year, about 22 million rocky debris is released through demolition. Of this, 12 million are concrete and 10 million masonry. Currently, only 2 million of this is recycled, while we produce 33 million new concrete each year. It should and can be done much better. Thanks to MIMO, we can make the 33 million sustainable to a much greater extent. ‘

More and better utilization of construction waste

MIMO is not a concept that disrupts existing working methods, but fits in well with initiatives that the sector is already developing, such as new types of concrete with less cement, slimmer construction, recycling of concrete elements and removable construction. The parties can weigh different strategies for sustainability and circularity against each other and combine them optimally in their own project. The new approach means that secondary material flows are used much more and better.

‘We use data on these material flows to optimize design for construction safety, environmental impact and cost. Released materials such as concrete aggregates, complete concrete elements and masonry are still recycled too little. This is due to uncertainties in the area of ​​structural safety, or because it is not clear whether dismantling and recycling can actually cost more than it generates. In MIMO, we can link all these requirements and variables to an optimal design and answer that question. ‘

Large selection of features

‘MIMO is what we call resource-based engineering’, says Siska. “Information about the properties of the available materials is central to arriving at an optimal design from there. The concrete sector is used to working with standard raw materials and concrete mixtures, but will have to switch to various other material flows, to other types of concrete. We want to work more with what is locally available in construction and demolition waste.

These flows just have a much greater variation in shape and properties. We have data on these properties and combine them with our models and optimization software developed here. This allows us to combine requirements based on an environment, circularity, safety and cost in an optimal design. Our models predict the effect of each recycled material on the desired concrete structure. In this way, constructive designers can make well-founded and objectified considerations. ‘

More information available

MIMO is now being tested on a limited scale. This shows the benefits of the method for the parties involved. In this way, customers get early solutions that measurably meet their requirements and that they can compare transparently with each other. Contractors and demolition companies gain better insight into the costs and benefits of smart disassembly and storage of materials.

Information on this is valuable for construction companies and engineering companies. Demolition and recycling companies can add value by informing in advance about material properties, which in turn are important for the design. The information, in turn, can help demolition companies determine the best demolition strategy.

Outdated rules

MIMO is therefore a promising solution to make concrete more sustainable, so that fewer primary raw materials are needed and CO2 emissions are reduced. However, there is still one obstacle.

Siska Valcke: “Something must be done about the current rules. It is outdated and leaves too little room for such measures. Now that more and more varied flows of raw materials can be used to make concrete “greener”, we need custom rules for this. We need to address this quickly with the sector and the government. ‘

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