Making better mixes: Low-carbon and circular concrete

12/9/2019 8:41 AM CET

Chances are, you probably don’t think much about concrete – but you should. While concrete is a basic building material that serves as the backbone for many bridges and buildings, it has an outsize environmental impact.

We created this Parkour exercise course with blocks made of 100 percent recycled concrete, fully replacing natural aggregate for a more sustainable solution.

For instance, cement, a major ingredient in concrete, contributes to about 7 percent of the world’s carbon emissions, more than all the trucks on the road, according to International Energy Agency statistics. Also, concrete production requires huge quantities of crushed stone. Skanska was founded in 1887 as a company manufacturing concrete products and we continue to create solutions to help concrete better meet the needs of society and our planet.

In Sweden, for example, we have developed concrete mixes with up to 50 percent less carbon emissions than traditional mixes. In the US, Skanska is one of the leaders in a partnership that has developed an innovative new tool to make it easier to select low-carbon concrete mixes. Also, in the Czech Republic, where supplies of natural aggregates are decreasing, Skanska is bringing to market a circular concrete approach that uses 100 percent recycled concrete and/or masonry.

We highlight these important initiatives below, which support Skanska’s Group target of net-zero carbon emissions by 2045.

An immediate positive impact

Cement is the grey powder that is the glue in concrete, binding together the sand and crushed stone. It’s produced by burning limestone in kilns heated to nearly 1,500 Celsius, a process that generates much carbon emissions. With our rapidly urbanizing world demanding so much concrete, cement’s environmental impacts become significant.

In Sweden this year, Skanska launched a collection of low-carbon concrete mixes called Green Concrete (Grön betong). In these mixes, we have replaced a portion of cement with either slag, a waste product from steel mills, or fly ash, produced by power plants. While carbon emissions decrease by up to 50 percent, these low-emissions mixes maintain their durability, strength and workability.

Skanska’s new collection of Green Concrete reduces carbon emissions by up to 50 percent.

One project which has benefitted from Skanska’s Green Concrete is a new grocery store outside Stockholm for leading Swedish retailer ICA. For this project, ICA set high environmental criteria, including for the building’s climate impact. Skanska’s Green Concrete was important to meeting ICA’s sustainability requirements – it cut carbon emissions from concrete by 40 percent.

“Given the large quantities of concrete typically consumed by projects, using Green Concrete has an immediate positive impact in significantly lowering carbon emissions,” says Ludvig Dahlgren, a technical specialist with Skanska Sweden.

Fly ash and slag have been used to offset cement for many years in some countries, including in Norway, where Skanska also is a leader in developing low-carbon concrete mixes. But in Sweden, concerns about the harsh climate and other challenges have slowed the safe re-use of those industrial waste products in concrete.

With our rapidly urbanizing world demanding so much concrete, the environmental impacts of cement – a key ingredient in concrete - become significant.

Skanska is now working to extend Green Concrete’s use beyond buildings to include civil infrastructure, a more demanding application given Sweden’s cold winters. Creating such new products to meet higher sustainability demands is helping transform the industry.

“The construction industry is not used to changing quickly. We are used to building in the same way as we have always done, while learning from some mistakes along the way,” Ludvig says. “Now, with increasing demands for concrete that is not only durable but sustainable, we need to change fast.”

Another way of reducing concrete’s carbon emissions is through the Embodied Carbon in Construction Calculator (EC3). This is a free and easy to use tool that enables users to benchmark and assess building materials to facilitate the selection of versions with reduced amounts of upfront carbon emissions. More information is in this press release.

Pioneering a circular approach

In the Czech Republic, waste from construction and building demolition accounts for up to half of the country’s waste, and the supply of natural aggregates is decreasing. To address both these challenges in a more sustainable way, Skanska in the Czech Republic has started producing concrete that uses 100 percent recycled concrete and/or masonry to fully replace natural aggregates. This circular approach enables new buildings to be constructed from other buildings at the end of their life cycle.

Rebetong recycled concrete "will help our generation and that of our children," says Skanska's Bob Slánský.

Benefits from using this concrete, called Rebetong, include less demolition waste sent to landfill; about 12 percent less carbon emissions compared to regular concrete; and reduced cost. Furthermore, as Rebetong – especially made of recycled masonry - has better insulating properties than regular concrete it helps lower energy consumption throughout the building lifecycle.

Skanska is the world’s first concrete supplier to implement Rebetong’s patented technology, developed by Czech company ERC-TECH. Furthermore, we are exploring bringing Rebetong to additional markets.

“This has much potential for business and for contributing to the circular economy and the environment in general,” says Bob Slánský, Head of Technical Development and Innovation with Skanska Central Europe. “It will help our generation, and that of our children.”