Swerock’s innovative recycled concrete was tested with a Sweco method
An innovation competition by the City of Helsinki looked for means to utilise the recycled insulation wool from demolished sites in concrete manufacturing. Wool can be used as a binding agent, replacing the commonly used cement. The competition winner, Swerock’s recycled concrete, was tested in a Sweco laboratory with a method developed for semi-dry concrete.
The cluster programme of circular economy by the City of Helsinki organised an innovation challenge in summer 2022, in cooperation with the EU-funded WOOL2LOOP project, Green Building Council Finland, YTEK, Saint-Gobain Finland and Verona. Companies in the concrete business had a few months to figure out how the recycled mineral wool powder could be utilised for manufacturing concrete. The challenge was won by one of the largest aggregates and ready-mixed concrete suppliers in the Nordic countries, Swerock.
“We want to develop environmentally friendly products that can be used in Finland all year round and that help us do our part in climate sustainability,” says Swerock’s Product and Development Manager Jesse Junnila. The recycled concrete developed for the innovation competition is not Swerock’s first recycled project. In ECO-Betoni, part of the concrete is replaced with blast-furnace slag, which can even halve the carbon dioxide emissions of concrete. “We also constantly invest in our equipment. We are now using a 47-metre hybrid concrete pump and we intend to continue investing in electric vehicles also in the future.”
The recycled wool used for the innovation competition came from the demolition worksite of Laakso Health Centre. Using recycled wool as a concrete binding agent reduced the demand for cement, which has larger climate emissions. Resource wisdom also improves as less virgin natural resources – soil and rock matter – are needed. “Replacing cement with waste fractions is circular economy at its best.”
Standardised method for testing semi-dry concrete
Swerock commissioned the Sweco laboratory to test its recycled concrete. “Our cooperation regarding the quality assurance of concrete has continued for several years now, and we have also had semi-dry concrete tested before with the standardised method developed by Sweco,” Junnila says. The competition jury praised the extensive series of tests and the research with different concrete types commissioned by Swerock.
The compressive strength and tensile strength of the fresh semi-dry concrete were tested in the Sweco laboratory. “Our method is the only way to test the strength of semi-dry concrete,” says Sweco Project Manager Noora Anttalainen. The concrete prisms for testing were made at the same time with the test masses, after which the prisms were stored in the laboratory and were left for 28 days to wait for hydratation, i.e. hardening. “The testing itself took a couple of hours.”
Junnila thinks that the most valuable observation in the testing was the great miscibility of the wool powder, which made it easy to use as a replacement for cement. The long-term shelf life and processing capabilities of recycled products are also important factors to review. “The wool’s impact on the processing capabilities of concrete was quite minor, and the strength was nearly identical to the benchmark level.”
Data security for product development
The series of tests are customised based on the product and the customer’s needs, and the data security of product development is managed carefully. “We have a confidentiality clause in place and we don’t need to know the exact concrete recipe, for example. Knowing the matters affecting occupational safety is enough,” Kivisaari says.
Junnila is sure that the testing process would have been much slower, more expensive and also harder if they had not commissioned laboratory tests on small amounts of concrete already during the early stages of product development. “It was definitely a major advantage to us that laboratory data was already available during the early product development,” he says. This revealed the possibilities of the product quickly, making it easier to scale the process up.
Next, Swerock will be looking for pilot sites for its recycled concrete. Based on the initial testing, the recycled concrete could be used for all general purposes of semi-dry concrete, such as under yard paving and in environmentally friendly concrete floors.
