Back in 2021, researchers came up with a recipe for greener concrete that had building waste and CO2 among its ingredients. Now the same team has used rubble from a demolished school and the greenhouse gas to produce bricks to build new structures.
As we noted in our coverage of the Calcium Carbonate Circulation System for Construction (C4S) project from the University of Tokyo in 2021, concrete production has a huge environmental cost. A large part of this is due to the high temperatures needed to heat limestone – a key ingredient in Portland cement – to create calcium.
The team points out that reserves of limestone are quite limited in countries such as Japan, leading to research efforts investigating the reuse of materials that already exist in the built environment. As such, the original C4S project sought to combine old concrete with carbon dioxide taken from the air or industrial processes to create a new building material called calcium carbonate concrete. But the blocks produced were fairly small and the compressive strength comparatively low.
Now the researchers have taken concrete from a demolished school building, ground it into a fine powder and then mixed it with CO2 from the air over a period of three months. This carbonated powder was subsequently pressurized with a calcium bicarbonate solution and layered in a mold before being heated to form a new building block that's reported "large and strong enough to build regular houses and pavements."
Not only does the new method make old buildings "an urban mine for creating new buildings," but the calcium carbonate concrete bricks can themselves be reduced to powder at the end of their build lives and the process repeated to create the building blocks for fresh construction.
"We are trying to develop systems that can contribute to a circular economy and carbon neutrality," said the team's Professor Ippei Maruyama. "In Japan, the current demand for construction material is less than in the past, so it is a good time to develop a new type of construction business, while also improving our understanding of this vital material through our research."
The next phase of the C4S project will be move to a pilot plant to bump up efficiency and develop larger building blocks as thoughts turn to commercial production. The team is also looking to build a two-story house using the calcium carbonate concrete bricks by 2030.
A paper on the new development has been published in the Journal of Advanced Concrete Technology.
Source: University of Tokyo