In 2021, researchers came up with a recipe for greener concrete that included construction waste and CO2. Now, the same team has used rubble and greenhouse gases from a demolished school to create bricks to build new structures.
As we noted in the University of Tokyo’s Calcium Carbonate Circulation System for Construction (C4S) project in 2021, concrete production has a huge environmental cost. Much of this comes from the high temperatures required to heat limestone, a key ingredient in Portland cement, to create calcium.
The team notes that limestone reserves in countries like Japan are quite limited, leading to research efforts exploring the reuse of materials already in the built environment. For this reason, the original C4S project aimed to combine old concrete with carbon dioxide taken from the air or industrial processes to create a new building material called calcium carbonate concrete. However, the blocks produced were quite small and had relatively low compressive strength.
Now 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 three-month period. This carbonated powder was then pressurized with calcium bicarbonate solution and placed in layers in a mold before being heated to create a new building block that is reportedly “large and strong enough to build regular houses and sidewalks.”
Not only does the new method turn old buildings into “an urban mine for creating new buildings”, but the calcium carbonate concrete bricks can also be turned into powder at the end of their construction life, and the process can be repeated to create building blocks for new construction.
“We are trying to develop systems that can contribute to a circular economy and carbon neutrality,” said Professor Ippei Maruyama of the team. “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 work and at the same time improve our understanding of this vital material through our research.”
The next phase of the C4S project will be to move to a pilot plant to increase efficiency and develop larger building blocks as they move towards commercial production. The team also plan to build a two-storey house using calcium carbonate concrete bricks by 2030.
An article on the new development in the Journal of Advanced Concrete Technology.
Source: University of Tokyo