Concrete, a material that often ends up in landfills after its use, is responsible for approximately 8% of global carbon emissions due to its production. However, researchers at the University of Tokyo have developed a groundbreaking method to recycle old concrete into new, robust building blocks. These new blocks are not only strong enough for constructing houses and pavements but also offer a sustainable solution to combat climate change.
The innovative process transforms waste concrete into new blocks that capture carbon dioxide, contributing to a circular economy. Remarkably, this method can be repeated, making it a truly sustainable and renewable approach. “We are trying to develop systems that can contribute to a circular economy and carbon neutrality,” said Professor Ippei Maruyama, the lead researcher behind this development.
The timing of this innovation is particularly advantageous for Japan, where the demand for construction materials has decreased. “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,” Maruyama added.
How the New Concrete Blocks Are Made
The process to create these new concrete blocks is surprisingly straightforward. Old concrete is first crushed into a fine powder and then reacted with atmospheric carbon dioxide. The powder is shaped into layers under pressure and heated to solidify into new concrete blocks.
The carbon dioxide used in this process is captured either from the atmosphere or from industrial emissions. In the researchers’ trials, demolished concrete from a school building was recycled through this method.
The process involves a three-month carbonation procedure, where the concrete components react with atmospheric carbon dioxide to produce calcium carbonate. The carbonated powder is then treated with a calcium bicarbonate solution and dried to form a new material known as calcium carbonate concrete bricks. This method not only strengthens the blocks but also enhances their durability for long-term use.
Sustainable and Reusable Construction Material
One of the most significant benefits of this process is that the concrete blocks can theoretically be remade indefinitely through the same method. “These blocks can theoretically be used semipermanently through repeated crushing and remaking, a process which requires relatively low energy consumption,” Maruyama explained. This concept turns old buildings into a kind of urban mine, where the material can be repurposed for new construction projects.
Limestone, a key ingredient in traditional concrete, provides strength and durability but is a finite resource. Countries like Japan have limited limestone reserves, making the recycling and reuse of materials increasingly important.
Several years ago, the research team initiated the C4S (Calcium Carbonate Circulation System for Construction) project, aiming to curb greenhouse gas emissions and repurpose construction waste. Initially, the project produced small blocks, but the latest developments have resulted in much larger and more practical blocks for construction.
“As part of the C4S project, we intend to construct a real two-story house by 2030,” said Maruyama. Looking ahead, the team plans to establish a pilot plant to improve production efficiency and work towards making this innovative material commercially available.
By Impact Lab
