Engineers create greener concrete using waste clay

When it comes to human-made materials, concrete is the most consumed product on earth. Each year, about three tons of concrete are consumed per person. The environmental impact of concrete is far less publicized than the impact of other human-made materials such as plastic. Concrete is made of water, cement, and fill materials like sand. Researchers say the concrete industry alone is responsible for about eight percent of the carbon dioxide emissions globally.

The production of concrete also consumes approximately 10 percent of the world's industrial water. Researchers from the National University of Singapore have shown they can reduce the amount of sand required to make concrete by substituting a common clay material easily obtained as waste from excavation work from construction sites around Singapore.

The clay is heated to about 700 degrees Celsius to activate it to enhance the bonding ability in the concrete. Activated clay was then used to replace up to half of the fine sand powder typically used in concrete manufacturing. The result was an ultrahigh-performance concrete which is an extremely strong type of concrete that can reduce the size of the structural elements and potentially reduce the amount of concrete required in a construction project.

Researchers say that tunneling and foundation works are common in Singapore and generate lots of excavation waste material. Disposal of the material is difficult because land is scarce in Singapore, providing limited space for landfill. The project marks the first time that low-grade waste clay has been used as a filler in concrete.

The team is currently looking into using waste clay for additional concrete applications. The research group is also exploring the use of other waste materials to replace the filler in concrete and the use of sea-water and sea-sand to reduce the reliance on freshwater and river sand imports in Singapore. Researchers are also looking at using concrete as a carbon capture material to reduce its carbon footprint.