Project OP7: Investigation of the Effects of Carbon-Conditioning on Recycled Aggregate Concrete

PhD Candidate

Mr. Anthony Butera

Chair Supervisor	Co-Supervisor

Prof. Vivian W.Y. Tam	Dr. Khoa N. Le

The utilization of recycled aggregate (stone) in concrete enables the reduction of landfill from construction and demolition waste. Unfortunately, recycled aggregate is characterized by poor properties and cannot be used in high quality concrete as a result of this weakness. Treating the aggregate with pressurized carbon dioxide, or carbon-conditioning, strengthens recycled aggregate and, therefore, allows the aggregate to be used within higher strength concrete.

The process of carbon-conditioning involves placing the recycled aggregate inside a sealed chamber. A CO₂ cylinder with regulator is then used to apply pressure to the recycled aggregate for various durations. After the carbon-conditioning, the aggregate is mixed into concrete in an identical fashion to classic concrete. This includes introducing the recycled aggregate into a mixer along with sand, cement and water in order to form concrete.

The CO₂ has a chemical reaction which the recycled aggregate, converting calcium hydroxides into calcium carbonates. As calcium carbonate crystals are smaller than that of calcium hydroxide crystals the aggregate is enhanced and made denser. This increase in density improves the properties of the aggregate and makes the concrete stronger.