Performance of green concrete pipes made exclusively from carbon-activated steel slag

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Concrete pipe is an important infrastructure product and is traditionally made of Portland cement. Production of one tonne of cement requires 1.8 tonnes of virgin materials, such as limestone and clay, consumes 1,400 kWh energy equivalent, and emits 0.8 tonnes of carbon dioxide (CO2). To make concrete pipe carbon negative "green" product, it is crucial that Portland cement be replaced by an alternate environment-friendly binder in the process. Steel slag is a waste generated from steel refining process and has never been considered as a stand-alone binder in the production of construction products due to its poor hydraulic properties. The method developed at McGill University uses the carbonation activation technique to make steel slag a primary binder for construction application. The use of steel slag as a primary binder in construction products will eliminate the use of Portland cement, reduce carbon dioxide emissions, convert industry wastes into value-added products, sequester carbon dioxide into stable carbonates, and consume zero natural resources. It has been successfully applied to masonry block production marketed by Carbicrete Inc. This Alliance project investigates the possibility of producing the concrete pipes using carbon-activated steel slag system. The concrete pipes are traditionally reinforced by steel and have a much larger market than masonry blocks. The proposed research will develop a new process for a high slump slag-based concrete carbonated at very low pressure in a flexible enclosure. The microstructure of the material will be characterised and durability of the slag-based pipe will be evaluated through the corrosion tests and the sulfate resistance tests. Alkali activation will be examined for its ability to enhance the alkalinity to protect steel reinforcement and promote post-carbonation hydration. Leaching behaviour of slag-based concrete will also be examined.