Production of slag-bonded construction blocks by carbonation

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Steel slag is a major by-product from the steel-refining process and is commonly used as aggregate for road construction. Because of its high calcium content, the use of slag as road aggregate does not justify its potential. On the other hand, production of Portland cement is an energy-intensive and a CO2 emitting process. If steel slag can be activated to replace Portland cement, it can be used to make building products that will show significantly reduced embodied energy and process emission. The research at McGill University has demonstrated that ground steel slag, once compact formed into a building product, can react with carbon dioxide to produce strength. This strength can be sufficient to make blocks or wallboards for construction applications. Carbon dioxide activation converts both the hydraulic and non-hydraulic calcium silicates in steel slag into a hybrid of calcium silicate hydrates and calcium carbonates, a special cementing matrix known to increase strength and durability. The use of steel slag as a primary binder in building products will eliminate the use of Portland cement, reduce carbon dioxide emissions, utilize industry wastes, sequester carbon dioxide and consume zero virgin materials. The slag-bond products are carbon-negative and their performance are comparable to commercial cement-based products. Based on our preliminary work, this proposed research will carry out a prototype production to showcase that full-scale slag-bond blocks can be produced at a competitive price. The project will investigate the optimized mix design to trade off the density and the cost, examine the possible use of low concentration gas of 95% purity or of 15% purity as flue gas, produce full scale construction blocks using flue gas activation, and conduct durability and certification tests of the new blocks. The goal is to produce green blocks that are economically competitive, technically comparable and environmentally beneficial. If successful, the product will be the first of its kind in the world.