Low-Carbon Concrete Development Through Incorporation of Carbonated Recycled Aggregate and Carbon Dioxide During Concrete Batching and Curing

The accelerated carbonation of fresh concrete and recycled aggregates is one of the safest methods of CO2 sequestration as it mineralizes CO2, preventing its escape into the atmosphere. CO2 injection during batching of concrete improves its strength and may partially replace Portland cement, as with supplementary cementitious materials (SCMs). The curing of concrete by incorporation of CO2 also accelerates early strength development, which may enable early stripping of formwork/moulds for precast and in situ construction. The carbonation process may also be used for the beneficiation of recycled aggregates sourced from demolition waste. The CO2 mineralization technique may also be used for producing low-carbon, carbon-neutral, or carbon-negative concrete constituents via the carbonation of mineral feedstock, including industrial wastes like steel slag, mine tailings, or raw quarried minerals. This research paper analyses various available technologies for CO2 storage in concrete, CO2 curing and mixing of concrete, and CO2 injection for improving the properties of recycled aggregates. Carbon dioxide can be incorporated into concrete both through reaction with hydrating cement and through incorporation in recycled aggregates, giving a product of similar properties to concrete made from virgin materials. In this contribution we explore the various methodologies available to incorporate CO2 in both hydrating cement and recycled aggregates and develop a protocol for best practice. We find that the loss of concrete strength due to the incorporation of recycled aggregates can be mitigated by CO2 curing of the aggregates and the hydrating concrete, giving no negative strength consequences and sequestering around 30 kg of CO2 per cubic metre of concrete.