Decarbonising the economy through CCUS relies not only on viable methods to capture CO2 but also efficient usage and/or storage of that CO2. In some instances, e.g. where large transport distances are required, or for countries which do not have large geological storage resources, utilising the captured CO2, or carbon capture and utilisation (CCU), may be the most effective way to decarbonise rather than transporting to a storage site. This new study investigates how captured CO2 may be used in building materials and explores the processes used to capture the CO2. The study looked into the effects of carbonation on material utilisation, the design of a potential typical carbonation plant, and undertook a market analysis of carbonated building products.
This study offers a valuable insight into how capture CO2 can be used in building material, with several key messages including:
- Accelerated carbonation products have the potential to be used as aggregates, fillers, reactive fillers, and supplementary cementitious materials (SCM).
- Carbonation is a relatively expensive method of CO2 utilisation unless there is substantial avoided cost associated with raw material disposal.
- There is a degree of discrepancy between theoretical and experimental uptake rates for different materials. The measured CO2 uptake is significantly lower than an estimation based solely on composition.
- It is important to consider the inherent trade-offs between each potential use – carbonating materials or use as an SCM.
- In many cases, carbonated materials should be preferentially used as a supplementary cementitious material or otherwise blended in to cement where possible.
- Non-Portland cementitious materials are frequently carbonated and can be used as an additive to cement and contribute to strength development in the final product. Note that the total amount of CO2 present in the cement should generally not be too high as it can reduce the pH of the cement binder and dilute its cementitious properties.
- Natural carbonation processes will occur which will reduce the additionality of accelerated carbonation.
- Carbonation can act as a waste treatment process, stabilising heavy metals.
- The main driver for carbonation processes is the avoidance of landfill costs where applicable.
- Current market prices suggest that the market for carbonated products is limited and will be closely linked to robust CO2 pricing mechanisms that recognise and value the mitigation service of carbonation.
- Further research is needed both to understand the potentials of more novel carbonated materials to store CO2, and their production processes, as well as to understand their material properties.
- There is currently insufficient pull from the construction industry for carbonated or low carbon emission produced products.