Capture: Regulating CaCO3 polymorphism to unlock the potential of carbonated steel slag as a cement replacement

The UK government pledges to achieve net zero emissions by 2050. Carbon capture and utilisation (CCU) in the cement and iron & steel sectors is considered a core measure toward this ambitious goal. An effective way of decarbonising the construction industry is to modify the Portland cement (PC) composition by reducing the clinker proportion. Replacing clinker with limestone (CaCO3, mainly calcite) proved to offset the CO2 emissions effectively while improving PC properties. Meanwhile, various alkaline solid wastes (ASW) have a significant potential of capturing CO2 whilst producing different CaCO3 polymorphs depending on the carbonation conditions. However, there is a lack of knowledge regarding the hydration characteristics of PC containing a range of CaCO3 polymorphs. In this proof-of-concept project, we will adopt steel slag (SS) as a representative ASW to validate the hypotheses that: (i) CaCO3 polymorphism can be regulated via controlling the carbonation conditions of SS and (ii) distinctively different CaCO3 polymorphs interact with PC differently. The main purpose of this project is to build a long-lasting partnership between researchers from the UK, China and Singapore, to collectively address the technical challenges of utilising ASW more efficiently and effectively as cement additives. The assembled project members from Cardiff University (UK), Nanjing Tech University (China) and Singapore Institute of Technology (Singapore) have complementary expertise in ASW characterisation and carbonation, cement science and structural engineering. The commonality of the team is our research interest in CCU in construction materials. Our intention is to share our knowledge and skills, advance the global understanding of ASW carbonation and utilisation in cement and concrete, and explore future research opportunities between academics from different countries.