Decarbonising industry and the economy is essential to improve the balance between our ecological footprint and the planet’s renewable resources. This would provide the best possible chance for humanity to mitigate the effects of climate change. Consequently, we need to rethink the way we build our cities. And to do this, we need to talk about cement.

Cement, the ‘glue’ in concrete, is the durable, waterproof and ubiquitous material upon which modern civilisation is built. Concrete is second only to water in terms of commodity use, and the world produces more than 10 billion tonnes of it each year.

Cement production alone (excluding other aspects of construction) accounts for around 8% of global CO₂ emissions, about half of which results from chemical reactions inherent in the production process. As other industries such as energy and agriculture reduce their share of emissions, cement production may account for nearly a quarter of all human-driven CO₂ emissions by 2050.

Modern alkali-activated cements (AAC) can enhance physical properties, and reduce associated CO2 emissions by >80%, compared to Portland cement. Additionally, these cements are produced primarily from supplementary cementitious materials (SCM) which are typically industrial by-products such as metallurgical slags, or naturally abundant minerals such as clays, further enhancing their sustainability.

These cements require an alkali ‘activator’ to provide a high pH in the fresh cement paste and drive reaction, setting and hardening. However, concentrated alkali solutions exhibit high viscosities and complex crystallisation behaviour, which dramatically affects the reaction mechanisms and kinetics, and physical properties of the resultant cements, even with only minor changes in mix formulation. A detailed understanding of crystallisation processes, fluid-particle and particle-particle interactions is urgently required for these next-generation low-carbon cements, to enable quality control and make them practical for use in large-scale construction.

This PhD uses in-situ surface-specific techniques, spectroscopic and microstructural characterisation to examine these interactions in AAC produced using a suite of alkali solutions and SCMs. Currently underutilised SCMs (e.g. electric arc furnace slags) are investigated, and benchmarked against AAC produced using blast furnace slag (industry standard). The knowledge obtained will be used to design novel AAC formulations with enhanced performance. This will drive implementation, and help decarbonise cement production.

We will examine how crystallisation processes, fluid-particle and particle-particle interactions affect (i) dispersion, fluidisation, and rheology of the fresh cement paste, (ii) reaction and setting, and (iii) physical property development of low-carbon AAC. We will use this information to design and test new AAC formulations for enhanced performance and quality control.

Specifically, it will develop a mechanistic understanding of crystallisation processes, fluid-particle and particle-particle interactions, by experimentally assessing:

• Surface chemistry of the activating solution and fresh cement paste.

• Reaction and setting, and fresh-state physical characteristics of the cements.

• Evolution of cement structure, phase assemblage and durability.

This will show how the nature of the raw materials affect: 1) dispersion, fluidisation, and rheology, 2) reaction and setting, and 3) physical property development. This will enable optimisation of cement formulations for enhanced sustainability, performance and durability, and hence drive industrial innovation.