Binks Institute for Sustainability: Low carbon cement using hydrothermal manufacturing techniques

The production of Portland cement is a significant source of carbon dioxide emissions – around 1500 million tonnes per year in 2019.

There are four reasons why the carbon emissions associated with Portland cement are high:

• its manufacture requires high temperatures – around 1400°C;
• these temperatures must currently be achieved through combustion of fossil fuels;
• during manufacture, decomposition of calcium carbonate leads to further CO2 emissions;
• the sheer volume of cement being used globally - around 4 billion tonnes per year - ensures high associated CO2 emissions.

Portland cement can be combined with other materials to reduce embodied carbon. For many years, these have been ground granulated blast furnace slag (GGBS) (from the production of iron) and fly ash (from coal-fired power production). Fly ash is destined to disappear in the near future, as the result of the ongoing phasing-out of coal combustion. GGBS is also likely to become scarce as steel recycling (which bypasses GGBS production) becomes the primary means of production.

This proposed PhD project aims to develop cements to replace GGBS and fly ash that can be manufactured at temperatures of less than 200°C using electricity. As a result, carbon emissions will be lower than Portland cement, but, more significantly, as electricity generation shifts further towards renewable sources, these will ultimately reduce to zero.

The approach involves the production of synthetic minerals called ‘zeolites’ from a variety of common waste materials using hydrothermal techniques. These techniques involve heating raw materials with water in conditions which lead to the development of pressure. This leads to the raw materials dissolving, reacting together and forming solid zeolites.

Zeolites undergo a ‘pozzolanic’ reaction whose products are similar to those of hardened Portland cement. However, there are many different types of zeolite, and identifying those most suitable for use as cement constituents is a major aim of the project. This will be investigated in the laboratory using X-ray diffraction, thermal analysis, mercury intrusion porosimetry and strength measurements.

Additionally, whilst low temperatures are required to manufacture zeolites, this is not the whole story. Water requires a large amount of energy to heat, and so another aim of the project is to devise and refine zeolite ‘recipes’ that minimise the water requirement, temperature and production time to reduce energy demand as much as possible. This will be investigated using similar laboratory techniques as described above, combined with measurement of temperature change during the zeolite-forming reactions and theoretical modelling.

Finally, the project will examine the sort of technologies which can be used to provide heat during manufacture in terms of energy efficiency and rate of temperature increase to identify suitable approaches to scaling-up to industrial magnitudes of production.

Supervision is provided by Dr Tom Dyer, who has expertise in materials science and cement chemistry, Dr Anusha Wijewardane who has expertise in thermodynamics and heat transfer, and Dr Wattala Fernando who will provide insight to the project on renewable energy systems.

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