Elucidating Steel Corrosion in Microstructure Engineered Cement

Carbon steel embedded in cement is the backbone of every modern building structure, and cement-steel grouting systems play a crucial role in containment structures for nuclear plant, and the proposed deep geological disposal facility for the UK’s nuclear waste. Advanced control of cement microstructure development through freeze-&-thaw processing and the introduction of cement-clay (bentonite) blended systems can be used to optimise the corrosion behaviour of carbon steel and steel-drums in cementitious environment. Grouting concepts using blends of bentonite clay and cement also provide an interesting opportunity to engineer physical and chemical properties for structural application, for example, by exploring gradual changes of porosity and rigidity/strength of cement matrices, with the low permeability and excellent plasticity of bentonite clays. This grouting system is widely used in civil engineering to form underground cut-off walls for pollution containment. The benefit of an optimised cement system is that the properties of the material can be controlled and designed to suit different application, for example, to immobilise different nuclear waste legacy streams or to tailor local corrosion behaviour. The proposed project is expected to open a new avenue for optimising cement hydration for enhanced corrosion resistance of building structures.

Novel approaches to characterise and fingerprint cement microstructure using image analysis and correlation techniques will be applied, and the development of steel corrosion and corrosion products elucidated. In-situ freeze-&-thaw processing of the cement and blended cement systems, combined with high-temperature curing treatments provide the means to control the cement hardening and local cement microstructure conditions. X-ray tomography observations in combination with analytical techniques will provide information, in-situ, about the effect of local cement microstructure on steel corrosion and crack nucleation susceptibility. The potential of local changes of cement microstructure for inducing corrosion hot-spots will be explored, to characterise preferred migration pathways within the cement matrix. The same methodology can also be used to control governing kinetics of local corrosion reactions.

The overarching objective of this exciting Ph.D. project is to provide a novel approach to advance the understanding of steel corrosion in cement/blended cement microstructure, and ultimately to use cement microstructure control to enhance the endurance and performance of steel-cement structure and containment systems.