An Electrochemical Approach to Study Carbonation of Novel Lime Based Materials

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This project seeks to advance the current understanding of carbonation in lime and cement materials. A novel approach is proposed where the reaction with carbon dioxide will be studied using micro pH electrodes. pH variations in a thin water film at the sample surface will allow the reaction mechanism to be determined. A detailed understanding of the surface morphology and composition will be provided by a comprehensive electron optical and surface analytical study. The reaction of these materials with carbon dioxide is or great interest as sequestration of carbon dioxide is a key initiative aimed at reducing climate change. Lime has the ability to adsorb significantly higher quantities of carbon dioxide during the setting process in comparison to alternative products such as cement and has important applications in the restoration and conservation of historic buildings in addition to renovation and new build projects. Cement acquires its strength from hydration of reactive silicate and aluminate clinker phases however in the long term carbonation of these phases can lead to a reduction in mechanical performance and the corrosion of steel reinforcements if present.Although the chemical process of carbonation is well known the mechanisms in lime and cement mortars are poorly understood. This research programme seeks to address this issue.In recent years the producers of low carbon footprint materials such as hemp and wastes from a range of industrial processes have expressed interest in the incorporation of their materials as fillers and additives in lime and cement products including mortars, renders, plasters and concrete. The addition of these environmentally friendly materials not only influence the micro and macro pore structure but soluble constituents may introduce ionic species into the pore water, the influence of which on carbonation is unknown. This proposal aims to study the carbonation process by monitoring ion concentrations at different locations within the liquid film on the surface of a calcium hydroxide substrate. Proton concentrations will be measured using specially manufactured microelectrodes consisting of nanostructured palladium hydride discs approximately 10 micrometers in diameter and electrodeposited on the end of a normal microdisc electrode. Held precisely with a micropositioner the pH microelectrode will be brought to within a few micrometres from the surface under investigation. In a similar way, commercially available ion selective electrodes will be used to determine the calcium ion concentration. In the second phase of the project the effect of ions leached from additives commonly used in conjunction with lime will be investigated. These can be divided into the following five groups, blast furnace slag (GGBS), bottle glass, wood ash, hemp and metakaolin.Additives of interest will include glass, ashes / slag and organic surfactants.