Experimentally Verfied Atomistic Modelling of Lime in Construction Materials

Since antiquity the construction industry has been using lime based binders to manufacture mortars, plasters and renders.Despite this history there is still a lack of fundamental understanding of the hardening processes and how these influence time dependent mechanical properties. In addition dolomitic limes, containing magnesium, exhibit enhanced properties when compared to their pure lime counterparts, however there is limited knowledge of the underlying reasons. Lime based mortars are ideal candidates to replace cement mortars in many applications where lower strength is an advantage such as new build housing, forms of construction utilising organic fillers such as lime-hemp, and conservation and restoration applications. Indeed lime mortars offer many advantages over cement in terms of moisture permittivity, ability to accommodate movement, self-healing properties and ability to sequester carbon dioxide. Cementious binders are produced at much higher temperatures compared to lime and have large carbon dioxide emissions associated with their manufacture. Atomistic modelling provides a unique opportunity to probe these mechanisms at a fundamental level thereby elucidating the processes responsible for developing the properties of industrial importance. Many existing and past studies of building lime binders have focused on bulk properties for instance through large scale bulk property testing, whilst not taking into account atom level processes. In recent years the cement industry has employed atomistic modelling of hydrated silicates as a means of understanding material behaviour. Recent studies have demonstrated that the morphology and composition of a lime crystal can influence the carbonation process, and by association mechanical behaviour. In addition magnesium containing dolomitic limes show improved performance in many respects including strength development. Rate of carbonation is an extremely important issue as this can dictate the speed at which a building can be erected and therefore the associated costs. The ability to improve the carbonation rate and therefore hardening rate through control of composition and morphology will lead to enhanced products with better environmental credentials. In the first instance this proposal seeks to develop atomistic models to describe the important aspects of lime binder behaviour and validate these against laboratory samples. Atomistic models will generate Raman spectra and X-ray diffraction patterns for direct comparison with experimental measurements. These initial models will then be developed further to investigate firstly carbonation and then time dependent and plastic mechanical properties. Additionally the research will investigate the underlying reasons for the improved performance observed in magnesium containing dolomitic limes. The project is expected to bring long term benefits to the construction industry over the coming decades. In the shorter term industry will benefit through planned workshops and site visits which will showcase the application of atomistic modelling to lime manufacturers. The project will support the development of enhanced projects through the new knowledge gained.