Optimization of Spatially Resolved Laser Ablation ICP MS to Study Transport Phenomena Concerning Concrete Durability

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The service life of concrete structural components is determined by the transport of substances like CO2, chlorides or acids through the pore system into the concrete interior and there the chemical and physical processes which occur. Transport processes in the pore system of concrete structural components in contact with water also control the release of environmentally relevant substances such as heavy metals. In all cases, the interfacial transition zone (ITZ) between the aggregate particles and the binder matrix affects transport and therefore service life decisively. In order to understand the effect of the ITZ on transport processes and thus the durability of concrete, it is necessary to know the distribution of the relevant substances in the ITZ, the hardened cement paste matrix and the aggregate.Laser ablation coupled with mass spectroscopy LA-ICP-MS is an analytical method with great potential for the spatial resolution of distributions of elements over the surface or in the depth of building materials. However, up to now the application of this method to concrete has been restricted by the accuracy of the quantitative analysis. This is due to the complex microstructure of concrete as a material.The first funding phase of the project focused on the optimization of LA-ICP-MS for application to concrete. Owing to the complexity of concrete composition with constituents of different hardness, polymineral aggregates and hardened cement paste, it was necessary to develop new evaluation strategies in order to obtain a quantitative assessment of the main elements, especially in the interfacial transition zone between the hardened cement paste and aggregate.Following the successful optimization of the method, the proposed continuation of the research work now focuses on the investigation of the transition zone and its effect on transport phenomena. To realise this, tablets are produced by compressing ground hardened cement paste mixed with aggregate particles as well as pressing ground hardened cement paste onto aggregate slices, i.e. idealized "concretes" without transition zones. Normal “concrete” specimens with transition zones are produced by pouring fresh cement paste onto aggregate slices or cubes as well as mixing the fresh paste with aggregate particles. The specimen compositions aim to cover a wide range of possible elemental compositions of the hardened cement paste matrix and provide information on the effect of selected mineral additions on the transition zone. Water adsorption tests are used to provide more information on the role of the transition zone in transport processes. The optimization of LA-ICP-MS for concrete with an improved quantitative analysis of element distributions in the hardened binder paste and the ITZ will enable significantly better quantification and understanding of the effect of microstructure on concrete strength, the transport of damaging substances and herewith the durability of concrete.