Transport- und Löseprozesse im Gesteinskorn beim Ablauf einer AKR sowie Grundlagenuntersuchungen an AKR-Gelen

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Within the research group 1498, sub-project 5 shall pursue the following 6 objectives: 1. It is to clarify, to what extent a mechanical pre-damage and cyclic loading can drive a critical amount of NaCl solu-tion into concrete. 2. The influence of processing-related micro cracks in aggregate grains shall be verified for another rock type. 3. By means of a nanoCT-system, the volume of ASR-gel formed in concrete prisms during the FIB cyclic climate storage test method shall be determined. The main ob-jective here is to elucidate, if there is a critical amount of gel that, if exceeded, will cause concrete deterioration as a function of the correspondingly measured expansions and the composition of the gels. This information is of particular interest for the modelling in sub-project 3. 4. Swelling pressures of synthetic ASR-gels will be measured as a function of their composition, water content and amount. With respect to its composition, besides the Ca-content it is the Na-content that is of particular interest here, because it is affected by an external supply of NaCl. Furthermore it shall be clarified, if the swelling ability of a gel is preserved below a certain content of water and what amount of gel is necessary to produce a deleterious pressure. In addition, the role of SiO2 dissolution for the swelling process will be investigated by measuring swelling pressures of rock powders subjected to artificial pore solutions. For a thermodynamic modelling, also solubility products and enthalpies of reaction will be determined for synthetic ASR-gels. The obtained data are of great importance for modelling the ASR damaging process within the scope of sub-project 3. 5. As a function of temperature and NaCl concentration, SiO2 dissolution rates shall be determined. For that purpose, the dissolution experiments already started in funding period 1 will be continued and extended, for what two more aggregates (crushed gravel, rhyolite) will be used among other extensions. By running an SEM/EBSD-analysis, by what size and deformation of single quartz crystals can be determined spatially resolved, quartz will be investigated before and after the dissolution attack. It is of major interest to learn what influence the dissolution attack has on the quartz microstructure and what link between microstructure and dissolution rate exists respectively. 6. By means of an image analysis software, concrete thin sections shall be used for a more quantitative instead qualitative and describing appraisal. The main focus is the detection of cracks to characterize the degree of the cracking more quantitatively (number, width, lengths and area of the cracks) and by deriving an appropriate specific value to compare the degree of damage caused by ASR for different concretes.