Experimentally supported multi-scale Reactive Transport modeling of cementitious materials under Acid attack (ExpeRTa)

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Service-life of civil infrastructure is dominantly limited by deterioration mechanisms of concrete, the most widely used construction material. Particularly, acid attack is degrading cementitious materials in concrete structures. With increasing interest in the durability of cementitious materials, a better understanding of the underlying reactive-transport phenomena for concrete material in multi-scale is essential. Hitherto, this is not yet fundamentally considered in the prevailing experimental and computational approaches trying to elucidate the acid attack mechanisms. Only homogenized numerical models have been used so far, neglecting concrete heterogeneity descriptions occurring across a range of scales. A fundamental approach is needed that couples the chemistry, i.e. reaction thermodynamics and kinetics as well as transport phenomena with a multi-scale distribution of concrete components. Multiscale reactive-transport phenomena in porous media in general just starting to be explored these days, but are likely to become a primary focus in several scientific fields rapidly.Key objectives of ExpeRTa are to investigate and elucidate the fundamental mechanisms that cause concrete degradation due to acid attack with an emphasis on heterogeneity effects in the reactive-transport characteristics across a range of scales. This includes: O1) pore-scale numerical modelling using Hymostruc 3D virtual microstructures and implementation of the reactive transport degradation model for acid attack; O2) Meso-scale numerical modelling and upscaling of the reactive transport model; O3) An experimental program on paste, mortar and concrete degradation regarding materials design and attack parameters; O4) Multiscale analysis, calibration and validation of the numerical models with the obtained experimental results.Planned experimental methods comprise: µ-XRF, SAXS, Nanoindentation, MIP, gas sorption, thermal analysis, XRD, light microscopy, ESEM with EDX, and 3D-µ-CT imaging. The experimental activities are designed in such a way that the results can be used to calibrate and validate the developed numerical models. The influence of concrete mix design (water-to-cement-ratio and Ca/Si -ratio in binder, aggregate type as well as amount and size), acid type and parameters of boundary (attack) conditions will be investigated. In this synergetic cooperation, the Darmstadt University team, as concrete durability modelling experts for reactive transport computations, will cooperate intensively with the KIT team, who are experts for material testing and analysis and experimental investigation of acid attack on cementitious materials. The results of this unique fundamental modelling approach combined with extrapolations based on established scientific principles and known calibrations from accelerated durability tests, will significantly enhance the accuracy of the concrete structures service-life predictions.