The benchmark problem presented in this paper deals with the leaching of calcium from hardened cement paste. The leaching of calcium results in the dissolution of the cement minerals which affects physical, chemical and mechanical properties of porous cement matrix. The dissolution of cement minerals in this case progresses heterogeneously as a consequence of a small-scale geometrical feature (crack) within a domain. Complexity of transport through cracked porous media combined with complex cement chemistry can lead to considerable modelling uncertainties. One possible way to get an insight into the robustness of modelling results is to perform benchmark based on (i) different transport models and solution methods (finite volume, finite element, etc.), (ii) different geochemical solvers and (iii) different coupling algorithms (sequential iterative and non-iterative). This benchmark is designed to gradually increase the complexity of the problem and in this way recognize modelling elements that are the most sensitive in terms of modelling results, e.g. evolution of physical and chemical properties. Five international teams participated in this benchmark exercise. The reactive transport codes used (HYTEC, MIN3P, OGS-GEM, ORCHESTRA, COMSOL Multiphysics-iPHREEQC) give similar patterns in terms of predicted concentrations of elements and the mineralogy. The level of agreement depends on the problem complexity related mainly to the weighting and conservation properties of different numerical methods, to the coupling between transport and reactive solver and the agreement of thermodynamic database.