On micro-level vulnerability of concrete surface layer in process of crystallization of hydrating Portland cement and upon mechanical load

Abstract

The target of this research is to make a system of data on discontinuity of the cement stone microstructure in concrete. To achieve this, the following issues have to be addressed: a) a justification for the presence of dislocations in cement stone and definition of their type needs to be provided; b) the source of the considered material weakness has to be identified; c) an explanation of formation and propagation of micro cracks starting at the surface and going deeper into the concrete needs to be given; d) an educated guess has to be made for the opening/depth ratio of micro cracks; e) information about the distances between micro cracks in the capillary walls of the cement stone should be obtained; e) binding energy in the calcium silicate crystalline hydrate has to be determined. The research results show that the mechanical properties of crystals and polycrystals in the cement stone (concrete) depend on the ratio of small-angle (θ≤10…150) and large-angle boundaries. Due to a relatively small number of large-angle boundaries, intergranular and plastic flow deformations are dampened under straining, resulting in cleavage in the areas where stress-raisers are found (pores, capillaries, submicrocracks, etc.).