Transformation of Singular Joint Deformations in Concrete Elements into Plural Cracks

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Joints are integral part of slab-shaped concrete components, e.g. industrial areas, parking and traffic areas, retaining walls, etc., in order to avoid undesired cracking. Thermally or hygrically induced deformations in the concrete component are concentrated in these joints. Simultaneously, joints must be tight. The durability of conventional joint sealants is limited to only a few years, resulting in high maintenance costs. Therefore joints are inherent weak points in this system. In the research project applied, an alternative concept shall be investigated in which the joints in unreinforced / only weakly reinforced concrete components are covered with thin, carbonreinforced concrete layers (CRC). The basic idea is that the relatively large singular joint movements in the base component are converted into plural, considerably smaller cracks in the covering layer. Such thin CRC-layers are subjected to special stresses in this application, both in the axial direction due to the joint movement and perpendicular to it, e.g. due to earth pressure or traffic loads. For this purpose, the bond must be interrupted at both sides of the joint for a defined distance in order to create corresponding expansion ranges in which the fine cracks can develop. In order to evaluate the suitability of such CRC-layers for bridging joints, on the one hand the crack development in CRC-layers at correspondingly high straining, and on the other hand the bond behaviour of this layer on the base component under the relevant exposures shall be investigated. It should be taken into account that the stresses in such slabs / layers are of two-axial nature and that tensile as well as compressive stresses can occur in the CRC-layer as a result of the joint movements. In concrete terms, following studies are intended: • At the CRC layers: – Load-bearing and deformation behaviour of CRC-layers under biaxial tensile and compressive stresses – Modelling of the biaxial bond between carbon reinforcement and concrete • At the composite system in the joint area: – Formation of micro-cracks in the CRC-layer in composite bodies under tensile stress (opening joint) with variations in bond braking – Stability of the CRC-layer under compressive stress (closing joint) with variations in bond braking – Risk of progressive delamination in case of cyclic stresses in this area.