Transformation of Singular Joint Deformations in Concrete Elements into Plural Cracks

接缝是板状混凝土组件的组成部分，例如工业区、停车场和交通区域、挡土墙等，以避免出现不必要的裂缝。混凝土构件中的热或湿引起的变形集中在这些节点。同时，关节必须紧固。传统接缝密封胶的耐久性仅限于几年，导致维护成本较高。因此，节点是该系统固有的薄弱环节。在所应用的研究项目中，应研究另一种概念，即在未加固/仅弱加固的混凝土构件的节点上覆盖薄薄的碳素加固混凝土层(CRC)。其基本思想是将基础构件中相对较大的单一关节运动转化为覆盖层中的多个、相当小的裂缝。在本应用中，由于接缝移动和垂直于接缝方向，例如由于土压力或交通荷载，这种薄CRC层在轴向上受到特殊应力。为此，必须在接头的两侧中断粘结一段规定的距离，以便产生相应的扩展范围，在该范围内可以发展出细小的裂纹。为了评估这种CRC层在桥梁连接中的适用性，一方面要研究相应高应变下CRC层中的裂缝发展情况，另一方面要研究在相关暴露条件下该层与基层构件的粘结性能。应考虑到，这种板/层中的应力是双轴性质的，由于接缝的移动，CRC层中可能会出现拉应力和压应力。具体而言，拟进行以下研究：·在CRC层：-CRC层在双向拉应力和压应力下的承载和变形行为--碳素钢筋与混凝土之间的双向粘结的模拟·在接合区的复合材料系统：-在拉应力(开口接缝)下复合材料实体中CRC-层中形成微裂缝，随着粘结制动的变化--CRC-层在压应力(闭合接缝)下的稳定性--在这一地区发生循环应力的情况下逐步分层的风险。

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.