Formation of construction joints in hydraulic structures

Project duration: 2009 - 2010

Hydraulic structures are often subject to massive impacts from the environment during their service life. These include, on the one hand, extremely high frost loads with high water saturation, but also mechanical effects such as ship impact and the like. In addition to the durability and, in particular, the water impermeability of the concrete itself, the proper execution of the potential weak point "joint" therefore plays a decisive role for long-term use. The latter aspect takes on increased importance in construction, since the various steps for the proper execution of joints are usually very time-consuming. In concrete and reinforced concrete construction, different types and arrangements of joints are provided, depending on the design and execution requirements. Essentially, a distinction is made between construction joints, movement joints and dummy joints. While construction joints are essential elements in the construction of hydraulic structures, movement and dummy joints are generally of secondary importance in this area of application. Construction joints occur when a concreting operation has to be interrupted for various reasons and the secondary concrete cannot be placed until the primary concrete has hardened. The connecting surface that results from the interruption of work is called a construction joint. Reasons for the arrangement of construction joints can be, on the one hand, scheduled interruptions caused by the work sequence, the performance of equipment and personnel, and the formwork technology used. Particularly in the case of massive structural elements, the division into concreting sections is also used as a design measure for limiting crack widths in order to reduce constraining and residual stresses due to internal and external constraints. On the other hand, construction joints can also be formed at short notice due to unforeseeable interruptions caused by unfavorable weather conditions, machine damage or delays in the delivery of construction materials. In general, the load-bearing capacity of a structural member is not reduced by the arrangement of construction joints, since the (connection) reinforcement passes from one member to the other and there is thus a monolithic connection between the two sections. Nevertheless, a construction joint represents a certain disturbance of the homogeneous structure.