During the construction of a monolithic structure it is advised for the work to be carried out continuously. However, this is often not possible. In such a case one is forced to use construction joints (or day joints). Construction joints in monolithic structures are areas of contact between hardened concrete and freshly poured concrete. Despite the fact that construction joints are invisible in the structure, they are usually weak points. Hence, they should be located at spots where any joint between hardened and freshly poured concrete has no material influence on the structure's safety. Such spots may not be found where the strongest bending moments are, and they may not be in hard-to-reach areas. Within ceiling slabs, as well as in concrete beams, a construction joint is recommended at a distance of about 1,5- or 1,4-fold of the span of the slab as measured from its support. In components, where large compression forces will emerge, the construction joints should be executed as perpendicular to the direction of these forces.
A construction joint may be made using stay-in-place formwork like Streckmax. The stay-in-place formwork is a profiled mesh, the task of which is to create as large a contact surface as possible between the hardened and freshly poured concrete.
The calculation of the joint's load bearing capacity using
the STC mesh must be conducted based on Eurocode 2.
Sometimes, there arises the necessity of creating a construction joint which, during use, shall be exposed to water pressure. Among such spots are included joints between a container's bottom slab and its walls. In order to seal and insulate such spots, special tapes are used, to be selected depending on the pressure, temperature as well as aggression of the liquids stored in the container. The tapes are placed vertically between the vertical bars of the support beam bearing the name Bestal. Bestal mounting beams are made of a STC type mesh and of reinforcement bars. The beam is supported by the top reinforcement layer of the concrete slab, and subsequently during its concreting, it is filled halfway, meaning, to the top edge of the mesh. This concrete creates a form of rib, ensuring stability for the sealing tape during concreting of the wall at a later stage.
Mode of installation
The Bestal beam is available in two variants, as a one-piece component and as a two-piece component. The first of these may be used at an arch or curve, because its main bars are trimmed, with the second one used for straight sections. The one-piece Bestal unit has vertical bars shifted with respect to each other, and such a system gives the option of placing, in the created space, of sealing tape. The batten is located on the slab's top reinforcement layer, and stabilised using tie wire. The situation is similar when using the two-piece Bestal batten, with the difference that the space for insertion of the sealing tape is obtained through moving two profiles so the batten's vertical bars pass each other by approximately 11 mm. After insertion of the sealing tape between the Bestal batten vertical bars, one can commence concreting of the slab, at the same time filling the Bestal batten with concrete all the way to the top edge of the mesh. Such insulation of a day joint will ensure complete protection against intrusions of pressurised water.