Test method for the suitability of plywood-based concrete formwork panels for exposed concrete surfaces
10. October 2023
Exposed concrete is the term used to describe concrete surfaces that remain visible after the concreting process and for which increased demands are placed on their appearance.
The exposed concrete surface is thus part of the architectural concept of a building and does not only fulfil purely constructive tasks. As is the case with ordinary concrete surfaces, shaping is carried out by the formwork, which serves as a mold for the fresh concrete and is removed after it has cured.
In the case of plywood-based formwork, the material can swell when moisture enters. This results in the formation of wave-like patterns on the formwork panel surface, the so-called rippling effect. These ripples also form on the concrete surface and are generally undesirable in exposed concrete. To date, there is no standardized method for characterizing wood-based formwork panels with regard to their tendency to form ripples. Furthermore, for fair-faced concrete formwork, the occurrence of rippling is only categorized as "permissible" or "not permissible". In the absence of a differentiated classification basis for ripples, an expert evaluation becomes necessary in the event of a dispute. Among other things, these circumstances represent an obstacle to the use of wood-based formwork panels for fair-faced concrete, which is why plastic formwork panels are preferred in this area.
The aim of a research project at the IHD is to develop a test method for evaluating wood-based formwork panels with regard to their tendency to form ripples and the degree to which they do so. In addition to the development of the method, the functional model of a test rig is to be designed and constructed in which formwork panels can be subjected to practical loads. For the evaluation of the rippling’s on the form lining as well as on the concrete surface, these are to be digitized by means of 3D scanners. The data obtained will then be used to determine geometric parameters and perceptibility limits that enable the ripples to be classified. The method should also be suitable for recording and evaluating ripples on concrete surfaces of structures.
The project with the grant number 49MF220245 is funded by the German Federal Ministry of Economics and Climate Protection within the framework of
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Photo: Swelling of the outer veneer of a phenol-coated plywood formwork panel (rippling effect) in the area of introduced damage in a laboratory test rig.