Qualification of the endurance strength enhancement of silane coated concrete parts

Abstract

High precision concrete can be used for precision machine parts as a replacement for natural stone to save costs and reduce the lead time (Hahm and Theska 2017 2nd Gas Bearing Workshop (Düsseldorf); Hahm et al 58th Ilmenau Scientific Coll. (Ilmenau); Hahm et al 13th Int. Conf. & Exhibition (Berlin); Berg et al 10th Int. Conf. & Exhibition (Delft)). In contrast to the base frames, moving parts need to have a high specific stiffness thus requiring a lightweight design. To guarantee reliability comparable to steel or aluminum parts, the endurance strength of the concrete parts has to be improved significantly. Reinforcement by implementation of steel or carbon fibers is not applicable since it results in thermal inhomogeneity. As an alternative, reinforcement can be provided by functional coatings. The application of a tailor made sol–gel coating and their effect on the mechanical properties of concrete parts represents the focus of this contribution. Coatings reduce the probability of fundamental damage effect mechanisms by closing superficial pores and cracks and by introducing internal compressive preloads. Additionally, the stiffness improvement due to the coating enhances the parts endurance strength by lowering the effective stress. The experimental results with a primitive specimen geometry and a combination of tensile and flexural tests proves the tendencies for strength enhancement in general different sol–gel compositions were investigated. The mathematical description has been evaluated based on these measurements to validate the influence on the endurance strength. To reduce the uncertainties of the measurements the specimen quality and test machine reproducibility needs a further improvement. A direct deformation measurement of the specimen during the tensile test is required to allow an entire evaluation of the presented model under consideration of skin effects. This way, the developed simulation method for coated machine parts with complex geometry can be fully applied.