Axially loaded grouted connections in offshore conditions using ordinary portland cement

[EN] A grouted connection (GC) is a hybrid connection which joins two telescoped steel tubes by filling the annulus between the steel tubes with grout. GCs are frequently used to enable a force fitted connection between piles and substructure of offshore wind turbines. At latticed substructures this connection is located at mudline level in wet ambient conditions (AC). Nowadays special grout materials are used to achieve not only best mechanical properties but also a good performance during grouting in offshore conditions.To reduce production costs the use of ordinary portland cement (OPC) is investigated as an alternative filling material within this paper. OPC has a much lower tendency to segregate, as there are no aggregates added. This leads to more simplified, stable and cheaper production processes offshore. Further focus is put on the failure mode of OPC filled GCs in submerged condtions.For an appropriate use of OPC offshore a feasible mechanical performance needs to be ensured. Investigating this, small and large-scale laboratory tests were performed at Leibniz Universität Hannover. Using the experimental test setup of previous investigations for special high performance grouts (HPG) [1, 2], enables a direct comparison of HPG and OPC. Documenting liquid and solid OPC properties, like slump flow and compressive strength confirms a stable material quality. Small-scale ULS-tests showed significantly lower ULS-capacities and a more brittle failing process compared to HPG. Lagre-scale tests confirmed the observed failure mechanisms of Schaumann and Raba for OPC filled GCs in submerged conditions [3]. Carried out tests showed significant influence of grout material and confirmed influence of grout annulus size on fatigue capacity.
The presented results were achieved within the research project ‘GROWup - Grouted Joints for Offshore Wind Energy Converters under reversed axial loadings and upscaled thicknesses’ funded by the German Federal Ministry for Economic Affairs and Energy (BMWi, funding sign: 0325290). The research partners were Institute for Steel Construction and Institute of Buildung Material Science, both at Leibniz Universität Hannover, Germany. The authors thank the BMWi for funding and all accompanying industry project partners (DNV GL, Senvion SE, Siemens Wind Power, Wilke & Schiele Consulting GmbH) for their support. Additionally the authors thank the material manufacturers for their support. Concluding thanks goes to Prof. Lohaus and his team from the Institute of Building Material Science for an excellent project collaboration.