Spalling is the main problem concerning safety in concrete structures under rapid heating. Despite being studied for nearly a century, its prediction remains a challenge. In addition, the main recommendations for its prevention are merely the addition of a fixed amount of polypropylene fibres, without accounting for mix design. This paper presents an experimental study focusing on the thermo-hygral mechanism contribution to spalling. The use of mercury intrusion porosimetry and X-ray microtomography for the determination of pore connectivity is considered a key parameter. The results of the experiment are used for the development and calibration of an analytical equation capable of predicting spalling in concrete samples. The equation is then validated using over 100 examples extracted from literature, achieving an accuracy of 91.2%. Based on the validation, the proposed equation is a step forward in the prediction of concrete spalling based on the mix design parameters.

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To combat global warming a transition towards renewable energy sources (RES) is essential. Although RES have much lower life-cycle emissions, they do not offer a continuous and fully predictable output like their fossil-fuelled counterparts. Energy storage is paramount in order to include the growing share of these intermittent sources into the grid and provide a reliable supply of energy. In 2016 a long term vision which involves the creation of an artificial island on the Dogger Bank in the North Sea was presented. The island would act as the central spill in an interconnected future economy fuelled by RES. Currently there are no competitive energy storage technologies under consideration that could contribute to this ‘energy hub’. In Europe pumped hydropower storage (PHS) represents over 90% of the grid-connected storage capacity and continues to be identified as the most cost-efficient energy storage technology available today and in the future. Unfortunately, conventional PHS is restricted to mountainous areas and the remaining potential (2291GWh) does not suffice to future demand (estimated at 3596GWh). The plans of developing a large wind farm via the construction of an island made it an attractive base to test the contribution and feasibility of a substitute to conventional PHS: inverse offshore pumped hydropower storage (IOPHS). It relies on the same principles as conventional PHS, only the process is inverted. When the wind farm generates a surplus of energy, the excess power is used to drive hydraulic turbines which pump the water out of the artificially created lake into the surrounding sea. Then when there is a higher demand for energy than the wind farm generates at that time, the sea water is allowed to flow back into the interior lake driving the same turbines. Although the idea of inverse offshore pumped hydropower storage has been around for years, it has never been constructed. The objective of this research is to identify the possible design alternatives and determine how the costs of an offshore pumped hydropower storage facility scale with the power and storage capacity, using existing construction technologies. The construction of the storage plant consists of four main elements: the dam, dredging works, turbines and the turbine housing...