Description
MFB Bauunternehmen carries out building construction and foundation work and builds, among other things, the foundations for wind turbines from different manufacturers. A single foundation takes roughly 700 to 1,200 m³ of concrete, placed in one pour that lasts several hours. These are massive structural elements: the hydration of the cement releases a lot of heat, the core heats up strongly and the edge zones cool down faster.
Challenges
How warm a foundation gets, and how evenly it cools down, decides its quality. If the temperature difference between core and edge becomes too large, restraint stresses and cracks occur. A core temperature that is too high can damage the structure, for example through delayed ettringite formation. That is why standards and guidelines such as DIN EN 13670, the German cement industry guidance sheet B 11 (Zement-Merkblatt B 11) on massive concrete elements and the German Committee for Structural Concrete (DAfStb) guideline on massive concrete elements address hydration heat, and why, depending on the project, measuring and documenting the temperature development is required or recommended.
Weather adds to it: in frost or strong sun, the foundation has to be insulated or covered in time. Striking the formwork and removing the insulation should also be released on measured values rather than on experience. And in the end, the complete temperature curve should prove proper curing.
Solution and results
MFB monitors the foundations with ISC LINK from Vemaventuri. Before the pour, temperature sensors are fixed to the reinforcement of every foundation: in the core, at the edge, near the surface and at the underside. The ambient temperature is recorded as well. Data loggers send the readings by mobile network to an online platform, where the site management, the foreman and the office see them live on smartphone, tablet and computer. The system calculates the temperature difference between core and edge automatically. If a limit is exceeded, an alarm goes out and the team can react straight away, for example by insulating or covering. All data is stored, so every foundation gets a measurement report for the project documantation.
The result: complete temperature proof for all foundations, temperature differences within the specified limits and fewer inspection rounds, especially at night and on weekends. Follow-up work such as striking the formwork can be planned and released on secured measured values.
