Talleres Alquezar has been using two BHS Sonthofen mixers in a modular plant, to produce a total volume of 400 000 m3 of hydrodam concrete in Portugal, since 2017. The twin-shaft batch mixer has debunked an industry myth that the technology is unsuitable for these types of concrete mixes, and has shown that it is the technology of choice during this major project. The Spanish plant builder was able to surpass high concrete requirements with regard to the suitability of the mixer for the project.
Three hyrdodams are being built on the Tâmega River, which are expected to generate 1760 GWh annually for the Iberian market once they have been commissioned. This is part of the Spanish energy group Iberdrola’s large-scale hydroelectric project in Portugal. 242 000 m3 of concrete is needed in Daivões for the dam wall alone, which is planned to be 78 m high and 265 m long. Alquezar is the project partner for the hydrodam.
Once built, the construction in Daivões is expected to dam up to 56.2 hm3 of water. The standards for the quality of the concrete are correspondingly high. The composition and processing of the hydro dam concrete has to meet very specific criteria to prevent cracks forming later on. The lower water content of hydrodam concrete and the large aggregates of up to 150 mm pose especially large challenges for the mixer and drive system. This total volume of 400 000 m3 also requires large quantities of aggregates to be processed. This meant Alquezar Daivões faced special challenges in the designing and construction of the plant.
Debunking industry myths
If concrete mixes, such as those being used in Daivões, have a high degree of viscosity, then the drive technology and mixer need to be particularly powerful. For 30 years, it has been widely assumed that twin-shaft batch mixers are less suitable for producing hydro dam concrete than other mixers. The end client in this project also held this assumption and was not convinced about using a twin-shaft batch mixer. However, José Antonio Chaure was convinced that the twin-shaft batch mixer would produce the quality that was required.
As a result, two twin-shaft batch mixers of type DKX 4.5, each with a capacity of 4.5 m3, have been integrated into the modular plant since 2017. Chaure has stated that he is satisfied with the decision to use the twin-shaft batch mixer: “The machine achieves higher mixture homogeneity in comparison to other common mixers. There was also next to no waste in this major project. This allowed us to not only prove to the client that the twin-shaft batch mixer is reliable technology, but it can even surpass the high requirements for the concrete.”
Alquezar operates two production lines in parallel to ensure both a high production volume and the operational safety of the plant when it is at a capacity of 250 m3/hour. According to the company, the compact design and the efficiency of the mixer paid off in this setup because the twin-shaft batch mixer requires a smaller installation surface in comparison to pan and planetary mixers, yet it still generates the same production volume.
The long service life of the mixer is another benefit and has increased the economic efficiency of the project. The plant used in the project had been deployed in a previous one and only required minor adjustments at a minimal cost. The Foz Tua hydrodam, also in Portugal around 50 km away from the current project in Daivões, was construction with similar concrete requirements in 2010. “After a brief period of maintenance work, we were able to continue using the plant for the new project without issue,” said Chaure. “We did not have to replace any parts, not even the gearbox.”
Alquezar has a corporate history with BHS Sonthofen, having worked together for over 30 years. The company regularly uses BHS machines, especially for mixing tasks where a high quality of concrete is needed.
Read the article online at: https://www.worldcement.com/europe-cis/12062019/bhs-mixers-used-in-project-in-portugal/