The 4th of April 2019, after the ducts manufacture, the refraction procedure is made. It has the aim of preventing the ducts from being harmed during the usual process by the abrasive substances contained inside said ducts. The concrete filling of the ducts is a complex task. First of all, a vertical structure assembly is required. Among the structure, each duct will be settled using a crane in order to keep them secured (this is called bracing). Once the ducts are settled, the concrete pouring inside them will take place. The concrete must be liquid enough to ensure the whole filling. Finally it will be left at ambient temperature for them to dry.