Restoration of Madrid Viaduct in Redondela
Description of social and environmental performance.
The viaduct structure, which supports the Vigo-Ourense railway line, is made up of two types of materials: granite and steel masonry. The steel area has a more marked deterioration due to tensions between the layers of primer from constant maintenance and different types of products applied at each stage; also the constructive typology of the viaduct favours crevice corrosion and the accumulation of water in different areas. This has resulted in a loss of certain sections, and significant distortion, thereby necessitating the integral rehabilitation of the viaduct. In relation to the rehabilitation of the metal structure, the use of a new primer was discouraged, so that a general cleaning of the metallic elements was performed, loosening the existing cracked primers, through hydrojetting, consisting of projecting a jet of high pressure water. The environmental problem of this cleaning method was the large amount of water used, as it required an average flow of about 20l/min per nozzle.
Once the cleaning procedure was selected, a water collection and recirculation system was designed in order to reduce the excessive consumption of water resources. This system consisted of a collection area where the water was channelled into a deposit (catch chamber) where it was filtered through a sieve located in the discharge pipe. The water was pumped from the pit up to the top of the trolley from where the clean-up was performed to gain height and using gravity, it was taken to the closest bracket, where it was discharged into tanks. The rest of the water was channelled into the municipal sewage works.
This collection and recirculation system allowed for the recuperation of 30% of the total water consumption intended for this use. Water that couldn´t be reused for subsequent washing (due to suspended particles which obstructed the water jet nozzle) was used to water the work camp area which was also used for all the material to access the viaduct.