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Hydrodemolition used to repair Italian viaduct

High-pressure water jets have played a vital part in the removal of damaged concrete on the multi-span Rio Verde viaduct in Italy.

The viaduct is one of the highest in Europe and carries the busy dual two lane A15/E33 Autostrada della Cisa over a steep sided valley in the municipality of Pontremoli.

Conjet hydrodemolition equipment was used to remove damaged concrete from the faces of the viaduct’s rectangular cross section concrete piers, which rise up to 136m from the valley floor to the steel deck. Damaged concrete is being replaced with a new and thicker concrete skin.

The 960m long twin steel deck viaduct, is supported on eight hollow reinforced concrete piers. It is a major structure on the route between Parma and La Spezia 100km south of Genova on Italy’s Mediterranean coast.

The spectacular viaduct was opened in 1975, but inspection by maintenance engineers showed the bridge piers were suffering from extensive calcium chloride damage, forcing the Italian Highways Authority and the Highway Engineering Department of Cisa Ltd to carry out extensive repairs and strengthening.

Specialist hydrodemolition contractor ABC Construczioni, working for the main viaduct repair contractor SEI-Idrojet, carried out the concrete removal on one pier at a time. The repairs were performed from a special, purpose built cradle and working platform that wrapped round the piers. The piers are 21m long and 8.5m wide at the base and tapering to 2.5 wide at the apex.

The ends of the platform were adjustable to compensate for the changing pier dimensions. The whole platform was supported, raised and lowered on wire ropes, which went up to pulleys on a steel support cradle at the top of the pier and back down to four synchronised winches anchored at ground level.

Conjet modified a standard robot feedbeam to fit onto and run along a rack on the inner sides of the platform in the fixed space between the pier and the platform. A Conjet Computer Control Unit, also mounted on the platform, was used to control the feedbeam and integral jetting nozzle. A Conjet 345-400kW Powerpack at ground level provided the high-pressure water at 1000bar and flow of 200l/min to the feedbeam’s nozzle. The feedbeam and nozzle, travelling back and forth along the platform’s rack, selectively removed damaged concrete to a depth of 70mm and below any exposed reinforcing. The process continued on one face of a pier as the platform was slowly raised to the top. On completion of removal of the concrete from one face, the platform was lowered and the Conjet feedbeam moved to another side of the platform for the process to be repeated on all four faces.

On completion of concrete removal another team followed on fixing additional reinforcement in stages to all sides of the tapering pier.  Shuttering panels 1.8m high were then fixed round all faces to support a new 220mm thick skin of self compacting concrete pumped into the formwork from ground level. After the concrete had set the formwork was removed and repositioned for the next 1.8m lift for the process to be repeated to the top of the pier.

On completion of repairing and strengthening a pier with an additional layer of concrete, the working platform was dismantled and re-erected on the next and then subsequent piers for the hydrodemolition and concrete repair process to be repeated.

Readers' comments (6)

  • Interesting piece. Not sure if/how the water/removed concrete is being collected and dealt with in an environmentally acceptable manner as would be required in the the UK. I guess the Italians are less stringent on such things?

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  • If water is used to remove the existing concrete, won't the water will intiate or increase the probabilty of corrosion with sufficient moisture and oxygen in the steel?

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  • If the water is used to remove the existing concrete, wouldn't the water will initiate or increase the probability of corrosion with sufficient moisture and oxygen?

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  • Interesting that this technique is used, they might want to think of liquids that can be used to replace water and reduce the effect of corrosion on the rebar. Something worth to explore.

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  • It would be interesting to know how the salt that caused the corrosion got into the piers and how they plan to prevent it being contaminated again.

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  • I wonder if any assessment of the reinforcement condition was carried out and mitigated for defects, and if the new concrete used has enough resistance against the future chloride attack. Also not sure of full height and all piers were infected?

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