Caderousse Dam

Formed of eight openings 22 metres wide (176 metres total length), the dam spillway draws off up to 12,500 cubic meters of water per second. Although the apron was repaired in 1997, erosion in the sacrificial wear layer of 2 to 30 cm has been observed, and the reinforcing steel was visible. The secondary concrete and part of the stone concrete were eroded, allowing uplifted water to leak. During an inspection in 2009, specifications were defined to repair part n°4 of the eroded apron with Ductal® with metallic fibres. The first reinforcement being a success, the Rhône National Company completed the repair of part n°3 using the same solution.

The mixing of ready-mix concrete, transport by truck and the pumping of Ductal® were keys for success on the worksite. With impact and abrasion resistance comparable to granite, (reference rock), Ductal® is the ideal concrete for renovating structures subjected to high impact and abrasion.

According to the CNR, the erosion was due in part to abrasion by sand but especially to the repeated impact of large granular material against the apron. Therefore, the implementation of concrete particularly resistant to the impact was required. The impact resistance of Ductal® with metallic fibres is close to that of granite. The CNR’s impact testing demonstrated that the wear volume of Ductal® with metallic fibres was less than 30 cm3. That volume is between 250 and 400 cm3 for ordinary concrete (type B25). The CNR tested abrasion resistance relative to glass. The abrasion index of Ductal® with metallic fibres at the bottom of the opening was less than 1, while traditional concrete is more than 2 relative to glass.

The company was hired for the work based on three key points for the pour:

• The requisition of a LafargeHolcim ready-mix plant to mix the Ductal® guaranteed homogeneous production and large volume (11 m3 in four hours).
• Transporting Ductal® by ready-mix truck facilitated a quick pour.
• Pumping the Ductal® allowed traffic to keep moving on the bridge and prevented a costly placement from the river.

The openings were dried and cleaned to proceed with the repair of the apron in the eroded areas. The low accessibility to the openings n°3 and 4 required the Ductal® to be pumped on more than 130m. Because Ductal® is a self-compacting concrete, it can be poured directly from the pump. A thin layer of curing compound was then applied to limit surface dehydration. The spillway was put back into service in 20 days.