The Paillon river passes through Nice’s urban area under a concrete covering built between 1860 and 1972. The top surface of the covering has undergone a renewal project, creating a big linear urban park “coulée verte” and a giant water mirror (3.000 m2), close to the Massena Square. The bearing capacity of the Paillon concrete covering did not allow the use of heavy fills and supporting layers and therefore an 80-cm thick lightweight expanded clay base layer was chosen as a support for the water mirror. The expanded clay layer also insulated and protected the many water and compressed air piping and wiring needed for the fountain’s water games (128 water jets).
Why Expanded Clay:
Adaptability to irregular shapes and easy filling of the spaces between the pipes, stiffness and lack of settlements over time, compressive strength, lightness, total incombustibility, fast installation were the key variables sought by designers that led to the choice of the expanded clay solution. The lightweight layer was made of expanded clay 3-8 (permeable lightweight concrete) bound with cement. Other lightweight solutions were considered but discarded due to material combustibility, slow and complicated installation, risk of settlement over time.
The special and continuous on-site production technique used to bond the expanded clay with the cement had very good feedback, thanks to the great productivity the job was accomplished within the jobsite’s tight planning schedule. Expanded clay was delivered to the site in tanker trucks equipped with suitable pumping gear. At the same time a cement slurry was produced on site using a suitable truck and continuously injected into the pump hose as the expanded clay was delivered. The mixing took place at that stage and permeable concrete was cast continuously. Casting took place in two phases. During the first phase the water runaway system was placed, then a first 40 cm of cemented expanded clay was cast. During the second part, the water and compressed air supply system together with the electrical wiring were installed on top of the first lightweight layer and then the final 40 cm thick layer of cemented expanded clay was cast.