Three seawalls - Artha (250 m), Sainte-Barbe (180 m) and Socoa (490 m) - protect the bay of Saint-Jean-de-Luz from the swell. Built under Napoleon III, they require regular maintenance. In 2016, three sets of "major repair" works were scheduled by the Pyrénées-Atlantiques office, following damage caused by recent storms.
A race against the tide
To repair the berm* on the Artha seawall, that lies in the middle of the bay, intricate works were carried out "against the clock", when wind, swell and rain allowed, using CXB Hyperfluide C35/45 XS3 Dmax 10 S4 "underwater" adapted concrete. The formwork and pouring were scheduled for a daily 4 to 5-hour window at mid-tide. The response team (a dozen masons and sailors from the Maritime and Fishing division) reached the site by boat, with materials dropped by helicopter from the Socoa Fort heliport. It was then a race against time to get the preparation work started... The concrete absolutely had to be poured 2 hours later to give it time to set ahead of the incoming tide. At this stage, the mixer trucks from the CEMEX production unit at Saint-Jean-de-Luz did not have a moment to lose: the helicopter was waiting for them. Twenty 2 to 3 minute rotations were anticipated. For this first portion of the works, CEMEX delivered 80 m3 of liquid concrete using 3 rotating raking wheels.
Water and salt resistant, and marine environment friendly concretes
To repair the seawalls at Sainte-Barbe and Socoa, CEMEX recommended innovative concretes, adapted to suit the new requirements of the Fisheries and Port division. The CXB Hydro solution was chosen for Sainte-Barbe. Non-leaching and seawater resistant, it has all the qualities necessary for undersea work. Being laitance-free (an accumulation of fine particles on the surface of fresh concrete due to an upward movement of water -as when excessive mixing water is used), it also handled the environmental challenges raised by the departmental waterways authorities: the risk of some concretes leaching into the seawater, particles harmful to the flora and fauna, pollution of beaches, etc.). On 19 and 20 September 2016, 12 m3 of this concrete were poured onto the seawall with excellent returns on plasticity and handling. The last portion of the work was started at the end of 2016. The Socoa seawall was strengthened using Promptis™, a new type of leach-resistant, ultra-quick-drying concrete. The race against time was won by partnering with the CEMEX Concretes Saint-Jean-de-Luz team. With these three sets of works, CEMEX affirmed its ability to offer targeted, innovative solutions, tailored to challenging environments. The swell-resistant nature of the three concretes will be carefully monitored over the coming months to optimise the strengthening of the seawalls.
* A narrow shelf, path, or ledge typically at the top or bottom of a slope; also : a mound or wall of earth or sand – Merriam-Webster Dictionary
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