Report by Liz white, editor
Repairing and resurfacing a massive dam wall is a daunting task at the best of times. When the dam wall in question is 48 m high, in a mountainous region, and shows cracks and escapes at some membranes – together with the fact that it was built in 1942 to 1949 with no steel reinforcement as a result of shortages in the Second World War – the challenges loom larger.
German equipment and technical support company WIWA (Wilhelm Wagner GmbH and co.KG) worked on repairing and coating the surface of the Griotte dam in the Rhone Alps, near Heuteluce, France, said WIWA’s international sales director, Murph Mahaffey.
The cracks and escaped notice during a 2006 inspection are, “a nice way of saying it’s leaking,” commented Mahaffey, noting that good co-operation between all participants was a crucial aspect to the project.
“All of us in this room, equipment and materials suppliers, contractors, architects, and specifiers – create the success of such projects,” said Mahaffey.
Project size and challenges
Dam 48 m x 510 m span (148 feet x 16 75 feet);
Between two mountain ranges, 5732 feet elevation;
Reservoir surface area 75 ha (8.7m ft.²);
Difficult weather conditions;
Cycling temperatures/elevation were demanding on a concrete structure. Water for the Tre-la-Tete glacier is corrosive, and the wind erosion is also an issue. Also, the dam has been painted/coated many times;
1200 kg polyurea sprayed at hundred at 10 bar, 70°C, and;
Applied over five days of changing weather.
Built in 1942 to 1949, the Girotte dam was the first such as sub-glacial inlet structure in the world, providing power for the environmentally sensitive region. The dam, with multiple buttresses and 18 arches, captures glacier run-off in spring, in a three sided natural basin the dam forming the fourth side.
Polyurea was used for the project due to its fast-setting and spray ability, offering high build, easy application and “the exceptional life we expect of polyurea,” the WIWA executive said, in a presentation at the PDA-Europe meeting held 15th to 18 November in Stiges, Spain.
The dam surfacing was carried out in mid-2010, when the water level was low enough to evaluate, mark and repair the wall.
Safety was important: the team needed to work in harnesses, and communicating with sprayers was difficult.
First the team expected all 18 arches from the top to base to identify and Mark cracks and then ground and covered the cracks, before applying a 2K epoxy primer, Mahaffey said. This was a relatively low-pressure application, with the material at 70°C, using heated hose, high delta heaters, and impingement mixing spray guns.
The team needed full access from the top to base – 48 m – with a hose only 45 m long.
As to the finished surface on the Girotte dam, “I would call it a success,” Mahaffey said. Adding that a decent performance to date is good and within specification.
Polyurea in a cold climate
After the heights of France, came the cold depths of Siberia. St Petersburg-based formulator Chimex has expertise in coatings resistant to extremes of cold as a result of its Russian location.
Alexey Ivanov, deputy technical director, noted that the glass transition temperature, Tg, of polyurea is vital. “Ours has a Tg of -40 C, which is good enough for many uses,” he said adding: “Russia is very cold and we need new systems with better Tg. Our vision is of a polyurea system with a Tg of -100°C.”
Chimex has already developed a polyurea with a Tg of -55° C for roofing uses in Russia’s coldest northernmost parts. Here the group used a 1.2 to 1.5 mm of special polyurea with a polyurethane primer (epoxy would be too brittle at the temperatures encountered). It also developed a special XT – 2002 grade of polyurea 1.2 to 1.5 mm thick for the roof of a natural gas plant in Urgenoy, in Siberia, near the Arctic Circle – home to Russia’s gas giant Gazprom. Here the temperature was -20°C, said Ivanov.
Chimex has coated 7000 m² of roof on its plant, with a further 1000 m² in 2011.
Ivanov also told the PDA-Europe meeting that Chimex has developed a special XT-2003 grade to protect metal/concrete surfaces from aggressive media, which has been used for a water plant in Vladivostok. Chimex has completed the first stage of the project with positive results, which “will allow us to extend the project all over Russia,” Ivanov said.
The hydrolysis-resistant material is now being tested in Moscow sewers and imploring for a copper industrial complex in Novogrod.
Water tanks need coatings
Using polyurea to coat and refurbish water tanks and reservoirs is a current “hot topic” in Spain, according to Hugo Heralt of Krypton Chemical.
In Europe, there is a high demand for repair of tanks built in the 1970s, Heralt said. Water is lost because of cracks and leaks. Chlorine in the water content may damage any steel reinforcements, leading to structural failure of the tank, he said.
Founded in Spain in 1999, Krypton develops technologies based on polyurea, PU and polyaspartics for construction, civil engineering and maintenance and has factories in Spain, and units in the UK, France and Chile.
Krypton uses polyurea for roof and floor coatings, and also tank repair, where Heralt stressed the advantages of using polyurea. It kills rapidly under most conditions and temperatures. It has a low cross link-density and flexible backbone structure, which leads to high elongation in the final product, and high hydrogen-bond content gives good solvent resistance. Heralt added that it is not as sensitive to humidity/moisture as hybrids or PUs.
In Spain, competing materials for tank repair can be costly, for example liquid applied membranes, or labour intensive, as with cements.
Any system must also be approved to EU and local potable water regulations, Heralt stressed.
Heralt noted the projects can need more than one polyurea layer for good results.
He has seen “a lot of failures than just spraying above. You need to protect from below also.”
Wood copes without primer
Amongst the novel uses of polyurea formulator Imexfa has developed our IMEX PW for portable water uses, with French sanitary approval and IMEX 54 – 800 for waterproofing nuclear reactors.
At the Stiges PDA-Europe meeting, Alain Descampes, proprietor of the Brussels-based company, described – a modified polyurea for wood protection with no primer.
Polyurea has various advantages for coatings: it “transforms the wood into a longer life waterproof media,” Descampes said. Polyurea allows the use of cheaper wood, and keeps wood’s benefits while “erasing its inconveniences.” Uses for coated wood are: in automotive parts; for horseboxes; for quieter trucks for night delivery-“a big potential for polyurea,” said Descampes. Polyurea can protect speakers at rock concerts, and turn containers into habitable spaces – in one case a prison!
While the fast setting of polyurea is good, the exotherm allows pinholes to develop in coatings on wood. A primer can eliminate this, but adds to the cost, time and the space needed. Descampes said that Imfexa’s modified polyurea as a same characteristics as a standard grade: gel time 10 seconds; tack-free 30 seconds; elongation above 300%; and tensile strength above 18 MPa. And it gives no pinholes while being easy to spray. So users can just “spray and store,” Descampes said.
Ex-head compost treatment plants ex-head
Concrete in treatment plants for biological waste (compost) need protection, according to Ylva Edwards of the Swedish cement and concrete research Institute (SCCRI). But while the environment in these facilities is aggressive, she said there is little information on how to compare protective products and test them.
These plans are a growing sector: Sweden now has 20 biogas plants, as well as 25 major and 80 smaller composting plants. The country is at the forefront here, as is Spain: both collect and treat household organic waste separately from other waste streams, Edwards said.
Edwards has surveyed some of the damage occurring in the reception tanks. Chemical analysis of the leachate showed it to be pH 4, with its strong acidity from acetic acid produced by the breakdown of food waste.
Analysis of the concrete and reinforcement at various sites showed some areas with leached cement paste, and exposed ballast and air voids.
Edwards concluded that treatment is needed and the SCCRI has set up a project to look at functional requirements for surface coatings, including polyurea. “We found it very difficult to test different products for chemical resistance,” she said, and the team has proposed a functional testing programme for membranes and systems, based on standardised tests.
The SCCRI has developed a special testing liquid for chemical resistance tests, and will test material properties at emotion in this liquid for various times at different temperatures.
Another proposal is for an abrasion test, similar to the Taber or flooring test. Next year Edwards said, she will start to test protective materials and then do some field testing.