SEA walls designed to protect vulnerable coastlines from erosion by the sea are themselves at risk from the pounding of the waves. It鈥檚 a problem likely to get worse if sea level rises or storms become more frequent because of global warming.
To protect these sea defences, the German chemical firm BASF has developed a spray-on polyurethane coating that is now being tested on the shores of the North Sea. Made by mixing two chemicals 鈥� a polyol and isocyanate 鈥� the coating can be applied directly to a loose layer of stone using a high-pressure spray, or mixed with crushed stone and sprayed in layers up to 30 centimetres thick. It cures in about 20 minutes, creating an elastic surface peppered with pores a few centimetres in size.
鈥淚n a conventional boulder and concrete reinforcement, the surface gets the full impact of the wave and starts to break away,鈥� says project leader Marcus Leberfinger. When the coating is applied, however, the elasticity of the material helps to absorb the energy of the waves. More energy is dissipated as heat as water forces its way through the pores.
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鈥淭he elasticity of the material helps to absorb the energy of the waves鈥�
The coating is being put to the test on the German island of Sylt. Once part of the German mainland, the island is shrinking under the constant battering of the North Sea, and is in danger of disappearing.
鈥淭he reinforced wall reliably withstood the huge impact of the waves during this past storm season,鈥� Leberfinger says. 鈥淧ast experience suggests that conventional concrete revetments would have failed.鈥� The spray could also be used to protect natural coastlines or stone structures from the elements, he says. The coating is expected to last about 20 years.
The porous nature of the plastic may also have benefits for marine wildlife, as the cavities make ideal habitats for crabs, limpets and marram grass. Environmental engineers at the Technical University of Hamburg-Harburg are monitoring the colonisation of the coating by sea creatures, and the impact of this on the coating鈥檚 effectiveness.
