Machine Design

Polyurethane protects dikes against nature's wrath

A specially designed polyurethane (PU) called Elastocoast now helps stabilize dikes that stretch nearly 500 miles (800 km) along Germany's northern coast.

The PU, from the Elastogran subsidiary of German-based BASF Corp., is reinforced with stone ballast revetments. The material serves as a first line of defense in the fight against the sea by absorbing the force of breaking waves and slowing the water's progression inland.

"Elastomer revetments rely on the permanent and elastic bonds of the PU to securely hold the reinforcing stones," explains Erik Pasche from the Institute of Hydraulic Engineering at Hamburg-Harburg University of Technology. The University partnered with Elastogran in developing Elastocoast. The PU and stone combination creates sturdy, porous revetments that stand up well to nature's wrath.

Elastocoast's inherent elastic and porous natures are key, says Pasche. The PU between the stones absorbs and dissipates the water's energy as it crashes down onto the dikes. In contrast, rigid and solid revetments made from conventional concrete and asphalt often develop tiny defects from pounding waves. These cracks eventually grow as the breakers gradually make deeper and deeper inroads into the revetment.

The two-component PU is mixed on site with the crushed stone. The mix has a working life of about 20 min and can be applied in covering layers about 15 to 30-cm (5.9 to 11.8-in.) thick. The mixture even hardens underwater.

Alternatively, the environmentally friendly Elastocoast can be sprayed on loose layers of stone ballast using a high-pressure technique. Elastocoast also provides benefits for nature. Flora and fauna can find new habitats in the porous structure of the cover layers.

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