In the second step, the fiberglass building blocks were placed within a predefined space in the company’s single flexible mold. Using a vacuum-assisted infusion process and an internally developed injection system, each lock gate was vacuum infused with Aliancys’ Synolite™ polyester resin from various positions within the mold.
The design was reviewed by the Netherlands’ Directorate-General for Public Works and Water Management (Rijkswaterstaat) and Royal HaskoningDHV. It took nine months and led to the development of regulations for the application of FRP for civil engineering structures in the Netherlands.
It took FiberCore Europe just one month to design the project, one week to build each of the eight lock doors and two weeks to equip them with a few steel parts, such as hinges. The four large gates were installed in early January 2016. “Because the prefabricated gates weigh no more than 24 metric tons (53,000 pounds) – a 50 percent reduction in weight from a comparable steel lock gate – they were easily transportable to the site. We were able to install one door in 15 minutes,” says Grefhorst. The light weight also means that the lock gates are very fast to open and close. Maintenance requirements are further reduced as the lighter weight minimizes wear on the lock gates’ hinges.
“The client had to plan the project with a new mindset,” notes de Jong. “There was money to recover as the FRP lock gates were ten times stronger than steel gates but comparable in price. The fast installation meant inconvenience was limited and downtime to shipping traffic was eliminated. Disruption was minimized for neighborhood residents and businesses.” In addition, long-term maintenance is also reduced since GFRP gates don’t require repainting or treatment as would be required by steel gates.
Test results indicate that the Wilhelmina gates will have a lifespan of at least 100 years. “Ships can hit the doors, and the gates will withstand the impact and still keep about eight meters of water from flooding our beloved country,” adds de Jong. “Our Ministry’s choice of FRP lock gates, as well as many bridges, means they have confidence in the technology.”
Rijkswaterstaat presented the Wilhelmina Canal lock gates project at a Smart Rivers conference of water authorities in Buenos Aires in 2016, generating international interest and the formation of an international working group to further the use of composites for hydraulic structures. “The range for applications goes beyond lock gates and bridges,” de Jong says. “We are looking at offshore structures, ship building, LNG storage and military applications in the future.”