HYDROCAST® (HC) Formworks

Synthetex specializes in manufacturing engineered, project-specific fabric formworks for the casting-in-place of concrete armor units and structures for a spectrum of underwater applications.  For more than 25 years, engineering, contractor and government clients around the world have relied on HYDROCAST to design and fabricate the special concrete formworks they need for their projects.  They know Synthetex will deliver only the highest quality products, materials and workmanship—guaranteed.

Custom Solutions, Our Specialty

As leading specialists in the fabrication of fabric formworks for underwater casting of concrete structures, Synthetex offers engineered solutions such as custom armor units for spillway aprons, bulkheads, tunnel and pipe plugs, and more.  Our expertise includes working with nearly every component and material used in concrete formworks today, including high-strength polyester and Kevlar® fabrics and sewing threads, and steel and high tenacity polyester reinforcement cables.  With newly expanded manufacturing capabilities, we’re able to offer end-to-end solutions in-house, delivering finished products that are designed and built to perform.

HYDROCAST fabric formworks provide a low cost in situ concrete alternative to natural rock and precast concrete where they are not possible or practical.  Cast-in-place, concrete armor units and structures eliminate the requirement for heavy lift cranes for placement, where rock riprap and precast concrete blocks may require lifts of tens of thousands of pounds.  As with our concrete grout bags, HYDROCAST can be positioned and filled with concrete from the surface in shallow water or by divers in deeper water.  Since the flexible fabric forms are cast-in-place, they intimately adapt to variations in the subgrade or bottom contours.  Installations do not require dewatering, a crucial advantage in emergency repair of scour aprons.

Synthetex worked closely with the U.S. Army Corps of Engineers and Bergmann Associates for the design of fabric forms for the underwater casting of armor units for the scour aprons of two Ohio River locks and dams.  The concrete armor units ranged in sizes, up to 36 ft long x 18 ft wide x 6 ft high, and weights in excess of 10 tons each.  The specification of a fabric formwork that can be deployed underwater and then pumped full with concrete avoided the lifting of the massive armor units.

Heavy-duty, puncture-resistant formworks designed to meet pumped concrete pressures were placed into reusable steel frames and lowered into place in rows and columns.  As the frameworks were lowered they were filled with water to offset buoyancy and to inflate the formwork to its rectangular dimensions.  As concrete was pumped into the formwork an equal volume of water was displaced. The flexible bottom allowed intimate contact with the uneven subgrade. And, all of this is performed entirely under water and constructed on a slope.

Alternative to Traditional Rock and Precast Concrete

HYDROCAST concrete grout bags meet the requirements for a reliable and economical cast-in-place alternative to traditional rock (riprap) and precast concrete for the armoring of sand-filled geocontainers.

Ronald Stive, director of projects, maritime and waterways at Royall Haskoning DHV, has reported a trend toward using sand packed into geocontainers at the core of a breakwater, a solution that could be ten times cheaper than traditional rock. “What we have noticed in the past ten years in our port and breakwater projects is that all around the world, people are in a hurry,” he noted. “They don’t accept that these types of structures will take years to design and to construct, so they are always looking for alternative ways to do it faster.

“Secondly, there is a trend to go into deeper water, and into areas where you don’t have quarries nearby and you may have problems where the seabed isn’t stable enough or there’s seismic activity. In these remote areas, you have to look for alternative designs to the traditional rubble mound type of breakwater, because of the fact that the materials are too far away or too costly to bring in.”

Applications for HYDROCAST custom fabric formed concrete units:

  • Concrete armor units for dam scour aprons
  • Concrete armor units for the main primary protection of breakwaters, levees and dikes
  • Artificial concrete reefs
  • Concrete armor units as the protection of sand-filled geocontainers
  • Pipeline and tunnel closures
  • Concrete quay walls and seawalls
  • Concrete sealing of large mineshafts and tubes
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