Bending without breaking: a Canadian invention helps with pavement slab durability

Concrete Producer, The, July, 2005 by Rick Yelton

In many portions of North America, builders and homeowners often avoid using precast slabs because they're concerned with ground heave caused by the freeze-thaw cycle. Now, with a recently patented design, producers can offer their installers a product that will allow them to build a patio that bends without deforming.

Engineers at Flexosol Inc., a small research and product development firm in Valcourt, Quebec, have created a new flexible precast concrete slab system. The new system solves the heave problem once and for all, says Gaetan Jalbert, the product's chief designer. His product, targeted for residential and commercial pavement applications, uses an innovative composite control joint. "It provides an aesthetic concrete precast slab which will flex with underground movements," says Jalbert.

The new control joint uses fiber-reinforced plastic rebar to provide an "axle with memory." It transfers the load stress coming from the top of the slab into the concrete mass. In summer, the flexible rebar permits the slab to flex under pressure coming from the bottom.

Product benefits

This control joint can be adapted to many designs and shapes. The first shape proposed, a 16-square-foot surface area slab, was submitted to a numerical modeling analysis (FEA) called MSC.MARC/MENTAT at the Sherbrooke University Civil Engineering Department in Quebec.

The new control joint offers producers, installers, and owners more benefits than traditional concrete slab designs, says Jalbert. First, it resists surface deformation from heave. The joint transforms individual slabs into a system, limiting the displacement of the edges and eliminating trip hazards.

For the owner, the new joint provides a product that's as durable as concrete itself. The joint will last the life of the pavement, since it doesn't contain materials that will corrode from salt. It also withstands additional loading forces from traffic. Since the rebar transfers load stresses throughout the entire surface, there's less chance of rutting caused by wear and tear.

For the installer, the larger coverage surface which will reduce manpower and time to install.

The control joint concept uses many composite rebars embedded into the green concrete in a specific position as a flexible axel to connect two or more concrete elements of any shape.

Each 625-pound slab is manipulated with a special grab anchor developed by Flexosol and is adaptable to most commonly used material haulers. The contractor lays the slabs on a smooth, well-compacted sub-grade. After placement, the contractor connects the panels with a composite flat bar that's 3/8 inches thick by 1 1/4 inches wide by 48 inches long.

The bars are inserted into a groove created at the precast operation on all sides of the slab. This rebar protects the slab's external joint from vertical movement and keeps the ground cover straight.

The joint system offers another advantage. After placement, a contractor can remove the precast slab for any sort of subsurface work or repair without excessive tear out or damage.

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To learn more, e-mail Gaetan Jalbert at jalbert@cooptel.qc.ca, telephone 450-532-2959, or visit www.flexosol.com, or circle 2 on the reader service card.