Can you envision a world where masonry buildings absorb the shock of bomb blasts without toppling? Where unreinforced masonry buildings maintain their structural integrity through hurricane-force winds and raging waters? Where, in less than a month, a 100-year-old brick building can be made new again—only stronger?
One scientist at the University of Arizona imagined just such a world. More impressively, the company he co-founded, HJ3 Composite Technologies, Tucson, Ariz., transformed his research from a possibility to a reality.
Dr. Hamid Saadatmanesh is a leading researcher in the field of high-strength composite systems designed to strengthen infrastructure. In 1994, he began developing carbon and glass composites that allowed masonry walls to survive earthquakes. Through a three-year research effort, Dr. Saadatmanesh proved that composite straps of carbon and glass fabrics could turn a weak and brittle masonry structure into a strong and ductile building. “The walls could cycle back and forth continuously under simulated seismic forces without any signs of structural failure,” says Saadatmanesh. In 1997, he was issued a patent for his method of strengthening concrete and masonry walls.
What are high-strength composites?
This technology combines the strength of materials such as carbon or fiberglass with the durability of high-grade plastics. The carbon or glass fibers are woven into a fabric that is less than 1/32-inch thick. The fabrics are then saturated with a solvent-free epoxy system that wets the fibers and provides adhesion of the fabric to the repair surface. Within 24 hours, the system cures and the adhesion transfers the strength of the fabric to the substrate.
The system is similar to external reinforcement with steel. The live loads created from earthquakes, blasts, and hurricanes pass through the masonry substrate and into the adhered carbon or glass composite system. “However, the differences between high strength composites and steel are considerable,” says Saadatmanesh.
“We can achieve strength equal to that of ¼-inch steel in a package that weighs less than four ounces per square foot and is less than 1/16-inch thick,” he says. In addition, the systems do not corrode and can withstand the most severe acidic or alkaline environments.”
These flexible materials are easy to install and can fit in hard-to-reach places without removing obstructions from the surface of the wall. The lightweight nature of the material eliminates the need for heavy equipment and because the materials are epoxy-bonded to the area of repair, coring, welding, and bolting are not necessary.How are they installed?
Proper surface preparation determines the success of high-strength composite systems. All masonry surfaces must achieve a surface profile similar to 60-80 grit sandpaper and must be cleaned of all dirt and debris.
Once proper surface preparation is achieved, 20 mils of saturating resin are applied to the substrate, the carbon or glass reinforcing material is laid dry against the saturating resin, and an additional 20 mils of saturating resin are applied to fully wet the material and bond it to the substrate. Additional layers of reinforcing material can be applied to achieve higher levels of strengthening.