The following article appeared in Masonry Construction Online... or go to our Newsroom for more of HJ3 in the media!

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Changing the Face of Construction

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?

Scientists at the University of Arizona imagined just such a world and one Tucson company was founded (HJ3 Composite Technologies) based on this research.

In 1994, leading researchers at the University of Arizona in the field of high strength composite systems designed to strengthen infrastructure began developing carbon and glass composites that allowed masonry walls to survive earthquakes. Through a three-year research effort, they 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, " said John Nighswander, of the University of Arizona.

In 1997, a patent was issued to HJ3 Composite Technologies for this 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," said Nighswander.

"We can achieve strength equal to that of 1/4-inch steel in a package that weighs less than 4 ounces per square foot and is less than 1/16-inch thick. In addition, the systems do not corrode and can withstand the most sever acidic or alkaline environments."

These flexible materials are easy to install and can fit into hard to reach places without the removal of 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 the 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 sandaper 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.

Masonry Applications

HJ3 focuses its research and development efforts on creating unique solutions for strengthening masonry. In 2005, the company introduced Stronghold™, which is designed to strengthen bowing and cracked foundation walls. The product is packaged in kits that include rolls of 4-inch wide precured carbon straps and a single component epoxy that bonds the carbon straps to foundation walls. Each strap is less than 1/16-inch thick, but delivers tensile strengths equivalent to a 3/8-inch steel plate.

Like steel I-beams bolted to basement walls, the carbon straps counteract external soil pressure that causes walls to crack and bow. Unlike steel I-beams, however, the carbon straps create minimal surface loss and easily blend into the wall surface, creating an aesthetically pleaseing repair.

Another system- Blastek- is comprised of advanced carbon fiber composites specifically engineered for the mitigation and containment of blast energy. "The concept is similar to retrofitting walls for earthquakes," said Nighswander.

"Most walls are not designed for the live loads created by impact or blast waves. The inertia from these events causes the walls to cycle back and forth, weakening the mortar joints and crushing the masonry, which leads to collapse."

In testing sponsored by the Department of Defense at the Energetic Material Testing and Research Lab in New Mexico, 212 pounds on TNT were detonated 33-ft. away from two unreinforced masonry walls- a control specimen and a wall retrofitted with Blastek. The explosion created a blast wave at the face of the unreinforced masonry wals that measured a peak load of 180 psi.

Upon impact the control specimen was obliterated, but the wall retrofitted with Blastek remained completely intact. The system allowed only 1.4 of the 180-psi force to transfer to the other side. Following the explosion, vibration in the wall quickly attenuated and it came to rest in the original position.

The application of high strength composites to masonry in need of structural repair, retrofit, seismic upgrading, and blast protection represents the beginning of the transformation the materials could deliver to the construction industry. While the technology provides unprecedented benefits to the standard masonry construction, it offers solutions as the industry confronts new challenges, such as the damage caused by the earthquakes that sacked major cities in Iran, Pakistan, and Turkey and the hurricanes that ravaged the south last year.