HOUGHTON--A new method has been developed for fracturing and stripping concrete structures that appears to be environmentally safer and more energy efficient than any method currently in use.

Francis Otuonye (O-tun-yeh) and graduate student Jian Jia of Michigan Tech's Department of Mining Engineering teamed with Chapman Young of Applied Geodynamics, Inc. of Steamboat Springs, CO to test the new procedure, called Controlled Foam Injection (CFI). The method is a result of independent studies by Otuonye and Young to reduce the adverse effects of rock fragmentation by blasting and to control the spread of fractures during blasting. CFI has proven successful in fracturing and stripping reinforced concrete structures such as road pavements and bridge decks. It could also be valuable in the demolition and/or rehabilitation of more massive reinforced concrete structures such as certain types of building foundations.

"In recent years, the increase in the size and number of heavy trucks on the nation's roads and highways has caused significant deterioration to the pavement on those roadways, which requires periodic resurfacing or reconstruction," says Otuonye.

"For most pavement reconstruction work, rehabilitation involves stripping the deteriorated pavement and applying a new surface, or fracturing, breaking, and removing the degraded concrete and applying a new pavement. In the former case, jackhammers or high-pressure water jets are frequently used to strip the concrete. In the latter instance, explosives or high impact breakers are frequently used to fracture and break up the concrete."

He says these current practices have not kept pace with society's requirements for energy efficiency and environmental safety. For example, small-charge explosive, water-jet and gas propellant techniques still generate significant noise, flyrock, and/or ground vibrations.

"New concrete breakage methods must be found that are suitable for automation," says Otuonye. "And the automation and control of such methods will be required for them to achieve required production rates and become independent of both intensive labor and operational problems in the highly variable environments of concrete breakage."

Otuonye and colleagues feel that Controlled Foam Injection (CFI) fracturing is the answer to the problem.

"The preferred demolition/excavation method should have the ability to pressurize a controlled fracture in such a way that pressures can be maintained to increase the number of fractures," he says. "The fluid used must have a viscosity that will allow the fracturing process to continue over a long period and thus at lower pressures. The fluid should also be able to store energy that can be used to maintain a desired pressure as the fluid expands into the developing fracture system. CFI uses a foam that has all of these required properties."

Otuonye explains that foam, which is a two-phase mixture of a liquid and a gas, can be made to have a viscosity several orders of magnitude higher than a gas or even water. As a result, foam will escape from a developing fracture system more slowly than a gas or water. With a much slower escape of the fracture-pressurizing medium, the pressures required to initiate, extend, and develop the desired fractures can be much lower than if a gas is used. The use of water alone is not sufficient because this relatively incompressible liquid will rapidly lose pressure as the fracture volume increases with fracture growth. The fracturing process will usually occur so rapidly that the needed fluid pressure in a water-based system cannot be maintained by injecting additional liquid into the fracturing system. In contrast, foam can maintain the pressures for efficient fracturing due to the expansion of the gaseous phase of the fluid. Thus, foam has the ability to provide the pressures for efficient controlled fracturing without requiring the excessively high pressures associated with explosives, propellants, water cannons, or electrical discharge.

Otuonye says field tests at MTU showed the CFI method reacted positively with steel reinforcement rods in concrete slabs to increase fracturing, while at the same time the lower energy used resulted in low airblast and flyrock and minimal damage to residual concrete.

There were some drawbacks, however.

"The CFI breakage tests demonstrated the intrinsic efficiency of the method, but revealed that CFI breakage alone may not be able to remove all of the damaged or degraded concrete to the desired level," says Otuonye. He suggests that combining CFI with hydrodemolition could result in the most effective, energy efficient, and environmentally safe system available.

"The greater the fraction of concrete that can be economically removed with CFI breakage, the less the requirement for hydrodemolition and the lower the required power for the combined system," he says.

He notes that the ability of CFI to interact with the reinforcing steel in slabs is a feature that makes the process attractive for the demolition of massive reinforced concrete structures such as foundations used for heavy turbines and generators in electrical power plants. If the concrete could be efficiently and completely stripped from the steel in such foundations, without the damage to the reinforcing steel that would be caused by explosive demolition, a new foundation could be poured around the original rebar structure. Similar remedial work could be carried out on dams, bridge piers, abutments, and comparable structures.

For more information, See High-Pressure Foam Method for the Fracture, Demolition, and Stripping of Concrete Structures
or contact Francis Otuonye at 906-487-2816 or email: frotuony@mtu.edu or Chapman Young at 907-879-3032; email: chyoung@cfiex.com

From: Tech Topics ---July 21, 2000

Using ingredients found in the typical bath and kitchen, Michigan Tech researchers are refining a new way to breaking up concrete and rock that promises to be far greener and safer than current methods.

Professor Francis Otuonye (Mining Engineering) and Chapman Young of Applied Geodynamics, Inc. of Steamboat Springs, Colorado, developed the method, called controlled foam injection, or CFI. Instead of using explosives, jackhammers, or high-pressure water jets, the reseachers drill a hole into the rock or concrete, insert an injection tube, and force a special foam inside at high pressures, from 300 psi up to 12,000 psi in some cases. The pressurized foam forms cracks, and the material breaks up, without the noise, dust, or danger associated with current techniques in mining and demolition operations. The technique could be automated, offering labor-saving benefits. Plus, it offers demolition teams more control than if they were using, say, dynamite. And it provides more staying power than water under pressure, since it stays in the fractures and keeps on expanding.

"In addition, the foam is benign," Otuonye said. "It doesn't hurt the environment; it can just be washed away."

Next to water, the foam's main ingredient is the detergent sodium lauryl sulfate, which is commonly used in shampoo. It also contains guar gum, a thickener that's found in many processed foods.

CFI could be used to help break up massive structures, such as building foundations slated for demolition or concrete highways that are under reconstruction. Otuonye believes that the CFI method could replace the use of explosives in fragmenting hard rock for mining operations, and in Canadian tests CFI has successfully fractured granite. "We wanted to see how it performed in an extreme case," he said.

The CFI work has been supported by grants from the Michigan Department of Transportation and the National Science Foundation, and Otuonye has been working with graduate student Jian Jia (Mining Engineering) on testing and improving the procedure

More Details about Controlled Foam Injection Project

Mining Engineering Web Site