HYDRODEMOLITION TAKES ON THE JACKHAMMER
By Diane Calabrese
From Cleaner Times, April 2000

Will hydrodemolition be to this century what the jackhammer was to the last? It's very possible. The reliable jackhammer is getting some serious competition from the force in a blast of water.

The jackhammer, which actually traces its origin to 1849, will not disappear any time soon. However, many contractors are now using hydrodemolition instead of jackhammers, especially when they must break up concrete and particularly when precision matters.

Despite its dependability, the jackhammer comes with several built-in liabilities that hydrodemolition does not have. For example, the drilling machine can cause damage well beyond where it is applied because pressure waves generated by its blunt force permeate a material. Then, too, its weight and its motion can weary an operator. And a quiet tool it is not.

Hydrodemolition: The Familiar Applications

Since 1989, AK Services, Inc. of Everett, Massachusetts has put hydrodemolition equipment and operators into service on behalf of companies tackling parking garage repair and bridge restoration. More recently, AK Services has been part of the team pressing on with the massive $10.8 billion Boston Central Artery/Tunnel Project, an effort that includes a tunnel located under existing transit lines.

"We do a lot of hand-held and overhead work," explains Carl Franson, Vice President of Operations at AK Services, who points out that relatively lighter hydrodemolition machines are a boon. "When holding on to a jackhammer when it's overhead, there is a big fatigue factor. Hydrodemolition equipment weighs 15 to 20 pounds. A jackhammer weighs about 60 pounds."

Franson says his company typically uses a pressure of 36,000 psi at 5 to 14 gpm. He explains the flow rate may be changed and depends on whether the application calls for the marrying of two pumps.

Jobs requiring finesse and selective removal are the sort AK Services takes. "We don't try to compete with companies doing big demolition jobs," says Franson. "We are doing specialty, finer work, removing small patches of concrete."

Precision is the essence of hydrodemolition. Trying to remove selected pieces of concrete with a jackhammer is like trying to push in a thumbtack with an ax. It can be done, but the damage to the surrounding area and the undersurface can complicate an application of new concrete to the surface, or do so much damage to the underlying area the new application deteriorates soon after it is put in place.

Hydrodemolition helps to prevent micro-cracking," says Franson. And prevention is at least twice as good as a cure. Because structural integrity is preserved with hydrodemolition, a surface that has had concrete removed is ready for a reapplication (bonding) of fresh material.

Concrete: The Number One Application

Commercial applications for hydrodemolition have been finding more and more markets in the last 15 years, but the method of using a highpressure jet of water to cut concrete has been known since the 1960s. Hydrodemolition is often used as a synonym for concrete hydrodemolition, a nod to its early association and heavy use in the setting. Although concrete is the most common target, hydrodemolition does have other applications, such as rock cutting and tunneling. The latter are expected to grow as new methods, which augment the power of water with an abrasive, are used.

Still, concrete makes an excellent candidate for hydrodemolition because of its composite make up. The force of water exploits the small (micro-) and large (macro-) cracks that exist and generates new fissures on impact.

Concrete is simply stone, brick fragments, sand and gravel, in some combination, held together by Portland cement. (The name Portland was affixed in a patent for a manufacturing process for the mortar. The color of the cement reminded the patent holder of the Isle of Portland off the British coast.)

Cement, the biggest portion of concrete, is made by crushing a rock type that contains primarily calcium, silicon, aluminum and iron. Making cement is a time and labor-consuming process. Mortars of various sorts were widely in use long before cement was developed. They include clay and volcanic ash (pozzolana). Today, cement additives can enhance adhesiveness, speed drying time and increase the tolerance of concrete to curing at low temperatures.

Irrespective of how the cement is made, getting the mortar away from the aggregate it holds together can be relatively speedy with hydrodemolition. Water manages to penetrate the smallest crevices in the concrete and encourages them to split. The expediency of hydrodemolition can be compounded by rotating high velocity jets of water.

Exacting and Fast

Because it produces accurate outcomes, hydrodemolition is a keen competitor. A jackhammer, after all, gives results that are certain, but also crude and rough.

"One of the nice things about ultra high pressure hydrodemolition is that it gives you more depth control," says Dan Gotz, marketing manager at Jet Edge in Saint Michael, Minnesota, a manufacturer of equipment for ultra high pressure hydrodemolition.

By moving the high pressure jet of water and varying the time the water jet stays in place, an operator can control the depth of removal. Obviously, pre-testing and predetermined time marks are necessary.

Jamie Layton, a regional sales manager for Gardner Denver Water Jetting Systems, Inc. in Carmi, Illinois, says, "With jackhammering, it is easy to go too far and do structural damage. With hydrodemolition, it is possible to remove what's bad - to stay at the surface, and not go below where you want to go."

Highway departments are more interested than they have ever been in using, or at least exploring the potential of hydrodemolition. In the past, on a highway project such as a bridge deck restoration, milling might be used to remove the top one and three-quarters inches of concrete, and then jackhammering would follow.

But increasingly, highway departments are calling for hydrodemolition to eliminate the worn concrete down to the rebar. The method is particularly attractive because it also cleans the rebar.

Cutting through and separating the pieces of concrete slab is another application for hydrodemolition in highway repair work. A slab more than 12 inches thick can be cut at rates of more than one inch per minute using a pressure as low as 10,000 psi and a 12 gpm flow.

Terminology for pressures used in hydrodemolition follow this scheme: (Low) high pressure is generally in the range of 12,000-15,000 psi with a flow of about 60 gpm. Ultra high pressure equipment has a force of 36,000 psi and a flow rate of 7.2 gallons. (Putting two hoses together, the flow can be doubled.)

Environmental Impact and Promise

Breaking up and cutting through concrete with high pressure or ultra high pressure water requires no abrasive. Because chemical additives are not necessary, no unwanted substances must be removed from recycled water for ordinary concrete hydrodemolition jobs. However, water must be filtered to comply with environmental regulations.

Ninety percent of the water AK Services uses in its equipment is recycled. The remaining 10 percent is filtered and disposed of by the contractor.

Wastewater filtration, pH adjustment and noise abatement (muffling) systems on equipment from a variety of manufacturers reduce the impact of hydrodemolition on the environment. The essence of hydrodemolition is environmentally friendliness: Absent are the flying dust and debris from alternative removal methods of drilling and blasting.

Price Comparison Requires Case by Case Evaluation

Cost is relative and only when long-term outcomes can be compared will it be possible to evaluate whether jackhammering or hydrodemolition is a more economical method. Currently, costs on the front side are typically the only ones considered during a bid process. But several factors must be considered when comparisons are made.

For example, a single piece of hydrodemolition equipment can do the work of several hydraulic jackhammers in the same interval. There is a saving in labor costs. (Note: In the April 1998 issue of Cleaner Times, Henrik Lundell considers some of the early evidence of how much faster hydrodemolition is and estimates the process may be 20 times or more faster than a jackhammering approach.)

In the longer time frame, a company using hydrodemolition probably saves costs in worker injuries and ultimately, worker's compensation, but these economies are harder to measure. (The vibration of a jackhammer takes a toll on the skeletal and muscular system of an operator.)

Both hydrodemolition and jackhammering leave rubble that must be removed by industrial vacuums or some other method. The removal costs money in both cases. Seasonal constraint is a minus for hydrodemolition. Temperature must generally be above the freezing point of water, so that water does not penetrate cracks, freeze and cause ancillary structural damage in the course of the removal.

Contractors who use equipment for more than just hydrodemolition can realize cost efficiencies if they are able to use the same piece of equipment in other high pressure jobs. For example, Gotz says, "On our equipment, you can change the manifold used for hydrodemolition and use the machine for any UHP cleaning"

There is another way contractors can realize cost savings with hydrodemolition on large jobs - bringing in robotic equipment. Layton points as an example to a remotely controlled robotic concrete renovation offered by Gardner Denver. A hydraulic swivel allows for overhead, vertical or horizontal work. And after it is programmed with the dimensions of an area, the machine can move across the floor or the milled surface.

"Some of the biggest advantages to the robot," says Layton, "are fewer people, no back injuries to the operator and the steady, faster production that is obtained."

Emphasis on Rehabilitation and Restoration

J. D. Frye is the owner of Jetting Systems & Accessories in Houston, a company that makes nozzles and accessories, some of which are used in hydrodemolition. Frye offers several observations about hydrodemolition, beginning with its specificity.

"If a contractor is in a situation where he only wants to remove a weaker material, hydrodemolition makes it possible to remove only that material," explains Frye. "You are not introducing shock-loading into the material, which is why doing hydrodemolition in rehabilitation is attractive."

However, Frye notes some cautions are built into the process. He says, "Operators must use appropriate pressure and flow and nozzle traverse rates, so as not to remove more material than desired, and to maintain an even depth of cut. If specification calls for one and one-half inches below depth of cut, you must monitor regularly.

"Otherwise, in weak spots, you might go below one and one-half inches, and inspectors, for a highway department, for example, wouldn't t be happy with the extra cut."

But Frye says the contractors he knows who are using hydrodemolition "generally speaking, like the results." And Fryre, who first watched the method take root about ten years ago, has noticed a growth in the use of hydrodemolition, albeit at a rate he characterized as more steady than stupendous.

Tempered Pace of Adoption

Five years ago in these pages, Bill Hall (Defining Hydrodemolition, Part 1, Cleaner Times, July 1995) predicted many factors, such as increasing awareness of the potential of hydrodemolition and the falling price of hydrodemolition equipment would contribute to the growth in use of the application. The growth has continued at a slow and steady pace.

No quantum leap has occurred in adoption for largely the same reasons Hall wrote about then. Contractors continue to use the methods they have known the longest. And job specifications by public entities continue to be written according to long established guidelines, which are slow to catch up with hydrodemolition specifications.

Both phenomena are changing, but gradually. Hall suggested that hydrodemolition experts must market their technique and get out the good word about the process. This suggestion still applies today.

And perhaps using hydrodemolition to remove concrete is one of the most difficult "sales" because of public bidding processes - demonstrating a future cost savings because a more costly method in the present does less damage and increases life after repair (reducing costs long-term), is never easy. Even so, hydrodemolition is in use in a variety of settings and cutting with jets of water is an accepted practice.

AK Services' Franson recalls the time a university called his company in to put holes in pre-stressed (precast) beams in a new structure. Ordinarily the holes would have been put in when the beams were made, but there had been a mistake. Because of the proximity to post tensioning cables, cutting with water
jets was the method selected to make holes.

High-pressure water is a force with which to be reckoned. With the use of an abrasive, such as garnet, it can even be used to cut holes in steel. And research and development just keep pumping out new ways to deploy high velocity jets of water. It is fair to surmise concrete hydrodemolition is just the beginning.

Diane M. Calabrese writes about construction, pallets, timber, butterflies, gardening, business and more. She is based in Silver Spring, Md.