By Diane M. Calabrese / Published September 2023
Easy on, easy off. That’s a nice idea but it rarely applies.
Many things are easily applied, such as blueberry jam on a toddler’s shirt, but difficult to remove. Others, such as concrete and coatings, take serious effort to apply and to remove.
Breaches in concrete on highways and bridge surfaces are more than an immediate nuisance—and danger—to drivers; they provide the entryway for more serious deterioration. Make that deterioration of the reinforcing steel, a definite negative outcome on bridges.
Restoring surfaces takes enormous investment of time and money as we know from the steady stream of tax revenue for federal, state, and local road projects. The task of removing faulty concrete is no less arduous than it was 30 years ago.
Yet in 2023, the removal process has become much more precise and faster, too, thanks to hydrodemolition. The exactness and speed achieved are just two of the plusses of hydrodemolition.
“Waterblasting is about 10 times faster than jackhammering,” says Tracy Arnold, CEO of Clean Sweep Hydroblasting in West Palm Beach, FL. “It is ideal for removal of concrete on bridge decks.”
A person using a jackhammer can easily strike rebar, which is not good. “When you strike a rebar, it vibrates, reverberates, and breaks the air-tight bond between steel and concrete,” explains Arnold.
The bond-breaking—the beginning of a process called spalling—allows steel to corrode and expand. That means more loss of integrity to concrete.
The psi used in hydrodemolition is typically in the range of 20,000 to 22,000. It can go much higher on unique jobs. “Because of the high pressure we use robots,” explains Arnold. “We take the human element out of it. There is less risk.”
Minimizing risk with the highest safety protocols is one requirement in hydrodemolition projects. Another is minimizing environmental impact.
Arnold explains that vacuum recovery of slurry is now increasingly coupled with recycling of water. The more intricate the tie between recovery, treatment, and reuse, the closer the environmental impact gets to zero.
Hydrodemolition is just one of the many types of hydroblasting projects Arnold’s company does. He has been in the waterjetting industry since he left Navy service (where he was part of a flightdeck crew on an aircraft carrier).
Being able to do more with less water—higher pressures, equipment in robotic control—not only is gentler on the environment and safer but also is helpful for company growth when there is a dearth of workers. “We used to carry a lot more people,” said Arnold. “I can’t find people to work for me.”
While Arnold deals with the all-too-familiar national issue of employee recruitment, his daughter, Marlee Arnold, got hooked on hydroblasting early on. So much so, she joined the company after earning a law degree and sitting for the bar.
“From the time I was a little girl, my father had me helping him with fixing equipment,” says Marlee Arnold, who now serves as general counsel at the company. “It made the industry part of my person.”
M. Arnold was just 24 years old when she joined the industry. She had already held one legal position. Even while studying and practicing law, she was thinking about the industry, especially about what technology can do and how advances in equipment would make more and more possible.
“While so many people know of sandblasting, few know of hydroblasting,” says M. Arnold. “Given the right blasting company, the world of blasting is virtually endless so long as they can think outside the box, which our company does.”
Perhaps an example? “Start with bridge repair,” says M. Arnold. “We’ve had projects where we’ve assisted in saving the beams by removing the concrete above it. Our robots can also fit into pipes and confined spaces, which protects people.”
A robot can maneuver in a three-foot diameter pipe and “do all the blasting work,” explains M. Arnold. “Small” and “incredible” descriptors apply. “The fact is, waterblasting can be used on anything from a ship to a plane to a building, tank, bridge, tunnel, and so forth.”
More innovation and more uses will come. “Our company is designing its own tech that will use AI,” says M. Arnold. “AI will never take the place of people, but it will make it overall safer, which is absolutely a phenomenal thing.”
From the Sunshine State to the North Star State and all points in between, those who run hydroblasting companies convey an enthusiasm for the outcomes it enables.
“Hydrodemolition is typically used during the concrete repair process of any structure requiring partial demolition,” says Brian Gleeson, vice president at Midwest Mobile Waterjet in St. Paul, MN. “The hydro method is specified because the process does not create vibration that can cause additional damage to the remaining structure.
“It also will not damage existing structural steel reinforcing, which allows the contractor to reuse existing structural steel and greatly reduce overall job cost,” continues Gleeson. That’s significant.
Efficient use of dollars makes it possible to do more with available funds. When tax dollars are involved, citizens want to see effective outcomes.
The control over the target area that hydrodemolition allows means that it does not add to damage as it readies an area for refurbishing. Hydro-demolition definitely fits among the first-do-no-harm roster of tools.
Gleeson cites some of the many benefits of hydrodemolition. “It is dust free, removes unsound concrete, and leaves most sound concrete. The demolition speed with one robot is equivalent to five to 10 laborers with jackhammers.”
The power of hydroblasting equipment aside, hydrodemolition is very much a TLC [tender loving care] approach. “It eliminates ‘micro-fracturing’ of remaining structure typically caused by a jackhammering method,” says Gleeson. And it will “leave a clean and very sound surface that is ideal for new concrete to bond to.”
Assess, then plan accordingly. Hydroblasting companies do not simply apply hydrodemolition to any and all concrete removal projects. They evaluate, and they rely on/scrupulously follow the prescription for the scope of work given by the owner of the structure.
Hydrodemolition harnesses power and focuses it on a substrate in a way a blunt instrument—e.g., a jackhammer, cannot. “The hydro-demolition process is fast and efficient when used on projects that are a good fit for the technology,” says Gleeson. “It is ideal when trying to salvage portions of an existing structure.”
Collecting water and treating it are part of a hydrodemolition project at any jobsite these days. “The process requires a great deal of water, which also has to be treated before discharge,” says Gleeson.
Three common projects make great use of hydrodemolition, says Gleeson. They are bridge overlays, bridge modifications, and concrete sounding.
“Bridge overlays require removal ‘scarification’ of a thin layer of concrete to create a clean profile for new concrete bridge deck,” explains Gleeson. “In bridge modifications—bridge widening or lane replacement—hydrodemolition is used so the existing steel structure can be salvaged and used to ‘tie in’ the new portion of bridge.”
Concrete sounding derives its name from the objective of reaching “sound” concrete, says Gleeson. “This is common for removal of concrete on marine structures, dams, spillways, etc. The actual depth is estimated ahead of time, but the true goal is to remove any unsound concrete even beyond the estimated depth. Hydrodemolition is a very good tool for this.”
Responding to requests for proposals (RFPs), which are detailed and specific about certifications and insurance a contractor must hold and document, is where the precision begins.
The RFPs—and the contracts awarded based on evaluation of submissions—detail virtually every requirement that must be met. A contractor is expected not only to produce a list of equipment to be used but also to provide certification from each manufacturer that equipment will be used in accordance with the OEM’s parameters.
Once equipment is approved, a contractor will have to have it calibrated by the structure owner’s engineer. And that’s calibrated on site.
During a project, a contractor will be expected to recheck calibration at designated intervals. The checks must be documented.
Containment not just of slurry, but also of any airborne debris, will be required. The structure owner may assign captured material to the contractor who must then add off-site disposal to expense computations.
Before moving from one phase of a project to the next, a contractor can expect the owner’s on-site representative to check and verify results. If the contractor’s equipment is deemed to have caused damage to the structure, the contractor will likely be responsible for the cost of repairs.
Things happen. Weaker concrete than anticipated could be blown out from a bridge deck, for example. That’s a definite stop while mitigation measures are taken. And, yes, that too will be detailed in an RFP.
As wastewater recovery and reclamation become better and better, and control of hydrodemolition tools becomes easier—e.g., with AI tech—one constant will remain: interested parties. From structure owners to the EPA and project auditors, many individuals will be scrutinizing any hydrodemolition effort.
Not easy, but essential.