Hydrodemolition, a technique that has been around for more than 30 years, stands out as an ideal method for contractors completing bridge renovation. Its unique manipulation of water is being used worldwide as an efficient concrete repair and rehabilitation technique.
Compared to jackhammers, hydrodemolition is an impact-free process, therefore eliminating vibrations that cause microfractures, miniscule cracks in sound concrete that significantly damage the structure’s integrity. The hydrodemolition robot leaves behind a “craggy” profile in the concrete after removing the initial layer of material. The irregular surface provides an ideal texture for bonding to the newly poured concrete.
Alternative techniques such as handheld breakers tend to leave layers of dust and damaged concrete with small cracks extending as much as 1 inch into the residual concrete. As a result, the profile could potentially spoil the bonding for new concrete.
Although hydrodemolition’s high-powered water jets are devastating to concrete, they do not damage steel rebar. As a natural result of the high-pressure water, rust and scale is removed, leaving the steel clean and intact.
In terms of bridge repair, hydrodemolition techniques reign supreme. The Swedish Cement and Concrete Research Institute reports a repair life expectancy of 21 to 35 years with hydrodemolition, compared to seven to 12 years with mechanical chiseling.
Worker strain is virtually eliminated as operators manage the hydrodemolition equipment through a control pack fastened around their waist. Other handheld methods produce heavy vibrations that can lead to long-term injuries, such as nerve damage and hand-arm vibration syndrome. These injuries can result in more worker’s compensation claims down the line, and may cause company insurance premiums to increase. Additionally, remote-controlled equipment doesn’t cause operators to fatigue as quickly as handheld tools, increasing productivity because the machine will perform at a consistent level.
Remote-controlled robots allow operators to monitor their work at a safe distance from hazards such as ledges common in bridgework, flying debris and harmful silica dust. In addition, by eliminating the need to stand near a ledge, contractors save time otherwise spent setting up fall abatement systems.
One operator generally controls the machine and can complete concrete removal tasks as fast or faster than multiple workers. For example, some hydrodemolition robots can remove as much as 800 square feet of concrete bridge deck at a depth of 4 inches per hour, a fraction of the time it would take a crew with handheld breakers.
The secret to the hydrodemolition process is the pressurized water penetration. The combination of high pressure, water volume and precise, robotic-controlled movements creates a powerful, efficient system. In comparison, operators using hand lances, an alternative method for some concrete removal and cleaning tasks, can’t handle the same reaction forces as a robot. This means a significantly higher concrete removal rate from the machine versus the hand lance.
The hydrodemolition machine’s stable design maximizes the effectiveness of its high-pressure jets. Innovative technology adjusts and maintains the distance from the nozzle to the point of impact, as well as the nozzle’s angle, movement and water exit speed. The computerized controls also allow consistent results impossible to achieve with a hand lance.
Additionally, hydrodemolition robots’ compact nature allows them to reach tight, confined spaces. Various design features and additional attachments also allow for work on any vertical, curved or horizontal surface. This greatly increases productivity and reduces the number of tools needed on a jobsite.
Hydrodemolition offers a quieter solution. Hydrodemolition robots generally produce less noise than a handheld pneumatic tool and the sound is limited by the machine’s hood. Noise from handheld tools also more easily travels through structures and can be amplified due to echoes. The reduced noise from hydrodemolition robots allows contractors to work in residential areas or avoid busy travel times by working during hours when noise levels are restricted.
In addition to the robot, a complete hydrodemolition system should include a high-pressure power pack and, potentially, a water treatment system to handle the slurry, depending on local regulations. Contractors can pair the robots with self-contained water treatment units that can handle up to 5,000 gallons per hour. The 20-foot units discharge clean water back into the environment after reducing pH values to 7 and turbidity levels to just 25 ppm. Crews commonly use a trash pump to recover used water and return it to the water treatment unit. A vac-truck can also be used to transport wastewater off-site.
This unique approach to concrete removal will only become more popular. The innovative method is one of contractors’ best tools for the efficient, cost-effective and precise removal of concrete from a variety of structures. It represents one piece of the puzzle in restoring structural integrity to the thousands of bridges in dire need of repair.