According to the Federal Highway Administration, nearly one out of every three bridges in the U.S. is rated structurally deficient. Because building new bridges to replace the thousands of old structures isn’t practical, the solution to ensure safety typically lies in replacing deck concrete with new material.

Hydrodemolition, a technique that has been around for more than 30 years, is a safe and efficient way to remove old concrete for repair and rehabilitation projects on buildings and airport runways as well as bridges.

What is Hydrodemolition?

Hydrodemolition removes layers deteriorated and damaged concrete via an automated robot that directs jets of water up to 40,000 psi at the surface. The high-pressure water exceeds the strength of the concrete to widen pores and microcracks, breaking it apart in a controlled manner.

Unlike jackhammers, hydrodemolition is an impact-free process that eliminates vibrations that cause microfractures: miniscule cracks in sound concrete that significantly damage the structure’s integrity. The robot leaves behind a “craggy” profile after removing the initial layer of material. The irregular surface provides an ideal texture for bonding to 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.

The high-powered water jets are devastating to concrete, but don’t damage steel rebar. Instead, rust and scale are removed, leaving the steel clean and intact.

The Swedish Cement and Concrete Research Institute reports a bridge repair life expectancy of 21 years to 35 years with hydrodemolition compared to 7 years to 12 years with mechanical chiseling.

Safety is Key

Whether diesel- or electric-powered, hydrodemolition robots are one way to lessen the potential for worker injury. The machines also can reduce both labor costs and insurance premiums compared to traditional methods, such as chipping hammers and handheld water jetting equipment.

Worker strain is virtually eliminated because operators manage the 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 increase worker’s compensation claims down the line, and may cause contractor 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 performs at a consistent level.

Remote-controlled robots allow operators to monitor their work at a safe distance from hazards, such as ledges, that are common in bridgework, flying debris, and silica dust. In addition, by eliminating the need to stand near a ledge, contractors save time otherwise spent setting up fall abatement systems.

Enhance Productivity

In addition to enhancing jobsite safety, hydrodemolition lowers labor costs while boosting productivity.

One operator generally controls the machine and can complete surface-preparation tasks as fast or faster than multiple workers. For example, some robots remove 800 square feet of concrete bridge deck at a depth of 4 inches in an hour, a fraction of the time it would take a crew with handheld breakers.

The secret to the process is the pressurized water penetration. The combination of high pressure; water volume; and precise, robotic-controlled movements creates a powerful, efficient system. 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 robot’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 provide consistent results that are impossible to achieve with a hand lance.

The robots are small and compact, enabling 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.

Reduced Impacts

Sound, vibrations, lane closures, and project timelines are all factors to consider when selecting the best approach for a bridge repair job. A crew of 10 laborers might get the job completed, but it’s noisy, disruptive, and may impact working hours.

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 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 25 ppm. Crews commonly use a trash pump to recover used water and return it to the water treatment unit. A vacuum truck can also be used to transport wastewater off-site.

A Unique and Unconventional Method

Demand for hydrodemolition robots is growing steadily. Their ability to prepare surfaces swiftly and safely, to remove target concrete while leaving sound concrete and undamaged rebar, increases efficiency when working on a variety of structures. They’re a valuable tool for any contractor called on to help restore structural integrity to thousands of bridges in dire need of repair.