Page 70 - Occupational Health & Safety, July/August 2019

CONSTRUCTION SAFETY
Just Add Water
Robotic hydrodemolition helps to simplify bridge repair.
BY PETER BIGWOOD
According to the U.S. Federal Highway Ad- ministration, nearly one out of every three bridges in the nation 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 replac- ing old bridge deck concrete with new material. Hy- drodemolition, 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.
What is Hydrodemolition?
Hydrodemolition is a concrete removal technique used in locations such as bridges, buildings, and air- port runways. The method uses high-pressure water jets as powerful as 40,000 psi manipulated by an auto- mated robot to remove layers of deteriorated and dam- aged concrete. The high-pressure water exceeds the strength of the concrete to widen existing pores and microcracks, breaking it apart in a controlled manner.
Compared to jackhammers, hydrodemolition is an impact-free process, therefore eliminating vibra- tions that cause microfractures—minuscule cracks in sound concrete that significantly damage the struc- ture’s integrity. The hydrodemolition robot leaves be- hind a “craggy” profile in the concrete after removing
the initial layer of material. The irregular surface pro- vides an ideal texture for bonding to the newly poured concrete. Alternative techniques such as hand-held breakers tend to leave layers of dust and damaged concrete with small cracks extending as much as 1 inch (10-20 millimeters) 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 wa- ter, rust and scale is removed, leaving the steel clean and intact.
The Swedish Cement and Concrete Research In- stitute reports a repair life expectancy of 21-35 years with hydrodemolition, compared to 7-12 years with mechanical chiseling.
Safety is Key
Whether diesel- or electric-powered, robotic hy- drodemolition units are one way to reduce injuries during concrete removal applications. The machines also can reduce both labor costs and insurance premi- ums compared to traditional methods, such as chip- ping hammers and hand-held water jetting equipment.
Worker strain is virtually eliminated as operators manage the hydrodemolition equipment through a control pack fastened around their waist. Other hand-
64 Occupational Health & Safety | JULY/AUGUST 2019
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