Comparison of methods
When the decision of partial or full demolition of a concrete structure is made, the process of selecting a demolition method starts. To be considered are local circumstances influencing the process as well as the kind and volume of the building material to be demolished. If the purpose is to repair damaged parts and the target is a sensitive structure like a road, bridge, dam wall, multi-story car park, airfield landing ground, concrete surfaced tunnel or similar there are just a few alternatives: hand held jackhammers, road milling machines or hydrodemolition.
Hand held jackhammersThere are several disadvantages with hand held jackhammers, including low efficiency, noisiness and difficulty in separating damaged concrete from undamaged. Vibrations when hitting rebars will cause loosening in bondage to concrete and thereby speeding up the corrosion process, causing lamination (meaning the concrete separates like slices along the rebars). Micro cracks will normally be created in the undamaged concrete. The result of how well the chipping turns out depends to great extent on the skill of the operator and his or her feeling for both the equipment and the concrete. The restrictions in working time need to be considered as well. Due to risk of operator’s injuries in form of circulation disturbances (white fingers) and hearing impairment, the user will have to take breaks. This method can for economical reasons be chosen when the area is very small, since the investment and start up costs are quite low.
Road milling machinesThe same disadvantages of creating micro cracks apply to road milling machines as well, but the risk for the operator is eliminated. Additionally, it is not possible to remove the concrete under the rebars, meaning additional work is required for the demolition to be complete.
Water-jet hand lanceHand lance is the simplest and least effective form of water jetting concrete, and is sometimes incorrectly referred to as hydrodemolition. The maximum allowed reaction force created by the water jet is 250 N for hand held equipment, compared to robots that are built for reaction forces from 1000N up to 4000N. Hand lances are normally not recommended, but in certain conditions where the concrete is confined or hard to reach it may be the only option. Though gaining many of the advantages that of hydrodemolition, working with hand lances means adapting to some of the disadvantages of regular jackhammers, such as the need of periodical rest, the inability to set the cutting to a certain depth, and the high risk of injury.
HydrodemolitionEven after nearly three decades, this technique is still unknown to many contractors and commissioners. Hydrodemolition was invented as a way to render a faster and more effective system for removing damaged concrete without the disadvantages listed above. The ability to remove a specified depth is a major difference compared to other methods. demolition is performed by a computer controlled robot, with settings specifying the outcome. Accessing the area under the rebar is also possible. The reinforcment is kept intact, and even cleaned from corrosion. Thanks to the appeared irregularity of the surface, the bond between the old sound concrete and the new replaced one is extremely strong. Independent laboratory tests have time after time shown that test samples are not breaking at the bonds when pulled to their breaking point. Measures show that working with a hydrodemolition robot is up to 25 times faster than working with a handheld jackhammer. Combined with a higher quality result, hydrodemolition is clearly the most efficient method, as displayed in the comparison chart below.
|Jackhammers||Road milling machines||Hand held water-jet||Hydrodemolition|
|Reaches under rebars||Yes||No||Yes||Yes|
|Requires periodical rest||Yes||No||Yes||No|
|Keeps rebars intact||No||No||Yes||Yes|
|High risk of injury||Yes||No||Yes||No|
|Pre-set quality depth||No||No||No||Yes|
|Good bonding surface||No||No||Yes||Yes|