WATER JET CONFERENCE - Waterjet Technology Association

for an abrasive, the abrasive particle size, and its rate of entry (usually measured in
pounds per unit time) into the stream of the water jet will have a significant impact on the
cutting rate and/or performance of the water jet. Since the water supplied (even potable
water) is not sediment free, nozzle openings tend to enlarge with use. The average life of
a water jet nozzle is estimated to be 800 hours. In general, water jets produce no dust,
have a good maintenance record, and are relatively safe as long as contact with the jet
itself is avoided. Operators can hand hold a water jet operating at up to 15,000 lbf/ sq in.
without excessive fatigue (Barron and Nichols, 1973). Reducing water flow permits an
increase in pressure and the upper limits of each vary with the operator.
Explosives. Explosives have the unique ability to concentrate a large quantity of energy
in a very small area. Indeed, one of the chief peacetime uses of explosives is in the
demolition of unwanted structures. Controlled explosions to produce a minimum amount
of damage to adjacent structures have been developed. Shaped linear charges are being
evaluated for cutting concrete and will be reported separately by another U. S. Army
Engineer Waterways Experiment Station (WES) laboratory.
Mechanical Means. Rotary action diamond saws are the most common type of saw used
to cut concrete ( Kubo et al., 1981). Saws are capable of making large, precise cuts with a
minimum of damage to the exposed concrete, produce no dust, and are relatively safe to
operate. The cutting shape is limited as well as the cutting depth (less than one-half of the
blade diameter). Blades tend to wear quickly and a high noise level is associated with saw
operation. The saw is usually powered by a gasoline engine, although other means are
available.
Thermal Means. Three thermal methods of cutting concrete by melting with intense heat
are currently in use, the powder torch, the thermal lance, and the powder lance -- a
combination of the first two. The powder torch employs intense heat generated by the
reaction between oxygen and powdered iron and aluminum to melt a cut into concrete
(Kubo et al., 1981). The thermal lance employs intense heat generated by the reaction
between oxygen and mild steel rods to melt a cut into concrete. The powder lance
combines some of the features of the powder torch and the thermal lance. Besides being
much too slow, these three methods obviously damage the remaining concrete to a depth
that has not been determined. The extent of damage depends on the degree of heat
employed and the time of exposure. These devices are most effective in cutting
reinforced concrete.
Method Combinations. The water jet with abrasives was explained previously. A water
jet with mechanical pick is currently under study. This method uses a water jet located art
finally in front of the mechanical pick hut now behind (or trailing) the pick. With the
water jet trailing the mechanical pick, the vertical force could be reduced 40% to 50%
and the cutting force approximately 33% (Styron, 1982a).
A device called a water wedge was demonstrated at the WES. In application the
water wedge is loaded with a 12-gauge blank shotgun shell which provides a basic energy
source. The device is then placed in a predrilled hole filled with water. When the shotgun
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