UFC 3-270-04
15 March 2001
cone (CRD-C 611/ASTM-C-939) at least twice each day. Typical flow-cone times vary between
16 to 30 seconds depending on the type of materials used in the grout mix. Strength require-
ments of the grout mixture should be specified. A common requirement is 600 pounds per
square inch (4,134 kilopascals) at 7 days as determined by ASTM-C-39.
6.6. Grout Pumping. Pumping and jacking operations should normally start at the lowest point
in a depressed area and work outward in both directions (Figure 6.3.). Pumping progresses by
lowering into successive holes an injection pipe connected to the discharge hose of the grout
pump. An expanding rubber packer is used to seal the open space between the pipe and the drill
hole. The injection pipe must not extend below the bottom of the pavement and it must be
equipped with a return line to circulate the grout while no grout is being placed. Lifting should be
done in increments of about 1/4 inch (6 millimeters) with frequent changes in injection locations to
keep slab stresses at a minimum and avoid cracking. The rate of grout injection should be
uniform and as slow as possible, usually a minimum of 1/2 cubic foot (0.014 cubic meter) per
minute to a maximum of 2 cubic feet (0.056 cubic meter) per minute. Initial pumping is normally
at the lower rate and is increased as lifting progresses. As the desired elevation is approached,
the lifting rate should be reduced. When grout is extruded from joints, cracks, or from the
pavement edge before the target elevation is reached, regrouting in new drill holes and additional
slabjacking will be necessary. Gauge pressures for slabjacking are normally in the range of 75 to
200 pounds per square inch (517 to 1,379 kilopascals) with short pressure surges up to 600
pounds per square inch (4,134 kilopascals) to initiate lifting of bonded slabs. Constant
observation and analysis of pressure behavior is the most important single factor affecting good
slabjacking. A rapid increase could signal a stoppage of flow that could be followed by a buildup
of pressure and excessive lift and cracking, if pumping continues.
A sudden reduction of pressure could indicate a loss of lift due to subsurface leakage. In
slabjacking operations, the temperature is important when raising slabs to correct faulted joints or
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