15 March 2001
7.7. Grout Injection. Grout injection proceeds by lowering into successive holes a pipe
connected to the discharge hose of the grout pump. The grout hole is sealed by a device called a
packer. Two types are commonly used:
7.7.1. The drive packer consists of a tapered pipe tapped into and out of the grout hole. Drive
packers are used with 1-inch- (25-millimeter-) diameter holes.
7.7.2. The expanding rubber packer consists of a threaded inner pipe, a thin-walled steel outer
sleeve, and a short rubber sleeve at the bottom. This type of packer is used with 1.5-inch-
(33-millimeter-) diameter and larger holes.
Movement of the slabs must be monitored during the grouting operation. To properly monitor
movement of the slabs, gauges capable of reading movement of 0.001 inch (0.025 millimeter)
have to be used. The base for the gauge should be 3 to 4 feet (0.91 to 1.22 meters) off the slab
being monitored. The gauges are set up at the outside edge of the slabs at the joints and are not
moved until grouting of the joint is completed. Typical pumping pressure should be in the 40- to
60-pounds per square inch (275- to 413-kilopascals) range. Grout injection should always start
with a low pumping rate and pressure. Pumping should stop if the slab begins to rise or when no
material is being injected at the maximum allowable pressure of 100 pounds per square inch
Pumping of short surges up to 200 pounds per square inch (1,378 kilopascals) are allowable for
the grout to penetrate the void structure. If grout returns through an adjacent hole, pumping
should stop, and the packer should be inserted into another hole. If grout is observed flowing
from joints or cracks in the pavement, pumping should continue until undiluted grout is observed.
Generally when pumping the four-hole pattern, pumping should begin at the centerline holes in
each slab first and then continue with the holes closest to the shoulder. This sequence will drive
any trapped water to the outside of the slab and through the transverse and shoulder joints.