19 June 2001
CPM-7: PREPACKED CONCRETE
Description: Placing coarse aggregate in the form and filling the voids with
grout. It is used on large repair jobs, and usually grout is pumped through grout
pipes from the bottom up.
Uses: Prepacked concrete is used where placement of cast-in-place concrete is
not practical. It is also used underwater where the tremie or pumped methods are
not practical due to inaccessibility. It is suitable for vertical surface repairs that
have a minimum thickness of 8 to 10 cm (3 to 4 inches).
Prior to injecting grout, be sure fines have not collected in the
coarse aggregate. Fines in the aggregate can impede the flow of
grout and create voids.
Preparation: Prepare the repair location in the same manner as for cast-in-place
concrete. Also, ensure grout pipes are well installed and fixed to forms or
reinforcing. A vent must be provided at the highest point.
Concrete Mix: Take careful measures to minimize drying shrinkage by selecting
a material mix design with a maximum allowable shortage of 0.05 percent and
proper curing. Coarse aggregate is sized to the size of repair. The sand-cement
grout is usually richer than a 1:1 mix. Admixtures are used as required by the
circumstances. Usually, a chemical admixture is used as an intrusion aid for the
grout. This suspends solids and provides fluidity. An air-entraining admixture is
used to obtain about 9 percent air in the grout.
Placement: Pump the grout soon after the aggregate is placed. Ensure that all
voids are filled and that segregation in layers does not take place. When forms
are filled, apply a closing pressure of about 0.1 MPa (14.5 psi) to drive out air
and water through the vent.
Curing: Use wet burlap for 7 days or a curing compound.