Interior Grouting / Cement Grouting
For interior grouting, holes of 25 mm or larger diameter are drilled at an angle to intersect the cracks, joints or voids at desired depth from the surface or close to the bottom of the void. Drilling is done with diamond core bits, rotary carbide bits, or percussion drills and grouting is done from the interior. Diamond or rotary bit drilling is preferred when the openings to be grouted are relatively narrow. This drilling method minimizes the debris and chances of choking the cracks are reduced. A vacuum is applied to the drill stem to further reduce the possibility of drill cuttings getting into the crack. All holes are thoroughly washed by circulating water through the system before grouting.
The amount and size of solids used in grout for interior operation depends on the size of cracks / openings that are categorized as follows:
- The crack opening in the first category is from 3 mm to 6 mm. Neat grouts consisting of hydraulic cement with latex are used for effective penetration in to the openings. Pozzolans and other admixtures may or may not be added and the water used is about 83 L in 100 kg of solids (water-to-solids ratio of approximately 0.8). These grouts can also fill branch cracks of width as low as 0.25 mm. Hydraulic cement grouts can also stabilize cracks to get compressive and shear strengths at the crack location. Some tensile strength is also developed but is unpredictable. Expansive cement grouts are widely used to prevent water movement.
- The mixing water is 42 to 50 L per 100 kg of solids (water-to-solids ratio of about 0.4 to 0.5) is used for crack widths of 6 to 12 mm. Lower range of water is used when water reducing admixtures are employed.
- For openings of more than 12 mm width, sand may also be added equal to one or two times the mass of the cementing material. Fine aggregates may also be used when filling large voids.
Some important considerations for the use of cement grouting are listed below:
a) Clean the concrete along the crack.
b) Fix built-up seats (also called grout nipples) at intervals along the crack to provide a pressure tight connection with the injection apparatus.
c) Seal the crack on the surface with a cement paint, sealant, or grout.
d) Clean the crack and test the outside seal by flushing the crack.
e) Inject the grout until the whole area is filled.
f) Cement grouts consists of suspensions of solid particles in fluid. The material may consist of cement and water or cement plus sand and water, depending on the width of the crack. Water reducers or other admixtures are used to keep the water-cement ratio as low as possible to maximize the strength and minimize shrinkage.
g) Manual injection gun may be used for small jobs but pumps are preferred for larger volumes.
h) The pressure of grout is maintained for several minutes even after the cracks are filled to insure good penetration.