Concrete Crack Repair Methods – Part III

Grouting

Portland cement grouting

Large cracks, particularly in gravity dams and solid concrete surfaces, could be fixed by filling with Portland cement grout. This method for stopping water leaks effectively but will not structurally bond damaged portions. The procedure consists of

  • cleaning out along the crack
  • installing across the crack at intervals built up seats (grout nipples)
  • seal the crack with cement paint, wax, or grout between the seats
  • flushing the crack to clean it and test the seal
  • Grout the whole area.

Grout may contain cement and water or cement plus sand and water. However, the water-cement ratio would be minimized to reduce shrinkage and to maximize the durability. Admixtures or water reducers may be used to improve the grout. For small cracks an injection gun may be used for larger areas pressure grout pumping will be required. The pressure should be kept up for several minutes after packing to insure good penetration of the grout into the concrete.

Dry packing

Dry packing is tamping or ramming into place a low water content mortar, which results in better contact between the concrete and the mortar. Because of the low-water-cement ratio of the product, there’s less shrinkage, resulting in a tight and good-quality bond improving durability, toughness, and reducing water penetration.

Before a split is repaired by dry packing, the section adjacent to the surface should really be widened to a slot about 1 in. (25 mm) extensive and 1 in. (25 mm) deep. The slot must be undercut so that the base width is marginally more than the surface size. Dry packing is only advisable for narrow slots cut for filling dormant cracks and not active cracks.

After mixing, to reduce shrinkage in-place, the mortar must left for 1/2 hour and then should be remixed prior to use. The mortar should be placed in layers about 3/8 in. (10-mm) thick. Each carefully squeezed within the area using a stick or hammer, and each underlying layer is scratched to facilitate adhesion with the next layer applied. The fix must be cured by utilizing perhaps a curing agent or a moist burlap over the crack’s length.

Overlay and surface treatments

If there will not be ongoing movement over the fractures floor cracks in slabs and architectural pieces maybe fixed using either a overlay or exterior treatment. Unbounded overlays may be used to cover, but not restore a slab. Overlays and surface solutions are only suitable for cracks caused by one time events and which do not penetrate the slab entirely.

Surface treatments

Reduced-viscosity resin-based material can be used for extremely thin cracks. They are best suited for slabs not susceptible to major wear. Bridge units and parking structure foundations, as well as different inside slabs could be coated effectively after fractures are treated by epoxy injection or by routing and closing. Resources for example urethanes, epoxies, polyesters, and acrylics are applied in thickness of 0.04 to 2.0 in. (1 to 50-mm), depending on the material and purpose of the repair. Skid- resistant aggregates in many cases are blended into the material or broadcast onto the outer lining to boost grip.

Overlays

Foundations containing uncover dormant breaks can be restored by making use of an overlay, including polymer modified Portland cement mortar or by silica fume concrete. If joints are positioned within the functioning cracks in the overlay straight over the active cracks they can be overlaid. In bridge applications, an overlay depth as low as 1-1/4 in. (30 mm) continues to be applied properly. Suitable polymers include styrene butadiene or latexes. The resin solids should be at the least 15-percent by weight of the Portland cement, with 20-percent often being ideal.