Interior Grouting / Cement Grouting
For interior grouting, holes with a diameter of 25 mm or larger are drilled at an angle to intersect cracks, joints, or voids at the desired depth from the surface or close to the bottom of the void. Diamond core bits, rotary carbide bits, or percussion drills are used for drilling, depending on the situation. Diamond or rotary bit drilling is preferred for narrow openings as it minimizes debris and reduces the chances of cracks getting choked. To further reduce the possibility of drill cuttings entering the cracks, a vacuum is applied to the drill stem. Before grouting, all holes are thoroughly washed by circulating water through the system to ensure cleanliness.
The size and amount of solids used in grout for interior operations depend on the size of cracks or openings. For cracks with a width ranging from 3 mm to 6 mm, neat grouts consisting of hydraulic cement with latex are used to effectively penetrate the openings. Additional admixtures such as pozzolans may or may not be added, and the water-to-solids ratio is typically around 0.8, with approximately 83 L of water used per 100 kg of solids. These grouts are capable of filling branch cracks as narrow as 0.25 mm and can also stabilize cracks to achieve compressive and shear strengths at the crack location. However, the development of tensile strength may be unpredictable. Expansive cement grouts are commonly used to prevent water movement in this category.
For cracks with a width of 6 mm to 12 mm, the water-to-solids ratio is lower, ranging from 0.4 to 0.5, with 42 to 50 L of water used per 100 kg of solids. The use of water reducing admixtures may further decrease the amount of water used.
For openings larger than 12 mm in width, sand may be added, typically equal to one or two times the mass of the cementing material. Fine aggregates may also be used to fill large voids.
Some important considerations for the use of cement grouting are listed below:
To repair cracks in concrete structures, a series of steps are typically followed. First, the concrete along the crack is thoroughly cleaned to remove any debris or loose material. This ensures a clean surface for effective repair. Next, built-up seats, also known as grout nipples, are fixed at intervals along the crack. These seats provide a pressure tight connection with the injection apparatus that will be used in the later steps.
After the seats are installed, the crack is sealed on the surface using a cement paint, sealant, or grout. This helps to prevent further water infiltration and prepares the crack for injection. The outside seal is then tested by flushing the crack to ensure its effectiveness.
Once the crack is properly sealed, grout is injected into the crack using an appropriate method. Cement grouts, which consist of solid particles suspended in fluid, are commonly used for crack repair. The composition of the grout, whether it’s just cement and water or cement with sand and water, depends on the width of the crack. Water reducers or other admixtures may be used to minimize the water-cement ratio, maximizing the strength and minimizing shrinkage.
For small jobs, a manual injection gun may be used, while pumps are preferred for larger volumes of grout injection. The grout is injected under pressure and the pressure is maintained for several minutes even after the cracks are filled to ensure good penetration and distribution of the grout.
In conclusion, repairing cracks in concrete involves a series of steps including cleaning, fixing grout nipples, sealing the crack, testing the seal, injecting grout, and maintaining pressure for proper penetration. Cement grouts are commonly used, and the choice of grout composition depends on the crack width.