1. General This specification covers the requirements for pressure injection grouting using a cement-based grout mix to fill voids, cracks, fissures, and joints in concrete, masonry, rock, or soil. The primary objective is to improve the strength, stability, and impermeability of the targeted structure or ground. The work shall be executed in a safe and controlled manner, ensuring compliance with all applicable standards and project-specific requirements.
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2. Materials
2.1 Cement: The cement used for grouting shall be Ordinary Portland Cement (OPC) of Grade 43 or 53, or any other type of cement as specified, conforming to IS 269:2015, IS 8112:2013, or IS 12269:2013. The cement must be fresh, free from lumps, and stored in a moisture-free environment.
2.2 Water: Water used for mixing the grout shall be clean, potable, and free from suspended solids, oils, acids, alkalis, or other impurities. It shall comply with the requirements for water used in concrete mixing as per IS 456:2000.
2.3 Admixtures: Chemical admixtures may be used to enhance the properties of the grout mix, such as to improve fluidity, reduce shrinkage, or control setting time. All admixtures must be approved by the Engineer and shall comply with IS 9103:1999. The use of admixtures shall be strictly in accordance with the manufacturer's recommendations.
2.4 Filler Material (if required): For grouting larger voids, fine sand or a fly ash-based filler material may be used. This material must be clean, well-graded, and free from organic matter. The filler material shall not affect the flowability or strength of the grout and shall be approved by the Engineer.
3. Grout Mix Proportions
The grout mix shall be designed based on site conditions, void characteristics, and the required grout properties. The mix design shall be submitted by the contractor for approval by the Engineer.
- Neat Cement Grout: A mix of cement and water. The water-cement (W/C) ratio shall be specified based on the application. Common W/C ratios for injection grouting range from 0.4 to 0.6 by weight.
- Cement-Sand Grout: A mix of cement, sand, and water. The proportion of sand shall be limited to maintain fluidity.
- Fluidity: The fluidity of the grout shall be measured using a flow cone (e.g., as per ASTM C939) and shall meet the specified efflux time. The typical efflux time for a neat cement grout is 20 to 30 seconds.
4. Equipment
- Grout Mixer: A high-speed colloidal mixer shall be used to ensure a uniform and lump-free grout mix. The mixer must be capable of mixing the grout thoroughly to prevent segregation.
- Grout Pump: A positive displacement grout pump shall be used to inject the grout. The pump shall be capable of delivering the grout at a uniform pressure and rate.
- Grout Packers: Grout packers, either mechanical or inflatable, shall be used to seal the injection holes and prevent grout from leaking out.
5. Workmanship and Procedure
5.1 Drilling of Injection Holes: Holes for injection shall be drilled at locations and to depths specified in the drawings. The hole diameter shall be suitable for the packers and injection equipment, typically between 25 mm and 50 mm. The holes must be cleaned thoroughly using high-pressure air and water to remove all debris, dust, and loose material.
5.2 Installation of Packers: Once the holes are cleaned, the packers shall be installed and securely fixed at the required depth. The packers must be watertight and capable of withstanding the injection pressure without failure.
5.3 Mixing of Grout: Grout shall be mixed in batches to ensure consistency. The water and any admixtures shall be added first, followed by the cement. The mixer shall be run for a minimum of 2 minutes after all materials are added to ensure a homogeneous mix.
5.4 Injection Process:
- Pressure Grouting: The grout shall be injected under pressure, starting with a low pressure and gradually increasing it to the specified maximum pressure. The injection pressure shall be monitored continuously.
- Sequence of Grouting: The sequence of grouting shall be from the bottom upwards for vertical holes or as per the approved grouting plan.
- Cessation of Grouting: Injection shall continue until the specified volume of grout is injected, the grout appears in adjacent holes, or the specified maximum pressure is reached and maintained for a minimum of 5 minutes.
- Monitoring: Grout pressure, volume injected, and the time for each stage shall be recorded on a daily log sheet.
5.5 Sealing of Holes: After injection is complete and the grout has set, the top of the injection holes shall be sealed with non-shrink grout or a similar suitable material.
6. Curing and Protection Grout shall be protected from premature drying, freezing, and any physical disturbance for a period of at least 7 days. The area of grouting shall not be subjected to any heavy loads or vibrations until the grout has achieved its required strength.
7. Quality Control and Testing
- Flow Test: Fluidity of each batch of grout shall be checked using a flow cone before injection.
- Cube Compressive Strength: Grout cubes of size 70.6 mm x 70.6 mm x 70.6 mm shall be cast at a minimum rate of one set of three cubes for every 5 cubic meters of grout injected. The cubes shall be tested for compressive strength at 7 and 28 days as per IS 516:1959. The minimum compressive strength at 28 days shall be as specified, typically in the range of 25 to 40 MPa.
- Permeability Test: For grouting intended for water sealing, field permeability tests (e.g., packer tests) may be conducted before and after grouting to verify the reduction in permeability.
8. Measurement Measurement for payment shall be based on the volume of neat cement injected into the holes, calculated in cubic meters (m3) or kilograms (kg) as specified in the Bill of Quantities. The unit rate shall be inclusive of the cost of all materials, drilling of holes, mixers, pumps, packers, labor, and all other incidental costs required to complete the grouting work to the satisfaction of the Engineer. The cost of any trial mixes or pre-grouting tests shall not be measured separately.
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