When it comes to reinforcing concrete structures using post-tensioned cables, the grouting process plays a crucial role in ensuring the longevity and stability of the cables. In this discussion, we delve into the materials, equipment, properties, and step-by-step procedure involved in the grouting of post-tensioned cables.
To create a durable grout, it’s essential to use clean potable water without any dissolved impurities. Avoid using sea water. Opt for OPC 43 cement for freshness and lump-free consistency. For ducts with an internal diameter exceeding 150 mm, use sand conforming to IS:383, passing through IS Sieve No. 150. Keep the weight of sand below 10% of the cement weight, unless plasticizers are added for workability.
Utilize admixtures that enhance grout properties, such as fluidity, reduced bleeding, air entrainment, or grout expansion. Ensure these admixtures conform to IS: 9102 and are free from harmful substances like chlorides, nitrates, sulfides, or sulfites that may damage the steel or grout.
Achieve a homogeneous grout consistency with a mixer featuring an agitator. This prevents cement separation. The mixer should have additional storage and continuous agitation before pumping into the ducts.
Use a positive displacement type pump for continuous grout ejection, avoiding pulsations. Install a pressure gauge to measure controlled injection pressure, with a minimum of 0.3 MPa.
To ensure proper workability, maintain a low water/cement ratio, ideally not exceeding 0.45. Conduct laboratory tests for each job periodically, focusing on compressive strength (not less than 17 MPa at 7 days).
Before initiating grouting:
During grout injection: