In this comprehensive guide, we’ll delve into the intricacies of grouting pre/post-tensioned cable ducts, covering materials, equipment, and crucial precautions for a successful grouting process.
To achieve effective grouting, it’s vital to maintain an optimum temperature, not exceeding 25 degrees Celsius. Enhancing grout workability can be achieved by reducing its temperature, using chilled water, or placing ice around the grout storage container.
In chilly weather, grout injection may need to be deferred, but with special precautions, it can still proceed. Prior to grouting, ensure the duct is free of frost/ice by flushing with warm water. If frost is anticipated within 48 hours post-injection, apply heat to the member for at least 48 hours to prevent grout temperature from falling below 5 degrees Celsius.
When cables are threaded post-concreting, temporarily stiffen the duct during concreting using strands, wires, reinforcement, or a rigid PVC pipe to facilitate the process.
Exercise extreme care during concreting to prevent sheathing damage. Needle vibrators should only be operated by experienced personnel to ensure safety.
To prevent duct blockages, move cables in both directions during concreting. After 3 to 4 hours, move the cables about 20 cms in both directions to minimize mortar leakage and reduce blockage risks.
Maximize the distance between cables to promote effective grouting, minimizing the chance of complications.
In stage prestressing, ensure cables tensioned in the first stage are promptly grouted. Drain water from other cables and use compressed air after grouting to prevent corrosion. For stage prestressing, keep all ducts filled with water containing 1% lime or run water until the grout has set.
Exercise caution at joints between precast members to prevent leaks from one duct to another.
Guard against water entry at vulnerable anchorage points by using an effective barrier. Fill recesses with mortar concrete and consider waterproof paint application.
Safeguard grouting vents during and after the process. Trim protruding vent portions and shield vent faces to prevent corrosion.