I have a residential Post Tension slab that was poured about 4 weeks ago. The cable stressing was done approximately 2.5 weeks ago but the cables are not cut off and the pockets not grouted yet.
There has been some heavy rain yesterday and now the lower tendon pockets (the ones going down the beam) are completely submerged in water (see 3 picture links below). More rain is scheduled all week . I found some information on this forum about how cable corrosion is one of the main causes for cable failure. I wonder if either the cables themselves or the integrity of the teeth inside the stressing pockets could be affected.
Should I be concerned or this is just a normal/inevitable part of the construction process ?
According to the Post-Tensioning Institute, cutting of the tails should be performed as soon as possible following stressing after the engineer has approved the elongation measurements. Once the tails are cut, they should be covered with a waterproof cap, ideally within 24 hours, but not exceeding 96 hours and grout filled as soon as possible thereafter. These pockets will need to be thoroughly cleaned before they are grouted.
“Under no circumstances should the grout pockets be left exposed for an extended period of time.”
My question is why is a residential slab using post tensioning cables? Especially because it’s sitting on the ground? Seems like some engineer was paid very well for this . That being said, rain will not harm those cables, as all concrete will contain, and absorb massive amounts of water during it’s lifespan.
Post Tension Cable (PTC) reinforced slabs are very common in residential construction, especially here where the vast majority are PTC reinforced. Rain and mud can harm those cables. The longer they sit in water the more likely they are to start corroding cables and the cable wedges holding them after tensioning. As for the mud it can interfere with proper grouting of the PTC former pocket opening if it is not properly cleaned.
I’ve seen my share of corroded cables and ungrouted openings on new construction both after they should have been grouted and at final inspections. I’ve even encountered my share of cables that have not been cut off. At the pre-pour inspection I’ve seen way more improper PTC placements than I should. What we see here is unfortunately common in Texas.
Thank you for the answers. I’m located in Houston, TX where Post Tension slab-on grade is pretty much the standard for most residential construction due to the expansive soils we have here.
Those pictures were from Monday and it has rained the whole week, so I’m sure that by now those pockets are completely covered in mud.
What is the best procedure after the rain stops and it gets dry? I assume, cut the cables, clean the remaining parts sticking out of the concrete and clean the pockets? Any specific products or best practice recommendations?
Best practice was not to allow that to occur in the first place. Now it will be up to the foundation company to determine best how to properly clean the pockets before sealing them. During the cleaning, and before sealing, they should also review them for any excess corrosion. With the grouting of the pockets (filling in) they will use a non-shrink grout applicable for this use. Of importance for this is to watch that the grout is not deteriorating/detaching later which can indicate possible dirty pockets when it was applied.
BTW Chuck is in your neck of the woods and a good Inspector as well! Have you lined up Inspector(s) for successive phases of construction?
I am unfortunately just barely outside of Chuck’s service area (by less than 1 mile) but I guess it doesn’t hurt to send an e-mail again and see if he could come do our pre-cover inspection and then the very final inspection.