Contrary to what your builder said, PT Foundation Systems can and do experience failures.
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Post Tension Foundation Crack


Post Tension Foundation Failures


I often get asked about Post Tension foundation system. From the information they learn from the home building community, homeowners are often surprised to learn there are indeed performance problems associated with these systems. From a soil standpoint, the uniform thickness Post Tension system almost exclusively installed in Arizona is very vulnerable to heave.

Aside from the typical heave problem that is common with Post Tensioned foundations, there are a few other problems. One in particular we are starting to run into regularly… corrosion of the system components.

Many Arizona homes are built on former farmlands. These soils usually have high amounts of sulfates and chlorides as a result of the fertilization processes. These mineral deposits in the soil when moisture is accumulated by a variety of sources and can carry these minerals into the concrete it is in contact with.  See my earlier post on moisture accumulation under foundations HERE.  

These minerals when leached into the concrete accelerate corrosion. They promote the chloride ion exchange as described in an earlier post (click HERE to read my earlier blog entry). This is a vicious cycle that results in corrosion of the cables and end points that are made of steel. Although the cables themselves are covered in plastic sheathing, unless they have encapsulated end points, they can still be vulnerable. As the cables and end points corrode, they increase in volume cracking the concrete and become weaker. This is exacerbated by the 28,000 lbs of tension of the cables, increasing the pressure on cracking.

As the components continue to corrode and continue to crack and spall the concrete, the tension on the cables can rapidly tear apart the concrete. When this happens the concrete can have catastrophic failure. Sometimes resulting in failure to support the structure. My next post will describe a project that is like several others along these lines!

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Glen K. Copeland wrote on March 1st, 2018 11:03:13am
Is the photo you show on Post Tension Foundation Failures a photo of a crack at the area between the PT slab and the monolithically cast turn-dow. Are you being more movement for PT slabs that have no to minimal turn-downs or deeper turn-downs.