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Conrete Expert Witness: Installation of Post-Tensioning Concrete Slabs

Construction of post-tensioned concrete slabs-on-grade is very similar to using rebar (reinforcing steel) with the exception of the tensioning step. Post tensioned cables are distributed throughout the center of the concrete slab. Commonly the PT (Post Tension) cables on installed at 48 inches on center in a concrete slab.

When PT concrete slabs are used in a residential setting the concrete slabs are usually 8 inches thick and use a 300 psi concrete mix design. When the concrete slab reaches the 2000 psi strength the PT cables are stressed.

Other types of concrete structures that typically use PT concrete slabs would be parking structures, bridges where extra strength performance is required. The procedure is very similar to residential PT concrete slabs with the exception of a technique called "draped". The PT cables are placed with the low point of the cable at the midpoint. This allows the highest tension to keep the concrete held tightly together.

PT cables (tendons) placement and stressing is usually done by companies who are certified and specialize in this type of work.

When something is perceived to go wrong with a post tension concrete slab whether it be performance or appearance a qualified concrete expert consultant with experience is of the utmost importance.

Building Forensics International (BFI) has qualified, experienced consultants who have performed countless concrete litigation investigations over the past 35 years.

BFI Staff Writer ~

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