NASCLA Accredited Commercial General ContractorConcreteMedium
A general contractor is overseeing the installation of post-tensioned concrete slabs for a multi-story building. After the concrete has reached sufficient strength, what is the next critical step before the tensioning process can begin?
- AApplying the final curing compound to the slab surface.
- BRemoving all formwork from beneath the slab.
- CCutting all temporary bracing and shoring.
- DVerifying the concrete compressive strength meets design specifications.
Show answer & explanationAnswer & explanation
Correct answer: D. Verifying the concrete compressive strength meets design specifications.
Before applying tension to the tendons in post-tensioned concrete, it is absolutely critical to verify that the concrete has achieved the minimum specified compressive strength. Tensioning concrete that is not strong enough can lead to cracking, damage, or structural failure.
Why the other options are wrong
- A. Curing compounds are part of the curing process, which should be well underway or completed, but strength verification is the direct precursor to tensioning.
- B. While some formwork might be removed, critical shoring and bracing may remain to support the slab until full post-tensioning is achieved, and strength verification is paramount before any tensioning.
- C. Cutting all temporary bracing and shoring before tensioning could be catastrophic if the concrete hasn't reached sufficient strength to support itself and the tensioning forces.
Post-Tensioning Strength Requirement
The minimum compressive strength concrete must achieve before tendons can be stressed in a post-tensioned system.
- Typically specified in design documents.
- Verified by cylinder breaks or non-destructive testing.
- Prevents concrete damage during stressing.
Memory trick: Tendons Laid, Concrete Poured, Strength Checked, Tension Applied.