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Post-tensioned slab vs conventionally reinforced rebar slab: which to spec
Post-tensioning buys longer spans, thinner sections, and fewer joints; rebar is simpler to build and cut into later.
Short answer
Pick post-tensioning when the slab has to span far, stay thin, deflect little, and crack little, and you can commit to the trained crew, the stressing sequence, and the scan-before-cut discipline for the life of the slab. Pick a conventionally reinforced rebar slab when the design is straightforward, the crew is general concrete, and someone will drill or core into the floor later. The single biggest deciding factor is how the slab manages tension: PT precompresses the concrete so service loads have to overcome built-in compression before the section sees net tension, while a rebar slab lets it crack and relies on steel to hold the crack tight.
Post-tensioned slab vs Conventionally reinforced rebar slab: side by side
| Factor | Post-tensioned slab | Conventionally reinforced rebar slab |
|---|---|---|
| How it resists tension | Tendons squeeze the slab into compression, so cracks stay closed and it spans farther on less depth | Concrete cracks in tension; rebar holds the crack tight but does not prevent it |
| Upfront cost / complexity | Higher: specialty PT crew, calibrated jacks, stressing schedule, special inspection | Lower: general concrete crew, standard bar or welded wire on chairs |
| Section thickness / span | Thinner slab, longer spans, less deflection for the same load | Thicker to carry the same span; deflection and cracking limit reach |
| Joints | Runs far between joints; large panels via pour strips, few or no contraction joints | Close contraction joints, commonly about 24 to 36 times slab thickness |
| Cutting / coring later | Never blind: scan and locate every hole; a cut live tendon fires the strand and dumps prestress | Drill, core, and saw freely; cutting a bar is a local, non-catastrophic event |
| Demolition / renovation | Engineered detensioning plan and specialty contractor; every tendon is a loaded spring | Conventional demolition; saw and break like ordinary reinforced concrete |
| Long-term failure mode | Corrosion of stressed steel; depends on continuous sheath/grout, sealed pockets, encapsulated anchors | Corrosion of rebar at inadequate cover; generally more forgiving of a local hit |
| Verification / QA | Elongation proves force, accepted near plus or minus 7 percent of calculated; witnessed stressing record | Bar size, spacing, and position on chairs; steel on the ground controls nothing |
| Best use | Long-span parking decks, transfer slabs, big flat plates, crack-sensitive floors | Typical slabs on grade, residential and light-commercial floors, jobs needing future penetrations |
Which should you pick?
Choose Post-tensioned slab when
- The slab must span far or stay thin where a conventional section would be too deep or too cracked (parking decks, transfer slabs, flat plates)
- Crack control and low deflection are performance drivers and you want few or no contraction joints
- A trained PT crew, calibrated stressing equipment, and code-required special inspection are in place
- The layout is fixed and future penetrations will be scanned and located before any cut
Choose Conventionally reinforced rebar slab when
- The slab is a standard slab on grade sized by load, subgrade stiffness, and flexural strength
- A general concrete crew is doing the work without specialty stressing equipment or inspection
- People will drill, core, or anchor into the floor later and you want that to be routine
- Future demolition or renovation should stay simple, with no detensioning plan required
Bottom line
It depends on span, load, and who touches the slab over its life. If the structure demands long spans, thin sections, low deflection, and tight crack control, post-tensioning earns its higher first cost and its stricter field discipline. If the slab is a conventional floor where a general crew builds it and someone will core into it later, a reinforced rebar slab is simpler, cheaper, and far more forgiving to cut and demolish. Both are governed by the structural drawings and the engineer of record, and a slab on grade of either type still lives or dies on the subgrade and the joints, not the concrete strength.
FAQ
Is a post-tensioned slab better than a rebar slab?
Neither is universally better. Post-tensioning precompresses the concrete so it spans farther on less depth, deflects less, and keeps cracks closed, which suits long-span decks and thin flat plates. A conventionally reinforced rebar slab is simpler to build, easier to cut into later, and forgiving in demolition. The load, the span, and the engineer's design decide.
Can you drill or core into a post-tensioned slab like a rebar slab?
Not the same way. You can core a PT slab, but never blind: scan and locate the tendons first, every hole, every time. Each tendon can hold roughly 24,000 to 33,000 pounds, and on an unbonded system cutting one fires the strand out of the slab and dumps the prestress along its whole length. A rebar slab has no stored force, so cutting a bar is a local event.
Does post-tensioning replace rebar and control joints?
It changes the strategy. Post-tensioning uses tensioned strand to squeeze the slab into compression so it resists cracking and can run with large panels or few contraction joints, where a plain slab needs closely spaced joints. PT slabs still use reinforcement in places like anchorage zones and pour strips, and the joint and stressing sequence come from the PT design.