Post-Tension (PT) Slab Build & Repair Specialists
Maintain the Structural Integrity of Your Building With Post-Tension Repair Services
What Are Post-Tension Slabs?
Frequently employed in commercial construction projects, post-tension slabs are particularly useful in areas demanding:
- Thinner slabs
- Increased space between columns
- Column-free spaces
These slabs allow for higher structures, more floor height, longer spans, and more efficient use of space. High-strength steel cables, or tendons, form a vital part of post-tension concrete slabs. Installed before the concrete is poured, the cables are tensioned during the curing process, increasing the concrete’s tensile strength.
While concrete excels in compressive strength, steel boasts impressive tensile strength. Together, these materials create optimized load-bearing regions, enabling the construction of thinner, longer unsupported concrete spans. Foundations made with post-tension slabs are less likely to deform and crack.
If the construction process of post-tension slabs seems intricate, the repair process is even more complex. Many Bay Area contractors lack the necessary skills to do post-tension repairs. In the Bay Area, Airtight Construction remains the preferred contractor for post-tension concrete repairs.
Do You Have an Existing Post-Tension Slab?
Before any work is even started on a concrete slab, you must know whether it is post-tensioned. The steel cables inside these slabs bear significant pressure, so they could injure someone if inappropriately handled. If cut, the tensile forces can pull the steel tendons out of the concrete. A loss of post-tensioning strength can lead to slab failure, causing substantial structural problems.
Those installing a new post-tensioned concrete slab must know the slab’s structural origin. Because of their potential hazards, post-tensioned slabs are usually clearly marked. They will bear a warning stamp against cutting or coring This inscription is a clear post-tension slab identifier.
Older buildings may not have post-tensioning signs. These signs may be damaged, lost, or removed over time, so look for alternative signs of post-tensioning. Small, circular patches in the concrete indicate cable holes filed after the curing process. These are clear signs of such slabs. Consulting your building plans could also provide valuable information about the existence and location of post-tensioned slabs.
CAN YOU REPAIR POST-TENSION PT SLABS?
It is possible to repair post-tensioned slabs, but the concrete contractor that takes on these repairs must be qualified to do the work.
While post-tension slabs are less prone to cracks, they may need repairs or periodic maintenance over time. ATC has contractors with the experience to work with post-tensioned concrete slabs.
DO YOU NEED POST-TENSION REPAIRS?
Never repair a load-bearing concrete structure until you know whether post-tensioned slabs were used in the construction process. If you are unsure, contact ATC. We can quickly identify a post-tension slab.
Before repairing load-bearing concrete structures at your building, it’s critical to identify whether the builders used post-tension slabs during construction. If you don’t know, Airtight Construction can help.
POST-TENSIONING SYSTEM COMPONENTS
Post-tensioning produces a tougher concrete slab than the sum of its parts. The parts that make up a post-tensioned slab include:
The Ducts
Thin sheet metal pipes run through the concrete. These are the ducts. They are tied together with screw couplings, then sealed. The ducts cover the steel tendons.
THE POST-TENSIONED STEEL TENDONS
The reinforcing steel wires in the concrete slabs are called “tendons” in the industry. They reside inside the ducts. The tendons are made of prestressing steel and sealed in a protective coating. The post-tensioning tendon gives the concrete slab its strength. The typical strand sizes are 0.50 and 0.60 inches. Post-tensioned cables have an average tensile strength of 243,000 PSI. A standard rebar has a PSI of 60,000, so you can understand why the construction industry uses post-tensioning in most big projects.
Anchors
Anchors hold the post-tensioned steel tendons housed at the ends. They are also used to join one or more pieces. They help to distribute the significant force of the post-tensioning tendons to the concrete.
How Post-Tensioned Slabs Are Installed
The components—metal or plastic ducts, steel strands, and cables—are deceptively simple. Together, they create a robust post-tension magazine that can support complex structures and high external loads. From complex residential construction in challenging soil conditions to expansive parking structures and commercial buildings with above-average floor heights, post-tensioning is a versatile system. Here’s how it’s installed:
The ducts and steel strands in a post-tensioned slab are similar to the conventional rebar installation in reinforced concrete. The construction engineer chooses the pattern. Then, the components are placed into the ducts to protect them from moisture damage inside the concrete.
One end of the post-tension cable is securely anchored. A plastic pocket holds the other end in place. One tendon may be joined to another if needed. The poured concrete is added and left to set until it is about 75% of its eventual strength. This takes between 20 and 23 days in North California with moderate weather conditions.
Applying the Proper Post-Tensioning Force
The post-tension cables are stressed to the proper tensioning force when the foundations are ready. Typically, they are post-tensioned to 80% of the strand’s tensile strength. A typical steel strand – a 1/2-inch grade 270 strand, creates a force equal to 33,000 pounds of force. The steel tendon stretches slightly under tensioning and the concrete compresses.
The tendon is anchored on the other side, once the tensioning is completed. The anchor ensures a permanent mechanical connection to keep the tension and concrete compression in place. The anchor pocket is sealed once the cables are trimmed.
THE BENEFITS OF POST-TENSIONED SLABS
While the post-tensioning process is quite complex, once a concrete slab undergoes tension, it offers a construction project many benefits. Post-tension slab benefits include:
DESIGN
When post-tension slabs are employed, the amount of concrete used reduces as thinner slabs are permitted. There are also fewer columns required, increasing the usable commercial space.
REDUCED DEAD LOAD
Lighter slabs mean reduced material weight with no reinforcement lost. A post-tension slabs are up to 30% thinner than conventional concrete slabs.
CONCRETE SLAB WEIGHT DISTRIBUTION
Post-tension slabs ensure weight distribution over the entire slab rather than just the footings and piers. They are particularly useful in enclosed parking garages because fewer columns enable better space utilization.
ENHANCED RELIABILITY
Post-tension slabs are durable and less likely to crack than regular concrete slabs. This means that over time, they need less maintenance, costing less. It is easier to control deflection with post-tensioning by balancing the post-tensioning after stressing.
POST-TENSIONED SLABS IN ADVERSE CONDITIONS
Post-tensioned slabs have helped property owners build on property where the soil has poor load-bearing capacity. These slabs have enabled building in areas previously considered not viable.
