What Are Post-Tension Slabs & Why Are They Used?

It’s no secret why builders use post-tensioning systems in their construction; these systems are critical to strengthening concrete used in modern large-scale building projects. The same argument applies to post-tension slabs—a method used when pouring the slab foundation in commercial or residential construction. This article further explores post-tension slabs and some of the advantages and challenges of their usage in construction projects. 

What are Post-Tension Slabs?

The concrete industry started experimenting with strategies and techniques to strengthen and reinforce concrete in the 1950s. The prestressing concept, now a standard in residential and commercial building construction, involves using a steel cable or tendon to squeeze and compress concrete before the concrete endures a structural load. As the construction industry continued refining its techniques to standardize prestressing, most builders eventually began using post-tensioning techniques for reinforced concrete slab foundations. The Federal Housing Administration officially endorsed the use of post-tensioned slabs in 1969, and the building method is now embraced and co-opted as the preferred method for builders.

Post-tensioned slabs contain a tendon, or steel cable, that runs crisscrossed throughout the center of the slab after the concrete has already hardened. As the poured concrete dries, the post-tensioned cables stretch and tighten, which applies a significant force to the concrete slab. This technique strengthens and compresses the concrete, which helps reduce cracking and structural instability caused by unstable soil conditions in marshes, swamps, and lake areas. The process helps residential homes and commercial buildings achieve greater load-bearing strength. Post-tension slabs are more durable and stable than traditional slabs that lack the reinforcement of steel cables.

Why Use Post-Tension Slabs?

Concrete slabs have inherent structural weaknesses; they are especially susceptible to expansion and contraction due to seasonal fluctuations and changing temperatures. Anyone that has experienced winter knows that thawing temperatures usually lead to potholes, broken water mains, and cracks in the pavement. Concrete slabs are no exception. The swelling and contraction of soils based on their contact with water is another element that adversely affects the integrity of concrete slabs. Poor and unstable soils found in Southwestern states and Mexico lead to issues with soil expansion, making it difficult for builders to lay concrete slabs.

Builders depend on post-tension slabs to reduce the risks of cracking, contraction, and soil expansion and strengthen the foundation’s structural integrity.

Post-Tension Slabs: Potential Challenges

Post-tension slabs are stronger than traditional concrete slabs; however, that does not necessarily mean a post-tension slab is without challenges. Read on to learn more about builders’ challenges when using post-tensioned slabs.

Long-Term Planning 

Post-tensioned slabs are an excellent foundation for a new structure, but builders must plan accordingly for proper drainage. Gutters, downspouts, roof pitches, and balconies redirect rainfall. Builders need to be aware of the location of drainage as it can seep into the foundation and lead to cracks.

Good Things Aren’t Cheap & Cheap Things Aren’t Good

Laying the foundation of a post-tension slab requires professional workers, quality materials, and expert knowledge to understand the job’s complexity. In the building and construction industry, it’s essential to research the service provider and contractors you partner with before signing a contract.

Check the Blueprints, Again

Since post-tension slabs require the addition of steel tendons to strengthen and reinforce the concrete, the tendons must precisely align as shown on the blueprints. Improper tendon locations can cause uplifting, as the tendon applies more force than the weight of the concrete. As a result, the concrete might be physically lifting the slab.

The Advantages of Post-Tension Slabs

Aside from producing crack-free tennis courts, smooth parking garages, and a secure foundation for someone’s new home, post-tension slabs offer builders an array of advantages compared to traditional concrete slabs. Here are a few of the major benefits.

Cost Savings

Post-tensioned slabs require less concrete than traditional ones, saving builders money. Post-tensioned slabs are an investment that helps homeowners reduce the risks of concrete contraction and cracks, which inevitably costs money to repair. That’s why post-tensioned slabs are an initial investment worth it in the long run.

Shed Some Weight

A lighter yet stronger slab of concrete allows builders to design their structure with less material and overall surface space, providing more space to build supporting pillars, walls, columns, and beams. Post-tensioned slabs are also thinner, giving builders more creative freedom when designing floors.

Minimize Risks

No matter how much planning goes into a construction project, things happen, and the idea for builders is to minimize risks. Post-tensioned slabs may help prevent cracks from forming, but concrete is not immune to the elements. The good news is that if cracks form on post-tensioned slabs, they are held together and do not spread as quickly as those on traditional foundation slabs. Therefore, post-tensioned slabs are a more durable solution.

Look to the Experts when it comes to Building Repair Services

Commercial and residential structures require rational planning and maintenance. Whether your building has a traditional concrete slab or a reinforced post-tensioned slab, building owners need to maintain the structure’s integrity. That’s why across the United States, owners and property managers rely on Valcourt as their trusted partner to protect their investments. Whether it’s waterproofing, restoration, or other commercial building services, Valcourt offers over 35 years of experience protecting properties from the elements. Contact A1Orange Building Services today!

Post Tension Repair: Common Concrete Problems & Myths of Post Tensioning Debunked

As early as the 1950s, a method of improving construction practices and reinforcing concrete emerged in the United States. The post-tensioning (or post-stressing) concrete method provides outstanding durability, increased design flexibility, and improved safety. This method also came the need for specialized concrete restoration and repair services. 

Many modern office buildings, commercial and residential towers, parking structures, and facilities rely on post-tensioned concrete. Keeping up with commercial building repair is critical as neglected upkeep leads to catastrophic building collapses, much like the Surfside Condo collapse in Florida in 2021- an event that claimed the lives of nearly 100 people. Due to the rising demand for post-tensioning, planning repair work on post-tension slabs and components is increasingly vital for commercial building maintenance. Commercial building managers and facility maintenance teams cannot afford to overlook understanding how to spot issues quickly and handle post-tension repair needs.

What is Post Tension Repair?

Post-tensioning is a highly specialized and advanced means for reinforcing concrete, making it more suitable for commercial applications, heavy load-bearing designs, and larger building structures. According to the Federal Highway Administration, “the tensile strength of concrete is only about 10% of its compressive strength.” As a result, plain concrete members are likely to crack when loaded. However, embedding reinforced steel into the concrete members helps them accept tensile stresses that plain concrete cannot. Reinforced steel is selected assuming that the tensile zone of the concrete carries no load and that tensile stresses are resisted only by tensile forces in the reinforcing bars. The resulting reinforced concrete members may crack but can effectively maintain the design loads.

The forces within post-tensioning tendons demand that owners, designers, and contractors who maintain these structures understand the dos and don’ts of repair and maintenance to keep their structures safe. 

Highly advanced design elements require specialized skills and a high level of technical knowledge to ensure the structure’s safety and that of individuals working around the structure. Properly implementing a post-tensioning system repair plan is vital to maximizing longevity and ensuring the structure remains safe and stable for as long as possible. Ultimately, post-tension repair work focuses on identifying and fixing issues involving concrete in slabs, support beams, columns, foundations, and more.

How Do You Know if Your Building Needs Post Tension Repair?

Post-tension concrete repair should begin as soon as issues become apparent. The longer the delay in repair, the more expensive the repairs will become. Concrete is popular because of its durability, but it’s also susceptible to cracks, chipping, and other issues. Routine checks and inspections are critical for building maintenance and upkeep if a commercial concrete structure utilizes post-tensioning.

Inspections of post-tensioned concrete structures should include the following regularly:

  • Visual inspection of facilities and critical problems areas – joints, support junctions, and large expanses
  • PT Corrosion Evaluation and regular moisture testing, especially in areas with high water intrusion risks
  • Chloride analysis of PT grout to avoid long-term exposure and corrosion of steel cables and casings
  • PH and chemical testing of structure to ensure no oxidation and to monitor accumulation on surfaces
  • Petrographic analysis, Scanning Electron Microscopy examination, and other tech-backed inspections
  • Cable Break Detection services to monitor tension support and durability on an ongoing basis
  • Regular feedback and communication between team members and staff about noted issues or concerns 

While it is a valuable material and commodity for commercial construction, post-tension concrete requires a more specialized approach to maintenance and upkeep. Working with post-tension repair contractors and finding a repair management company specializing in post-tension concrete services are critical to keeping buildings in good standing. Working with industry experts makes the process easier, whether it concerns repairing a post-tension slab or maintaining building components correctly.

Common Concrete Challenges Requiring Post-Tension Repair

All buildings degrade and break down over time, but there are a few potential issues that can affect post-tension concrete more than others. Using post-tension repair services can help reduce common concrete problems and make commercial building services easier to manage. Some common issue items include:

  • Cracks in the concrete foundation or support structures
  • Uneven floors and shifting concrete in large expanse areas
  • Cracking grout lines or signs of separating and peeling concrete
  • Leaning chimneys or other structures supported by the post-tensioned system
  • Loose or damaged components expose the tensioning system
  • Chipping of concrete in critical support and expanse areas
  • Signs of flaking, rusting or breaking down of concrete structures
  • Advanced age of the structure or long periods since the last inspection or repair work

Building owners should have these areas periodically examined periodically by a qualified structural engineer for post-tension repair. The condition survey will check for potential problem areas, note any procession of damage, make recommendations for repair and maintenance, and work with your team to start the necessary steps to address issues.

What Causes Degradation in Post-Tensioned Structures?

Maintenance and upkeep are vital for a post-tensioned structure’s continued service and longevity. Structural deterioration due to exposure to moisture, corrosive elements, and the simple passage of time can lead to a loss of structural integrity, causing issues with structural safety and stability.

Most instances of repair and maintenance work on post-tensioned structures come down to one of the following concerns, all of which a post-tension repair company can assist with:

  • Voids and air pockets within the concrete structures create weak points
  • Trapped moisture between strands and between wires within the structure
  • Water seeping into the structure through cracks in building envelope seals
  • Grout segregation, deterioration, or breakdown goes unchecked
  • Water penetration from anchorage pockets, joints, cracks, flashing, and seals
  • Water penetration due to floods, roof damage, plumbing issues, or leaky windows
  • Chloride-contaminated grout and exposure to other corrosive chemicals
  • Dissimilar grouts used in the same tendon create chemical reactions
  • Improper installation of post-tension cables and anchors during construction
  • Poor maintenance and upkeep early on in the lifespan of the structure
  • Damages and concerns left unchecked and unaddressed for too long

Like all building materials, post-tensions concrete offers advanced benefits and features, but it is not perfect and still requires routine checks and maintenance work. Keeping up with this is vital to commercial concrete building construction and upkeep.

Debunking Myths Around Post-Tensioning and Repair

Post-tension concrete’s popularity also comes with various myths that can cloud judgments and impact maintenance protocols. The following are some of the most common myths that repair experts encounter when working with commercial maintenance teams.

MYTH: It is difficult to cut holes and add features to post-tensions slabs and structures.

REALITY: Post-tensioned structures are just as doable and can be easily customized. In this regard, there is not much difference between typical concrete structures and post-tension concrete. Tendon layouts can allow for future aesthetics or building repair needs.

MYTH: Parking garages and structures are more expensive when made with post-tensioning.

REALITY: Keeping long-term budgets in mind when comparing material and construction costs is crucial. While upfront costs for a post-tensioned system might be more, it will require less maintenance and upkeep and save management money in the long run.

MYTH: Post-tensioned buildings experience more shortening than they would otherwise. 

REALITY: All concrete will experience some degree of shortening due to the nature of concrete building materials. It is inherent in the curing process as it will shrink, and there is no stopping it. Contractors control building geometry, and post-tensioning is no more prone to shrinking.

MYTH: Post-tensioning is not possible with below-grade applications.

REALITY: Below-grade applications are structures located below the main building. Post-tensioning concrete can be used in these cases quickly. Benefits of below-grade applications include less cracking, improved durability, thinner slabs, and easier excavation. 

MYTH: It is always better to use more post-tensioning.

REALITY: Post-Tensioning is no compensation for sloppy design and is no cure-all. Excessive use can lead to overbalancing effects -deflection problems, cracking, shifting, bowing, or severe blowouts, all of which can be costly to fix. Too much of a good thing can be a bad thing.

Why Working with A Commercial Building Services Provider for Post Tension Repair

Ensuring commercial building repair and proper maintenance of post-tension concrete structures remains an essential part of facility management. Building owners and managers cannot afford to overlook even minor issues with structural integrity. Failure can lead to catastrophic building collapse, loss of life, and severe property damage. With post-tensioned systems showing up everywhere, repair work on the systems has become increasingly vital for commercial building maintenance. Contact The A1orange Group today to learn more and find support with a leading post-tension company.