It’s no secret why builders use post-tensioning systems in their construction projects; these systems are critical to strengthening concrete used in modern large-scale building projects. Post-tensioning involves placing prestressed steel “tendons” that are embedded in the concrete and tightened once the concrete hardens. The additional stress of tightening compresses the concrete into its strongest state, ensuring it can support the external service loads (weight) imposed by the structure. The same strength-gaining principle 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 pre-stressing strategies and techniques to strengthen and reinforce concrete in the 1950s. The pre-stressing 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 pre-stressing, 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 this building method is now embraced 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. These unstable soil conditions may occur where projects are sited in or near marshes, swamps, and lake areas. The post-tensioning process helps residential homes and commercial buildings achieve greater load-bearing strength. Post-tension slabs are more durable and stable than traditional concrete slabs that lack the reinforcement of steel cables.
Why Use Post-Tension Slabs?
Conventional 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 frequently 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 that using 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 provide 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 systems and design them to prevent any water seepage into the foundation that can lead to cracks.
Good Things Aren’t Cheap & Cheap Things Aren’t Good
Correctly laying the foundation of a post-tension slab requires professional workers, quality materials, and expert knowledge to understand the job’s complexity. Today, the Post-Tensioning Institute provides a training and certification program for installers, inspectors, engineers, and others directly involved in post-tensioned concrete construction. 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 allowing the construction of crack-free tennis courts, smooth parking garage surfaces, 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 slabs, 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 that’s worth it in the long run.
Weight Reduction
A lighter, yet stronger post-tensioned concrete slab 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.
Risk Minimization
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 will be held together and will not spread as quickly as those on traditional concrete foundation slabs. Therefore, post-tensioned slabs provide a more durable solution.
Look To The Experts When It Comes To Building Repair Services
Commercial and residential structures require rational planning and maintenance. 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.
Whether your building has a traditional concrete slab or a reinforced post-tensioned slab, building owners need to take steps to maintain the structure’s integrity. Movement, corrosion factors, and exposure can cause damage to the cables used in post-tension slabs, and exposed cables can pose a safety hazard to pedestrians. Valcourt has years of experience in repairing post-tension cables to restore the integrity of the concrete.
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 Valcourt Building Services today!