When looking to obtain the biggest bang for your concrete buck, you can’t go wrong with post tension technology. From a simple slab on ground project to the construction of a complex system of freeway interchanges, post tensioning your concrete elements can provide superior strength with less material.
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Tensioning your concrete grants it the ability to better counter expected service loads by way of internal compressive force. A great way to envision the compressive forces of post tensioning is to imagine moving several wood boards from one place to another. You could stack them and allow gravity to hold them together as you pick them up, or you could clamp them horizontally until the force of compression holds them together for vertical lifting.
Two methods serve the purpose of adding internal tension to a concrete structure depending on the site of fabrication.
This method works well if the concrete is pre-fabricated and brought to the site for positioning. Steel tendons are tensioned prior to the pour. Once the concrete, poured into form around the tendons, has reached the required strength, the tension is released and the tendons act to regain their original length which creates the effect of pulling the outer concrete towards the center.
If the construction design calls for on-site concrete pouring, technicians place plastic or thin-walled metal tubes in a parabolic (wavy or curved) pattern around which the concrete is poured. The steel tendons are then run through the tubes and mechanically pulled until stretched about eight inches in a hundred feet, at which point they are anchored to the outer edge of the slab, compressing it inward as the tendons try to return to their former lengths.
Post tensioning concrete works well everywhere with almost no disadvantages. In fact, the potential for corrosion, present with any non-stainless steel product, comprises the bulk of any drawback. Since grease and encapsulated anchors can inhibit rust on channeled tendons, using pre-stressed or post tension concrete affords many benefits with no real shortcomings.
Colorado, as a proud member of the Southwestern states, hosts expanding or shifting soils in many areas which can wreak havoc on foundations and roads. However, by using post tension concrete, unstable ground poses far less of a threat to your projects than other concrete systems.
While Colorado has experienced few strong earthquakes for eons, an active fault line stretches the length of the front range and can produce a tremor from time to time. Pre-stressed and post tensioned concrete have both the compressive and tensile strength to better maintain cohesion during earthquakes.
Tensioned concrete enjoys greater durability and overall strength than normal reinforced concrete. You can design longer unsupported spans with thinner pours. This makes it great for auditoriums, parking garages, bridges, roofs and custom architectural designs.
Because the internal compressive force holds the concrete together better than rebar alone, it reduces shrinking. Joints can be fewer and farther between. Furthermore, any cracks that develop tend to be held tight. This helps prevent the water intrusion that can decompose concrete through Colorado’s yearly freeze-thaw cycles.
Post tensioning means less concrete and rebar must be used to obtain the same strength and durability. You may need only 80 percent of the concrete and only 25 to 40 percent of the rebar otherwise essential for your project. While post tensioning does require special technicians to properly engineer and install the steel tendons, the cost can be offset by the reduction in material costs.
Needless to say, if you use less material, you can also shorten your building timeline.
Pre-stressing and post tensioning involve specifically trained, certified and experienced personnel. This is not something that can be accomplished by an ordinary concrete crew. Barton Supply provides not only the necessary post tension products, but also the expertise and on-site service. Please call us for more information about post tension concrete construction.
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.
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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.
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 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.
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.
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.
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.
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.
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.
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.
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.
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 Valcourt Building Services today!
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