The foundation in question was a posttension cable reinforced foundation as opposed to a foundation which is reinforced with steel rebar see the typical photograph in this article. Intermittent concrete keys were specified to transfer slab shear forces from one side of the construction joint to the other. Often, it is recommended to reinforce the concrete slab through a process called posttensioning. Several methods exist for prestressing concrete, with. Over tensioning, bad prepration design layingcuring of concrete, bad structural design, bad load estimation and temperature, right.
As a result, even though post tensioning is meant to help prevent a slab from cracking, the slab can still crack if the tensioning process is done incorrectly. First, slab and beam cracking is a common concern and an indication that attention and repairs are needed. My firm was recently hired to look at cracks that had developed in a posttensioned floor slabongrade. Posttension basics how posttensioned slabs are built the. I had a call this morning from a prospective client who was concerned about cracks in the concrete foundation of the home they. Defects such as slab cracks can be costly to repair after construction. A posttension slab is a slab of concrete that has been prestressed using a specific method to increase the strength of the concrete. Bonded and unbounded posttension structures present unique challenges for maintenance and repair. For example, a concrete wall can support tons of weight from above, but will crack easily if. The advantages of pt as noted in the opening page are the lack of cracking or at least very. This means the foundation is reinforced by cables laid in a grid arrangement and tensioned after the concrete cures sufficiently with the intent to create compression in the foundation concrete to resist cracking.
Post tension slabs are a form of prestressed slabs which means they are compressed prior to use so that the slabs. Posttensioning institute education pt applications repair. Information about how posttensioned concrete is constructed. The cost of repairing concrete slab foundations varies depending on the extent of the damage. This method is a better way to construct a slab foundation to be more resistant to cracking and deflection.
Post tensioning steel cables or rods are added to exterior of concrete beams. Tulsa home builders 918 6885660 can a post tension slab have. The best way to ensure this doesnt happen is to educate your construction teams on the best practices for designing and constructing post tensioned slabs. Sounds like normal concrete shrinkagecuring cracks, even for a posttension slab. How to create a concrete slab using the posttensioning method. Over tensioning, bad prepration design laying curing of concrete, bad structural design, bad load estimation.
Stem wall repair contractors, fix, repair, patch, spalling, oxidized rebar, waterproof, and paint all stem wall. Liftechs crack repair and sealant service is an affordable and effective way to protect and preserve your concrete for many more years, before replacement is your only option. Now assuming all these are taken care of, no cracks should be there. Epoxy injection high strength epoxy is injected into cracks in concrete to weld back concrete to monolithic properties. Slab crack concrete repair colorado concrete work liftech. For instance, sps crack injection repair is most effective in restoring concrete. Posttensioning methods for reinforcing concrete the.
Post tension repair schnell contractors concrete repair. How to evaluate and manage posttensioned concrete page. Post tensioning is a technique for reinforcing concrete. Post tension slab although concrete is a strong material for construction, it is not resistant to breakdown especially where longer concrete slabs are required like in a bridge or a length. Concrete repairman llc foundations, stem walls, and. Sealing cracks in posttensioned deck concrete construction. The structural slab was not waterproofed before putting on the topping. Shrinkage cracks in concrete slabonground foundations are a significant.
Whats the solution of cracks in the post tensioning slab. The posttensioning method is the best way to create stronger, more reliable concrete slabs. A posttensioned foundation is a concrete slab foundation that is reinforced with stranded. Post tension pt tendon systems are primarily used for large slab construction projects. Once the concreted has cured dried for 57 days, the. Once the slab cures, qualified personnel apply tension and grout the cables. The use of post tension tendons allows the engineer to design for larger slab construction spans typically used in parking structures or high rise.
Shortening crack mitigation crack evaluation tn451010616. Tunneling versus busting through slab for plumbing repairs. Preventing cracks on posttensioned concrete slabs pro. Until the cables are stretchedelongated, they cannot provide any crack. Whether the repair is to a beam, slab, or other structural member other factors, such as budget the following sections discuss some of the options for repair and replacement of posttensioning tendons. Posttensioned concrete repair posttensioned concrete. Most concrete slab foundations were and are built with steel rebar or post tension cables for strength.
Typical cost of repairing concrete slab foundations. The lobby level of the garage has a 4inch topping on a 10inch posttensioned slab with posttensioned beams spaced at 27 feet. With around 30,000 pounds of inward pressure, posttension cables compress concrete, enabling it to better resist cracks caused by soil conditions. Significant overbalancing of the weight of the concrete with post tensioning can actually lift and crack the slab. Post tensioning repair robinson parking garage structural. Structure magazine posttensioned concrete construction. How to repair shrinkage cracks on a concrete slab youtube. Post tension slab eliminating cracks and joints in concrete. Post tensioned foundation information for the homeowner. Since the early 1950s, post tension tendons have been used in the design of concrete structures. Many people dont understand how they work and the benefits. Post tensioned slabs are a great tool to help reduce joints and control cracks. Preventing cracks on posttensioned concrete slabs pro builder.
When a construction team properly understands and follows the correct procedures for repair and rebar. Slab foundation repair cost what you can expect to pay. To adhere the port to the concrete, apply a small amount of epoxy around the bottom of the port base. Repairing damaged concrete slab post tension repair and. An understanding of the use and operation of post tension. Although aalami and barth were conservative in estimating the lineal ft of restraining cracks requiring repair, it seems difficult to believe that there are 4 times more lineal feet of cracking in a post. Shrinkage crack considerations for posttensioned foundations. Thus, when the posttension cable tension is applied to the edges of the slab, the inward side of each grade beam. Concrete repairman llc foundation repair glendale arizona. Posttensioning tendons, which are prestressing steel cables inside plastic ducts or sleeves, are positioned in the forms before the concrete is placed. Advantages of using posttensioning for your next repair, rehabilitation and. For these reasons, the average cost to repair cracks in a slab foundation ranges. Another important reason why posttensioned structured cracks is the. Having all the facts before you begin repairs will help you choose the right.
Place the port at one end of the crack and repeat until the entire crack is ported. If there arent many cracks in the posttensioned slab and you have good reason to believe that there wont be many more, you might successfully seal them from. There are a wide variety of reasons for utilizing post tension slabs versus conventional slabs. In addition to having more movement, a posttensioned slab will have substantially less rebar than a conventional system, which is one of the main economic benefits.
Concrete can support a lot of weight in compression, but is weak in tension. The robinson center parking garage, located in downtown little rock, was showing signs of deterioration within the slabs and beams. Campbell said that home foundations with steel rebar in the concrete slab would generally serve the homeowner 25 to 30 years before accumulated stresses from soil movement or other factors did any. Any post tension slab inspectors out there i am building a new home in longview, texas, and they poured our post tension slab 7 days ago. Shrinkage cracks in poured concrete are easily recognizable and can be distinguished from other types of cracks that occur later in the life of a foundation wall or floor slab the photograph of cracks above. Lots of cracks in new post tension slab inspectionnews. Cracks, cracks, cracks what is a reasonable level of cracking. Posttension cables are steel wires inserted into plastic sheathing laid in place while pouring the concrete slab. The foundation in question was a post tension cable reinforced foundation as opposed to a foundation which is reinforced with steel rebar see the typical photograph in this article. The lobby level of the garage has a 4inch topping on a 10inch post tensioned slab with post tensioned beams spaced at 27 feet. Because all shaw homes slabs are posttension concrete, cracks are. Posttensioning is a method of reinforcing strengthening concrete or other materials with highstrength steel strands or bars, typically referred to as tendons. Signs of foundation problems concrete slab foundations. Homeowners are getting crushed by flawed posttension.
Usually a sign in the garage or stamp in the slab will indicate if your home has a post tension slab. Unlike conventional inactive rebar, which only helps keep the slab intact after. Removing the interior floor finishes to make repairs to the slab is both expensive and time. As part of a proactive effort, the owner selected the. A post tension slab is a concrete slab or foundation that contains high tension cables running through the concrete to increase strength and reduce cracking typically in areas with poor soil conditions. These downward extensions act as concrete cleats that are built in trenches dug into the soil. Because of heavy traffic the topping slab is now cracking and allowing water to pass through and become trapped above the structural slab. By using posttensioned tendons to compress the concrete, the formation of visible shrinkage cracks can be greatly. Slab foundation repair terms structured foundation. Slab foundation repair cost can be expensive and may even cause collateral damage with extra costs as well. Post tensioning actively loads the structure one of the main differences between a post tensioned beam or slab and a typical reinforced concrete element is that the strands drape or profile inside the concrete their. By the third day, i noticed a crack in the back patio. Flexural cracks develop when the tensile strength of concrete is exceeded under load.
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