It was built in dec of 1993 by lennar and we bought it in 1998 from the original owners. Further, the risk of cracking varies between cured, uncured and reinforced concrete. Similarly, a slab will crack if too much weight is placed in one spot, or if the soil settles unevenly, bending the slab. Post tension slabs reduce settling issues this giant checker board is actually the guts of an unbonded post tension slab. The slab was decorative concrete it had been stained a dark brown, scored and polished. Post tension slab eliminating cracks and joints in.
Posttension foundation repair expert phoenix arizona. Less concrete and steel are needed for the same structural capacity and the slab stiffness is increased so that the slab is better able to resist bending caused by differential soil movements. Slab foundation repair cost what you can expect to pay. What begins as a hairline crack can become a bigger complication. Advantages of using posttensioning for your next slabonground project. A post tensioned foundation is a concrete slab foundation that is reinforced with. How to create a concrete slab foundation using the post.
Post tensioned slabs are a great tool to help reduce joints and control cracks. Second, the nonuniform thickness of fill soil under the foundation can be a major contributing factor in damaged slab foundations. Posttensioning, which is a form of prestressing, has several advantages over standard reinforcing steel rebars. Foundation is designed to resist or span over moistureinduced deformations in the soil below, while still maintaining its top surface within permissible level tolerances. Signs of foundation problems concrete slab foundations. To create a slab using this method, plastic sleevecovered steel cables are laid in a grid running in both directions. Most, but not all, cracks extended from edge to edge. Those post tension cables can break one day and go flying out and might kill someone. Posttension concrete slabs are used to create a monolithic single pour slab that is stronger than a traditional slab without. 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 of a beam. Many people dont understand how they work and the benefits. Before a posttension slab is poured, highstrength steel strands or cables, called tendons, are laid in a tight grid. The slip sheet must be installed directly under the slab between it and the bearing surface which allows the slab to move smoothly across the ground. Flexural cracks develop when the tensile strength of concrete is exceeded under load.
The first edition of the post tensioning manual was published in 1972, and as of the time of this writing 2018, they are up to their 6th edition. Post tension slabs are used to create a monolithic slab that is stronger than the typical slab and foundation that is poured in stages. Shrinkage cracks in concrete slabonground foundations are a significant. Avoiding post tension errors result in the best chance of a crackfree post tension foundation. A psc is applied with a compressive stress on the cross section in advance before the application of loading on. The posttensioning method is the best way to create stronger, more reliable concrete slabs. Examine the sloping foundation walls wherever masonry foundation materials and surfaces are visible. The dsld engineer said the cracks are normal in post tension slabs but i don. Every foundation will need some level of excavation or soil work, even if its only grading 2 an existing site for a slab. Conventional concrete slabs are limited in length and thickness. Usually a sign in the garage or stamp in the slab will indicate if your home has a post tension slab. Posttension basics how posttensioned slabs are built. A slab foundation is a large, thick slab of concrete that is typically 46 thick in the center and poured directly on the ground all at one time. In general, its more expensive to build a posttensioned slabongrade foundation than a traditional one.
Also, because aci 302 says a reasonable level of cracking is from 0% to 3%, it implies that no. Posttensioned foundations use highstrength steel to actively reinforce residential foundations to minimize cracking and increase performance. Slab foundation repair cost can be expensive and may even cause collateral damage with extra costs as well. Until the cables are stretchedelongated, they cannot provide any crack. But since a posttensioned slab does not have excess rebar to minimize and distribute cracking, restraint cracks will be large and very noticeable. What is the difference between normal slab and post.
Post tension foundation repair on this foundation repair job in phoenix arizona we had to repair about 160 linear feet of this post tension foundation. Shrinkage crack considerations for posttensioned foundations june 1, 2015 shrinkage cracks in concrete slabonground foundations are a significant public relations problem to home builders. The advantages of pt as noted in the opening page are the lack of cracking or at least very narrow cracks and the ability to span farther. The post tensioning method is the best way to create stronger, more reliable concrete slabs. Issues in posttensioned construction concrete construction.
This in turn causes wall cracks and ceiling cracks. A normal slab is basically a rcc reinforce cement concrete slab where as a post tentioned slab is the psc prestressed concret slab. They are usually reinforced with rebar or posttensioned tendons. 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. Post tension construction uses cables to reinforce the concrete and resist the movement caused by the expansive soil. This hybridisation helps achieve the formation of a much thinner slab with a longer span devoid of any columnfree spaces.
Hello all i am very concerned about the foundation of my home in houston, tx. Post tension slab is a combination of conventional slab reinforcement and additional protruding highstrength steel tendons, which are consequently subjected to tension after the concrete has set. Discovering a crack in the foundation of your home can be unsettling, as this could represent extensive damage to your homes foundation, which could mean costly repairs. The pti design procedure is used to design a slabon grade foundation that will respond elastically to forces the foundation is exposed to including those that are the consequence of. Slabs built with rebar and cables have a degree of flexibility that allow bending or flexing over a period of time. Post tensioned foundation information for the homeowner. Information about how posttensioned concrete is constructed. For this, the concrete slab is tensioned with a process called prestressing and the slab of concrete which comes out after this process is known. Some of the cracks are more than 30 feet long, and i can feel a slight difference in the rise on each side you can even. Post tension slabs are used in many parts of the country continue reading why post tension slabs are used in phoenix. Preventing cracks on posttensioned concrete slabs pro builder.
Several methods exist for prestressing concrete, with posttensioning being a very common one. Posttension basics how posttensioned slabs are built the. While its theoretically possible for an entire foundation or even building to settle or. Posttensioning is a form of prestressing concrete to provide reinforcement and overcome concretes weaknesses. Posttensioned slabs typically have less cracking and less permeability when detailed. The first edition of the posttensioning manual was published in 1972, and as of the time of this writing 2018, they are up to their 6th edition. A oneinch change in slope, if it happened after construction, would often be expected to produce vertical or stairstepped cracks in the foundation wall. Posttensioning will reduce cracking and keep any cracks that might. Post tension slabs, while an improvement over traditional slabs for our area, still experience edge curl or edge lift which is where the corners heave upwards.
How to create a concrete slab using the posttensioning method. Structural function of pt foundation acts as a buffer between the soil below and the superstructure above to prevent unacceptable deformations in superstructure. Having all the facts before you begin repairs will help you choose the right company and avoid unexpected cost and delays. Our field technicians are experts at repairing and restoring foundations of all types and on this job we discovered that some of the damage had be caused by another contractor that failed to. When the foundation cracks, it causes separation at the joints allowing water, moisture or bugs to enter a home. The cables are typically stressed tensioned within 710 days of the slab being poured, so before they are tensioned it is very common to see cracks appear in the concrete especially at areas that project like the l you. Post tension v conventional cph structural engineering. Shrinkage crack considerations for posttensioned foundations. Many say its better because hairline cracks will not form as easily.
This change was made because posttension slabs are cheaper which. It reduces or eliminates shrinkage crackingtherefore no joints, or fewer joints, are needed. Help bad cracks in post tension slab pics inspectionnews home. Many people dont understand how they work and the benefits and challenges. Over tensioning, bad prepration design layingcuring of concrete, bad structural design, bad load estimation and temperature, right.
Post tension slab eliminating cracks and joints in concrete. Now assuming all these are taken care of, no cracks should be there. The type of reinforcement used when preparing the foundation rebar or post tension cables, as well as the spacing of the rebar or cables, can affect the strength of the foundation. Long concrete slabs elevated above the ground are limited in length due to the danger of cracking.
Post tension uses steel tendons that will be tightened after the foundation has had time to cure. By the third day, i noticed a crack in the back patio, and by the fourth, there were sprawling cracks throughout the entire foundation. This method is a better way to construct a slab foundation to be more resistant to cracking and deflection. Offset cracks cause a difference of height in the concrete on either side of the crack. Posttensioned concrete slabs have been used since the 1930s, and. When we first looked at the house, we noticed a few cracks in the sheetrock around a column and one on a bumpout over a window in the kitchen. It allows slabs and other structural members to be thinner. Below are some specific types of cracks that are found in slab foundations. 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.
Correction of foundation and structural problems can be very costly and occasionally foundation cracks will be a warning sign of other structural issues with a home. 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. Things you should know about cracks in slab foundation. The post tensioning institute designed post tensioned foundations. Excavation is one of the biggest parts of the foundation building. Many houston area structural engineers feel that the inherently weaker residential posttensioned slab are at risk from two major factors first, the nonuniform weight distribution of the house puts great stress on the slab foundation. Foundation cracks happen as a result of many factors that include upheaval and settlement. Homeowners are getting crushed by flawed posttension. This tension makes the concrete slab and foundation much stronger than concrete without reinforcement and helps reduce cracking. For example, a concrete wall can support tons of weight from above, but will crack easily if pushed sideways forcing it to bend.
This was present throughout the home, no floor covering anywhere. 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 posttensioned slab than in a jointed slabonground. This stronger, thinner slab also saves money on concrete. In addition to having more movement, a post tensioned slab will have substantially less rebar than a conventional system, which is one of the main economic benefits. Since pt is simply reinforcement, there really arent any specific decorative applications related to post tensioning. Steel reinforcement bars are therefore required in the slab. Concrete can support a lot of weight in compression, but is weak in tension. Posttensioning institutes design of posttensioned slabsonground, pti design. But since a post tensioned slab does not have excess rebar to minimize and distribute cracking, restraint cracks will be large and very noticeable. They require a specific level of thickness to maintain their strength usually at least 4 inches for a slabongrade foundation. The advantages of pt as noted in the opening page are the lack of cracking or at least very narrow cracks and the ability. In most cases, this is due to an uneven seat for the slab itself, such as poorly compacted subsoil, invasive pressure from tree roots, previous concrete slabs that have not been removed, or repeated expansions and contractions in the rebar. The edges of the slab are thicker as wide as 24 in order to allow for extra strength around the perimeter. Should i get a foundation engineer to come out to look at it.
Lots of cracks in new post tension slab inspectionnews. All concrete will shrink during the curing process which lasts up to a year after the time concrete is placed in the forms. A posttensioned foundation is a concrete slab foundation that is reinforced with stranded steel cables that are tensioned after. All concrete will shrink during the curing process which lasts up to a. Posttension slab alert magnolia home inspection services. Most residential foundations in the united states are constructed with rebar or wire mesh as their reinforcement to minimize shrinkage cracks and to resist the stresses created by the. 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. Post tension slab advantages and disadvantages of post. 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. However, if you have discovered a crack in your foundation you may be wondering if all foundation cracks are the same, or if certain cracks should be more cause for concern than others. I am building a new house in north texas, it has been 17 days since the foundation was poured, i live close to the construction site, so ive been going 24 times a week.
A concrete slab is susceptible to soil expansion and contraction, which can lead to cracking. The danger posed by a crack in slab foundation depends on its direction, width, and depth. Common manifestations of distress may include slab cracks due to. Why post tension slabs are used in phoenix, gilbert, and.
We were told they were just from bad tape and float in the sheetrock. Depending on the extent of the damage, you may also have to put up the homeowners in a hotel during the repair. Costs can be higher depending on the depth of the foundation and the condition of the soil and. Home builders can avoid cracks in a posttensioned concrete slabongrade foundation by preventing certain errors made during installation. I had a call this morning from a prospective client who was concerned about cracks in the concrete foundation of the home they. A posttensioned foundation is a concrete slab foundation that is reinforced with. 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. Preventing cracks on posttensioned concrete slabs pro.
Many foundations utilize post tension cables, while others are reinforced with. A posttension slab is a slab of concrete that has been prestressed using a specific method to increase the strength of the concrete. Most concrete slab foundations were and are built with steel rebar or post tension cables for strength. 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. Cracks, cracks, cracks what is a reasonable level of cracking. At granite, we perform slab foundation repairs as well as pier and beam foundation repairs a concrete slab foundation problem needs prompt evaluation and. Post tension slab working principle, components and. My firm was recently hired to look at cracks that had developed in a posttensioned floor slabongrade.
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