Post tension concrete cracking

Posttension parking garage repair structural technologies. B9472, is staffed with an experienced team of skilled professionals who undertake all aspects of structural concrete rehabilitation, restoration, repair and reinforcement for a variety of commercial and industrial buildings, parking structures and slabs. Known cases add significant amounts of rebar to attempt to better control the cracking. Q recently we completed construction of a hotel parking garage. A seven level parking garage located in milwaukee, wisconsin was in need of significant repair. The tendon profile, which is typically in a concave shape. Since pt is simply reinforcement, there really arent any specific decorative applications related to post tensioning. Post tensioning is a method of reinforcing strengthening concrete or other materials with highstrength steel strands or bars, typically referred to as tendons. Posttensioned concrete courts provide many advantages, the design of the system will greatly decrease the chances for cracking, settling and ponding. Drying shrinkage is caused by the loss of moisture from the cement paste constituent, which can shrink by as much as 1 percent. Post tensioned tennis court cracking concrete engineering.

The use and proper construction of slip details is therefore critical for the performance and aesthetics of post tensioned concrete. The tensile face indicates what portion of the beam requires reinforcing for strength. Avoiding post tension errors which result in cracking. It is very questionable of how much of the post tension compression forces actually go into the concrete slab and how much is in the restraint elements i.

The materials used to post tension concrete members are ultrahighstrength steel strands and bars. As a result, its best to construct a posttensioned slab, giving the slab the strength to resist stresses caused by the soil. Pt cables are used to compress the concrete and reduce cracking, whereas rebar is dormant until the concrete cracks. Post tension v conventional cph structural engineering, inc. Resistant to weather fluctuations and extreme conditions. Pretensioning is accomplished by stressing wires or strands, called tendons, to predetermined amount by stretching them between two anchorages prior to placing concrete as shown in fig. Fortunately, aggregate provides internal restraint that reduces the magnitude of this volume change to about 0. Post tension concrete dubaiuae, cairoegypt and riyadh. Post tension slab eliminating cracks and joints in concrete. Nawy the stateoftheart in the evaluation of the flexural crack width development and crack control of macrocracks is described. Also, because aci 302 says a reasonable level of cracking is from 0% to 3%, it implies that no cracking, 0%, is a possible, reasonable level. Avoiding posttension errors which result in cracking.

Post tension services of texas ptst is a full service post tensioning company based in dallas. One of the main differences between a posttensioned beam or slab and a typical reinforced concrete element is that the strands drape or profile inside the concretetheir vertical location changes along the length of the member. Four reasons why concrete cracks bright hub engineering. A posttension slab is a slab of concrete that has been prestressed using a specific method to increase the strength of the concrete. The base has proven its longterm structural strength. Top 10 biggest mistakes made in posttensioned concrete design. Post tension slab services post tension concrete, cable. Steel strands are run through the concrete in a grid pattern. Read more about post tension slabs and why you should not cut or core one if a garage has a post tension slab there is usually either a sign stamped in the concrete floor saying it is a post tension slab or a plastic sign on the garage wall stating its a post tension slab. Recently, it was reported that many serious longitudinal cracks occurred at the bottom of top slab of prestressed concrete psc boxgirder bridges which are not.

Reinforcement helps extend the life of concrete, overcoming cracking that is inherent in the material and preventing its failure. Any cracks that do occur prior to the tensioning process will tend to close due to the added compression. Typically a 4 thick concrete slab should have the concrete joints around 812 feet apart. Horizontal applications such as beams, slabs, bridges, and foundations typically employ strands. Post tensioning, which is a form of prestressing, has several advantages over standard reinforcing steel rebars.

The typicalconventional pour strip which is a leaveout of 8 to 4 feet with the post tension concrete slabs stopping at each side of the leaveout and reinforcing bars running from the initial pour into the leaveout and bars from the second pour running to the face of the initial pour. Pretensioned concrete is a variant of prestressed concrete where the tendons are tensioned prior to the concrete being cast 25 the concrete bonds to the tendons as it cures, following which the endanchoring of the tendons is released, and the tendon tension forces are transferred to the concrete as compression by static friction. Posttensioned concrete slabs are typically expected to crack less than other slabs because posttensioning produces a compressive stress that must be exceeded before enough tensile stress develops to cause cracking. Through our proven preconstruction services approach, project construction management systems, and designbuild techniques, our teams is ideally suited to handle the complex projects of the institutional sector. There are several post tension slab problems which can be avoided. Pre tensioned and post tensioned concrete is not well understood. Post tension slabs superior foundations services jackson. As a building material, concrete is strong in compression, but weak in tension. Structure magazine cracking moment and safety of post. Cracking in posttensioned concrete box girders generally results, in a broad sense, for the following reasons. Results indicate that endregion posttensioning can be easily and effectively applied. Posttensioning methods for reinforcing concrete the. The materials used to posttension concrete members are ultrahighstrength steel strands and bars.

It can withstand strong mother nature storms, cushioned systems can be applied on the slab and works great both indoor and out. Posttensioning is a method of reinforcing strengthening concrete or other materials with highstrength steel strands or bars, typically referred to as tendons. Posttensioned concrete is a variant of prestressed concrete where the tendons are tensioned after the surrounding concrete structure has been cast 25 the tendons are not placed in direct contact with the concrete, but are encapsulated within a protective sleeve or duct which is either cast into the concrete structure or placed adjacent to it. It allows slabs and other structural members to be thinner. Post tensioning tendons, which are prestressing steel cables inside plastic ducts or sleeves, are positioned in the forms before the concrete is placed.

When errors are made onsite during the post tensioning process, the ability of the reinforcement to prevent cracking is decreased. The cause of cracking in post tensioned concrete box girder bridges and retrofit procedures walter podolny, jr. First off, one could argue that posttensioning is superior to conventionally reinforced concrete in a pure engineering sense. 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. Types of pour strip options pros and cons tech sales ps0.

It has the following benefits as compared to unbonded post tensioning. But since a posttensioned slab does not have excess rebar to minimize and distribute cracking, restraint cracks will be large and very noticeable. A typical posttensioned foundation with the forms set and ready for concrete. In order to ensure that the post tension slab used will have the best chance of avoiding cracking, as well as ensuring the longevity of post tension slabs, there are several possible errors to consider. 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 during bending. Shrinkage cracking there are basically three types of everyday cracking. The tensioning process effectively compresses the slab preventing it from cracking. Posttensioning is a method of reinforcing strengthening concrete or other materials with highstrength steel strands rebars, typically referred to as tendons. Throughout the garage, on every slab, post tensioned tendons needed replacement and deteriorating concrete required repair. Pretensioning and posttensioning in prestressed concrete design pretensioning in prestressed concrete. In this article, ill be giving homeowners some necessary information about the characteristics, advantages, disadvantages, and common questionsconcerns that i receive regarding posttensioned foundations.

All the post tension compress forces are intended to go into the slab. Bonded posttensioned concrete is the descriptive term for a method of applying compression after pouring concrete and the curing. The cause of cracking in posttensioned concrete box. Post tensioned concrete courts provide many advantages, the design of the system will greatly decrease the chances for cracking, settling and ponding. Cracks, cracks, cracks what is a reasonable level of cracking. Issues in posttensioned construction concrete construction. It is based on extensive research over the past 50 years in the united states and overseas in. The use of post tension tendons allows the engineer to design for larger slab construction spans typically used in parking structures or high rise. The use of post tension tendons allows the engineer to design for larger slab construction spans typically used in parking structures or high rise condominium construction.

We recommend using pt for temperature and shrinkage reinforcement. Most often the cracks extend across the entire foundation and occur prior to tensioning of the tendon cables. Reduced cracking, reduced weight, and reduced maintenance all translate into savings, and are concrete solutions that have made pt the premier way to reinforce concrete construction. Several methods exist for prestressing concrete, with posttensioning being a very common one. Most of time using the correct proportions of the ingredients and workmanship could reduce concrete surface cracking defects. Posttensioning compresses concrete, enabling it to resist both shrinkage cracks and cracks caused by difficult soil conditions. I have been retained as a third party to evaluate a post tensioned tennis court. The slab was decorative concrete it had been stained a dark brown, scored and polished. On the premise that those who ignore history will be condemned to relive it, this paper attempts to document those types of problems that lead. Post tension pt tendon systems are primarily used for large slab construction projects. Before a posttension slab is poured, highstrength steel strands or cables, called tendons, are laid in a tight grid. The reason is because posttensioning is a method of precompression, which means the concrete is put into a state of compression, which allows the. Pretensioning and posttensioning in prestressed concrete.

You must keep it a liquid to get it to form into the shape you want. Usually a sign in the garage or stamp in the slab will indicate if your home has a post tension slab. I had a call this morning from a prospective client who was concerned about cracks in the concrete foundation of the home they were building. Post tensioning in concrete slab benefits and advantages. 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. 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. Types of pour strip options pros and cons tech sales. Since the early 1950s, post tension tendons have been used in the design of concrete structures. In this article, ill be giving homeowners some necessary information about the characteristics, advantages, disadvantages, and common questionsconcerns that i. Over tensioning, bad prepration design layingcuring of concrete, bad structural design, bad load estimation and temperature, right. Posttensioned foundation a typical posttensioned foundation with the forms set and ready for concrete.

When moment is drawn on the tension side, the diagram matches the general drape of the tendons. All concrete will shrink during the curing process which lasts up to a. Common cause of cracking in concrete is restrained drying shrinkage. We know how to collaborate with public and private sector clients. It allows us to build slabs on expansive or soft soils. Structural reliability ccl posttensioned slabs show reduced cracking. Post tensioned slabs are a great tool to help reduce joints and control cracks.

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. The slab is five inches thick with tendons spaced at 30 iches o. The lobby level of the garage has a 4inch topping on a 10inch posttensioned slab with. After the concrete has been placed the cables are tensioned to 27,000 lbs. We specialize in new construction post tension slab projects and post tension repair work for both commercial and residential applications in dallas, fort worth, arlington, keller, plano, mansfield and throughout the metroplex, texas, oklahoma, colorado, louisiana and new mexico. It reduces or eliminates shrinkage cracking therefore no joints, or fewer joints, are needed. Whats the solution of cracks in the post tensioning slab. Types of cracks in fresh and hardened concrete causes and. Mar 09, 2020 as a result, its best to construct a post tensioned slab, giving the slab the strength to resist stresses caused by the soil. Shrinkage crack considerations for posttensioned foundations. Preventing cracks on posttensioned concrete slabs pro. 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. Many people dont understand how they work and the benefits and challenges. Shrinkage crack considerations for posttensioned foundations june 1, 2015 shrinkage cracks in concrete slabonground foundations are a significant public relations problem to home builders.

Preventing cracks on posttensioned concrete slabs pro builder. Crack width evaluation in posttensioned prestressed concrete. In total, the repair included the installation of 631 new. The tendons change their vertical location in the beam to follow the tensile moment diagram.

Jul 22, 2019 post tensioned slabs are a great tool to help reduce joints and control cracks. This method of reinforcing concrete enables a designer to take advantage of the considerable benefits provided by prestressed concrete while retaining the flexibility afforded by the castinplace method of building concrete structures. Im told that the cables can be partially stretched to help offset the cracking in. My firm was recently hired to look at cracks that had developed in a posttensioned floor slabongrade. Post tensioned foundation information for the homeowner. Engineered to offer maximum durability, ptc is the answer to crack control. Post tension systems can be used to retrofit an existing structure to increase load capacity. Nov 25, 2008 post tensioned concrete is a term heard more and more in the construction industry today. A 24 hour initial stress was performed and a final stress 2 days later. Current structural concrete design standards require that posttensioned slab systems be provided with mild steel or posttensioning tendons to control potential transverse cracking due to shrinkage and temperature effects that may occur soon after. Post tensioning reinforcement reduces cracking in concrete by adding compression. When errors are made onsite during the posttensioning process, the ability of the reinforcement to prevent cracking is decreased.

By the third day, i noticed a crack in the back patio, and by the fourth, there were sprawling cracks throughout the entire foundation. Consequently, although posttension slabs will generally hold together, they have a higher propensity for cracking than do slabs built with plenty of rebar. Apr 05, 2020 a post tension slab is a slab of concrete that has been prestressed using a specific method to increase the strength of the concrete. Other types of cracking, such as the result of differential settlement, are also mitigated by using a post tension slab. Now assuming all these are taken care of, no cracks should be there. With the right watertocement ratio, you can get a liquid that flows. Shrinkage crack considerations for post tensioned foundations june 1, 2015 shrinkage cracks in concrete slabonground foundations are a significant public relations problem to home builders. The use and proper construction of slip details is therefore critical for the performance and aesthetics of posttensioned concrete.

First off, one could argue that post tensioning is superior to conventionally reinforced concrete in a pure engineering sense. It reduces or eliminates shrinkage crackingtherefore no joints, or fewer joints, are needed. Hair line crackings in garage floor post tension slab. Bridge division office of engineering federal highway administration washington, d. The cause of cracking in posttensioned concrete box girder bridges and retrofit procedures walter podolny, jr. This video describes the benefits and challenges of both methods and describes how they are built. The scope of the project included providing extensive general concrete repair and maintenance and posttensioned repair. Home builders can avoid cracks in a posttensioned concrete slabongrade foundation by preventing certain errors made during installation.

Several methods exist for prestressing concrete, with post tensioning being a very common one. Lots of cracks in new post tension slab inspectionnews. Sep 02, 2019 pre tensioned and post tensioned concrete is not well understood. In order to ensure that the posttension slab used will have the best chance of avoiding cracking, as well as ensuring the longevity of post tension slabs, there are several possible errors to consider. Pt beams and slabs have an inherent advantage over nonpt members when it comes to. The reason is because post tensioning is a method of precompression, which means the concrete is put into a state of compression, which allows the concrete to take on flexure without cracking. The cause of cracking in posttensioned concrete box girder. The concrete never comes under tension, and it does not crack.

Comparing pre tensioned and post tensioned concrete. Pretensioning and post tensioning in prestressed concrete design pretensioning in prestressed concrete. All concrete will shrink during the curing process which lasts up to a year after the time concrete is placed in the forms. 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. Many people dont understand how they work and the benefits.

This was present throughout the home, no floor covering anywhere. Top 10 biggest mistakes made in posttensioned concrete. Rebar reinforcement in this case is technically allowed by code but in our experience, a properly designed posttensioned concrete slab will minimize cracking due to shrinkage. Posttensioning, which is a form of prestressing, has several advantages over standard reinforcing steel rebars. Sealing cracks in posttensioned deck concrete construction. Structural reliability ccl post tensioned slabs show reduced cracking. Posttension services of texas ptst is a full service posttensioning company based in dallas. This area is typically shored and reformed after the primary forming has been removed. The settlement induces a bending moment in the slab, resulting in tension on one face and compression on the other. Pretensioning and posttensioning in prestressed concrete design. Post tension v conventional cph structural engineering.