Have you ever driven through a big construction area, like where work is being done on a bridge or large parking structure? The material used most in these kinds of constructs is concrete, formed into huge slabs and placed throughout like giant Legos.The concrete industry has come a long way since they first began laying foundations with these pre-constructed slabs, and one of the most important tools for creating them has been the post tensioning pumps that are used to "season" each slab before use.The Need for New Methods of Forming Concrete.There was a time when the use of concrete in the construction industry was limited to just foundations and bases for structures, even though it was certainly the cheapest of all the materials involved in any construction.Steel and iron dominated, as they were easier to use as uprights and supports, no matter how much more they cost.When technology advanced to the point where concrete slabs could be pre-made in and around metal and wood forms, cured and brought to a job site, it was then that concrete took its rightful place as the heart of vertical walls and curved bulwarks that would not have been possible before.The transportable slabs were made possible by the development of prestressing technology, where steel bars and cables are interlaced within the hardening concrete to make it more stable and denser than the ordinary molds.After further study, post tensioning practices were brought into play, enabling construction crews to adjust the tension of the cables within the hardening concrete, in order to strengthen it to handle particular forces it would encounter later, like vibration, seismic activity and temperature changes.By creating such a flexible inner environment within the material, it increased its lifespan, and made it less vulnerable to cracking, splitting or any other form of degradation.This technology made concrete the material of choice for large scale infrastructure projects, like bridges and roadways, significantly reducing overall material costs.The Necessity for Hydraulics.As with all technology, success will breed more tests, more experiments with existing practices to see if it can be improved.Testing on the tensile strengths of the steel imbedded within the concrete forms were soon found capable of being improved by using tightly laced cables instead of rods.The cables weighed less and were more flexible in terms of seismic strength than the rods could ever be.Once that was determined, the next question was, what can we do to improve this?Further examination revealed that while the cables were stronger as a whole than the previously used rebar or steel rods, thinner cables bound together, and stretched throughout a concrete form while it was still curing could potentially up that tensile strength by as much as 4.5 times, or greater, than the original tensile strength of the cables.This meant lighter weight forms that nearly tripled its durability under most conditions, a definite boon for the industry.Post tensioning the cables by hand or jack could not be relied upon to provide accurate and even pressure throughout the form, so the development of post tensioning pumps that used regulated hydraulic pressure was soon adopted throughout the industry.How it Works.Cables made up of at least cold drawn steel wire are cut to the desired length, and bundled together in numbers of two to four, with lubricating paper wrapped between each length.The cables are then placed within the concrete forms along the length of the beams, and the concrete is then added.Once the concrete begins to cure or harden, the collars attached to the ends of each cable bundle length are hooked to hydraulic pumps designed for the purpose of post tensioning.Once engaged, the post tensioning pumps will stretch the attached cables at a regulated rate of pressure, so as to avoid crushing or otherwise damaging the surrounding concrete.On average, these cables will be stretched at least six inches for every 100 feet of cable, for greater tensile strength of the whole.Once done, steel plates are set to, just behind the collars, along with shims to hold the collars in their current position.
Tuesday, August 21, 2012
The Importance Of Post Tensioning Pumps In The Concrete Industry
Have you ever driven through a big construction area, like where work is being done on a bridge or large parking structure? The material used most in these kinds of constructs is concrete, formed into huge slabs and placed throughout like giant Legos.The concrete industry has come a long way since they first began laying foundations with these pre-constructed slabs, and one of the most important tools for creating them has been the post tensioning pumps that are used to "season" each slab before use.The Need for New Methods of Forming Concrete.There was a time when the use of concrete in the construction industry was limited to just foundations and bases for structures, even though it was certainly the cheapest of all the materials involved in any construction.Steel and iron dominated, as they were easier to use as uprights and supports, no matter how much more they cost.When technology advanced to the point where concrete slabs could be pre-made in and around metal and wood forms, cured and brought to a job site, it was then that concrete took its rightful place as the heart of vertical walls and curved bulwarks that would not have been possible before.The transportable slabs were made possible by the development of prestressing technology, where steel bars and cables are interlaced within the hardening concrete to make it more stable and denser than the ordinary molds.After further study, post tensioning practices were brought into play, enabling construction crews to adjust the tension of the cables within the hardening concrete, in order to strengthen it to handle particular forces it would encounter later, like vibration, seismic activity and temperature changes.By creating such a flexible inner environment within the material, it increased its lifespan, and made it less vulnerable to cracking, splitting or any other form of degradation.This technology made concrete the material of choice for large scale infrastructure projects, like bridges and roadways, significantly reducing overall material costs.The Necessity for Hydraulics.As with all technology, success will breed more tests, more experiments with existing practices to see if it can be improved.Testing on the tensile strengths of the steel imbedded within the concrete forms were soon found capable of being improved by using tightly laced cables instead of rods.The cables weighed less and were more flexible in terms of seismic strength than the rods could ever be.Once that was determined, the next question was, what can we do to improve this?Further examination revealed that while the cables were stronger as a whole than the previously used rebar or steel rods, thinner cables bound together, and stretched throughout a concrete form while it was still curing could potentially up that tensile strength by as much as 4.5 times, or greater, than the original tensile strength of the cables.This meant lighter weight forms that nearly tripled its durability under most conditions, a definite boon for the industry.Post tensioning the cables by hand or jack could not be relied upon to provide accurate and even pressure throughout the form, so the development of post tensioning pumps that used regulated hydraulic pressure was soon adopted throughout the industry.How it Works.Cables made up of at least cold drawn steel wire are cut to the desired length, and bundled together in numbers of two to four, with lubricating paper wrapped between each length.The cables are then placed within the concrete forms along the length of the beams, and the concrete is then added.Once the concrete begins to cure or harden, the collars attached to the ends of each cable bundle length are hooked to hydraulic pumps designed for the purpose of post tensioning.Once engaged, the post tensioning pumps will stretch the attached cables at a regulated rate of pressure, so as to avoid crushing or otherwise damaging the surrounding concrete.On average, these cables will be stretched at least six inches for every 100 feet of cable, for greater tensile strength of the whole.Once done, steel plates are set to, just behind the collars, along with shims to hold the collars in their current position.
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