Lets think about the little concrete balloon again; and lets say you have a respectable pressurized fill level of 85% at the point of refusal. Good luck trying to get that concrete balloon 85% full without some exhaust. Anyway, how would one propose to achieve 90% fill level? Stay on the crack longer? Lower the pressure? No! It would require you to jack up the pressure. Only makes sense doesn’t it? Is it so hard for the pressure tout's to understand that increasing the pressure could, and will with enough force applied, extend the crack? Why? Because the entrapped air, the unvented void, will pressurize and exceed the strength of the matrix. At what pressure the extension would transpire is directly related to the design strength and condition of the matrix. Apply 3000psi pressure to a crack in a 2500psi matrix and it will give. If the greatest advantage of high pressures is production, what is the greatest disadvantage? And why do pressure injection specifications restrict the amount of pressure that may be applied during the injection process?
We have used vacuum injection on just about all configurations of concrete, masonry and stone. In addition to individual crack repairs, vacuum can repair spider/map cracking by the square foot instead of the conventional lineal foot basis. Our vacuum processes can have an entire area repaired and back in service before a pressure application could be set up; and at a fraction of the cost. Unlike pressure injection, vacuum injection can be safely used for the repair of an unrestrained element. Topping slabs, mosaic tiles, delaminations, etc., can actually be simultaneously held together using the same vacuum forces used to perform the repair. This notion that high pressure cannot "blow out" a crack is nonsense. It is generally believed that any pressure in excess of 40psi has the potential to further damage concrete. REMR Technical Note CS-MR-3.9 states, "The pressure used for injection must be carefully selected. Increased pressure often does little to accelerate the rate of injection. In fact, the use of excessive pressure can propagate the existing cracks, causing additional damage." And what of ACI 301-05? "…pressure can propagate the existing cracks, causing additional damage." Despite hollow preaching claims otherwise, the perils are real and well accepted. The chance of further damage, propagation of the crack condition, is significantly increased by following conventional pressure injection methodology.
Moreover, the matrix contains, at minimum, very nearly the same amount of moisture as the relative humidity of the atmosphere. Oh I know about the water insensitive epoxies used for pressure injection. But, its back to that basic physics law when it comes to material penetrations, you cant put two things in the same place at once. If there is moisture in the pore structure, there is moisture in the pore structure. Nothing will get in unless the moisture is displaced. Pressure applied to the crack will not do it. The flow and roll of the repair resin along the interior walls of the fracture may pull some of it out, but what happens to the moisture? We have found that because a manufacturer says so, does not necessarily make it so. Most touted "water insensitive" epoxies will not bond when mixed with water. The failure to bond issue that this causes has been explained by the pressure injection folks. It doesn’t need to bond its been said. They go on to explain the mere fact that the member has cracked indicates it has relieved the pressures exerted in the first place. So, all one needs to do is fill the dormant void. But what if the pressure is not relieved, and even if it is, what is the need to get the material so deep into the fracture? Is 90% fill better than 70%? Sure it is. Consider a crack only filled 80% full. At the leading edge of the repair resin is a weakness. Apply pressure and the crack will radiate from this unrestrained line and form a new fracture; that is, if the fracture is totally bonded the entire 80%. Of course, if its not bonded, the fracture will just open up again when/if it comes out of compression. Many times my pressure injected crack looked fine, but six inches over, a new crack developed. Coring of the existing repaired crack could reveal the new crack emanates from, and because of, the partially filled fracture. There is little argument against "the more complete the fill, the more permanent the repair".
Tecvac, Inc. routinely fills cracks as narrow as .001". Moreover, there are petrographic reports from CTL Labs that indicate cracks as narrow as 5 microns wide being filled using vacuum technology. We sometimes use pressure assist, but our success is directly attributable to our combination of vacuum and ultra-low viscosity repair materials, not pressure. True, the technology and the repair resins we use are a bit more complicated, but its not brain surgery and, for the injection of typical in-depth cracks in concrete members, our prices are quite competitive. Our repair resin of choice is low molecular weight methylmethacrylate (MMA). This material shares all of the physical properties of epoxy, yet is just about as thin as water. It has the ability to migrate into places epoxies will never see. MMA has some drawbacks of course, but this material will outperform epoxy in every instance when it comes to injection. It smells nasty, tends to bubble when put under pressure and is not easily metered. So, there is obviously not a lot of enthusiasm from epoxy manufacturers or epoxy pump manufacturers. But lets take the splash of water example again; splash a cup of water on a concrete wall or sidewalk. See how the capillary action sucks the water deep into the matrix? Now splash a cup of honey right next to it. Very thin epoxies are claimed to be 40 centipoise, but most used for pressure injection approach 100 or better. MMA is 5-7 centipoise. See the difference? Imagine the same two materials trying to get into that .001" wide fracture. Pressure honey or vacuum water. Oh, you have a crack that is 6" wide? We can thicken MMA to paste if need be, and apply it at 20 degrees below zero. Epoxy will not bond to epoxy. Yet we can drill into/behind a shallow epoxy pressure injected crack, where the material only penetrated 1"¬2", pull our MMA up against and bond to the shallow epoxy filler; if its cured. What do you do with shallow penetrated and improperly mixed epoxy? A pin head of initiator in a 5 gallon bucket of MMA will fire! We can remove our set up without grinding or marring the surface of the concrete. ...The benefits of vacuum injection and its superiority over pressure injection go on and on.
Witnessing these benefits, its not hard to understand why we, those of us in the vacuum injection industry, marvel at the natural wonder and the overwhelming power of vacuum. We don’t expect pressure injection folks, and those with beneficial interest in that part of the concrete repair industry, to embrace, or even understand this technology. However, we do understand pressure injection. Tecvac technicians have performed 100's of gallons of pressure injected epoxy and know what it has to offer. We are ready for any challenge and hopeful that the results would bring the pressure injection folks into the present. The days of wooden wheels and buggy whips are a thing of the past. But hey, if you think our "new fangled vacuum contraption" will get you killed, then ride on in your buggy...
We have used vacuum injection on just about all configurations of concrete, masonry and stone. In addition to individual crack repairs, vacuum can repair spider/map cracking by the square foot instead of the conventional lineal foot basis. Our vacuum processes can have an entire area repaired and back in service before a pressure application could be set up; and at a fraction of the cost. Unlike pressure injection, vacuum injection can be safely used for the repair of an unrestrained element. Topping slabs, mosaic tiles, delaminations, etc., can actually be simultaneously held together using the same vacuum forces used to perform the repair. This notion that high pressure cannot "blow out" a crack is nonsense. It is generally believed that any pressure in excess of 40psi has the potential to further damage concrete. REMR Technical Note CS-MR-3.9 states, "The pressure used for injection must be carefully selected. Increased pressure often does little to accelerate the rate of injection. In fact, the use of excessive pressure can propagate the existing cracks, causing additional damage." And what of ACI 301-05? "…pressure can propagate the existing cracks, causing additional damage." Despite hollow preaching claims otherwise, the perils are real and well accepted. The chance of further damage, propagation of the crack condition, is significantly increased by following conventional pressure injection methodology.
Moreover, the matrix contains, at minimum, very nearly the same amount of moisture as the relative humidity of the atmosphere. Oh I know about the water insensitive epoxies used for pressure injection. But, its back to that basic physics law when it comes to material penetrations, you cant put two things in the same place at once. If there is moisture in the pore structure, there is moisture in the pore structure. Nothing will get in unless the moisture is displaced. Pressure applied to the crack will not do it. The flow and roll of the repair resin along the interior walls of the fracture may pull some of it out, but what happens to the moisture? We have found that because a manufacturer says so, does not necessarily make it so. Most touted "water insensitive" epoxies will not bond when mixed with water. The failure to bond issue that this causes has been explained by the pressure injection folks. It doesn’t need to bond its been said. They go on to explain the mere fact that the member has cracked indicates it has relieved the pressures exerted in the first place. So, all one needs to do is fill the dormant void. But what if the pressure is not relieved, and even if it is, what is the need to get the material so deep into the fracture? Is 90% fill better than 70%? Sure it is. Consider a crack only filled 80% full. At the leading edge of the repair resin is a weakness. Apply pressure and the crack will radiate from this unrestrained line and form a new fracture; that is, if the fracture is totally bonded the entire 80%. Of course, if its not bonded, the fracture will just open up again when/if it comes out of compression. Many times my pressure injected crack looked fine, but six inches over, a new crack developed. Coring of the existing repaired crack could reveal the new crack emanates from, and because of, the partially filled fracture. There is little argument against "the more complete the fill, the more permanent the repair".
Tecvac, Inc. routinely fills cracks as narrow as .001". Moreover, there are petrographic reports from CTL Labs that indicate cracks as narrow as 5 microns wide being filled using vacuum technology. We sometimes use pressure assist, but our success is directly attributable to our combination of vacuum and ultra-low viscosity repair materials, not pressure. True, the technology and the repair resins we use are a bit more complicated, but its not brain surgery and, for the injection of typical in-depth cracks in concrete members, our prices are quite competitive. Our repair resin of choice is low molecular weight methylmethacrylate (MMA). This material shares all of the physical properties of epoxy, yet is just about as thin as water. It has the ability to migrate into places epoxies will never see. MMA has some drawbacks of course, but this material will outperform epoxy in every instance when it comes to injection. It smells nasty, tends to bubble when put under pressure and is not easily metered. So, there is obviously not a lot of enthusiasm from epoxy manufacturers or epoxy pump manufacturers. But lets take the splash of water example again; splash a cup of water on a concrete wall or sidewalk. See how the capillary action sucks the water deep into the matrix? Now splash a cup of honey right next to it. Very thin epoxies are claimed to be 40 centipoise, but most used for pressure injection approach 100 or better. MMA is 5-7 centipoise. See the difference? Imagine the same two materials trying to get into that .001" wide fracture. Pressure honey or vacuum water. Oh, you have a crack that is 6" wide? We can thicken MMA to paste if need be, and apply it at 20 degrees below zero. Epoxy will not bond to epoxy. Yet we can drill into/behind a shallow epoxy pressure injected crack, where the material only penetrated 1"¬2", pull our MMA up against and bond to the shallow epoxy filler; if its cured. What do you do with shallow penetrated and improperly mixed epoxy? A pin head of initiator in a 5 gallon bucket of MMA will fire! We can remove our set up without grinding or marring the surface of the concrete. ...The benefits of vacuum injection and its superiority over pressure injection go on and on.
Witnessing these benefits, its not hard to understand why we, those of us in the vacuum injection industry, marvel at the natural wonder and the overwhelming power of vacuum. We don’t expect pressure injection folks, and those with beneficial interest in that part of the concrete repair industry, to embrace, or even understand this technology. However, we do understand pressure injection. Tecvac technicians have performed 100's of gallons of pressure injected epoxy and know what it has to offer. We are ready for any challenge and hopeful that the results would bring the pressure injection folks into the present. The days of wooden wheels and buggy whips are a thing of the past. But hey, if you think our "new fangled vacuum contraption" will get you killed, then ride on in your buggy...
Tecvac, Inc.
800 847-9324
www.tecvacinc.net
I didnt know you could use a vacuum technique for concrete repair. That is pretty crazy!
ReplyDeleteBefore, I'm not aware that vacuum is superior than Conventional Pressure Injection Techniques, but thanks to your blog, now I understand.
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