Vacuum technoloy has been proving its merit in the repair of concrete, masonry and stone since the processes were patented the early 1970's. While Tecvac, Inc. has not employed any horses in its efforts, we have been performing a variety of vacuum processes since 1991. Many years prior to our conversion to vacuum, I would guess that we pressure injected as much epoxy as any of the other injection contractors in the area. We know the difference vacuum makes in the permanence of repairs and there is no question about its unprecedented qualities, especially when coupled with the right repair resin. We have vacuum applied epoxies and urethanes, but when performing structural repairs, methyl methacrylate is our product of choice; and for good reasons. Oh, I don’t suppose I blame the pressure advocates, especially those pump manufacturer's who's lively hood could be jeopardized with any notion that vacuum could un-do the prevalence of conventional pressure injection superiority. Howbeit, it sort of reminds me of the buggy builder though, talking about Henry Ford. No doubt, the guy had been building buggy's for 100 years and knew a thing or two about buggy's…, but he knew little about automobiles or Ford Motor Company.
Lets start with the basics and the propagation of vacuum's total superiority to conventional pressure injection. As you might know, everything is porous. A typical crack has fissures, voids and interconnecting cracks located in the side walls of the fracture. These fissures, voids and interconnecting cracks continue on a microscopic level. Imagine sealing and pressurizing one of these little voids with air …like a concrete balloon. Is it hard to see how air and/or moisture can be trapped in the tiny fissures of the matrix? Imagine filling the concrete balloon with a pressurized liquid. How full do you think you would get it? Yet, using only a modest 10in of vacuum would reduce the pressure inside the cavity by half. But, lets just say we can only lower the pressure in the fracture area to 14psi from 14.7psi… and apply Boyle's Law. One cubic inch, one cubic foot or 1 cubic meter of air will evacuate! But vacuum, stand alone or assisted, employs the application of the most basic physics law...…You cant put two things in the same place at once. Despite assertions otherwise, this is a very important law to be mindful of when considering vacuum vs. pressure.
With that said, it has long been touted within the realm of pressure injection, and continues to be touted with numerous methods and apparatus to accommodate the purpose, that low pressure is better than high pressure. Now, if vacuum will eliminate ALL pressure, how can it be said that vacuum cannot reasonably be considered useful? That vacuum will contribute little, or be rarely useful to the pressure injection processes? Doesn’t it make sense that this lower pressure zone, induced by vacuum, would be more receptive to resin installation? Try the Boyle's Law thing.
The installation and penetration of the repair resin is hence, two different animals. While pressure injection continuously labors against atmospheric pressure, vacuum injection flows because of atmospheric pressure. Think about injecting at a very modest 25psi. It is only serving its purpose by overcoming 14.7psi atmospheric (1bar). Why would it take 100, 200 or 1000psi to move material in a fracture zone? Porosity? Fluid resistance? Why would a vacuum applied to the same set-up, the same fracture zone, pull the material into the fracture right out of an open bucket?...well, it does. Vacuum injection is starkly adverse to pressure injection; the vacuum process actually de-pressurizes the repair resin and, naturally de-pressurizes the entire fracture zone.
Yes, all concrete is porous. The example of splashing a cup of water on a wall is evidence of that fact. However, while this porosity is remarkably useful when installing low-viscosity repair resins, it is not very useful when attempting to pressurize an enclosed fracture and then expecting the porosity of the concrete to dissipate entrapped air. What is air entrained concrete? More to the point, its not that concrete is good or bad at trapping air, it will tenaciously resist air moving through it. Pick up a piece of the roughest open-surface concrete you can find, so thin its fragile to the touch, and try to blow air through it. How much pressure do you think it would take to force air through a piece of solid concrete? Our vacuum processes can seal a piece of plastic to a concrete surface so tight it is impossible to remove with out destroying it. How do we do that if air is moving through the concrete? There is a profound difference in air and moisture vapor moving through a concrete matrix and the dissipation of pressurized air during an injection process. I would pose this question to a competent and conscientious pressure technician…or pump manufacturer.