You know, concrete is probably the most widely used construction material in the world. It’s difficult, if not impossible, to name a construction project that doesn’t at least have a little bit of concrete on it. Most of them have a lot of concrete involved. Above ground we’re in skyscrapers, and buildings, and bridges, and such. Below ground is where we come into more problems. We get into corrosive elements. We get into water that can cause and crack concrete. Becomes a little trickier underground.
Concrete exposure can reduce service life in a number of ways. First off, there can be spalling, where the concrete flakes off either through rebar that’s corroding or other reasons. Secondly, we can have incrustation where you have buildup that develops from the media that’s within the concrete and reduces flow capacity or reduces the service life. We can also have abrasion in a pipeline where we have abrasion that wears the concrete out and eventually exposes the rebar, the reinforcing steel, and can have a failure, structural failure. And then there’s leakage. Leakage of exfiltration or infiltration can eventually erode the pipe and cause a structural failure as well.
But probably the more common one that we see is corrosion. And there’s a number of different types of corrosion in an industrial facility. We may have corrosion related to a chemical or a product they’re storing in that concrete basin. The most common thing that we see is microbial induced corrosion or micro biologically induced corrosion, often referred to as MIC. And this can occur in any a number of situations, but where we see it the most is in a wastewater environment. And in that wastewater environment, one of the byproducts of anaerobic decomposition is hydrogen sulfide gas. Concrete, itself, is a calcium based product of calcium based material. So it has a very high pH. It’s a base. A pH around 11 or 12.
And as that hydrogen sulfide rises and condenses on the upper portions of the structure, there’s bacterium. One of these bacteria is thiobacillus. Similar to this, we’ll convert that hydrogen sulfide gas into sulfuric acid. Now we all know that acids and bases don’t get along very well. So over time, as that acid builds up, it’ll develop a biofilm. And that biofilm, as it becomes more and more acidic, will corrode the concrete. As more concrete corrodes, it becomes like dust or chalk and can flake off. And ultimately we can get down to the reinforcing steel, which can itself corrode and cause a complete structural failure.
For instance, once a wastewater transmission system, such as a pipe or a manhole, is in place and it starts to deteriorate, there’s been infrastructure that’s been built around that. So now, we have concerns with bypassing the existing sewer. We may have traffic control, or we may have to upset traffic patterns, and both of these can be very costly. Often, even more costly than the repair itself. For these reasons, particularly when we’re in environments such as a wastewater or corrosive environment, these are the reasons that we’ve developed Concrete Protective Liners, such as Sure-Grip and Ultra-Grip.
Concrete Protective Liner is a thermoplastic geo membrane, or membrane, or liner that has locking extensions or anchors on one side. And these anchors cast into concrete. So the purpose is to protect concrete against corrosion, or leakage, or infiltration and inflow. It may also assist with abrasion. It’s more abrasion resistant than concrete, and protects the concrete so the concrete doesn’t degrade and the structure doesn’t fail over time.
So, depending on the chemical that’s involved, we may use a different resin. If there’s a different temperature that the media is exposed to, we may use a different resin. These include polyolefins, such as polyethylene and polypropylene, but we also make Sure-Grip Concrete Protective Liners out of ECTFE or PVDF. You may know these as Kynar, or Halar, or Zuluf, are some of the trade names associated with those two materials. They’re floor polymers, and they’re more for high end applications where corrosion is extreme.
But what we’re doing with polyethylene, the most common used of these, is we’re selecting material that is affordable, but it’s also resistant to a wide range of chemicals. Regardless, we’re going to pick the right resin that is immune to the corrosive materials that we’re containing.
AGRU manufactures its Concrete Protective Liners using the flat dot calendar extrusion process. What that is, is we have an extruder just like you would see in many things. I think of it if I were talking to a kid, it’s like the play dough set that you used to have, where you stuff the play dough in and push the button, and it extrudes it. And when it comes out of that extruder, it goes into a dye. And the dye is the shape, whether it’s a star, or a round, or a square, that play dough would come out of is what shapes that material we use.
What’s called a coat hanger dye. And that coat hanger dye allows us to push the material all the way out to the full width of the sheet that we’re manufacturing. And as soon as the resin comes out of that dye, it’s immediately hit with two profile rollers. And at that point, whatever is embossed in those rollers, in this case the anchors for the Sure-Grip or the Ultra-Grip Concrete Protective Liner, that is formed right there coming out of the dye. The remainder of the construction process or the manufacturing process is purely cooling the material, trimming the edges, and wrapping it up for sale and distribution.
Other products are not necessarily failing to be corrosion resistance. They’re failing in their adhesion or they’re locking into the concrete. So, under back pressure considerations, they may fail. And if they’re not attached to the concrete, they’re not protecting the concrete. Whether they’re resistant to corrosion or not, they have to be attached to the concrete.
So AGRU has made Concrete Protective Liners for over 34 years now. And in that time, we’ve had several revisions to our anchor design to enhance its ability to withstand back pressure design. We’ve got a mechanical anchoring system. It fits similar to the V-shaped AGRU anchor. This ensuring that it’s properly bonded, properly anchored mechanically in that concrete to ensure that it stays in place.
To better understand what hydrostatic back pressure is, let’s look at a couple of examples. Think about a scuba diver. They’re constantly concerned about regulating pressures. The deeper they go, the more danger it becomes because the pressure gets greater. The same thing occurs in a groundwater environment. If we’re building a structure below the water table, as we get below the water surface in the groundwater, we have those same pressures.
For instance, if I take this water bottle and I poke a hole down here in the bottom, I’ve got almost a full bottle of water. So when that stream comes out of that hole, it’s going to spray out because it’s got all this hydrostatic back pressure acting on it. By the time this water bottle gets empty and the water’s down to here, it’s just going to be a bit of a dribble coming out. The deeper we go, the more pressure we have pushing up against the Concrete Protective Liner. And that’s why we want to make sure that it’s properly anchored, properly designed, so it doesn’t pull out of the concrete surface.
The core benefits of Concrete Protective Liner are protecting the concrete. Says it in the name, whether that be from corrosion, abrasion, spalling, incrustation, or leakage. Any of these can result in a shortened life, service life, or life expectancy of that concrete structure, which that it’s either going to have to be rehabilitated or replaced.
Most of the time rehabilitation or replacement is a lot more costly than the initial construction itself. This may be due to bypass pumping if you’re in a sewer system. If it’s a structure that’s in a roadway or in a developed area, it’s going to be a lot more difficult to access as well. And these can lead to excessive costs.