Alchatek Blog

Inflow and Infiltration (I&I)

Inflow and infiltration (I&I) refer to the entry of groundwater and rainfall-derived water into wastewater and stormwater collection systems through defects such as cracked pipes, deteriorated manholes, faulty connections, and other openings. This excess water can overload the capacity of wastewater treatment plants and collection systems.

Inflow refers to water that enters the sewer system from direct connections such as roof drains, yard and area drains, foundation drains, surface runoff, or street wash waters. Infiltration refers to groundwater that enters the sewer system from the surrounding soil through defective pipes, pipe joints, connections, or manhole walls. Infiltration is the focus of polyurethane grouting.

Managing I&I is important for preventing sewer overflows, reducing treatment costs, and minimizing energy consumption.

Understanding the Risks: What are Sanitary Sewer Overflows (SSOs)?

Sanitary sewer overflows (SSOs) are a prevalent concern, posing significant public health threats. EPA data indicates an alarming 23,000 to 75,000 SSO incidents annually in the U.S. These overflows, laden with raw sewage, are carriers of bacteria, viruses, and other harmful entities, potentially leading to conditions ranging from mild stomach discomforts to severe diseases like cholera and hepatitis.

The Financial Implications and Opportunities

Tackling these issues often requires a significant financial commitment. The EPA's Clean Water State Revolving Fund (CWSRF) has allocated hundreds of billions of dollars for diverse water infrastructure projects. Established in 1987, this initiative offers states the autonomy to address their unique water quality challenges.

A Cost-Efficient Approach to Mitigating Infiltration in Sanitary/Stormwater Systems

Here's an efficient plan employing flexible polyurethane grout that promises a robust return on investment:

1. Assessment: Start with inspecting lift stations and manholes.
2. Identification: Locate and prioritize significant leaks.
3. Targeted Repair: Utilize flexible polyurethane grout for precise point repairs.

A single crew can often mitigate leaks in two standard 8' deep manholes a day. This swift mitigation can lead to substantial savings. For instance, addressing leaks in just a single day can easily amount to around $30,000 in annual savings, based on local water treatment costs. In mere months, the cost of the repair is already recouped.

For municipal managers overseeing stormwater and wastewater systems, embracing flexible polyurethane grout for leak repair is a strategic move. It's not just about ensuring infrastructure longevity, but also safeguarding public health and achieving economic efficiency.

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I remember my first day on the job back in June of 1985. We were working nights in the subway tunnels of Atlanta, sealing leaks in the ceiling. The crew handed me a 30-pound hammer drill and told me to drill holes in the ceiling at a 45-degree angle. Sure, what the heck is a 45-degree angle? I put on a lot of muscle that summer drilling overhead and hauling 50-pound pails of resin all over the Southeastern U.S.

Drilling holes into concrete seems like a straightforward process. However, it must be done correctly or everything you do afterward is a waste of time. Often, contractors put their least experienced technician on that job because it is manual labor and can be taught quickly. But knowing a few of the basics can help a newbie drill like an expert.

First, you have to understand that the beginning of the hole is where the injection port makes its seal against up to 3,000 pounds per square inch of injection pressure. It is important that the hole stay round, especially when using hammer in type ports. That means you have to keep the drill bit in a straight line.

Why a 45-degree angle? This is the best way to intersect the crack halfway through the structure (which is your goal). For example: On a 10” thick wall, come off the crack 5”, drill at a 45-degree angle and you should hit your target. Just start with your drill bit straight into the wall, give the trigger a few bumps to make an indention in the concrete with the bit, and rotate your drill so that the angle is halfway between your starting position and the wall.

How far apart should you space your holes? It depends on the width of the crack. Tighter cracks need tighter spacing because the resin won’t travel as far. Wider cracks can have wider spacing because the resin will travel with ease. A rule of thumb is to drill your holes no farther apart than the thickness of the concrete. Drill, flush, and pump a test hole with water to get an idea of how far the resin will travel.

Be sure to pull the drill bit out every four or five inches of penetration to clean out the drilling dust. Otherwise, you are likely to bind up your drill bit, which is not fun to try to remove.

Sometimes you will have to drill straight into the crack. I always try to angle drill first, but with extremely tight cracks you may have to compromise and drill straight in. Go as deep as you can, but make sure you don’t go all the way through.

Another tip: If you stagger your holes from one side of the crack to another, be sure not to intersect a hole you already drilled. This causes all kinds of problems.

We will talk about flushing drilling dust out of your holes later, but I can’t repeat it enough. If you want a successful injection job you have to flush the drilling dust out of the holes from the back. Otherwise, the dust will form a paste that gets forced into the crack and blocks your resin from getting where it needs to be. Splashing water on the front of the hole doesn’t really help. Be sure to get a small hose to the back of the hole and flush it with clean water.

In the next article, we'll take a look at what to do when you inevitably hit the injection contractor's nemesis...rebar!

5 Steps of Crack Injection - Overview
5 Steps of Crack Injection - 1. Drilling Holes
5 Steps of Crack Injection – 1. Drilling Holes (Continued)
5 Steps of Crack Injection – 2. Flushing Holes
5 Steps of Crack Injection – 3. Installing Ports
5 Steps of Crack Injection – 4. Flushing Cracks
5 Steps of Crack Injection – 5. Injecting Resin

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The approach and departure slabs adjacent to a bridge in McKenzie County, North Dakota had settled, leading to an uneven and hazardous road surface. A geotechnical contractor was brought in to level the road surface and mitigate any further settlement. 

Powerful Polymer

The contractor selected AP Lift 475, a two-component, hydrophobic, structural lifting polymer designed for airport, highway, and railroad applications. It can be used to stabilize structures, fill voids, and lift slabs supporting tremendous loads. In addition to tremendous in situ load-bearing capacity, AP Lift 475 is also traffic-ready in less than one hour.

Painless Procedure

AP Lift 475 was injected through the approach and departure slabs to fill subterranean voids, compact the existing subgrade, and lift the settled structures. As the material was injected, the material rapidly expanded, compacting the subgrade soils. Once the subgrade was compacted and the load-bearing capacity of the soil improved, the material raised the settled slabs.

Rapid Result

The approach and departure slabs were lifted to their proper elevation and the underlying soil was improved to mitigate future settlement. This work was performed in two days. 

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A general contractor working on new luxury apartment construction in Queens, NY reached out to a local leak seal specialist after discovering hairline cracks in the base joint of a fire protection storage tank. (A fire protection storage tank stores water for use in fire suppression systems.)

Powerful Polymer

Cracks in concrete come in all widths and sizes. Some of the most difficult ones to inject are the hairline cracks. The thinnest flexible polyurethane grouts on the market are between 100cps - 200cps which makes it difficult if not impossible to get them to penetrate a hairline crack. Spetec AG200 is an acrylic-based grout and it is 18cps, or about 5-10 times thinner than the thinnest flexible polyurethane. Clearly, a thinner grout will penetrate cracks much more effectively. Spetec AG200 is almost as thin as water, but when it polymerizes it forms a flexible hydrophilic gel. This gel features 500% elongation, which may sound like overkill to some, but 500% movement in a hairline crack is not much. The ultra-low viscosity and field adjustable set time make Spetec AG200 ideal for thin and hairline cracks.

Painless Procedure

The crew followed the standard crack injection procedure:

1. Identify crack locations.
2. Estimate the amount of material needed.
3. Prepare the surface of the crack.
4. Drill injection holes at a 45-degree angle.
5. Flush out injection holes with water to remove any debris.
6. Insert injection ports on both sides of the crack.
7. Inject water into each port.
8. Start injection of material.
9. Always grout twice.
10. Add water again.

Spetec AG200 was successfully injected into cracks and the base joint of the firefighting water reserve tank.

Rapid Result

The defects in the tank were easily penetrated by Spetec AG200 and the job was a success. This allowed the general contractor to get back on schedule with the building construction.

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There are five basic steps to be done when placing a crack injection. This is crack injection 101. Learn these steps and you will be well on your way to understanding what it takes to seal a water leak in concrete with products such as Spetec PUR F400 and Spetec GT500. In future articles, we will explore every one of these steps in more detail and address the multitude of options (such as port selection, hole spacing, depth, what to do when you hit rebar, etc.) But for right now, we are going to discuss the most basic steps.

Step 1: Drill holes. Use a hammer drill to drill holes in the concrete that intersects the crack. These holes are usually drilled at a 45-degree angle to intersect the crack halfway through the structure so that the resin is forced toward the front and back of the crack.

Step 2: Flush the holes. When you drill, you create concrete dust. If you don’t flush this dust out of the holes, it will be forced into the crack during injection and may clog the crack, preventing the resin from getting where it needs to go. Put a flexible hose all the way to the back of the hole so that water flushes the dust from the back of the hole to the surface of the concrete. Flush until clean water is flowing.

Step 3: Install your injection port. The port is what seals the hole and gives the injection pump a direct connection to the crack.

Step 4: Flush the crack. Unless the water is pouring out of the crack, you will need to inject clean water through the injection port and into the crack. This serves several purposes:

• Cleans the crack of dirt and other contaminants to allow the resin to flow freely.
• Gives you an idea of how far and how easily the resin will flow into the crack when you start injecting the foam.
• Helps to open areas where the resin wouldn’t otherwise flow. Water is thinner than resin and will penetrate deeper and into tighter areas.
• Ensures the resin will have enough moisture to react with.

Step 5: Inject the resin. Always use the lowest pressure that will continuously feed resin into the crack. Slowly turn up the pressure as necessary to get the resin flowing. My rule of thumb is to keep injecting even if resin starts to flow out of the crack. As long as more resin is going in than is coming out, you are improving your chances of success. When the resin isn’t moving further along the crack, move to the next port.

Sounds simple, right? Well, it is and it isn’t, as we will discover in the next several chapters of this blog series...

5 Steps of Crack Injection - Overview
5 Steps of Crack Injection - 1. Drilling Holes
5 Steps of Crack Injection – 1. Drilling Holes (Continued)
5 Steps of Crack Injection – 2. Flushing Holes
5 Steps of Crack Injection – 3. Installing Ports
5 Steps of Crack Injection – 4. Flushing Cracks
5 Steps of Crack Injection – 5. Injecting Resin

Want in-depth info on crack injection procedures and products?

The terms hydrophobic and hydrophilic may not mean anything to the average person. But, to a contractor, these terms can mean a world of difference. Hydro means water while phobic means “to fear” and philic means “to love”. Alchatek offers both hydrophobic and hydrophilic polyurethanes, so it is important to be aware of the differences between the two types.  

Hydrophobic Polyurethanes

Hydrophobic polyurethanes naturally repel water (similar to the way oil would repel water and stay separate if you were trying to mix them in a glass). These products push water out of the area in question as they expand. Hydrophobics are used with catalysts which allow you to adjust the set time. They also have zero shrinkage after curing.

Check out these hydrophobic polyurethanes:

• Spetec PUR HighFoamer 
• Spetec PUR F400
• Spetec PUR H100 
• Spetec PUR H200 
• AP Fill 420
• AP Deep Lift® 420
• AP Lift 430
• AP Lift 435
• AP Lift 440
• AP Lift 475
• AP Soil 600 
• AP Fill 700
  
• AP Fill 720

Hydrophilic Polyurethanes

Hydrophilic polyurethanes naturally mix with water before curing (similar to the way gin and tonic mix thoroughly in a glass). This characteristic allows for a very strong chemical and mechanical bond, as water helps pull the material into the pores of the concrete. These products do not require a catalyst. You can pump them straight out of the pail.

Check out these hydrophilic polyurethanes:

• Spetec PUR GT350
• Spetec PUR GT380
• Spetec PUR GT500

Don't Oversimplify These Concepts

Don't get caught in the trap of oversimplifying hydrophilic vs. hydrophobic.  There are varying degrees of each (see chart below for more information on how this is measured).  

Some hydrophilic materials will keep absorbing water (10-15 times their original volume).  Others (such as Spetec PUR GT500) only absorb as much water as is necessary for their reaction and then they reject the rest.  Yes, hydrophilic gels will shrink like crazy in the absence of water, but Spetec PUR GT500 won't.  It is completely safe to use in a dry environment.

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Carrington Woods Lake Dam is located in Baldwin County, Georgia. A consulting firm collaborating with a general contractor called in geotech specialists Atlas Structural to stabilize an abandoned below-grade culvert pipe that had deteriorated over time. The pipe ran underneath a spillway. With supporting soil migrating into it, its unstable condition threatened the integrity of the structure.

Powerful Polymer

The technicians chose single-component AP FIll 720 for the job. The deteriorating pipe was 100 feet long, and due to the circumstances at the site, grouting could only be done from one end. Getting a two-component foam 100 feet up a pipe before it cured would have been impossible. AP Fill 720, featuring a very flexible set time adjustment range with the catalyst, allows technicians to pump the material for great distances before it starts to react and cure.

Painless Procedure

AP Fill 720 does not have to be heated and only needs moisture for reaction. The crew had two electric injection pumps, one pumping AP Fill 720 with an accelerator and the other pumping water. They had 150-foot lines on each pump. Both pump lines were run through a 100-foot PVC tube. The technicians used a video camera, mounted five feet back from the end of the PVC tube, to monitor the fill. The crew pumped both water and poly in unison for a good reaction. As the pipe filled up, they slowly withdrew the PVC and continued pumping until the pipe was full. The process basically consisted of pumping, extracting the tube a foot, and repeating - until the entire 18" x 100' pipe was filled.

Rapid Result

The deteriorated pipe was completely filled and stabilized. Soil migration was stopped and the threat to the structure of the spillway above was eliminated. This job was completed in only three hours. Complete removal or filling with concrete would have taken days. In addition, concrete does not expand, so a 100% fill would have been impossible. AP Fill 720 expanded to fill 100% of the pipe. The consulting engineer and general contractor were very happy with this result.

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When the residue of plants or animals is converted into soil, the process is known as decomposition. Bacteria, fungi, and worms break down this residue, taking nutrients from them and leaving the remaining portion. Organic molecules are broken down into simpler inorganic molecules. This biological process changes the makeup of the soil and can therefore lead to soil instability.

What are the causes of decomposition?

When soil has a high concentration of organic materials, the soil will naturally begin to decompose. Throughout this process of decomposition, the mass and form of these organic materials will change. Up to 90 percent of organic material will actually disappear over the course of the decomposition process, which means the mass of the soil will decrease substantially, reducing the quantity of available soil. The causes of decomposition can be broken into two main groups: manmade and natural. Trash pits or buried construction debris can cause manmade decomposition, while tree stumps and peat content can cause natural decomposition. 

What are the signs of decomposition?

Sinkholes, unstable soil, and low spots are all indications of soil decomposition. When soil begins to decompose and shift, it can compromise the integrity of buildings, foundations, and other manmade structures. 

How can decomposition be addressed?

In some cases, it is possible to dig up the cause of decomposition. For example, it might be possible to extricate a trash pit or old construction debris from the soil. However, in other cases, this simply isn’t feasible. You can’t easily extricate a trash pit after you have already built on top of it. If removal isn’t an option, the best solution is to envelop the area with polyurethane soil stabilization material. This process is known as encapsulation, and it essentially works to compact the area and reduce the amount of oxygen and water that can get to it, thereby helping to slow decomposition.

Want in-depth info on soil stabilization procedures and products?

What is freezing and thawing?

As the name suggests, a freezing and thawing cycle refers to a natural phenomenon in which soil freezes in cold weather and then thaws out again once the temperature warms up. Freezing and thawing in northern climates is good news for farmers, as it helps to loosen up the soil and reduce compaction, which makes it easier for crop roots to grow. However, for construction engineers and contractors, this process can prove to be incredibly problematic, especially if they are building on fine-grained soils with silt or clay factions, which are more prone to freezing and thawing.

What are the problems associated with freezing and thawing?

Essentially, freezing and thawing cycles accelerate soil instability. Soil with pores containing small particles of frozen water is known as permafrost. Building on permafrost is fine, as long as the soil stays frozen, but things become problematic once the permafrost begins to thaw. Freezing and thawing of permafrost cause soil to become soft and less compact. Subsequently, this causes structures, such as roadways, railways, foundations, and pipeline supports, to sink. Obviously, this can cause major headaches.

How can the problem of freezing and thawing be mitigated?

Alchatek soil stabilization products can be used to compact the ground and displace water particles in the soil pores. Depending on the soil type, this could prevent frost heave, resulting in a stronger, more consistent base to build on.

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Many types of infrastructure, including roads, bridges, and buildings, depend on compacted soil in order to stay in place. Therefore, in order for these structures to last, a specific degree of compaction must be achieved. When soil does not adequately compact, the problem is known as poor compaction, and that can lead to more serious issues. Concrete repair contractors always need to be on the lookout for signs of poor compaction which include settling slabs, cracking foundations, and dips in roadways and railroads.

What causes poor soil compaction?

There are a variety of causes of poor soil compaction. However, much of it boils down to soil texture and soil properties. Some soils are more prone to compaction than others. Excess soil salt content, high clay fraction soils, low pH soils, and soils with high water content tend to compact less favorably. It should also be noted that decisions made by construction contractors and their teams can also influence soil compaction. For example, failure to select proper compaction equipment or compaction materials can contribute to poor compaction. Furthermore, some areas are more prone to poor compaction than others, such as portions of soil set against a foundation.

How can poor soil compaction be corrected?

Luckily, poor compaction can be corrected. The solution is to strengthen the soil until it is properly compacted. As mentioned in the previous post, voids can be filled, soil consolidated, and water migration halted with Alchatek soil stabilization products. Once the bearing capacity of the soil has been increased with this process, then the structure can be lifted if necessary.

Want in-depth info on soil stabilization procedures and products?