Alchatek Blog

Lifting a settled bridge approach slab with polyurethane foam requires specific knowledge of proved repair procedures for these types of structures. Here's an overview...

Look for a Hidden Sleeper Slab

Larger roads and highways will often have a hidden sleeper slab that spans underneath the pavement and the approach slab. It is designed to help transfer the traffic load from the roadway to the approach slab. If there is settling at a bridge approach you must determine if there is a sleeper slab in place. Drill through the pavement where it meets the approach slab and if you hit more concrete underneath the pavement you have found the sleeper. If there is a sleeper present where there is settling you will need to perform deep injection a couple of feet below the sleeper - just for soil stabilization. Rural roads and private roads typically do not have a sleeper slab present. Always ask the client if there are drawings available.

Deep Soil Stabilization Followed by Lifting

At least one level of deep injection is required for approach slab/pavement lifting. This is for soil stabilization. 4' spacing and 4' below the pavement is standard. Do not exceed more than 30 lbs per point at a given depth. It is advised to always have a DCP (dynamic cone penetrometer) test done in order to determine the blow counts. Low blow counts indicate weak soil zones that need to be targeted for deep injection. Lifting will be done directly through the pavement/approach slab, the same way you do standard slab lifting. Do the deep injections first and then finish with the injections directly beneath the slab.

Fill Voids with Polyurethane

Watch for voids under the approach slabs where they meet the bridge abutments. There are typically voids in this area that need to be filled. When filling them, it is good to have an observer under the bridge because the foam can fill the void up and come over the abutment, depending on how the structure is designed.

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Sealing Joints with Grout and Oakum

Whether injecting with a pump or a cartridge, it's always helpful to have AP Oakum on hand. Liquids will take the path of least resistance and oakum is very adaptable for controlling them. For example, joints are typically easier to inject than cracks, and precast joints are about as easy as they come in regards to injection work. They are also very common routes for water infiltration, whether in manholes, culverts, vaults, and tunnels. Since joint injection does not require the consistent pressure provided by electric injection pumps, you can often make these repairs with cartridges instead.

Simple and Effective Leak Seal Method

Time and time again, it is easy to look like a hero with nothing more than a cartridge of Spetec PUR F400, a handful of AP oakum, and a flathead screwdriver. Lastly, be confident. Don’t confuse high-flow leaks with high-pressure. When you're working less than 20’ below grade, you are only dealing with a few psi of pressure even if it is a high-volume leak.

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Sealing Steam Leaks with Polyurethane

One of the most high-tech veneer manufacturing companies in the United States chose Alchemy-Spetec to train their maintenance techs to stop a steam leak in their facility. You heard that right. Not liquid water, but steam leaks! Prior to milling the veneer, they heat the logs in a bank of steam vaults. Rather than tearing down/rebuilding these cracked, leaking vaults they opted to inject the cracks with Spetec PUR F400, a hydrophobic flexible polyurethane grout. Replacing the vault would not only have been a lot more expensive, but it would also have resulted in a costly interruption to their milling process. No one likes downtime.

Polyurethane Leak Seal Training

Saturday is the one day of the week that the vaults are offline, and that is when I conducted the complimentary field training for their employees, who had never done any injection work before. Within a few hours, they understood how to handle the grout, how to use the grout pump, and how to accomplish their injection work. They can now self-perform their crack injection as needed.

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I was a Machinist Mate in the Navy and thus almost all of my training was mechanically focused. One class I had was Electrical Theory for Mechanics. The quick summation by the Senior Chief instructor for it was "Electricity is magic and when the smoke comes out the show is over." Being on a submarine it was deemed a good thing to keep water and electricity separate. My first time ever using polyurethane chemical grouts was on a group of sixteen conduits entering a below-grade mechanical room. While electricians may understand the "magic" of electricity they often fall short as waterproofers. Combined with the fact the numerous electrical cables coming through a conduit can be notoriously hard to waterproof and it is a recipe for leaks and electrical problems. In this post, I'll share step-by-step instructions, along with a couple of photos from a recent job one of our customers completed in a San Francisco condo complex.

Oakum soakem is a kindergarten-skill level procedure that makes waterproofing these types of penetrations easy. I refer to this as fingerpainting with chemical grouts.

1. For PVC and HDPE pipe roughing the surface will increase the mechanical bond and is recommended.
2. Wet the application area.
3. Soak oakum in either Spetec F400, GT500, or GT380 resin until saturated.
4. Pack soaked oakum into pipe joint to be sealed. If necessary, pack multiple layers. Ensure it is under compression.
5. Allow grout to cure.

Often this is all that needs to be done, but it can be followed up with injection to fill the conduit if required.

1. Stab injection needle through the cured grout and oakum plug.
2. Inject grout.

Photo: Contractor on a recent job in San Francisco, addressing multiple conduit leaks with electric injection pump, a pail of Spetec PUR F400, and Oakum.

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Sealing Leaks in Concrete with Polyurethane

Water is RELENTLESS. Leaks appear in all kinds of structures, from underground parking garages to municipal treatment tanks to elevator shafts. Everything from fine hairline crack leaks to gushers can threaten the long-term integrity of the structure and surrounding property. Fortunately, pressure injection of polyurethane grout into the crack or behind the leaking wall (depending on the application) creates a durable and rugged positive side repair. A relentless solution to a relentless problem.

A wide variety of leak seal solutions are available to address almost any type of concrete leak. (Call the Alchemy-Spetec technical support team at 404-618-0436 for assistance in choosing a product for your specific project.)

Polyurethane Leak Seal Solutions - Crack and Joint Injection

Crack and joint injection products are generally used for smaller non-gushing leaks:

Spetc PUR GT380
Activates as Foam or Gel Depending on Amount of Water Added
Ideal for Manhole Rehabilitation

Spetec PUR GT500
Most Dry-Cycle Resistant Hydrophilic Grout
Ideal for Cracks with Intermittent Leaking

Spetec PUR GT350
MDI Based Grout
For Wet Dynamic Cracks & Joints

Spetec PUR F400
Flexible Hydrophobic Grout
Ideal for Dynamic Cracks & Joints

Spetec AG200
Acrylic Injection Resin
Used in Special Situations (Contact Alchemy-Spetec Support for More Info)

Polyurethane Leak Seal Solutions - Curtain Grouting

Curtain grouting products are generally used for gushing leaks or multiple smaller leaks in proximity:

Spetec PUR H100
Semi-Flexible
Ideal for Structures with Some Movement

Spetec PUR H200
2,050 psi Compressive Strength, Fastest Cure Time­­
Ideal for Soil Stabilization

Spetec PUR Highfoamer
50x Expansion
Cost Effective for Large Voids

Spetec Boom! Seal
Two-Component, High Expansion (35x), Hydro Insensitive
Used in Special Situations (Contact Alchemy-Spetec Support for More Info)

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Alchemy-Spetec's AP Fill 700 and AP Fill 720 are one-component polyurethanes used for filling voids in supporting soil surrounding a structure.  Situations in which these materials might be used for void fill include soil adjacent to retaining walls, basement walls, seawalls, and infrastructure boxes.  

Benefits of One-Component Void Fill Foams

• Their slow reaction time allows for the material to travel farther from the injection point, fill more voids, and permeate more soil before curing.
• They're ideal for encapsulating underground debris (decaying organics, roots, buried construction waste).
• On small jobs, they can be installed with a very small, portable pump that can be lifted and transported by hand. 

Differences Between AP Fill 700 and AP Fill 720

• AP Fill 700 features very low viscosity, making it ideal for permeating fine soil with small voids.
• AP Fill 720 is extremely rugged and durable when cured, while still retaining some flexibility. Its high expansion rate makes it ideal for filling larger voids.

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A contractor in Atlanta was recently called in to seal off a rain-induced ceiling leak in a new construction high-rise penthouse suite. Sealing off the water intrusion from the roof above was not an option, due to the rooftop swimming pool directly above the penthouse. So, they had to get into the ceiling from the interior of the suite and repair the leak from the underside.

Powerful Polymers

The crew on this job injected Spetec PUR F400, a water-reactive, hydrophobic, flexible, single component polyurethane resin. This product is ideal for sealing off active leaks in cracks.

Painless Procedures

Leaking concrete structures can be permanently repaired with concrete crack injection & curtain wall procedures using water-activated polyurethane foam. Pressure injection of these liquid polyurethane resins forces the material into leaking cracks or behind leaking walls depending on the application. After the polyurethane injection is complete, the polyurethane resin rapidly reacts with water to form a watertight seal.

Rapid Results

In this case, the leak was shut down in less than two minutes. This all went down literally right before the new tenant was scheduled to begin moving in. (No pressure there!)

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What Causes Leaks in Concrete?

Imperfect Construction
Concrete construction is by no means a perfect science. New construction often requires Leak Seal treatment follow-up work. If the initial construction isn’t properly sealed at the time of construction, leaks are bound to appear sooner rather than later.

Weather and Wear
Concrete naturally decays over time. Exposure to extremely hot temperatures and extremely cold temperatures can take their toll over time. Even structures located in mild climates will begin to decay purely due to the aging process.

Unstable Soil
Unstable soil can undermine the integrity of concrete structures and cause cracks to appear. Loose soil has four main causes: soil erosion, poor compaction, freeze/thaw cycles, and biological decay. If soil is the main culprit, additional stabilization and slab lifting treatments may be required in order to prevent further cracks from appearing.

What is Curtain Grouting?

Curtain grouting is the process of injecting water-reactive resin behind the leaking wall in a grid pattern (from the negative side). The water on the other side mixes with the grout and cures to a solid mass covering the surface of the wall on the other side (positive side). In addition, you don’t have water pressure dislodging external “patches” over time, as can be the case with other methods.

Curtain grouting is often required when there are gushing leaks, multiple leaks in proximity, cracks cannot be identified, the walls are made of material that does not respond well to crack injection (such as masonry, stone, and CMU), or previous leak seal methods have failed.

The most well-known Alchemy-Spetec product for this application is Spetec PUR H100, a one-component, closed-cell, hydrophobic, water-reactive, solvent, and phthalate-free, low viscosity resin. If there are large voids involved, Spetec PUR HighFoamer (a similar product with a higher expansion rate) may be a more cost-effective option.

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Unstable soil can be defined as soil that will not stay in place on its own, and therefore requires extra support. It should be noted that unstable soil can threaten the stability, security, and safety of infrastructure and can damage, degrade, and even destroy a number of structures, such as buildings, bridges, and roads. There are a variety of factors that can cause unstable soil including erosion, poor compaction, freeze/thaw cycles, and decomposition.

The Causes of Unstable Soil

Erosion
Poor drainage, improperly placed downspouts, leaking drain pipes, and broken water lines are common culprits.

Poor Compaction
When backfilling on a job site, the contractor is supposed to compact the backfill by driving over it with heavy equipment. However, this isn’t always done properly for one reason or another.

Freeze/Thaw
Processes of freezing and thawing essentially accelerate erosion processes. Cold weather freezes moisture trapped in tiny cracks. When this water freezes, it expands, subsequently pushing on the rocks and breaking them into smaller pieces. As processes of freezing and thawing continue, rock and sediment are continually broken down.

Biological Decay
Construction trash pits, buried trees, and other biodegradable materials all break down. Sometimes structures are built over these areas.

Stabilize Soil with Polyurethane

Loose soil can be consolidated, voids can be filled, and water migration halted by permeating the soil with one of the AP series products of ultra-low viscosity polyurethane resins. Once the bearing capacity of the soil has been increased with this process, then the structure can be lifted if necessary.  Learn more about Soil Stabilization Products here.

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Crack Injection Explained

Crack injection has many advantages over other methods.  For example, if you’re sealing a leak in a water tank, you can inject from the outside of the tank. So the tank can remain in service while you repair it. Having to dry a crack, like you do with epoxy resin, is not needed as this material reacts with water. The material also remains flexible at all times.

Crack injections can be applied in both vertical cracks and in horizontal cracks. With vertical cracks, it is imperative to start at the bottom of the crack and work your way up the crack until it is filled. This forces the material up and through the crack and will simultaneously push the water up and out as well. With horizontal cracks, injection can be started at either the left or right end.

Read more from Charlie Lerman's article Crack Injection Explained.

Curtain Wall Grouting Explained

Curtain wall injection is the process of drilling holes through a structure in a diamond pattern, then injecting the grout into soil on the other side. This procedure creates a curtain wall made of a resin/soil mixture that prevents water from getting back into the structure. It is often required if there are multiple cracks or leaks in a wall. Filling each individual crack may cause you to waste time following the water from crack to crack. Curtain wall grouting allows you to stop multiple leaks at one time and protects the structure on a long term basis.

This procedure was first performed in 1960 on a sewer manhole with a multiple leak problem. As described above, chemical grout was injected through to the outside of the manhole. This created a “positive side seal” (on the side the water was coming from), blocking water from penetrating the joints of the structure.

Read more from Charlie Lerman's article Curtain Wall Grouting Explained.

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