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- Structural Concrete Repair
- Crack Injection Specification
- Surface Preparation
- Bonding Old-to-New Concrete
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Can you inject a structural crack while the facility is in use or under loads?

The answer depends on the epoxy system. ChemCo's workhorse injection resins can withstand vibration during cure like that which would be encountered on a parking deck or elevated transportation structure. Don't forget to use a surface seal (like StripSeal™) that can take a little flexing. Otherwise, you might find that your hi mod seal has cracked or will leak.


What size cracks should I repair?

The American Concrete Institute (ACI) suggests that a condition survey and evaluation be conducted to determine the cause of cracking as well as whether the crack is static or active. This study is best suited to a professional civil or structural engineer who will consider chemical contamination, on-going corrosion activity and the marginal physical properties of the existing concrete. ACI committee 224 has offered the following crack width guidelines:

Exposure condition Tolerable crack width (in.) Tolerable crack width (mm)
Dry air or protective membrane 0.016 0.41
Humidity, moist air, soil 0.012 0.30
De-icing chemcals 0.007 0.18
Seawater and seawater spray: Wetting and drying 0.006 0.15
Water retaining structures (excluding pressure pipes) 0.004 0.10


Why did my surface seal crack overnight?


In geographic areas with large daily temperature fluctuations (for example, high country desert), concrete structures will expand and contract significantly. Often this movement is concentrated along existing cracks that could have originated with other causes such as difficult finishing conditions or temporary overloads. If a cracked section of concrete was sealed at a time of the day when the substrate temperature was near its peak, the two sides of the crack will move away from each other as the concrete cools during the early morning hours. A rigid epoxy seal will often crack under these conditions. The solution: use StripSEAL which is flexible or inject on the same day the seal is applied.


Doing a critical crack repair on an architectural surface?

You should requrest one of our injection resins in a special clear version to better hide the injected crack after repair. Then use StripSEAL as your injection seal. Occasionally, StripSEAL may have a slight darkening effect on very light concrete surfaces (including the open pores of a sand-blasted precast panel). To remove any traces of this light stain, bring along some vinegar (weak acetic acid) to the jobsite and rub or brush it over the previously sealed area and flush with lots of water. StripSEAL is a very popular repair material at many precast yards.


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Can you inject a structural crack while the facility is in use or under loads?

The answer depends on the epoxy system. ChemCo's workhorse injection resins can withstand vibration during cure like that which would be encountered on a parking deck or elevated transportation structure. Don't forget to use a surface seal (like StripSeal) that can take a little flexing.


Need a clear injection resin?

ChemCo Systems crack injection resins are shipped standard as a amber resin with a medium grey-purple colored hardener. This is helpful to visually insure proper mixing. However, for some architectural and restoration applications, it is useful to have a clear system. When you place your order, simply specify clear.


Why use an epoxy bonding agent for placing repair concrete over old concrete?

Many applications and specifications call for low cost polyvinyl acetate based bonding agents for cementitious repairs. However, for installations of shallow patches, particularly those less than 6 inches deep, ACI 546R-96 suggests that polyvinyl acetate based bonders not be used in applications exposed to moisture or subject to occasional submersion. Most experts suggest use of an epoxy bonding agent under these conditions. Without the epoxy, thin repairs are subject to poor curing conditions caused by moisture evaporation and capillary absorption by the base concrete and thus rarely develop acceptable bond strengths.


Best time to install a concrete coating?

Probably after your guys are really sweaty and tired! After maximum substrate temperature has been achieved—usually after 3 p.m. on a hot summer day. This minimizes blistering and microscopic pinholes caused by water vapor evolution from the substrate.


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Need extreme heat durability in your coating or adhesive?

One of our epoxies has a high HDT of 165°F, but we can evaluate the possibility for even greater temperature resistance if you can provide post-cure heat above that of ambient temperature (say 125°F). Mother Nature offers free post-curing in Texas and Florida, but she doesn't offer much help in Canada.


Is your injection resin leaking out the bottom or backside?

Inquire about our slump-pumping or paste injection techniques. We'll pass along some of our published articles, too.


When does 1 + 3 = 3.2 ?

That's what might occur when you mix 1 volume of epoxy binder and 3 volumes of graded sand to form a custom-engineered grout. If you call us, we will explain how to save big dollars by working with locally available sands and shipping only the epoxy. Why make the freight companies rich?


Ever have trouble injecting epoxy or chemical grout into drilled ports?

The problem may be your drill bit! If you've bumped up the injection pressure and still can't get flow in your drilled ports, try using a hollow core bit with a water swivel instead of a solid rotary impact bit. The solid bit works a little faster, but often it leaves fine cuttings that plug even big cracks.


Ever need to ship epoxies by air?

It can be done but sometimes not in the quantities that you would like. Why? IATA rules describe special packaging requirements for any air shipments that contain hazardous goods. Many (but not all) of the hardener ("B") components are considered corrosive. Depending on the category, these international rules restrict the volume per container, the type of container and outer pack, and whether the shipment is allowed on passenger or limited to cargo-only aircraft.


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Ever need to patch or repair a wet or underwater substrate?

What if the concrete is subject to flowing water or tidal action? Successful repairs are possible when you use the best surface preparation, understand the techniques of working with a wet surface and use the best wetting adhesives. Call us for recommendations for working in tunnels and pipes, filling voids containing water, underwater patching materials and grouts, and underwater crack injection techniques.


Looking for a custom polymer mortar or grout application?

Call us and ask for Chris Olson. He'll develop a mix that is optimized for the critical properties needed on your project. If necessary, we can do environmental exposure and strength testing in addition to calculating binder and aggregate volumes in our tech service lab. This service came in handy recently when an amusement park needed an emergency grout recommendation to open a new ride over a weekend.


What is the best way to clean up an epoxy spill?

That depends on whether it is a fresh or cured. If it is fresh, you can contain it with sand or kitty litter (you should always have a bag on hand), then shovel the absorbed material and wash the residue with water. Any uncured remnants can be emulsified with liquid soap of the kind used for hand washing dishes. If it is cured, but not a big quantity, a propane torch or hot air gun will often be enough heat to soften the epoxy so that it can be pried loose with a putty knife or trowel. For large quantities, use a solvent-based epoxy stripper.


Need to fix a thinly spalled floor, deck or road section with heavy usage?

Cut out the spall's perimeter walls vertically and remove any loose material in the center by shot blast, sand blast or high-pressure jet. If the area is subject to high impact or extreme temperature fluctuations, our best product is the CCS Binder, Patch, Nosing, Slurry. Premix the adhesive, and then add 3-4 volumes of 20 or 30# mesh kiln-dried sand to get either a self-leveling or trowelable consistency. For small jobs, hand mixing the sand is OK, but for large projects, you will need a mortar mixer to get sufficient shear and throughput (don't use a concrete mixer). If you need a maximum strength finished mortar, call us for suggestions on the best gap-graded mix for your application.


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Is there a simpler, less costly method to provide additional external support to existing concrete structures?

Yes, this non-proprietary procedure is a related to steel plate bonding and is commonly called rebar stitching. It may often be an efficient alternative to glass or carbon fabric wrapping, but since no company is actively marketing it, often the structural engineer doesn't even consider it. The repair is often fast, inexpensive and requires no special tools. Installation is straightforward. First, it is critical to know the depth of coverage of the existing steel so that the old reinforcement is not damaged.

The engineer calculates a requirement for increased strength, estimates a safety factor and then creates a pattern of steel or FRP reinforcing bar to be installed. The contractor saw cuts channels at specified depths in the concrete surface, ties the bar together at intersections, then fills the channel with a structural grade epoxy adhesive. If the channel lies on a horizontal deck, the filling is by gravity, otherwise the channel may need to be sealed with a temporary overlying form so the epoxy paste or liquid can be pumped into the hollow space. Unlike fiber wrapping systems, dowel holes can be drilled in any direction to better anchor the bar placed in the surface channels.


What type of concrete repair might qualify as a candidate for rebar stitching?

Parking and bridge decks, slab on pan floors, locally overloaded areas, missing or insufficient rebar, anchoring large patches and spall repairs to sound concrete, beams and piers—all might be excellent stitching applications. Stitching benefits include: a) fast installation, b) localized repairs, c) low material and labor costs, d) no special equipment required, e) damp and wet substrates are OK and f) repaired surface can bear traffic. Call us if you need an adhesive recommendation for stitching.


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Looking a free training program to refresh or upgrade your field crews' skills in structural concrete repair or crack injection?

Call us—we might be able to help. Assuming we have room geographically in our Kemko applicator program to fit your company, we can plan a practical, hands-on training session of about a day and a half with little lead-time.


Want to save a few bucks?

Just combine your epoxy needs to a total of 60 gallons or more and you will qualify for a minimum of a 5% discount. Spend the savings on your lovely wife.


Performing a crack injection job requiring surface ports?

Give the Kemko ports a try. We now carry ports fabricated in your choice of 2 materials: ABS (black) and nylon (cream translucent). Both port materials feature a base flange with superior bonding compared to ports made of polyethylene (i.e., ours won't blow off like poly). If you are also looking for a good source of the wedge shaped golf tees for use as port plugs, we can help there too.


Your normally safe crewman just poured epoxy on his shirt or pants leg, what should he do?

No matter what article of clothing, the best response is to remove it quickly. With short term dermal exposure to our products, there is usually little harm as long as the skin is washed thoroughly and completely with lots of soap and water. Long term exposure to some part B's may cause alkali chemical burns. Last piece of advice: don't wear the dirty clothing home.



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