Concrete Epoxy Injection

CVLE 519

Concrete Technology

Dr. Adel El Kordi

Professor

Civil and Environmental

Engineering Department

Faculty of Engineering

Epoxy Injection Resin is a system for welding cracks back together. Thiswelding restores the original strength and loading originally designedinto the concrete. Epoxy injection restores the structural qualities, theconcrete design intended. It creates an impervious seal to air, water,chemicals, and other contamination.

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Introduction

Cracks

• A crack, obviously, is a sign of failure caused by:

1. stresses

2. Inadequate design

3. Improper curing

• One of the dangers of a structural crack is the effect that it has on the reinforcing bar. The reinforcing represents one of the main structural values of the concrete.

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The conventional basis for cathodic protection (CP) relies on shifting the potential of the steel to more negative values. CP of steel reinforced concrete structures can be achieved by polarizing the steel reinforcement with an external direct current(DC).

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Cathodic Protection Using Active Corrosion Control In the passive cathodic protection, the steel in the structure is made the “cathode” and a more easily “sacrificial” metal is connected to it, acting as the “anode”. The chemical reaction between the two metals generates an electrical current. The sacrificial metal then corrodes, protecting the original structure. Eventually that metal part has to be replaced.

For both environmental and operating cost reasons, the traditional passive protection is being replaced by active corrosion control. In the ‘active’ method, a sophisticated electronic current control system is used to inject a reverse current to that generated from corrosion to protect the structure. This is also known as impressed current cathodicprotection (ICCP)

Crack Analysis

1. As with all repair and rehabilitation of concrete, the initial job analysis is by far the most important step. Epoxy Injection Resin will weld concrete cracks but, of course, will not repair the cause of the cracking.

2. Analyze each potential injection application to determine the exact causes of the cracking. Correcting the cracking problem can be fairly simple, or may be difficult involving design changes.

3. Consult a structural engineer when design changes are necessary. Do this before starting the injection. Repairing cracks by Injection is effective after these design changes. Prevent future cracks by fixing the original cause of the cracking, when ever possible.

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Epoxy injection resin has twopurposes:1. It effectively seals the crack

to prevent the damagingmoisture entry.

2. It welds the structuretogether. Most peopleassume that this welding ofthe structure is the mostimportant result of the repair.Actually what is mostimportant is the sealing.

Epoxy injection purposes

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The sealing properties of theinjection prevents prematuredeterioration of thereinforcing. This can be ofequal, or in some casesgreater importance than thestructural welding. It wouldtheoretically always bedesirable to get this weldingeffect.

Sealing properties

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Parking garages are an example of cracking problem that require a structural engineering analysis.

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Floor cracks

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Slab cracks

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Injection Preparation

• Proper job preparation is essential to insure maximumresults. Preparation before injection is even more important.Once the resin is in the crack, there is no turning back. Thetwo most effective systems for setting injection ports:

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Drilling for Ports

• It is extremely important that the drilling of all ports be done with vacuum attached drill chuck and hollow drill bits. Concrete dust can be detrimental to the injection processes in several ways.

• For example, any dust remaining in the drill hole near a crack can combine with the very low viscosity injection resin, forming a semi-paste. This paste can slow or even block the resin flow. Drilling very tight crack with a solid drill forces dust into the crack. This seals the crack from resin flow.

Surface PortsDrilled

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Determining the spacing of ports is done by a highly experience applicator. This spacing is a factor of the tightness of the crack and the depth of the concrete substrate. Spacing is normally between four (4) and eight (8) inches.

spacing of ports

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Port Setting and Sealing

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Align ports directly over cracks Sealing the exterior of cracks

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Epoxy crack injection can restore the original strength and

loading of concrete. Epoxy injection creates an impervious

seal to air, water, chemicals, ...

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This system ensures that the crack will be thoroughly filled

with epoxy, making the crack not only structurally sound but

preventing water intrusion

Testing The System

• Test cracks that are ill defined, or if dust or debris is in the crack. This testing may be done by injecting water into the crack area.

• Water left in the cracks will not effect the injection process or the curing of the Epoxy. Heavier injection resin forces the water out the cracks. Water injection helps clean the cracked areas. More important, is that it helps avoid the unexpected. This process of flushing the cracks is commonly skipped by more experience contractors, who can tell if there will be a flow of resin, by just looking at them. However, when in doubt, water testing is a must.

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Testing The System

If the cracks contain algae, chlorinated water containing copper sulfate is injected. After pumping , this mixture is left over night. The next morning the crack is flushed by pumping fresh water, into it. This flushes it out before resin injection begins.

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Efflorescence

• Efflorescence builds up on the bottom of a crack in a horizontal slab. Water in the crack extracting soluble calcium hydroxide is the cause. The water evaporates at the surface leaving the lime, which later reacts with the carbon dioxide in the air to form limestone. The inside of the crack, is frequently free of limestone and making it suitable for injection.

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On vertical cracks, injection is start at the lowest point, and continue upward on the crack area. While injecting the lowest port, resin will flow to and out of the next higher port.

Inject

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EPOXY PUMP, EPOXY INJECTION PUMP, EPOXY MACHINE AND INJECTION GUN

• Epoxy Injection Resin Systems should be of very low viscosity for most applications. That way it will flow in the smallest hair line cracks. Resin can travel several feet from the point of injection. It may take some time before reaching the next port or penetrating through pin holes in the surface. Coring samples have shown that epoxy injection effectively fills cracks including small voids and hairline cracks.

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Injection During Extreme Weather

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Injection During hot Weather

• A hot substrate results in premature jelling of the resin with sequential loss of penetration. During extremely hot weather an open bridge deck may exceed temperatures as high as 140 Degrees F. Special precautions are necessary before injection work can be done in such weather.

• The precaution may be shading the bridge, and water cooling. Always check substrate temperature. The injection machine and its hoses require isolation from extremes of temperature.

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Injection During cold Weather

• A cold substrate will cause an increase in the viscosity of the injection resin. This slows down the rate of injection. Epoxy injection undertaken during cold weather also requires special precautions.

• When doing injection work in freezing conditions, determining if there is ice present in the crack is critical. Determining if a cracks inner surfaces are ice coated, is equally important. When injecting under these conditions, the resin will not bond to the substrate and no structural rebonding will result. It is usually safer to preheat the portion of the structure you are injecting.

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Injection Against A Head of Water

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• It requires a slightly different procedure than normal injection. If water is running from a crack, applying a hydraulic cement (fast setting) seals the cracks and sets the ports. Epoxy pastes will not set up under this type of wet condition. The hydraulic cement seals the cracks and diverts all water flow through the injection ports.

Injection Against A Head of Water

• Hydraulic cement is fast setting, but it does not have the strength needed for an Injection Sealer. Epoxy Concrete Bonder can have the strength to prevent leaks while injecting. After the hydraulic cement cures applying Epoxy Concrete Bonder. That solves this problem.

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Injection Against A Head of Water

• The injection process follows the procedures described before. The Injection resin forces the water out of the crack and through the adjacent ports. The resin has an amber color and does not look like water. Pure resin flows from the higher port before capping and moving on. The head of water will require increasing the injection pressure used.

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Epoxy Resin Properties

• Epoxy Injection Resin should be ASTM C881 Type 1 Grade 1. For maximum filling of cracks a low viscosity injection resin must be used. ASTM C881 allows a viscosity of up to 2000 CPS. However, the viscosity should be in the 300 -600 CPS range for most injection applications. Any thicker you get poor fill (or you have to pump at excessive pressure), any thinner and you get excessive leaks.

• Tensile and Bond Strengths are very important, to prevent re-checking if the structural member injected is put into tension. In general the Tensile Strength (ASTM D-638) should never be less than 45 MPa. Injection Resin should have a bond strength of 50 MPa or greater. Compressive strength with most epoxies will be close to or in excess 70 MPa. The resins that we have It is the Epoxy Bonders used to seal the ports should be:

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CONCLUSION

1. Epoxy Injection Systems is very effective at repairing concrete cracks when used according to manufacturers recommendations.

2. Job analysis and proper preparation are very important to insuring the maximum performance from the Epoxy Products, or any other concrete repair products.

3. The right equipment is critical. Proper setup continuous mixing epoxy injection machines must always be used with no exception.

4. Injection staff and management must have the training and experience to do the work right the first time.

5. Epoxy injection has to be done right the first time. There is no second chance. So it is critical that your injection work be done by well trained and equipped, experienced personnel.

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