Repairing Cracks in Concrete by Injecting Epoxy Resin

CSI Division
Division 3 - Concrete
Section
Concrete Repair
Last Modified

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Prior to inclusion in GSA’s library of procedures, documents are reviewed by one or more qualified preservation specialists for general consistency with the Secretary of Interior Standards for rehabilitating historic buildings as understood at the time the procedure is added to the library. All specifications require project-specific editing and professional judgement regarding the applicability of a procedure to a particular building, project or location. References to products and suppliers are to serve as a general guideline and do not constitute a federal endorsement or determination that a product or method is the best or most current alternative, remains available, or is compliant with current environmental regulations and safety standards. The library of procedures is intended to serve as a resource, not a substitute, for specification development by a qualified preservation professional.

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We’ve reviewed these procedures for general consistency with federal standards for rehabilitating historic buildings and provide them only as a reference. Specifications should only be applied under the guidance of a qualified preservation professional who can assess the applicability of a procedure to a particular building, project or location. References to products and suppliers serve as general guidelines and do not constitute a federal endorsement nor a determination that a product or method is the best alternative or compliant with current environmental regulations and safety standards.

PART 1–GENERAL

1.01 SUMMARY

  1. This specification provides guidance on patching cracks in concrete by injecting an epoxy adhesive.

  2. Epoxy Injection should be used for dormant cracks, i.e., cracks that remain unchanged. Dormant cracks generally pose little danger. However, if left unrepaired, they will provide channels for moisture penetration.

  3. The calculated maximum crack width for concrete should not exceed 0.3 mm. Consult a professional to determine the cause for cracking and its source, as superficial repairs can aggravate the problem.

  4. Read “General Project Guidelines” along with this specification. These guidelines should be reviewed prior to performing this procedure and should be followed, when applicable, along with recommendations from the Regional Historic Preservation Officer (RHPO). The guidelines cover the following sections:

    1. Safety Precautions

    2. Historic Structures Precautions

    3. Submittals

    4. Quality Assurance

    5. Delivery, Storage and Handling

    6. Project/Site Conditions

    7. Sequencing and Scheduling

    8. General Protection (Surface and Surrounding)

  5. For guidance in monitoring cracks, see “Monitoring and Evaluating Cracks in Masonry”.

1.02 REFERENCES

American Society for Testing and Materials (ASTM)

PART 2–PRODUCTS

2.01 MATERIALS

  1. Epoxy Resin (Abatron, Inc., Sika Corp. or approved equal).

    1. For Fine Cracks:

      1. Epoxy shall be a two-part type, low viscosity epoxy adhesive material containing 100% solids and shall meet or exceed the following characteristics when tested in accordance with the standards specified.

      2. Characteristics of Components:

        • Component A - shall be a blend of modified epoxy resins.

        • Component B - shall be a blend of modified amine curing agents.

      3. Test Method Requirements:

        • Component A - Brookfield RVT, 700 maximum; Viscosity @ 77 +/- 3 degrees Fahrenheit, cps; Spindle No. 2 @ 20 rpm.

        • Component B - Brookfield RVT, 240 maximum; Viscosity @ 77 +/- 3 degrees Fahrenheit, cps; Spindle No. 2.

      1. Properties of Combined Components: When mixed in the ratio of two parts Component A to one part Component B by volume; or 100 parts Component A to 44 parts Component B by weight, properties shall be:

        • Potlife, 60g @ 77 +/- 3 degrees Fahrenheit, minutes; 25 minutes maximum.

      1. Properties of the Cured Adhesive: When cured for seven days @ 77 +/- 3 degrees Fahrenheit, unless otherwise specified, properties shall be:

        • Ultimate Tensile Strength: ASTM D638; 8000 minimum.

        • Compressive Yield Strength, psi: ASTM D695*; 15,000 minimum.

        • Heat Deflection Temperature: ASTM D648*; 130 Fahrenheit minimum.

        1. NOTE: Test specimens must be cured in a manner such that the peak exothermic temperature of the adhesive does not exceed 77 degrees Fahrenheit.

    1. For Wide Cracks:

      1. Epoxy shall be a two-part gel epoxy adhesive material containing 100% solids and shall meet or exceed the following characteristics when tested in accordance with the standards specified.

      2. Properties of Combined Components: When mixed in the ratio of two parts Component A to one part Component B by volume; or 100 parts Component A to 34 parts Component B by weight, properties shall be:

        • Potlife, 200g @ 77 +/- 3 degrees Fahrenheit, minutes.

      1. Properties of the Cured Adhesive: When cured for seven days @ 77 +/- 3 degrees Fahrenheit, unless otherwise specified, properties shall be:

        • Ultimate Tensile Strength: ASTM D638; 1,500 psi minimum. 2) Compressive Yield Strength: ASTM D695; 6,000 psi minimum.

        • Heat Deflection Temperature: ASTM D648; 105 Fahrenheit minimum.

  1. Surface Seal: (Epoxy Mortar or Oil-Free Clay)

    1. Description: The surface seal material is that material used to confine the injection adhesive in the joints or cracks during injection and cure.

    2. Properties: The surface seal material shall have adequate strength to hold injection fittings firmly in place and to resist injection pressures adequately to prevent leakage during injection. The material shall not leave a residue upon removal.

    3. NOTE: Provide adhesive crack fillers and other related materials that are compatible with one another and with substrates under conditions of severe weather, demonstrated by sealant manufacturer based on testing and field experience.

2.03 EQUIPMENT

Equipment for Injection:

  1. Type: The equipment used to meter and mix the two injection adhesive components and inject the mixed adhesive into the crack shall be portable, positive displacement type pumps with interlock to provide positive ratio control of exact proportions of the two components at the nozzle. The pumps shall be electric or air powered and shall provide in-line metering and mixing.

  2. Discharge Pressure: The injection equipment shall have automatic pressure control capable of discharging the mixed adhesive at any pre-set pressure up to 200 psi + 5 psi and shall be equipped with a manual pressure control override. For injection of the gel epoxy, the equipment shall be equipped with the above features and be able to pump at up to 5,000 psi.

  3. Ratio Tolerance: The equipment shall have the capability of maintaining the volume ratio for the injection adhesive prescribed by the manufacturer of the adhesive within a tolerance of + 5% by volume at any discharge pressure up to 200 psi. For gel epoxies, the ratio will be checked by weight at up to 5,000 psi.

  4. Automatic Shut-Off Control: The injection equipment shall be equipped with sensors on both the Component A and B reservoirs that will automatically stop the machine when only one component is being pumped to the mixing head.

  5. The manufacturer of the injection equipment and the manufacturer of the epoxy resin adhesive for injection shall be one and the same.

PART 3–EXECUTION

3.01 EXAMINATION

  1. Examine the nature and severity of the crack:

    1. Note directions and widest point of cracks.

    2. Note sloped floors, bulging walls and doors that do not fit.

  2. Determine the probable cause of cracks:

    1. Foundation erosion.

    2. Decay of materials.

    3. Structural failure.

    4. Change in materials or geometry.

    5. Thermal and moisture changes.

  3. Determine possible consequences if cracks are left unrepaired.

  4. Evaluate alternative methods of repair.

  5. For cracks associated with thermal movement, look for:

    1. Horizontal or diagonal cracks near the ground at piers in long walls, due to horizontal shearing stresses between the upper wall and the wall where it enters the ground.

    2. Vertical cracks near the ends of walls.

    3. Vertical cracks near the top and ends of the facade.

    4. Cracks around stone sills or lintel, due to expansion of the masonry against both ends of the tight fitting stone piece that cannot be compressed.

3.02 PREPARATION

Surface Preparation:

  1. Do not proceed with installation of joint sealers until contaminants capable of interfering with their adhesion are removed from joint substrates.

  2. Surfaces adjacent to joints or other areas of application shall be cleaned of dirt, dust, grease, oil or other foreign matter detrimental to bond of epoxy injection surface seal system.

  3. Entry ports shall be provided along the crack at intervals of not less than the thickness of the concrete member at that location.

  4. Surface seal material shall be applied to the face of the crack or end. For through cracks, surface seal shall be applied to both faces.

  5. Allow enough time for the surface seal material to gain adequate strength before proceeding with the injection.

3.03 ERECTION, INSTALLATION, APPLICATION

  1. If the crack is still damp when repairs are going to be made, be sure to use an epoxy appropriate for damp conditions.

  2. Seal both sides of cracks with an epoxy mortar or oil-free clay, leaving small holes through which epoxy resin will be injected. 1/8” to 1/4” diameter tubing can be used to form holes. Holes should be 2”-4” long and roughly 8” apart.

  3. Inject two-component epoxy using device as provided by manufacturer.

  4. Injection of epoxy adhesive shall begin at lower entry port and continue until there is an appearance of epoxy adhesive at the next entry port adjacent to the entry port being pumped.

  5. When epoxy adhesive travel is indicated by appearance at the adjacent port, injection shall be discontinued on the entry port being pumped, and epoxy injection shall be transferred to next adjacent port where epoxy adhesive has appeared.

  6. Perform epoxy adhesive injection continuously until cracks are completely filled.

  7. If port-to-port travel of epoxy adhesive is not indicated, the work shall be stopped immediately and the engineer notified.

  8. When cracks or joints are completely filled, epoxy adhesive shall be cured for sufficient time to allow removal of injection or port sealing devices.

  9. The outermost quarter inch of the crack shall be filled with a colored epoxy material of the installers choice subject to prior approval of the RHPO. The colored epoxy filler shall match the existing material which it is filling and shall not be discernible from a distance of 15 feet.

3.04 ADJUSTING/CLEANING

Upon completion of work, remove all seal material and other residue from site. Remove and clean exposed surfaces of residue or staining resulting from this work.

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Last updated: Aug 13, 2017
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