Repair Procedure

  • Surface preparation.
    • Remove any damaged or loose concrete.
    • Avoid damage to sound concrete that is to remain in place by saw cutting the perimeter of the
      repair
       area or taking other appropriate measures acceptable to the Engineer.
    • Unless otherwise approved by the Engineer, use only hand tools or power-driven chipping hammers (15-lb. class maximum) to remove concrete.
    • If the damage occurs at the end of a member and prestressing strand is exposed, recess the strands a minimum 3/8-inch using a torch or other approved method. Do not overheat or damage the surrounding concrete.
      NOTE: In the past some Contractors and Fabricators opted not to recess prestressing strands in spalled areas so the protruding sections could serve as dowels for the
      repair
       material. While the strands would serve well as dowels in those circumstances, they could be exposed to moisture and chlorides if the
      repair
       fails over the life of the structure. For that reason it is more important that the strand be completely recessed.
    • Ensure substrates are clean and sound. Remove any contaminants, including laitance, oil, dust, debris, or other foreign particles.
    • Just prior to coating or
      repairing
      , blast the repair area using a high-pressure air compressor equipped with filters to remove all oil from the compressed air.
    • For minor spalls in which a short longitudinal section (less than 4 inches) of mild reinforcement or prestressing strand is exposed, the steel should NOT be removed. Nor should sound material behind the steel be excavated unless more than half the bar circumference is exposed, in which case the spall should be classified as Intermediate.
    • It is not necessary to install dowels or provide other mechanical anchorage in applications less than 1 ½ inch thick. The Engineer may require dowels, typically stainless steel expansion anchors, in thicker applications to help tie the
      repair material
       to the parent material in case of a delamination.
  • Mixing.
    Measure the proper quantity of each component per the manufacturer’s requirements, then dispense into a clean container. Do not estimate the proper amounts while adding the different components.
    Mix the liquid components thoroughly using a low-speed electric drill (400 – 600 rpm) and a clean “Jiffy” type mixing paddle. Do not mix Type VIII neat epoxy or epoxy mortar by hand.
    • If utilizing whole batches, mix the liquid components for a minimum of 3 minutes or in accordance with the manufacturer’s instructions.
    • If using partial batches, mix for at least 1 minute or until the material is well-blended and uniform, whichever is longer.
    Slowly add the sand or other approved aggregate to the epoxy compound while mixing with an electric drill and paddle. Mix the material until the epoxy mortar is well-blended and all sand particles are coated (1 minute minimum after the sand is added).
    Mix an adequate amount of additional neat epoxy compound for use as a waterproofing and bonding layer.
    Set times vary significantly depending on type of epoxy and ambient conditions (temperature, wind, humidity). In hot weather (greater than 90°F) place a partial batch in a cup to determine set-up time, and adjust production volumes accordingly. 
    Adhere to manufacture's storage and shelf life recommendation.
  • Neat Epoxy Application.
    • Surface must be dry and clean prior to application of the repair material.
    • Brush, roll, or scrub the material into the prepared substrate to ensure that all small voids are filled.
    • Cover the entire damaged area, including exposed steel reinforcement and dowels when applicable, with at least 10 mils of the neat epoxy compound.
      NOTE: Members of the repair crew should have a wet-film thickness gauge to periodically check that neat epoxy is being installed in adequate application depth. Inspectors should also carry wet-film thickness gauges so they can verify adequate minimum thickness.
  • Epoxy Mortar Application.
    • Apply a layer of neat epoxy compound to the substrate as outlined above to serve as a bond coat layer for the repair mortar.
    • Trowel-apply the epoxy mortar into the repair area while the bonding layer is still tacky. If the bonding layer loses its tackiness prior to
      repairing
      , clean the epoxy surface and apply additional neat epoxy before proceeding.
    • Limit repair depth to 1 inch when using epoxy mortar unless otherwise approved by the Engineer. In multiple lift applications wait until previous lift has cured sufficiently to prevent sagging prior to applying the next lift. Apply a bonding layer of neat epoxy between each lift.
  • Finishing.
    The Contractor should consult the Engineer before
    repairing
     minor spalls in which an aesthetic treatment will later be applied.
    As noted above, the Engineer may require that white or gray sand be used to produce epoxy mortar if a
    repair
     will remain visible in its final configuration. Such
    repair
     should not be easily discernible if viewed from more than 25 feet away. The Engineer will review other methods proposed for blending
    repairs
    .
  • Curing.
    The required time for the material to cure properly can increase significantly when the ambient temperature is below approximately 50°F. If artificial means are used to heat the in-situ neat epoxy or epoxy mortar, ensure that the air around the repair material does not exceed 130°F.
    Moist curing is not required.