Spalling of concrete is a breakaway of the concrete surface, extending to the top layers of reinforcing steel. It leaves the concrete surface patchy and pitted while exposing aggregate underneath.
As soon as spalling is spotted, it should be repaired; otherwise, it may impact the integrity of the concrete element and affect the ultimate capacity of the member.
The repair technique to be adopted for concrete spalling varies based on the severity of the damage, type, and location of the concrete structure. It should be performed based on recommendations of applicable codes such as ACI Code and BS EN 1504.
The epoxy resins to be used in the mortar for the repair of spalled concrete shall have the standard requirements as mentioned in the table below:
|Pot Life||90 minutes at 25 degrees Celsius |
60 minutes at 30 degrees Celsius
45 minutes at 35 degrees Celsius
|Bond Strength||12 MPa|
|Tensile Strength||16 MPa|
Proportioning and Mixing of Epoxy Mortar
- The resin and hardener shall be mixed before adding the dry filler.
- The mixed ready-to-use mortar should not contain lumps of unwetted filler and should be uniform in color.
- For a total weight of 1 kg or less, hand mixing will be sufficient.
- For quantities above 1 kg, the components shall be mixed for 3 minutes at a slow speed (400-600 rpm) with a jiffy mixer.
- The stirrer shall be moved up and down and along the sides until an even streak-free color is obtained. Whipping in an excessive amount of air shall be avoided.
- If no power is available, a flat putty knife may be used to reach into the corners of the can and hand mixing done for at least 5 minutes.
Surface Preparation of Spalled Concrete
- The surface upon which epoxy is to be placed shall be free of rust, grease, oil, paint, asphalt, loose material, unsound concrete, dust, or other harmful materials.
- Since cured epoxy does not provide an adequate bond with any material, all overlay, whether epoxy or cement-based, shall be done within the pot life of the base epoxy layer.
- Contaminants, such as oil, grease, tar, asphalt, paint, wax, curing compounds, or surface impregnates like linseed oil, including laitance and weak or loose concrete, shall be removed.
- When bonding to asphalt, the surface should be roughened, so that clean aggregate is exposed.
- Epoxy bonding agents shall not be applied when it rains or in standing water.
- The surface must be dry.
- Two general methods of surface preparation shall be followed:
- The mechanical method includes grinding, grit blasting, water blasting, and scarification.
- The chemical method includes acid etching with 15 percent by weight of hydrochloric solution, followed by repeated flushing with a high-pressure stream of water.
Applications of Epoxy Mortar
- Epoxy primer coat shall be applied with the help of stiff nylon bristle brushes or hard rubber rollers, or spray gun depending upon the nature of the surface and extent of the work area.
- The coating shall be uniformly thick as far as possible.
- Before the primer coat is fully cured, epoxy mortar shall be applied using trowels and floats.
- The interval between the application of primer coat and epoxy mortar shall be approximately 15-30 minutes depending upon the ambient temperature.
- Seal coat shall be applied after curing for 24 hours, after mild roughening of the surface of the mortar.
Coverage of Epoxy Mortar
The coverage of the resin mix would depend on the system of resin used. However, as a general guideline, the coverage area shall be as under:
- Primer Coat- 1 kg of resin hardener mix covers an area of 3-6 square meters per coat depending on the finish of the concrete.
- Epoxy Mortar - 1 square meter of surface requires approximately 20-24 kg of epoxy mortar when laid to a thickness of 10 mm.
The seal coat applied covering the area of 4 to 6 square meters per kg, depending on the temperature of the application.
Handling Precautions of Epoxy Mortar
- Epoxy resins can cause skin irritation to the people with sensitive skin, if incorrectly handled.
- The resin and hardener should not be allowed to come in direct contact with the skin.
- The most effective way of protection is achieved by wearing rubber or polythene gloves.
- Rubber gloves, with a cloth liner, and protective clothing shall be worn.
- Barrier creams are recommended but are not substitutes for protective clothing.
- Eyes shall be protected where splashing could occur while spraying or mixing.
- Good ventilation shall be ensured, and inhalation of vapors avoided.
- If materials are sprayed, a respirator shall be used.
- In case of skin contact, the area shall be immediately washed with a cleaner, followed by soap and water.
- If contact occurs with the clothing, it shall be immediately changed to prevent further skin contact, and if the contact occurs with both the components (resin and hardener), the clothing shall be discarded.
- All emptied, used buckets, rags, and containers shall be removed from the site. These shall be stored in waste disposal bags and suitably disposed of.
The required bond strength is 12 MPa and tensile strength is 16 MPa for epoxy mortar used to repair spalling concrete.
For a total weight of 1 kg or less, hand mixing will be sufficient. For quantities above 1 kg, the component shall be mixed for 3 minutes at a slow speed (400-600 rpm) with a jiffy mixer.
The interval between the application of primer coat and epoxy mortar shall be approximately 15-30 minutes depending upon the ambient temperature.