Regardless of configuration (vertical, overhead, or horizontal), the best repair method for minor spalls is typically neat epoxy or epoxy mortar. Epoxy that is formulated for concrete repair has very tenacious bond and performs well in thin applications.

Excavating the concrete to expose all corroded sections of the bar is

an effective way to mitigate

corrosion, but that typically requires the removal of sound material. Such measures are usually unnecessary unless the minor spalling is occurring over a large area.

Applying epoxy over thin spalls in which a small amount of steel is exposed will not typically stop corrosion. However, it provides an excellent waterproof barrier and can significantly slow down the rate of corrosion if properly applied.

Building up thin spalls with epoxy mortar is generally an aesthetic decision. Mortar should not be applied if the

repair

will occur over vehicular or pedestrian traffic. In those cases only neat epoxy should be applied.

Proprietary, bagged concrete repair materials are typically used to

repair

intermediate spalls. Use only preapproved materials meeting the requirements of , “Concrete Repair Materials.”

A common mistake when choosing bagged cementitious concrete repair materials is to select those with compressive strengths far higher than needed. Materials with lower compressive strengths typically perform better since they also have a lower modulus of elasticity, and therefore greater ductility. For intermediate spalls it is typically desirable not to redistribute loads into the

repair

material. Limiting compressive strength and modulus of elasticity are the best ways of achieving that.

Vertical and Overhead Repairs:

In most cases a Contractor will opt to use a trowel-applied repair material in vertical and overhead applications. The maximum lift thickness of trowel-applied materials is 2 inches or the maximum permitted by the repair material supplier, whichever is less.
In deeper applications the Contractor may propose to
repair
using pneumatically applied cementitious material, in which case they should follow the provisions set forth in Item 431. Pneumatically placed concrete is not addressed in this manual. The Engineer must approve use of pneumatically placed concrete in lieu of the repair methods outlined in this manual.
The Contractor may opt to use form-and-poured bagged material or batched concrete, which is often a better option since it can be extended with coarse aggregate. Most trowel-applied materials do not include coarse aggregate, which can lead to drying shrinkage cracking if not applied or cured properly.

Major spalls typically involve deep repairs to members in which capacity has been reduced as a result of damage

and deterioration

. The repair is meant to restore capacity of the damaged member. The best option in such applications is to use batched concrete with properties similar to the parent material.

When the mix design is unknown, the Engineer and Contractor should select an approved concrete mix that meets the requirements of the anticipated service loads.

In smaller applications it is often not practical to specify batched concrete when rehabilitating or repairing existing structures. The Engineer should determine when a preapproved bagged material is more appropriate and offer that as an alternative to batched concrete.