Chapter 2: Damage Assessment and Repair Types

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Section 1: Defining Concrete Spalls

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Description

Spalls are categorized based on severity of damage per the definitions in this Section. Once a spall has been categorized, then an appropriate repair material and installation procedure can be selected.

Reference: Standard Specification Item 429, “Concrete Structure Repair.”

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Notes

Based on severity, spalls can be categorized as minor, intermediate, or major. Appropriate repair materials and methods differ significantly depending on the spall depth, size (area), and configuration (horizontal, vertical, or overhead). The guidelines in this section help define various spall types. These are general definitions; depending on the circumstances, an Engineer may define spall severity differently than these definitions, on a case-by-case basis.

This section does not apply to spalls in the riding surfaces of bridge decks. Refer to the Chapter 3 sections on Bridge Deck Repair when addressing such damage.

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Spall Categories

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  • Minor Spall:
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    • Damage is less than 1 inch deep and it covers an area less than 12 square inches. However, if the majority (more than 50%) of a reinforcing bar circumference or strand is exposed due to inadequate cover then the spall would be classified as Intermediate even if it is less than 1" deep.
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    • The Inspector may elect to designate patches that cover areas larger than 12 square inches as minor depending on the location and extent of the damage.
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    • A deeper spall (2" maximum) can be categorized as minor as long as it does not progress beyond the outer layer of reinforcement.
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  • Intermediate Spall:
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    • The damage exposes a majority (more than 50%) of the outer cage of reinforcing steel or strand circumference, or the damage is greater than 2" deep.
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    • The maximum depth of an intermediate spall is 6 inches.
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    • No significant stresses are likely to develop due to service loads.
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  • Major Spall:
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    • Damage extends well beyond the outer cage of reinforcement.
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    • Significant stresses are likely to develop in or immediately around the patch material due to service loads.
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Selecting an Appropriate Repair Procedure

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  • Minor Spall:
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    • 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.
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    • Excavating the concrete to expose all corroded sections of the bar is the only way to stop 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.
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    • 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.
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    • Building up thin spalls with epoxy mortar is generally an aesthetic decision. Mortar should not be applied if the damage will occur over vehicular or pedestrian traffic. In those cases only neat epoxy should be applied.
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  • Intermediate Spall:
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    • Proprietary, bagged concrete repair materials are typically used to patch intermediate spalls. Use only preapproved materials meeting the requirements of DMS 4655, “Concrete Repair Materials.”
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    • A common mistake when choosing bagged 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 patch material. Limiting compressive strength and Modulus of Elasticity are the best ways of achieving that.
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    • Vertical and Overhead Repairs:
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      • 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.
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      • In deeper applications the Contractor may propose to patch 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.
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      • 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 shrinkage cracking if not applied or cured properly.
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  • Horizontal Repairs: Form-and-pour materials are typically the best option in horizontal applications because they can be extended with coarse aggregate, which significantly reduces the potential for shrinkage cracking.
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  • Precast Concrete Production Yards: Batched concrete is readily available in precast concrete plants. Therefore, fabricators should typically use batched concrete (same mix design) as that used to fabricate the damaged member, even when the spall is classified as intermediate.
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  • Major Spall:
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    • Major spalls typically involve deep repairs to members in which capacity has been reduced as a result of the damage. 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.
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    • 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.
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    • 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.
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