Proprietary concrete repair materials - primarily pre-bagged mixes to which you add a fixed amount of water - are becoming more popular for repair of structural concrete for a couple of reasons. First, most of these products are produced using fairly strict quality control measures. This means that performance of the finished product is consistent and predictable. Second, an increasing number of products are available for a wide range of applications.
Selection of Materials
Consider several material properties when selecting or reviewing a particular repair product. These include strength, permeability, adhesion (bond), corrosion resistance, and application method. Base selection of a repair material on its intended purpose. Repairs that will carry loads, such as bearing repairs, need a higher strength. Repairs for protection of reinforcing steel, such as restoring concrete cover, don't necessarily need high strength, but they should have adequate bond and lower permeability. The key to selecting an appropriate repair material is to understand its purpose in the repair.
Many products are capable of obtaining very high strengths, some at a very early age. Strength is often the best selling point for various products. In general, the higher the early strength gain, the lower the service life of the repair. This is because the ingredients used to obtain high early strength (lots of Type III cement, accelerators, water-reducing agents, etc.) can result in repair concrete with a higher potential for shrinkage cracking and more brittle than the concrete it is repairing. Use a material with strength appropriate for the type of repair.
Some products produce very dense, low permeability patches suitable for repairs in marine environments or where exposure to salt is high. Other products contain corrosion inhibiting admixtures that can reduce corrosion of steel in the new concrete. Without additional mitigation measures, these products often accelerate corrosion in the surrounding original concrete (referred to as "patch-accelerated corrosion" or "halo effect").
Adhesion is also an important property to ensure that the repair material will adhere to the original concrete. Keep in mind that adhesion is most affected by the quality of the original concrete. No repair product, no matter how well made, will adhere to an unsound substrate.
Application method is another key factor to consider. Repair products can be applied by several methods: forming and pouring, pressure grouting, troweling, or pneumatic methods (shotcrete). The 2004 specification for Concrete Structure Repair (Item 429) refers to a new DMS-4655, "Rapid-Hardening Cementing Materials for Concrete Repair." This document, which will be online, will list pre-reviewed repair products by application: vertical or overhead, horizontal applications such as decks, and pneumatic methods. The list will not be comprehensive but can be used as a guide to review products not on the list.
Most if not all proprietary repair products have specific mixing and placing requirements. These are usually printed on the bag but can come as a separate sheet of instructions. Follow these instructions exactly as stated. Even slight deviations can result in poor performance of the repair. The instructions will also identify limitations on the use of the product. TxDOT encourages major suppliers of repair products to provide their instructions in English and Spanish.
Surface preparation is the most important step in the repair process. Failure to remove all unsound concrete will result in a repair that will not perform as desired. The American Concrete Institute (ACI) and the International Concrete Repair Institute (ICRI) both have excellent references for evaluating the quality of the prepared substrate.
Contact the Bridge Division’s Field Operations Section at (512) 416-2265 for more information on repair products and their application. Engineers in this branch are experienced in concrete repairs and familiar with most of the repair products on the market.