Many choices exist in today's market for materials to repair concrete. Manufacturers produce a variety of materials: cement-based, acrylic-modified, epoxies and other chemicals, all of which can be confusing.
The first step in choosing a repair mortar is to determine the structural soundness of the parent concrete. For a long-term fix of concrete that is weak, unsound or severely cracked, it may be more cost-effective to replace rather than repair. If you are going to go ahead with the repair, you need to determine the cause of concrete distress and the concrete's ongoing use.
If the strength and integrity of the parent concrete has not been compromised, a repair mortar and application method can easily be selected for the repair. When a visual assessment shows severe distress such as extensive cracking in structural elements or any distress that may affect the integrity of the structure and beyond your expertise, it is best to enlist the aid of experts. A professional consultant or engineering firm may be required for extensive evaluation involving testing.
Before involving more expertise, consider a few more questions. Does the service environment contribute to the problem? Is the area interior or exterior? Will freezing and thawing occur? What type of traffic loads is the parent concrete subjected to? Is the area subject to extreme heat or cold, such as near or in furnaces or freezers? Will the material be in contact with chemicals, such as deicing salts? Is the repair time sensitive? Is the area to be in use during the repair? Are there specific times for the repair to be conducted? These questions and others will aid in the selection of a repair mortar.
Substrate preparation is critical to the success of repair. During the site condition survey, the methods and equipment required to properly prepare the area should be determined. Factors to consider in the selection process include the type of repair required, i.e., cracks, partial depth or full depth; size of the repair; condition of the concrete; and type and amount of contaminates on the concrete. In addition, the methods and equipment should be chosen to conform to any environmental requirements or time-sensitive issues on the jobsite. Can water, chemicals or dusty abrasives be used? Note more than one type of preparation and/or cleaning method may be required to suitably prepare the concrete for repair.
Selection of the repair mortar
The workability of the product is an important consideration. Repair mortars are formulated to be trowel applied, pourable, pumpable, spray applied, flowable or self-leveling.
Flowable mortars work well in fairly flat horizontal applications. Spray applied mortars are best suited for large volume applications involving vertical and overhead placements. Trowel or hand-packed applied mortars can be formulated for vertical, horizontal or overhead applications. Normally vertical and overhead trowel applied mortars are formulated to hang well during placement. Trowel applied horizontal repair mortars normally will contain slightly larger sands to provide for better abrasion resistance. Form and pour mortars are normally designed to include aggregate for more volume repairs. These are also pumpable for faster placement.
The set time and speed of strength development is also an important factor. How soon will the area be required to be reopened to traffic? A bridge deck repair on a busy roadway would require a mortar with rapid setting, high early strength development, while a repair to a residential sidewalk in most cases would not.
Other important considerations for the physical properties of the repair mortar include freeze/thaw resistance for areas subjected to repeated freezing and thawing and coefficient of thermal expansion, for repairs subject to changes in temperature. Material should be similar to that of the concrete being repaired.