Structural concrete condition assessment and repair methodologies

Concrete repair is becoming more frequently required as the concrete industry develops and grows. However, with the increasing number and age of concrete structures as well as recurrent maintenance deferrals and increased public awareness of deterioration and maintenance needs, repair is becoming a major focus of design and construction activities.

In short, performing a concrete structural assessment includes:

• Conducting a condition survey with a scope that is consistent with the perceived condition of the structure and the owner’s repair objectives. This is performed by a professional engineer to document and evaluate visible and concealed deterioration, distress, defects and damage, as well as potential future deterioration and distress.
• Determining the cause of the damage or deterioration. Such causes can include:
  • mechanical damage, such as impact or abrasion
  • design, detailing, or construction deficiencies
  • chemical damage, such as alkali-aggregate reaction
  • physical damage related to cycles of freezing and thawing or thermal movements
  • corrosion of the steel reinforcement caused by improper placement
  • carbonation of the concrete
  • chloride ingress into the concrete to the reinforcing steel
• Assessing the application and service conditions to which the concrete repair material is, or will be, exposed.
• Determining the repair objectives, including desired service life.
• Selecting a repair strategy, including consideration of an appropriate protection system in conjunction with future maintenance, while keeping in mind what is required to preserve or protect the structure and repairs, and what actual maintenance is likely to be available.

Repair procedure and methods

A repair project typically involves removing deteriorated, damaged or defective concrete. After removing the concrete, the most important step in repairing a concrete structure is preparing and cleaning the surface of the repair area. Common surface preparation techniques include abrasive blasting, shot blasting, water blasting and cleaning methods.

Quality control and assurance procedures are required throughout the concrete removal and surface preparation stages. These can be accomplished through visual inspection, soundings and using a covermeter or other means to locate reinforcements. Sounding is an excellent means to identify delaminated and debonded concrete; however, identifying subsurface cracks, microcracking and the extent of deterioration or other internal defects may not be determined by these methods alone. Other means of evaluation should be used to properly identify the extent to which concrete is deteriorated or damaged and to verify its complete removal in the repair process. Various evaluation methods (ACI 228.2R and ICRI 210.4) can provide valuable information about the condition of the concrete repair before, during and after concrete removal.

There are various repair techniques for restoring damaged and deteriorated concrete and reinforcing steel. Each repair method has unique advantages, depending on specific project factors, such as physical constraints of the repair area and costs. Here are different concrete repairing methods that can be applied at the discretion of the professional engineer,

• Crack repair
  • Epoxy injection
  • Injection grouting
  • Polyurethane sealants
  • Strip-and-seal systems
• Surface repair and concrete replacement
  • Conventional concrete repair method consisting of forming and pouring on horizontal surfaces
  • Form and pump (vertical and overhead repair – partial depth)
  • Hand applied (vertical and overhead repair)
  • Shotcrete (vertical and overhead repair – partial and full depth)
  • Low-pressure spraying (vertical and overhead repair – partial depth)
  • Preplaced aggregate (vertical and overhead repair – partial depth)

Conclusion

BBA’s structural engineering team has worked on various types of concrete assessment and repair work for aged structures, such as powerhouses, penstocks, tunnel plugs and chemical concrete containment structures. We have experience with epoxy and resin injections, shotcrete and grout and will be able to support clients in maintaining and upgrading their concrete structures.