In today’s lexicon, the word “concrete” has come to symbolize strength and the image of being set in stone. Yet, for all its seeming permanence, concrete has come under attack from both natural and manmade forces since the time it was first formed and poured. The relative rate of degradation resulting from these assaults depends on a wide variety of factors of which only some are controllable. Fundamental understanding of these factors provides the foundation for recognizing when your facility is need of repair.
There are any number of variables that can affect the strength and integrity of concrete. For example, concrete made with too much water, or water with impurities or chemical compounds beyond certain thresholds, will impact its durability. In addition, the relative size and coarseness of the aggregates in the concrete play a role in the size and thickness of the structural components in which they are to be used. Also, proper curing is critical to the integrity and strength of concrete.
Additionally, man-made forces affect degradation and are often controllable. These fall into two general categories: deterioration in structures built more than 40 years ago when the marketplace was less knowledgeable about concrete, and degradation due to obvious design deficiencies or neglect. For instance, if chemicals or some other mildly aggressive agents spilled onto a concrete surface and were not properly cleaned up, they could cause degradation or exacerbate an already-existing problem. High-pressure or high-temperature venting and physical forces such as flexing, overloading, or repeated impact are other potential contributors to the deterioration process.
Foremost among all causes of concrete degradation is the internal damage caused by the corrosion of the embedded reinforcing steel. In addition to deterioration of the steel itself, the corrosion affects the concrete surrounding it, which results in cracking, delamination, and spalling. Since virtually all of the concrete found in structures is steel-reinforced, this is a widespread problem.
Unfortunately, the manner in which concrete deterioration manifests itself typically does not indicate the true depth, complexity, or severity of a problem. The first small crack in its protective lining invites intrusion by moisture or corrosive agents. Eventually and inevitably, the outward symptoms of scaling, cracking, and spalling gradually begin to appear in buildings.
Creating a Successful Repair
Concrete repair integrates new materials with existing materials to form a composite structure that can withstand environmental conditions and operational processes, while at the same time provide extended service life. The need for concrete repair is typically first witnessed by maintenance personnel. Cracking or spalling may be visually apparent and an engineer should be consulted to diagnose the problem. A typical team for a repair project includes the owner, a specialty repair contractor, the consulting engineer, and a material representative.
A range of advanced solutions, far beyond the simple concrete patch, can be utilized to implement an effective concrete repair program. Basic understanding of these options - surface repair, protection, stabilization, strengthening, and waterproofing - will allow selection of the best program for your facility. A concrete repair specialist also can help determine both the underlying cause of the problem and the optimal solution.
Peter Emmons is president at Hanover, MD-based Structural Group (www.structural.net).