Above: During visual inspection, the investigator notes and documents freeze/thaw damage on a concrete pier cap. Right: The core sample from a bridge deck shows an asphalt layer over the concrete base. The core reveals longitudinal cracking that would not be apparent on surface examination. Photos: CTL Group
Concrete bridges are major investments and critical to their local transportation systems. They also are subject to deterioration due to traffic, trauma, and exposure to the elements. Therefore, prudent owners schedule periodic condition evaluations to keep bridges functioning safely and make the best use of maintenance resources.
A thorough condition evaluation, when performed by qualified engineers and technicians, can accomplish several tasks:
- Assess the structure's existing condition and document any damage or distress.
- Determine the causes of any observed deterioration.
- Identify the potential for future deterioration.
- Indicate the most appropriate rehabilitation methods.
- Estimate the structure's remaining service life.
Such information is important to any infrastructure management program.
Condition evaluation relies on visual inspection, nondestructive testing, and material sampling and testing. Each requires specialized skills and training to yield the most accurate and useful results.Visual Inspection
The simplest and most common approach, visual inspection can produce much useful information. A methodical, hands-on inspection can identify and document visible distress and its severity in concrete. It looks at cracking; scaling or exposed aggregate; spalling; exposed or corroded reinforcement; efflorescence and other stains; and honeycombing.
A thorough visual inspection might also include hammer sounding of the concrete surface. This technique can help investigators locate and identify areas of near-surface delamination.
Visible damage and distress provide clues about underlying deterioration mechanisms that can be extremely useful in developing a cost-effective, targeted follow-up program.Nondestructive Testing
Once a visual inspection has identified likely trouble spots, nondestructive testing can be used for additional in-depth information such as:
- The size, location, and orientation of reinforcement and other embedded steel
- The concrete's quality and structural integrity
- The location of any hidden damage or deterioration
- The potential for and current rate of corrosion in embedded steel.
Certain nondestructive techniques also can evaluate large areas quickly or with less disruption of service than would be required with more invasive evaluation methods (see sidebar).