Several nondestructive tests can be used to evaluate concrete bridges.
Certain nondestructive techniques can evaluate large areas of concrete bridges quickly or with less disruption of service than with more invasive evaluation methods. Here are a few:
Impulse response testing detects delamination, honeycombing, cavities, and variations in structural support or restraint. It uses a low-strain impact to send a stress wave through the tested element. The impactor is usually a 1-kg sledgehammer with a built-in load cell in the hammer head.
Impulse radar testing can detect the presence and location of steel reinforcement, prestressing steel tendons, conduits, pipes, and other embedments. It also can assess the thickness of reinforced concrete structural elements, measure cover depth, locate areas of poor consolidation and voids, and detect large areas of delamination or debonding.
Ultrasonic pulse velocity testing employs low-frequency mechanical energy to evaluate hardened concrete quickly. It is used in the field to measure concrete quality and strength and to detect honeycombing.
Corrosion measurements are either standard half-cell potential measurements or direct corrosion rate measurements made by applying an anodic current pulse to reinforcement and measuring current flow rates that correlate directly to corrosion rates.
More specialized (less common) techniques
Impact echo employs transient stress waves and their reflection to rapidly detect, locate, and classify flaws within hardened concrete. This test is most often used to detect voids in pre-stressing tendons.
Laser vibrometer testing is used for force and damping measurement of stay cables and hanger cables.
Ultrasonic pulse-echo testing can detect wire breaks in stay-cable anchorages.
Thermography detects temperature differences throughout a tested element and can indicate cracks, areas of delamination, or variations in material composition.