It has not been kept a secret that America’s bridges are doing poorly in terms of durability. According to the American Society of Civil Engineers (ASCE), a shocking 25 percent of bridges across the United States are structurally deficient or functionally obsolete, but many of them are still in use. In addition, the average age of the nation’s bridges is resting at 42 years, as old 80 years. In order to ensure the safety of Americans traveling using these infrastructures every day, increasing bridge inspection rates is necessary, along with the best tools for the job. In order to improve this poor infrastructure, it is important to understand and select the correct combination of tolls to provide the best information.
Below is a list of key inspection techniques ranging from destructive methods such as coring and chipping, to non-destructive testing, to evaluate the properties without causing damage
1. Acoustical Techniques: Used to detect delamination, the separation of coating or the splitting of a structure into layers. This test is non-destructive and is performed using a chain drag or hammer to identify the changes in sound pitch. The advantage to this method is the lack of training needed to perform the tests and the low costs of equipment. On the other hand, not all tests may be accurate due to hearing biases and cannot be tested on bridges with asphalt overlays.
2. Infrared: This method looks into changes in infrared radiation to indicate delamination from the surface of concrete. Once again, this method cannot be performed on bridges with asphalt overlays, however, it can be performed quickly in a moving vehicle, thus minimizing bridge downtime. On the other hand, the data must be obtained when there is a large thermal gradient between the bridge and ambient temperatures.
3. Visual Inspection: The straightforward approach that only requires the naked eye to inspect for potholes, cracks, spalling etc. This is a good starting point, however, this approach does not provide a proper assessment of what is happening on the interior, and only analyzes issues in need of immediate repair. Damages are easy to take note of, but the most costly at this stage.
4. Coring and Chipping: Even using non-destructive tests, coring and chipping may be needed to some extent to connect to the rebar or justify findings. Cores can also be used to analyze the mechanical and chemical properties of the concrete, as well as, its strength. All this information goes beyond the possibilities when using non-destructive testing. Although more can be learned through coring and chipping with added reassurance, there is a higher cost when taking apart the infrastructures one is attempting to maintain and repair.
5. Ground-Penetrating Radar (GPR): This non-destructive test uses electromagnetic radiation to detect the reflected signals from subsurface structures. GPR assesses the quality and uniformity of concrete surfaces and deterioration on bridge decks using the reflective signals to detect changes in material, voids and cracks. This technology is well-suited for strict budgets and provides quantitative data as opposed to subjective.
6. Half-cell Potential: This method assesses the voltage between the rebar in the concrete and an electrode placed on the concrete’s surface. This method can detect corrosion before it progresses to the point of delamination, allowing the problem to be solved before ever arising. This test method is being innovated by many civil engineering firms, especially Giatec Scientific. The Canadian-based company is the only one in Canada currently producing concrete testing technologies. Their XCell tablet is used to test the half-cell potential in concrete, and with its Bluetooth capabilities, all the data is stored and shared to other connected devices, in particular, laboratories for a full analysis. This company is also releasing the iCor product in the year 2015, that for the first time ever, will not need direct connection to the rebar. These two products would be of great help to the hypothetical bridge inspection initiative America should consider pushing forward.
With so many ways of inspecting the current bridges, it is time to push an initiative forward to ensure these techniques are being used to their full potential. GPR technology is becoming more popular as it enhances inspection results, however, as the half-cell potential tests are becoming more innovative each year. With companies such as Giatec Scientific continuing to innovate, bridge inspection techniques should be advanced enough to push forward the initiative to make America’s infrastructures safer and more durable.
Sources: Roger Roberts, Structure Magazine
, CBS Minnesota
, Rhodes University