Hello Professor Albert,
Thank you for the question. Some of the bridge deck data sets featured in this research were collected last year around this time. A few of them were collected the morning after it had rained and we did not encounter problems where we could not see the rebar reflections. Additionally, we have been monitoring reinforced concrete slabs that are ponded with a salt solution for a few days and then the salt solution is removed for data collection. Similar to the bridge decks, we have not encountered any problems viewing the rebar reflections during data collection.
The data we have collected has solely been on bare concrete decks and reinforced concrete slabs without any concrete or bituminous overlays. Based on the ability to see the rebar reflections the morning after it had rained, and a few days after ponding, I do not anticipate issues while scanning bridge decks with overlays. However, working with bridge decks with overlays is the next step in our research, and therefore I would have a more conclusive response at that time. Of course the data cannot be collected during precipitation conditions.
Nicole

Hello Professor Shin,

Thank you for the kind words and your question. You are completely correct, it is very difficult to determine thresholds based on visual inspection because many times corrosion is not yet visible on the surface of the deck! I use the amplitude of the reflection at the rebar level to define the health state of the bridge. However, through my studies, I have found that one amplitude value cannot be used to quantify all bridge decks. Therefore, I use statistical calculations, more specifically the mean and skewness, of the amplitudes to characterize the deck. Once you calculate these parameters, the graph provided in the presentation can be used to determine how much (%) the bridge deck is corroded. It can then be at the discretion of agencies to determine at what percentage they believe the bridge should be repaired/replaced.

Nicole

Hello Professor Buneo,

Thank you for your question. Yes, visual inspection and chain drag are the primary methods currently used to determine deterioration quantities of bridge decks. However, as you pointed out, this method is for advanced stages of concrete deterioration when delaminations are present. Many researchers have investigated this question by using chain drag and GPR to quantify deterioration of the same bridge deck. These researchers then obtained cores at various locations of the deck to verify the findings and saw that GPR correctly identified deterioration more reliably than chain drag.

For each of the bridge decks we have analyzed we also obtained a chain drag survey. We found that while the chain drag method identified a large portion of the deterioration, it missed areas that were corroded but not yet delaminated.

Nicole

Hello Professor McDonald,

Thank you for the question. As soon as corrosion is identified, in my opinion, action should be taken. Much of my work is geared toward preventative maintenance and this is certainly a form of that. If the corrosion is in its early stages, there are methods available that can extract deicing salts from the concrete which can slow the process. In later stages, areas of the concrete cover that are corroded can be extracted, the rebar can be cleaned, and new concrete can be poured. This is often carried out in Massachusetts. If most of the bridge deck is corroded, all of the concrete cover can be removed by methods such as hydro-demolition, which cleans the rebar while extracting the above concrete. After this a new deck can be poured.

The research I have completed has not taken in account earthquake areas. However, if the corrosion is in its later stages, where cracks and delaminations have formed, earthquakes could certainly ‘aggravate’ the cracks and delaminations, extending their length and severity. Therefore, decks that are in this state should most definitely be checked of their integrity after an earthquake event.

There are ways to avoid corrosion of the rebar. Reinforcing steel with coatings (i.e. epoxy) are available to reduce the corrosion risk. Also, some bridges are created by using fiber reinforced polymer composites. However, these materials require a larger initial upfront cost, which some agencies are not willing to spend.

Nicole

Hello Professor Pfromm,

Thank you for your question. There is physics as to why these phenomena are seen. First of all, electromagnetic signals are scattered when they come in contact with materials of differing dielectric properties. An example of this would be at the concrete-rebar interface. Additionally, with a higher dielectric constant and higher conductivity, the attenuation of the electromagnetic signal increases, or in other words, the amplitude of the signal is decreased.

We have recently conducted experiments to identify what component (i.e. chloride, cracks etc.) of corrosion contributes the most to increasing the dielectric constant and conductivity. We have completed chloride analyses of the concrete, and have computationally modeled these various components of corrosion. We found that it is the chloride that is the main contributor in attenuating the signal (or increasing the dielectric constant and conductivity).
Nicole

Excellent, thanks!

Hello Professor Drayton,

You are absolutely correct. These methods will allow for quick, immediate and accurate assessments of bridge decks. Agencies can then prioritize which decks need attention immediately, and then allocate the necessary funds to do so. Some of the decks we analyzed were around Boston, Massachusetts, and the district we spoke with seemed very impressed with out methods and findings. We are in the process of speaking with other nearby agencies to show them all of the advantages of these methods compared with their traditional methods like visual inspection and chain drag. It seems that agencies are impressed and are moving towards these methods. However, it does have an initial up front cost so that is causing the change to be slower than desired.

Thank you for your comment.

Nicole