Judges’ Queries and Presenter’s Replies

  • Icon for: Mary Albert

    Mary Albert

    Judge
    May 21, 2013 | 03:12 p.m.

    This technique shows promise under dry conditions, but radar cannot penetrate water. Do you anticipate that water retained in cracks or between layers in roadways may cause problems?

  • Icon for: Nicole Martino

    Nicole Martino

    Presenter
    May 21, 2013 | 07:46 p.m.

    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

  • May 21, 2013 | 07:05 p.m.

    very nice approach to the problem, as defined. Congratulations on your findings. I guess the main question I have is what is the output that you used to define the health state of the bridge so that threshold values for your measurements can be set? I would imaging it is difficult to choose thresholds based on current appraisal techniques such as visual inspection. So when is the bridge in danger of some sort of catastrophic failure due to the rebar condition and how will the severity be scaled?

  • Icon for: Nicole Martino

    Nicole Martino

    Presenter
    May 21, 2013 | 07:57 p.m.

    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

  • May 21, 2013 | 07:48 p.m.

    Well done! I’m not familiar with the chain drag method you mentioned but apparently it is still widely used. Can your own methods be used validate or invalidate the chain drag method in cases of advanced deterioration?

  • Icon for: Nicole Martino

    Nicole Martino

    Presenter
    May 21, 2013 | 08:10 p.m.

    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

  • May 21, 2013 | 10:46 p.m.

    Very nice job. Here in the Bay Area with daily reports about the troubles associated with bolts, rods and cables in the new Bay Bridge I can see that this is a really important problem. My question is once you identify corrosion in the rebar, at what point do you need to take action (and does it depend if you are in an earthquake area), what action do you need to take? Is there anyway to eliminate/avoid corrosion in the first place perhaps through different materials of construction or methods of use?

  • Icon for: Nicole Martino

    Nicole Martino

    Presenter
    May 22, 2013 | 08:58 a.m.

    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

  • Icon for: Peter Pfromm

    Peter Pfromm

    Judge
    May 21, 2013 | 11:53 p.m.

    Nice work with potentially big engineering impact! Is there a hypothesis (based on physics and physical chemistry) why you see these phenomena in GPR? Can you propose experiments to find out about underlying phenomena?

  • Icon for: Nicole Martino

    Nicole Martino

    Presenter
    May 22, 2013 | 09:08 a.m.

    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

  • Icon for: Peter Pfromm

    Peter Pfromm

    Judge
    May 23, 2013 | 10:48 a.m.

    Excellent, thanks!

  • Further posting is closed as the competition has ended.

Presentation Discussion

  • Icon for: Brian Drayton

    Brian Drayton

    Faculty
    May 23, 2013 | 11:25 p.m.

    Hi,
    To my non-engineering eye, this looks like it could be a big help with triage, in these times when there’s a big repair backlog and constraints on money for maintenance. Have you been talking with depts of transportation about trying this out, perhaps in comparison studies with some other method, so they can see relative benefits?

  • Icon for: Nicole Martino

    Nicole Martino

    Presenter
    May 24, 2013 | 08:46 a.m.

    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

  • Further posting is closed as the competition has ended.

Icon for: Nicole Martino

NICOLE MARTINO

Northeastern University
Years in Grad School: 3
Judges’
Choice

Quantifying Reinforced Concrete Bridge Deck Corrosion Using Ground Penetrating Radar

Throughout the life cycle of a bridge deck the most costly component is the deck. This is most commonly due to the damaging effects of corrosion of the reinforcing steel. Current inspection methods that decide which areas must be repaired, or which decks need to be replaced are visual inspection and chain drag. Both of these methods are only successful if the deterioration process is in an advanced stage, and visually observable cracking and spalling, or delaminations are available for deterioration quantification. However, the deterioration process starts well before these signs are noticeable, and if the process can be detected in its early stages, the cost of repair will be significantly decreased, and the life cycle of the deck will be increased. The goal of this work is to use nondestructive evaluation techniques like ground penetrating radar (GPR) and half-cell potential (HCP) to develop relationships that departments of transportation can use to quantify corrosion of bridge decks quickly, efficiently, and accurately. To accomplish this, the corrosion process was better understood by analyzing laboratory slabs subjected to an accelerated corrosion process, yielding a correlation coefficient of over 86%. Additionally, various in field bridge decks were analyzed with these methods to develop a relationship between GPR and the amount each bridge deck was corroded, resulting in a correlation coefficient of over 92%. This relationship will allow for the immediate understanding of the condition of a bridge deck, and will aid in deciding which areas require repair.