Concrete Deterioration & Repair – 2017

AE 537  Building Failures Presentation by Bob Pirro – Struc’tur’al

Bob Pirro’s presentation on the assessment of Concrete Deterioration problems and follow up Repair/Restoration procedures is a great overview on a topic that could be an entire course in itself.  Mr. Piro provides a version of this seminar every year to Penn State students in what is always ranked as one of the best presentations in the AE 537 Visiting Practitioner Series.

One of the best lessons highlighted in the  presentation is when Mr. Piro demonstrates with visuals and discusses the consequences of lack of attention and maintenance that occurs even when there are early signs of a problem.  Early problems are not always cheap to fix but the costs go up exponentially if repairs are not performed in a timely fashion.  This is one great point, among many, that Mr. Piro made during his presentation.

Bob Pirro is the Senior Vice President of Structural Group.  He has been with Structural for over 27 years and has extensive solution building experience in the field of infrastructure restoration.   Bob manages all the East Coast offices for Structural and has over 950 people in his employ, who perform about $150 Million in restoration annually. In his spare time, Mr. Pirro serves as an Expert Witness for many attorneys and legal firms practicing in the AEC field.  Bob has authored several publications in the field of restoration and previously served as  a International Concrete Restoration Institute (ICRI) board member.  Bob received his Bachelor of Civil Engineering from Penn State in 1987.   He has been delivering a form of this seminar to Penn State for 16 years.

Struc’tur’al collaborates with clients to improve infrastructure by combining our award-winning specialty construction, repair and maintenance services with our proprietary technologies to provide innovative solutions for demanding engineering and construction challenges.  Founded in 1976, Struc’tur’al has earned recognition as one of the industry’s leading specialty contractors and is consistently ranked high in Engineering-News Record (ENR) magazine’s list of the Top Specialty Contractors. With locations nationwide, STRUCTURAL serves the commercial/government, industrial, energy and transportation markets.

 

Suggested Readings – Reference material for discussion / commentary purposes:

There are many resources on this topic, not to mention all the code requirements and code commentaries available to the industry.  The link below will take you to a site maintained by the Portland Cement Association (PCA) which is a good starting point.  Concrete deterioration and problem examples shown on the site include more details on  many of the same topics discussed by Mr. Pirro as well as other common concrete deterioration issues.

PCA Concrete Technology –  Durability

An excellent practical and illustrated source of assessment of problems related to concrete damage and deterioration comes from a project on the topic of historical preservation and restoration of historic thin shell concrete structures  that Professors Boothby and Parfitt worked on a number of years ago.  Of likely interest to AE 537 students is the fact that many of the examples in the concrete deterioration assessment module prepared by Dr. Boothby came from the University Park campus of Penn State.  A number of the actual structures shown in the examples have been repaired (some better than others), torn down or replaced while several of the less severe examples can still be seen around campus if you take the time to look.  You can review these  examples by using the link below to access an interactive Power Point slide show that permits you to view photographs of the damaged elements and try to guess the cause, suggested repair or additional procedures that would be necessary to determine the cause and suggested repair process.

 

Professor Parfitt discovers a concrete thin shell hyperbolic parabolid structure that formerly served as a car dealership show room in Vestal, NY.

Concrete Deterioration / Assessment  Slide Show:

The slide show below was put together a number of years ago to demonstrate various types of concrete deterioration and their possible causes.  Penn State students should be able to recognize some of the examples from campus buildings however many of these examples have been repaired.

module iiie assessment – investigation of deteriorated concrete – boothby

 

Follow Up Discussion:

For this discussion, I am looking forward to your thoughts and comments on the topics presented by Mr. Pirro and anything interesting to supplement the discussion that you find in the PCA reading and the campus concrete deterioration slide show.

 

Practitioners viewing this material or the student comments and questions are encouraged to participate.

mkev

 

 

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45 Responses to “Concrete Deterioration & Repair – 2017”

  1. CamilleS
    October 9, 2017 at 11:35 am #

    I was really struck by the graphic in Bob Pirro’s presentation on Concrete Evaluation and Repair Techniques that showed the timeline of exponential cost of repairs increase versus time. The prolonged time before repairs is a decision based mainly on the owner of a structure, and without proper education on the behavior of concrete overtime and the meaning of visible failures, I can see why owners are putting off decisions to repair. For example, Mr. Pirro showed a chain dragging investigation over a delaminated parking deck. Although the spalling was shallow and in two small locations, the extent of the delamination discovered was almost ten times the area of the spalls. In the development of spalls, there is chloride infiltration, rebar corrosion, delatimation withing the deck, to finally spalling. There could be a long period of time that a problem exists and can be fixed, but the effects are not visible to the untrained eye. Therefore, I agree that preventative inspections by engineers should be a part of regular maintenance, even if there is not a visible problem.

    I really enjoyed Mr. Pirro’s case study of the 50 year repair on the cooling tower. I really enjoy the way that engineers have to design repairs beyond just pouring new concrete. The problem is in the chemical condition of the concrete, and therefore good repairs require a chemical repair as well. While partial depth repairs and cleaning corrosion on rebar can fix the visible problem, I enjoy seeing how longer repairs fix the chemical process of deterioration, and how they used electrified wires to prevent further deterioration. I wish I paid closer attention in chemistry and electrical engineering to follow along with a greater understanding, but I enjoy learning about how they use other engineering beside structural engineering to approach these building failures.

  2. Keunhyoung Park
    October 6, 2017 at 8:42 pm #

    The lecture of Mr. Pirro showed us the rehabilitation cases of deteriorated concrete structures. Thanks for the lecture I could link concrete’s deterioration theory with practical cases.

    Concrete is highly beneficial material in construction industry because they can provide high strength and durability to the structures of various form. Furthermore, combining concrete and steel make a drastically improvement in structural capability and environmental endurance. In addition, huge production of lime stone decrease the manufacturing cost of concrete. Because of these merits of concrete, developing concrete technology allows us to build higher buildings and longer bridges. However, as all other structures, concrete structures has its own deterioration process due to its characteristic.

    As we know, concrete is mixed material composed of cement, aggregates, water, and several admixtures. And the cement, which has a initial roll of adhesion of aggregates, is highly alkalescent material from limestone. That means concrete keep its internal reinforcing steel bars from outer acid invasion such as water. However, chemical infiltration through porosity or cracks occur steel corrosion. Then steel expending due to the corrosion increase cracks so that chemical infiltration would be increased. In the lecture of Mr. Pirro told us how to repair by doing partial repair construction, or how to prevent by containment methods such as inspection of concrete state. As he mentioned, main virtue is that finding and fixing when its damage was in minor step is important to be safe and to reduce cost.

    On the other hand, although attack of chemical and moisture is one of most problem for the concrete, load effects from thermal loads or excessive loads are also critical causes for the concrete. For example, dam or mega concrete foundation have mass concrete structure. These massive volume of concrete without proper calculation will be a cause of massive failure from the curing heat. If they are constructed appropriately, concrete element with long length and huge depth will have a great thermal displacement. Due to the deformation, concrete structure can get a severe stress. In other case, girder with unexpected load will have a crack or serious damage since concrete have few tensile strength. These unexpected or prohibited loads cause damage in concrete structures and lead to structural failure.

    Last, Mr. Pirro pointed out that faulty workmanship. There are so many human faults in construction sites as much as concrete structures are widely built. Building construction require delicate and accurate management to achieve its numerous capability. The human error would be one of the most causes while we assess a building failure.

    The lecture gave a lot of lessons about management of concrete structures. I could conceive how to prevent severe damage of the concrete structure, and how to repair them by understanding the characteristic of the concrete from the Mr. Pirro’s lecture.

  3. Megan F.
    October 6, 2017 at 3:58 pm #

    Mr. Pirro gave a great presentation in class on concrete and concrete repairs. It was very interesting to learn about the common failures of concrete. Concrete is a very strong and durable material that is used in so many different structures. However, over time it can deteriorate and accumulate damages. This summer I assisted a lot with façade inspections on concrete buildings. It was interesting to see the process of investigation, removal, and repair of the concrete. Some areas the concrete had already spalled off but in other areas the concrete was very close to falling off the building so we would pull the loose piece out to protect the areas below. We then would mark the locations for the concrete to be removed and then squared off. The concrete needs proper surface preparation in order for the new concrete to bond. Pins would then be inserted to attach the new and existing concrete. This process actually took longer than I expected because a lot of the concrete repair locations were not squared off correctly or pins were not placed at sufficient spacing requirements. We would often have to return the next day to re-inspect and approve for the new concrete to be placed.

    • mkev
      October 9, 2017 at 5:10 pm #

      Megan,
      It always takes longer than you think. Did you have any first hand observations on how much the deteriorated rebar expands? In other words, how much larger than it’s original condition when placed?

  4. WangjaeY
    October 5, 2017 at 8:34 am #

    It was a great lecture from Mr. Pirro. There were many aspect that I have not learned about concrete such as concrete behaviors related to PH level, which is one of most driving forces to the corrosion. We as a designer often think only designing the structures rather than repairing the structures.
    I also realized that there was many interested ways to evaluate the concrete condition and how to repair. concrete is the material that requires a great attention during the design and construction. Many of the case studies provided by Mr. Pirro were the faulty workmanship during the construction. I was impressed about the repair cost vs. time that the building owners did not care much in the initial failure phase to repair even though they could save a lot of money to repair and maintain the structure if they maintain the structure correctly in the earlier phase. I was wanted to see other repair technics that Mr. Pirro prepared in the slide, but we did not have enough time to cover all.

  5. benP
    October 5, 2017 at 8:29 am #

    The part of the presentation that I found most intriguing was cathodic protection. From a field practicality standpoint, using stainless rebar has to be challenging. The cost of it is astronomical, and stainless is a lot harder, brittler metal then the standard rebar. This could create challenges cutting it and bending it. However, if we could use the same rebar the industry has always used, but make it last a lot longer, wouldn’t that be ideal? Cathodic protection does this. I did more research into this topic, and found what looks to be a sales pitch of one of Mr. Pirro’s competitors.
    This system is explained at the following link: http://www.vc-austria.com/fileadmin/media/downloads/broschueren/englisch/vc_reinforced_concrete_protection.pdf
    My understanding is the concrete is placed, a copper coating is then sprayed on the concrete, then covered by a carbon fiber mat. The copper is then powered by very small amounts of electric that will then neutralize the metals so they will not rust. It says the operating costs are very minimal, at one point comparing consumption to a light bulb.
    I would like to thank Mr. Pirro for presenting to our class, it would be very cool if he had a project in this area that used cathodic protection that we could look at.

  6. HarryB
    October 5, 2017 at 8:16 am #

    From Mr Pirro’s lecture it appears that biggest concern in concrete is keeping the rebar safe from penetrating pollutants. Mr Pirros explained that these pollutants could be chemicals and water. Both of these pollutants cause cracking corrosion of the rebar and cracking in the concrete. Cracks in the concrete make an easier pathway for pollutants to the rebar which makes the problem worse. From Mr Pirro’s presentation and Dr Boothby’s slide show the presence of water seems to be the most dangerous threat to concrete. In most of the slides in Dr Boothby’s presentation freeze thaw cracking could not be ruled out due to how common the failure is.
    This brings up another interesting point from the lecture which is the compounding nature of a lot of the failures in concrete. When caught early the failure does not cost that much to fix but if you let the failure worsen the cost increases exponentially. I have found this to be a common theme throughout the presentations in class.

    • David K
      October 8, 2017 at 10:14 pm #

      Harry,

      It does appear that water penetration is the most common cause of concrete failure. Freeze-thaw effects are most nearly never “ruled out” as a cause for a majority of the United States. However, southern regions of the country may show fewer cases of this based on the severity of thermal cycling. It also appears that water penetration may not be the primary cause of the initial failure, however, once the concrete failure begins water penetration can accelerate the deterioration process.

      • Richard T.
        October 9, 2017 at 5:27 pm #

        Dave,

        I believe that thermal cycling plays a huge role in the deterioration of concrete. In coastal regions such as the ones that Bob mentioned in his presentation it surprises me that the salt content in the air actually causes concrete to spall. What would you think would be the most cost-effective way to protect against that type of deterioration?

    • mkev
      October 9, 2017 at 5:12 pm #

      Harry,
      Many of those Dr. B examples were on campus. Did you see them or something similar when you were looking for your campus failures photographic examples?

    • Shangmi X.
      October 10, 2017 at 6:54 am #

      Harry,
      I am agree with you about protecting the rebar in concrete from penetrating pollutants is the key action. Corrosion of the rebar is the most common problem appears and is the major cause of the concrete failure. It is also depends on the surrounding environment of the building. The freeze thaw damage you mentioned is commonly happened in the cold regions where the water absorbed by the concrete can freeze then create cracks. However, some chemical components in the air and rain/snow can cause other problems to the concrete to fail. We should understand the surrounding condition to make effective actions according to it.

  7. Shangmi X.
    October 5, 2017 at 8:02 am #

    Mr. Pirro talked about the concrete failure problems and repair techniques. Before this presentation I know that concrete is the mixture of aggregate, cement and water. Concrete is always need to be reinforced that concrete carries compressive loads and steel carries tensile loads. But the chemical side of the concrete failure is I didn’t pay attention to before.
    Mr. Pirro brought up that corrosion is an electrochemical process which increases the volume of the rebar. When the metal gets the chance to touch the air which the air contains oxygen and maybe chloride, This will have big chance to get corrosion then the concrete fails. Also when the concrete gets carbon dioxide on the surface will cause the crack. Testing the ph value of the concrete is a way to test the concrete which is new to me. There are also other causes including moisture, thermal, load effects and faulty workmanship. I think being familiar to the concrete behavior will have a big help to understand the causes of the concrete failure.
    After seeing the example cases of concrete failure, I think we should always pay attention the concrete surface. The small crack on the concrete surface can cause a huge failure to the building. We need to find the problem and repair it as soon as possible to avoid bigger failure which will cost way more to repair later.

    • Shubham K.
      October 9, 2017 at 11:27 pm #

      Shangmi,

      I completely agree with you on paying attention on maintaining concrete structures. I think what a lot of owners don’t realize is that cracks on concrete structure could possibly lead to bigger and more costlier issues. Trying to save money in the short term could end up costing the owner a fortune.

  8. Jared P
    October 4, 2017 at 10:48 pm #

    Tuesday’s guest lecture Bob Pirro gave a great talk on what causes corrosion and deterioration of concrete. One thing he said that was interesting was that concrete best prevents reinforcing steel from rusting when its above 13 on the ph scale. The electro-chemical process of corrosion is minimal with highly basic concrete.
    For those who wish to remember chemistry, the way corrosion of steel occurs is when you have water and electrolytes (salts) permeating the concrete, causing the steel to oxidize. Oxidation is when the atoms give up electrons Reduction is its counter reaction. The steel in the presence of water and salt will act as a battery driving current from an anode end to a cathode end. The electrons are shed from the iron atoms of the anode (weakening the chemical composition of the steel) and sent to the cathode end. The iron atoms on the cathode side accept the electrons and bond with alchol produced within the salt water solution to create FeOH, which is the rust we see on the surface of the steel (expanding the volume of the original steel). Batteries usually are acidic which is why the ph for concrete prevents corrosion with a high ph level.

    • mkev
      October 9, 2017 at 5:13 pm #

      Nice summary Jared!

  9. JeremyS
    October 4, 2017 at 10:05 pm #

    The lecture that Mr. Pirro gave provided the class with information on common reasons that concrete fails and practical solutions. The lecture was personally interesting for me because over the summer I got to examine several concrete failures and take samples from the members. Unfortunately I never got to know what the repair process would be for those failures. Also I never suspected so much chemistry would be involved in predicting the strength of the concrete. Through my internship I also got to take chloride ion samples however I did not get to see or interpret the results. Mr. Pirro talked about how the chloride ion tests would be used to determine the concretes PH level. Furthermore he discussed the correlation between PH and corrosion and that at a certain PH level the member would start to corrode. It is most likely that the number one cause of concrete failure or deterioration is due to either corrosion or water penetration. This leads to questions such as when does the corroded concrete need repair and what are the best methods for repairing the concrete? Also what can be done when an owner refuses to repair a deteriorated structure?

    • HarryB
      October 5, 2017 at 8:33 am #

      Jeremy,

      Looking back on the presentation, if an owner refuses to repair a structure the problem only compounds. Mr Pirro demonstrated this with his $10x, $30x, $100x slides. The natural progression if the owner continues to neglect the failure is the building falls down or is ruled unsafe for use. In the event of a collapse due to owner neglect, and drawing from Mr Boyer’s MEP forensics presentation, I wonder if forensics companies can determine levels of owner neglect. Insurance companies might be less willing to pay out if they know that an owner let his building deteriorate on purpose.

      • mkev
        October 9, 2017 at 5:17 pm #

        Good question Harry. Unless there is a collapse, most of the work of concrete repair is considered maintenance and is not covered by insurance. And, you are on the right track. If deterioration is obvious and not addressed as maintenance it can in many cases be used as a reason to deny a claim. That is why Mr. Pirro’s 1x, 10x etc. example is so compelling as a lesson. Most owners have to pay this out of pocket.

        • mkev
          October 9, 2017 at 5:17 pm #

          PS: Good question for Mr. DiMenno when he lectures on Thursday.

    • Nick S.
      October 5, 2017 at 8:43 am #

      Jeremy,

      To answer your question about when to repair the concrete, in my opinion, you would have to begin to take measures for removing and repairing the failed concrete area as soon as it is discovered. How I look at it is in the same light as a cavity. The cavity is the failure and if you do not do something to remove the issue it will only continue to get worse. The same happens in the concrete scenario, if you allow the corroded area to spread it will only make things worse, creating more headaches and costing the owner more money. To answer your question about the owners refusal to do anything about the failure, you should document the situation and notify the governing body in which the structure resides. If you do nothing you are not following the engineering ethics that we are expected to abide by. However, I would hope that when an owner is notified of the issue they would take the right precautions to make sure anyone using structure is safe as safety should always be the number one priority.

      • mkev
        October 9, 2017 at 5:20 pm #

        Nick,
        You are correct that if you decide it is a dangerous situation you need to find a way to take the issue further in light of no action by the owner. That said, you can not compel an owner to do maintenance. Much of the routine damage still does not make a structure unsafe.

        Let’s look at the opposite scenario. What if the structure isn’t safe but you say it appears to need maintenance but is OK for now? Are you liable if it fails in the short term?

    • Geoffrey T.
      October 5, 2017 at 11:22 pm #

      Hi Jeremy,

      As Mr. Pirro mentioned, the longer they wait, the more expensive they cost. So, I think when it comes to repairing spalling concrete or corroded reinforcement bar, I would advise the owner to repair it as soon as possible.

      Sometimes, we might meet a stubborn owner who does not care about their building at all. The only thing that we can do is to advise them the consequences of delaying the repair. In the end of the day, it is their decision to repair it or not. Another thing that we may want to look at is the reason behind the owner’s delay. Maybe cost is one of the reasons. If that is the case, we can suggest different repair options, so that we can keep the cost low, but at the same time keep the building safe as well.

      • mkev
        October 9, 2017 at 5:23 pm #

        Good idea Geoffrey. In many cases cost is the issue. Most forensic firms try to present several different repair ideas from a budget perspective. Perhaps you can do the 5 year repair at half the cost. As long as the owner recognizes it is 5 years in lieu of 20 years that might be an option. Not likely the best life cycle option but a safe option.

      • benP
        October 9, 2017 at 9:02 pm #

        I wonder from a ratio standpoint, how many of the repairs were done correctly. The amount of attention to detail and steps that Mr. Pirro discussed are rather elaborate for the average trades-person. If you think about the average concrete sprawl, using some of what Mr. Pirro taught us, the first step, maybe the most missed is to determine the area that needs to be repaired. If this isn’t done right, then all of the following steps will be compromised. Next there is a proper cutting procedure, followed by a proper chipping procedure; concrete cleaning, rebar cleaning, existing concrete treatment, existing rebar treatment, new rebar installed, new concrete installed, new sealer installed. (I may have missed a few steps) Believe it or not, this is a lot of steps that can be missed, even for a reputable company. Also keep in mind that some of these repairs are done in very tough working conditions upside down in a hot dusty climate. What says the craft worker doesn’t perform just one of these steps properly? Potentially in a short period of time, the repair will need repaired.

        • Perry H.
          October 9, 2017 at 11:50 pm #

          Ben
          This is an interesting point you bring up. My guess is that the ratio of improper repairs to correct repairs is pretty large. And like you said most of these poor repairs stem from not diagnosing the problem correctly the first time. A concrete sprawl can seem like a small problem with an easy fix when in fact it is pretty complex and without the proper knowledge of the problem by the repair person the failure will continue to come back.

  10. Shubham K.
    October 4, 2017 at 10:00 pm #

    Bob Pirro from struc’tur’al presented in our building failures class. It concentrated on common failures with concrete and repair techniques with some case studies at the end to share his personal experience with concrete failures.

    Occurrence of concrete failures is very common, but before this presentation, I never knew the cause for it. Mr. Pirro explained that Ph-level of concrete is the immune system of concrete. As Ph in concrete drops, reinforcing starts accumulating moisture and starts corroding. From the presentation, there are six main causes for concrete problems; embedded metal corrosion, disintegration, moisture effects, thermal effects, load effects, and faulty workmanship. It was very interesting to learn how each of these causes affect a concrete structure.

    Mr. Pirro also explained importance of repair and compared cost vs time of repair. It was interesting to see how cost to repair an unmaintained building increased exponentially with time. Presentation also introduced some repair techniques like proper surface repair and placement techniques. Upgrade techniques to strengthen a section were also discussed. Traditional techniques like adding new reinforcement to carbon fiber (FRP) sheets applied to beams.

    Mr. Pirro briefly explained workings of devices like pulse velocity and impact echo which can help engineer measure strength of a particular section without damaging it. I was surprised when he said how some engineers still like to use old style methods of testing like using water barrels for tests.

    • mkev
      October 9, 2017 at 5:26 pm #

      Water is still used more than you would think. It sometimes is the less expensive option. In lieu of barrels, you sometimes see water bladders used that can be filled on the spot. Most times with water or dead weight in general you don’t want to test to the 100% load. There are test protocols for testing as a percentage of the total but monitoring deflections to make sure it is behaving in a linear fashion and thus the 100 percent load can be predicted.

  11. EllenW
    October 4, 2017 at 9:43 pm #

    The presentation given by Mr. Pirro was very thorough and informative, covering the causes and repairs of deteriorating, damaged concrete.

    During my internship with SK&A this summer, I was able to participate in concrete surveys, estimating the extent of delamination and spalls in order to give the owner a cost estimate for repair. I was able to chain drag and hammer sound the structure, marking the areas for replacement and recording the square footage of each patch. It was interesting for me to learn how and why the spalls and delaminations were formed and how the propagate through the structure. The repairs detailed by SK&A followed what Mr. Pirro showed in his presentation, with a 90 degree cut in the concrete down to a level 3/4″ below the existing reinforcement. Additionally, in parking garages, a traffic coating was installed over the repaired slab to provide traction for the cars as well as an additional layer of protection for the reinforcement, extending the life of the repair.

    I also found the comparison between damage level and cost to be very interesting and matched my experiences from the summer. As a damage level one, there was a garage that I surveyed which had isolated areas of delamination, concentrated around the entrance (where wet cars deposit the most chlorides from deicing salts used on winter roads). The estimate for this job was relatively inexpensive because the owner maintained the condition of the structure very well. On the other end of spectrum there was a garage I visited that was extremely damaged, to the point that I don’t think I would have felt comfortable leaving my car there. Columns along the expansion joint were rust stained and deteriorated, and you could see daylight through the expansion joints themselves. The bottom rebar mat on the slab soffit was exposed and corroded in many areas, and spalls were very apparent on the top of the slab. Once the soffit became delaminated, the spalls would just fall onto the cars parked below. Additionally there was a concrete beam which had the concrete cover missing from the bottom and at least 4 inches up the side of the rebar cage. The rebar was corroded and had area loss to the point of a #4 bar having the cross section of a toothpick. the beam, supporting columns, and the floor slab all had rust stains. Part of this garage had been repaired earlier and I could not believe the difference. I don’t know how much this repair cost, but it is not hard to believe that it was 100 times the cost of the earlier case.

    Thank you to Mr. Pirro for taking the time to come speak to our class.

  12. Richard T.
    October 4, 2017 at 9:32 pm #

    I want to thank Bob for coming to Penn State and talking to the students about the type of work he’s doing. I found the cases that he presented to be very interesting.

    One in particular was the collapse of the parking garage in Atlantic City. It was unfortunate that people died during this event, but hopefully we can learn from the mistakes so that things like this won’t happen in the future.

    What I also found interesting was on Bob’s reflection on the lifespan of structures and of his work. The fact that some owners want a repair to last 50 years versus other owners who only want it to last 10 years or less. Which is interesting because as an engineer you want to do your best work but you also have to respect the budget of your client.

    Another technology that I’ve never seen before that Bob showed us was the use of an induced current on a concrete structure to reduce the rust that may occur in the reinforcement. In school you learn to provide concrete cover to reduce rust or to spec epoxy coated rebar but these new improvements in the industry have yet to make it into our classes and I find it interesting that it is like that and not the other way around.

    I want to thank Bob once again for coming to our class and speaking to us about his work.

    • mkev
      October 4, 2017 at 10:00 pm #

      Richard,
      The Atlantic City garage collapse was the one at the Tropacana Casino. I recommend everyone in the class take a look at the details of that collapse by looking at the case study on the Failures Wiki,
      To me it seems just like yesterday but my guess is to the class 2003 is ancient history. https://failures.wikispaces.com/Tropacana+Casino+Parking+Garage
      MKev

  13. Perry H.
    October 4, 2017 at 9:14 pm #

    During Mr. Bob Pirro’s presentation, the repair of the cooling tower really stood out to me because I had not heard of the process of cathodic protection before. Also the magnitude of the repair was very impressive. In order to understand the process of cathodic protection the chemical definition of corrosion must first be discussed. Corrosion is a reduction-oxidation (redox) reaction which occurs when iron comes in contact with oxygen. The basis of this redox reaction is the transfer of electrons from the iron to the oxygen. The loss of electrons by the iron is called oxidation and this is how rust forms. A video which explains this is linked below.

    The process of cathodic protection is simply a way to replace the electrons that the rebar losses which prevents the rust from ever forming. This is done through the introduction of an anode which is an active metal that readily loses electrons and a D/C power source to push the electrons to the cathode which is the rebar that is being protected. The video linked below examples the process graphically.

    Mr. Bob Pirro also mentioned a way to monitor if corrosion is taking place in the system that was implemented in the cooling tower repair. I am wondering how this is done and what equipment is used to do this?

    Oxidation Definition:
    http://study.com/academy/lesson/what-is-oxidation-definition-process-examples.html

    Cathodic Protection:
    https://www.youtube.com/watch?v=VbzM-ph78us

  14. David K
    October 4, 2017 at 8:57 pm #

    Bob Pirro’s presentation provided a brief look into the various failure modes of reinforced concrete structures and the corresponding repair processes. In majority, failures in concrete structures appeared to involve the rusting and deterioration of steel reinforcing bars. Bob explained that once reinforcing begins to deteriorate within the concrete, it begins to expand and leads to cracking on the exterior surface. Surface cracks can accelerate the concrete deterioration process because moisture can more easily reach the steel reinforcing, leading to a more widespread failure.

    The aspect of the presentation that I found the most interesting was the information on the various ways in which steel reinforcing can begin to fail.

    Ph level – The Ph level of a concrete structural element effectively acts as the “immune system,” as Bob stated. A high Ph level protects the reinforcing steel from beginning the corroding process. Once the Ph is lowered, this allows the reinforcing to become much more vulnerable to moisture.

    Chloride penetration – When salts are introduced to the concrete either through road salt in the winter months or through the curing process (when slightly brackish water is used in the mixing process of the concrete), they very quickly begin to corrode the reinforcing bars and “pop” the concrete leading to spalls.

    Carbonation – The last cause of reinforcement failure that Bob mentioned was that of CO2 penetration into the concrete. Similar to chloride penetration, excessive CO2 can accelerate the oxidation process of the reinforcing steel and cause the concrete to pop and spall.

    I would like to thank Bob for taking the time to speak to us on this topic. This was my first exposure to the various chemical processes that lead to the deterioration and failure of concrete structures.

    • mkev
      October 4, 2017 at 10:02 pm #

      Bet we all wish we had paid more attention in Chemistry Class now that you see how we use it in practice. AE trivia: MKev started out as a Chem Eng. major but quickly decided he was much more interested in structural engineering.

  15. Geoffrey T.
    October 4, 2017 at 5:43 pm #

    On 10/3/2017, Mr. Pirro came to our Building Failures class and shared about concrete evaluation and repair techniques. When Prof. Parfitt mentioned that Mr. Pirro was one of the experts in concrete industry, I certainly believe that. Mr. Pirro’s knowledge in concrete evaluation and repair was very extensive and I enjoyed his talk immensely.

    Based on his talk, there were six major problems in concrete, they are embedded metal corrosion, disintegration, moisture effects, thermal effects, load effects, and faulty workmanship. The interesting thing that I never learned before his presentation was the fact that concrete pH increased as it cured. As an architectural engineering student, we often learned how to design the system using specific material without understanding how the material behaves. Thus, it was really interesting to see how Mr. Pirro shared with us the chemical properties of concrete and how it affected the building quality over time.

    Another thing that Mr. Pirro shared with us was how struc’tur’al used technology to evaluate concrete quality. For example, one of their scientists evaluates concrete using petrography. Petrography helps to evaluate concrete’s durability, surface distress, cracking, chemical attack, scalling, chloride content, etc. Mr. Pirro also shared with us the importance of technology in the forensic industry and how it improved their business as concrete specialist.

    Mr. Pirro also shared with us about how the cost of repair will exponentially increase with procrastination. As the damage got worse, the repair cost will also increase. Thus, Mr. Pirro advised us that it was important to have a budget for preventative maintenance to make sure that the building condition was monitored once every couple of years to avoid huge repair cost.

    Overall, it was a very enjoyable talk by Mr. Pirro. From his presentation, I not only learned what was the common problems in concrete, but also strategies to repair them.

    • CamilleS
      October 9, 2017 at 11:19 am #

      Geoffrey,
      I agree that it is important to understand that concrete behaves chemically, because as Mr. Pirro emphasized, the carbonation or concrete or the infiltration of chlorides into concrete causes spalling and corrosion. These behaviors can weaken the structural integrity of the cross section of the concrete and should be accounted for in concrete design, not just the required strength and serviceability of the design. In a harsh environment, such as brackish water or parking garages, designs should be made to provide protection against these chemical exposures such as traffic coatings or sacrificial anodes. This preventative design could limit the cost of more extensive repairs in the life of the structure.

    • WangjaeY
      October 9, 2017 at 11:03 pm #

      Geoffrey,

      I was also focused on the pH of concrete related to the corrosion. I never thought about the pH level of concrete affects the corrosion. This was a something structural engineers learn about the behavior of concrete. especially in forensic engineering. I also think that regular maintenance should be required in building structure to maintain the building structure itself as well as the safety of occupants.

  16. Pete Pitilis Jr.
    October 4, 2017 at 11:37 am #

    Nick,

    I agree that prefabricating concrete will help mitigate certain concrete failures, however, I believe there are certain failures that can’t be avoided even in prefabricating. For example, one failure Mr. Pirro discussed was a failure due to poor aggregate. If poor aggregate was the cause of the failure then whether or not it was constructed on site or in a shop the same failure would occur. Also, some concrete elements in a building have to be constructed on site due to their properties governed by the building layout/shape. Therefore, prefabricating isn’t always an option and is usually utilized in modular construction. Finally, prefabricating concrete could potentially lead to other failures due to difficult connections and the need of skilled workmanship.

  17. Tyler J
    October 4, 2017 at 8:13 am #

    I would first like to thank Bob Pirro for coming to Penn State to present on the topic of concrete deterioration and repair. His presentation was another topic in this class that I had some knowledge of, but am amazed at the depth of knowledge that someone like Bob has.

    One item Bob touched on significantly was the idea that the pH surrounding rebar is the root cause for oxidation and ultimately failure. When concrete is initially placed. the pH level is basic, around 13.This high pH level acts as cathodic protection for the rebar, helping it to not rust. Due to various reasons such as water infiltration, chloride penetration, and carbonation the pH level drops over time. This allows for oxidation to occur and rust to form.

    I also found it interesting that epoxy coated rebar is no longer thought to be as effective as it once was. If you drive through any road construction in Pennsylvania, the majority of rebar you see is epoxy coated. Epoxy coated rebar is extremely susceptible to cuts and dings. If the rebar is damaged in this way during installation, the benefits of the epoxy coating are minimal. Additionally, epoxy coated rebar cannot establish a strong bond with the concrete due to the coating. This can lead to rebar slippage, and ultimately to failure.

    Also interesting was the Repair Cost vs. Time graphic shown in the presentation. If concrete is properly maintained, and repairs are done at the first sign of a problem, the cost is minimal. However, if the problem is let go, the cost for a major repair or replacement can be significantly higher. A question was asked about the types of repairs that the majority of clients are looking for. A similar question has been asked in previous presentations and the answer never seems to change. The desired longevity of a repair/design is up to the client. For example, in a buildings enclosure, cheaper materials can be used or higher quality materials can be used. This decision is typically made by the owner with regard to the amount of money they want to spend and the life they would like from a building. In concrete, a cheap repair may work for a couple years, but will ultimately still lead to failure.

  18. Nick S.
    October 3, 2017 at 4:59 pm #

    On Tuesday, October 3rd, the AE 537 Building Failures class had the pleasure to hear a presentation by Mr. Bob Pirro. Mr. Pirro is a 1987 Penn State graduate from the Civil Engineering (CE) program. Currently, Mr. Pirro. is working for struc’tur’al where he is Senior Vice President of the East Coast division. As the VP he is responsible for more than 950 employees. To begin the lecture Mr. Pirro gave a brief introduction on struc’tur’al and explained how they provide design build services for its clients, adding that the company performs a majority of its own work. Struc’tur’al is able to do this because of how they own so many domestic operations including Pullman, VSL, and Structural Technologies. Struc’tur’al performs work primarily in the infrastructure repair market with offices all over the world and this year they are expected to reach the $560 million mark.

    After the introduction to who struc’tur’al is the presentation focused on discussing concrete, how it can fail, and repair techniques. Mr. Pirro began this part of the presentation by asking what is concrete and stating that concrete is made up of three components; aggregate, cement, and water. He stated that concrete performs good in compression and poor in tension, adding that there are six different causes to concrete failures. After discussing and showing examples of how each, Mr. Pirro showed some ways struc’tur’al repairs these failures.

    Overall, I was found the lecture extremely beneficial and insightful into the the world of concrete. I always knew that concrete could fail, as seen around the Penn State campus, that it could fail in different areas. But I never really understood the way and knew there were six different ways it could fail. These two topics are what really stood out. First the why, I never understood that ph levels in concrete played such an integral role. When ph is high it provides a layer around the steel and when it drops, corrosion process starts. The second in how there are so many different ways concrete can fail. It is my belief that one way to help mitigate concrete failures is through the use of prefabrication. By using a prefabricated design you allow for work to be performed in ideal conditions and allow for a quality product to produced.

    Additionally, what stood out during the presentation was the use of carbon fiber to help concrete structures from failing. The example that Mr. Pirro gave was of a cooling tower where they upgraded the structure with carbon fiber at different levels of the exterior and interior. I found this quite interesting and found an article in Concrete Construction (link below) that talked about the use of carbon fiber on concrete structures. It stated that,

    “Carbon fiber has very high tensile strength and is also very lightweight. When bonded to the exterior of a concrete column, beam, or slab, it can add significant strength without adding weight that would increase the load on foundations and other structural members.”

    It goes on to state that these wraps can be sometimes be 30% to 50% less expense than traditional strengthening methods. This would allow the owner to save money without sacrificing quality. The article also discussed the benefits, applications, and installation of the product.

    To conclude I found the lecture extremely beneficial in providing insight in how concrete structures fail. It shows that attention to details in extremely important, not just to the building envelopes, but all the way down to the foundations and structure. From this I believe, when the applicable, the use of prefabrication will become more and more the method of choice as owners, construction managers, and contractors begin to understand the quality of product they can receive.

    Link: http://www.concreteconstruction.net/how-to/materials/wrapping-it-up_o

    • Tyler J
      October 4, 2017 at 8:36 am #

      Nick,

      The article you referenced regarding the FRP wraps was a great read. I too found this technology to be interesting. As the article points out, though it is expensive, FRP wraps are often cheaper than the alternatives.

      The article also mentions a secondary benefit to these wraps in that they are impermeable. Not only is strength added, but these wraps can be used to keep any additional moisture from penetrating into the structure. This can keep water that has already caused rust and weakened a system from doing any more damage. Because of the impermeable layer the FRP wrap forms, it is used on many tanks and pipes.

      Also mentioned are the various materials used in FRP systems. Though carbon fiber is the most common material, there are others such as glass, basalt, and aramid that also work depending on the desired level of strength. As this technology did not exist 30 years ago, it will be interesting to see how it progresses over the next several decades.

    • Pete Pitilis Jr.
      October 4, 2017 at 11:37 am #

      Nick,

      I agree that prefabricating concrete will help mitigate certain concrete failures, however, I believe there are certain failures that can’t be avoided even in prefabricating. For example, one failure Mr. Pirro discussed was a failure due to poor aggregate. If poor aggregate was the cause of the failure then whether or not it was constructed on site or in a shop the same failure would occur. Also, some concrete elements in a building have to be constructed on site due to their properties governed by the building layout/shape. Therefore, prefabricating isn’t always an option and is usually utilized in modular construction. Finally, prefabricating concrete could potentially lead to other failures due to difficult connections and the need of skilled workmanship.

    • Megan F.
      October 4, 2017 at 9:24 pm #

      Nick,

      I agree that FRP reinforcement was very interesting to learn about. It is a great way to strengthen an existing concrete structure without adding more concrete or penetrating the surface. Once the FRP sheets are placed, they become an integral part of the concrete. After reading more about FRP systems in structure magazine (link below), I have a better understanding for how it works. FRP systems are applied to concrete structures for flexural and shear strengthening as well as column ductility improvement. FRP systems resist corrosion so they can be utilized in any location unlike reinforcing steel. The strength of FRP sheets have the same strength as reinforcing however it is much lighter (about one-fifth the weight). Most of the properties are given from the manufacturer but can also be determined following design guides and ASTM/ACI standards. It also cannot be assumed that FRP sheets can be applied to any type of concrete. ACI determines whether or not the structure qualifies for FRP reinforcing. In the event that the FRP reinforcing is compromised, the structure must maintain its strength to carry existing loads without collapse. FRP systems also have a long life intended to last for the life of the structure it is bonded to.

      Link: http://www.structuremag.org/?p=8643

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