Concrete Deterioration & Repair – 2018

AE 537  Building Failures Presentation by Bob Pirro, Senior Vice President – 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 30 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.  This lecture is one of the longest running visiting practitioner lectures in the class. 

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.  While it is a little dated, the same or similar problems can still be seen today.  Penn State students should be able to recognize some of the examples from campus buildings however many of these examples have been repaired but you may still be able to figure out where they occurred.

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.

 

 

 

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24 Responses to “Concrete Deterioration & Repair – 2018”

  1. SamZ
    October 4, 2018 at 3:31 pm #

    The biggest take away Mr. Pirro’s presentation for me was of getting a real grasp of how reinforced concrete can actually be not all that durable and how susceptible it is to the effects of the elements. Much of the deficiencies that cause this issue can be related back to poor craftsmanship, quality control, and design. Poor craftsmanship when consolidating and placing concrete can lead to a whole plethora of issues, to name a few honeycombing, over consolidation, and finishing before the concrete is done bleeding can all lead to cracking or wounds in the concrete making it more susceptible to water infiltration and freeze thaw effects. Quality control issues like too much water in the mix can reduce concrete strength and lead to finishing issues. Design issues can create problems as well. Concrete cover is a critical issue as well, many of the photos in Boothby’s slide show so how too little concrete cover can led to rebar corrosion. Also ponding and or poor drainage in concrete areas causes water and salt infiltration leading to corrosion.

    All of the issues above can be compounded when the concrete is exposed to the environment, many of the examples from both Mr. Pirro’s presentation and Boothby’s slides were outdoors or unconditioned spaces like parking garages and often had issues made even worse by the presence of salt either from the sea or from winter road maintenance.

    Reinforced concrete has been toted as a “miracle” for how well steel and concrete work together but honestly after a look into reinforced concrete failures the material is not as robust or durable as it seems it should be. I think is because the reinforcement which gives the concrete its strength is also its greatest weakness. The fact that steel expands when it corrodes is the Achilles heel of reinforced concrete, proper maintenance can extend the service life of a building but is all reinforced concrete destine for failure? One of the oldest concrete structures in the world is the Pantheon. It’s almost 1900 years old and doesn’t have a single piece of reinforcement, plain concrete is something that should be given more thought. Alternative reinforcing methods such as the external carbon fiber sheets seem promising and utilizing other materials that are not as reactive as steel inside the concrete may lead to longer service life especially in salty and moist environments.

  2. Jackson H
    October 4, 2018 at 10:52 am #

    Bob Pirro’s lecture was good exposure to someone who has dedicated their professional career to understanding almost everything about concrete construction, failure, and repair. Concrete almost inevitably cracks, and owners often automatically assume that the structure’s integrity is compromised. As the engineer and certainly as an owner, it is valuable knowledge to know what cracks are acceptable and what cracks indicate that there is an underlying structural issue that needs to be addressed. As shown in the presentation, there is an exponential relationship between the time that a repair is initiated and how much that repair costs. If the problem is remedied when corrosion is first noticed it may cost up to 100 times less to repair than if the owner waits until total structural failure. Small issues especially with corrosion inevitably get worse until failure occurs. That is why it can be so useful to detect the early warning signs of concrete failure which may not be so obvious to the layperson.
    The question that was asked about self-healing concrete was interesting. I have heard about SACON, (Shock Absorbing Concrete) before since the ARMY uses it extensively to construct training shoot houses and barricades that are projectile resistant, but I have not heard about this bio-based self-healing concrete. I know that the research into the self-healing concrete is still in its early stages, but I am curious to see if there are advantages to it over SACON since SACON focuses on preventing mechanical damage in the first place and self-healing concrete patches itself after the damage has occurred. I wonder what the limitations to what the bio-based concrete are and to what extent it can “repair” itself.

  3. Katie W.
    October 4, 2018 at 8:23 am #

    The presentation and the reference documents show how important concrete maintenance and repair is. Cracking may not seem like a huge issue, but it can let in moisture which will cause the rebar to rust and lower the strength of the structure. We design structure with a factor of safety, but it is definitely not enough to neglect the rebar. Loss of strength can lead to even bigger failures as we have seen previously in this class.
    Mr. Boothby’s presentation really hylights for me the effect water can have on concrete. Many of those damages were caused by freeze thaw cycles, improper drip edged and ponding. Mr. Pirro’s presentation on concrete was actually not the first I heard from his company. I attended a lunch-and-learn session presented by Structural about post-tensioned concrete maintenance and repair at my internship last summer. Water was also a huge issue in that presentation, as you could probably assume. In post tensioned concrete, it could be even more dangerous, as is the repair and maintenance of it. The cables can rust and can be difficult to replace. They have so much force inside them that if released suddenly they could break straight through the concrete and hurt someone. I am curious whether or not concrete code requirements and the industry itself have gotten more strict over the years because of issues like this. Obviously, this does not happen to every building, but it seems fairly common, even just from walking around campus and from the documents.

  4. Clayton T
    October 4, 2018 at 8:22 am #

    We’ve all be taught concrete will crack, in fact, it’s expected of it, it’s taken into account in capacity equations but we don’t consider it any further. Mr. Pirro shed some light on the deterioration of concrete over time not only due to the concrete cracking but variables such as the mix components like aggregates, environmental conditions, and man-made conditions. Concrete irregularities and failures are diagnosed with various prescribed methods developed through the years but there is rarely a prescribed solution. Within cases like massive cooling towers the chemical process of steel corrosion was the primary source of concern, not necessarily a focus of structural engineers typically while a low current had to be placed in the rebar cage, in this case, the structure wasn’t the only concern but the feasibility of the work and the possibility for the plant to continue to function without interruption. Another interesting fix would be the application of carbon sheeting to the bottom of concrete beams to increase the tensile strength, though not common in new construction and with owners unfamiliar with the material, it is innovative repair strategy. Concrete restoration and repair in a business sense come down to the amount of time the structure is occupiable, the extent of the repair and cost of the repair all leading to the final decision as to how to approach it.

  5. Sierra S
    October 4, 2018 at 6:11 am #

    Bob Pirro’s presentation, I felt, took the big picture issue of building failures and narrowed it down to a single component, concrete. This is not to say that other parts of the building didn’t influence the failure or occur alongside of the concrete deterioration. The ability to focus on one aspect of the building allowed for a deeper investigation to occur within the one hour presentation.

    One of the failure cases covered looked at chlorides working its way through the concrete until it reaches the reinforcing steel. The infiltration of the chloride lowered the pH of the concrete which, once to the steel, was the catalyst for the steel to try to go back to it’s original state of iron ore. This is due to the chlorides ability to break down the protective film on the rebar. As mentioned in the PCA durability article, the presence of chlorides in the concrete is not an issue unless there is steel in the system.

    One of the specific failures due to chloride infiltration that caught my eye was where the entire structures was built with brackish water in the concrete mixture. This structure was deemed to be beyond repair. Due to the incorrect mixture the reinforcing steel completely separated from the concrete which compromised how the building was designed to function. One curiosity I had about this issue is how often it happens in the industry. Also, Bob Pirro discussed some ways to test to see how much chloride is within the concrete but I am wondering if this is a standard test during construction. Could this test be performed when concrete cylinders are pulled for strength testing?

    • Abby S
      October 8, 2018 at 6:34 pm #

      Sierra,

      I also found the brackish water failure to be very interesting. I have never heard of this before and was also curious as to whether or not this happens often, leading me wonder what types of quality control methods are in place for concrete mixing water. You posed a similar question about testing procedures for chlorides in the concrete. I did a quick Google search and found one method that is used to test concrete cores called chloride ion penetration. In this test, a concrete core is immersed in a different solution at each end. Then, an electrical current passing through the core is measure to determine the resistance to chloride ion penetration. It seems that this would be able to done when cylinders are pulled for strength tests, but I am not sure how often it is actually carried out. I am curious if this is an issue that is investigated often or if it is so uncommon that the tests are not regularly considered. Either way, it seems that a simple test would have showed that the concrete mixed with brackish water was insufficient and probably would have avoided this major failure.

  6. Steven B
    October 4, 2018 at 2:55 am #

    Mr. Pirro stressed the importance of the pH levels within the concrete and the surrounding environment throughout his presentation. He demonstrated how even when there are no cracks present, moisture and chlorides will attack the concrete, slowly working its way down to the reinforcing bars. He showed us a number of inspection techniques that all required access to the concrete and the ability to take samples if necessary. Foundations however are not easily accessible. Where deterioration of walls and floors may be evident to even the average person walking by, this is not possible for foundations. This underscores the importance of designing and constructing the foundation correctly. There are areas in Pennsylvania that have soils that have high concentrations of chlorides and sulfates. It is incumbent on the engineer to understand the environment around a proposed structure and how that environment will affect their concrete design. Issues related to deterioration of the concrete foundation will probably not present themselves until they are in an advanced stage. Due to this fact foundation repair will always be expensive, as Mr. Pirro stated, the longer you wait the more costly it gets.

    • Katie W.
      October 9, 2018 at 7:35 am #

      I think you bring up a very valid point that many times it can be hard to catch until it it is too late. As you said, foundation are buried underground and remain unseen for the majority of their lifespan. If a failure were to occur, it would most likely only be noticeable at a more advanced level that is more difficult to repair. I looked up signs of a failing concrete foundation and found that it can cause cracks and issues throughout the whole building above it, which makes a lot of sense. Uneven floors and differential settlement can also be signs to look out for.

  7. Jordan O
    October 4, 2018 at 1:21 am #

    Mr. Pirro’s presentation highlighted many of the different ways that concrete fails in any given site. There are a huge number of reasons concrete could fail, most of which are due to a volume change which leads to cracking. Often times these failures are difficult to prevent because concrete is expected to crack and owners often think nothing of it. It is hard to know if a significant amount of water is reaching the reinforcement or if there is too much water in the mix without doing constant tests after installation or re checking concrete composition before it is poured. This is another good opportunity to bring up the potential benefits of commissioning. During the construction phase, having a commissioning agent on site could ensure that all of the proper measures are taken in the placing of the concrete. While it should not feel like a baby sitting job, Mr. Pirro pointed out that often times the workers on site will pump more water into the concrete mix to save money. This could lead to issues in the concrete later on in its lifetime and having an experienced or knowledgeable individual on site could save an owner money in the long run. Throughout the life of a building, a commissioning agent could be involved in periodic inspections of all of the buildings systems to help prevent failure. Included in this would be a knowledgeable person to evaluate any existing concrete cracks and determine if they are caused by anything that could lead to more significant, costly damage if left untreated. Many of the cracks we observed throughout the concrete on campus were good examples of some of the variations of failure presented in class, but it would be interesting to see if having a commissioning agent periodically inspect these buildings could save the university larger repair costs in the long run.

    • Josiah M
      October 8, 2018 at 8:34 pm #

      Jordan,

      Contrary to your point about owners overlooking cracks, I believe that it’s the engineers who seem to brush off an owner bringing up cracks. Although, I completely agree that the severity of these cracks, when it comes to water penetration. I think that it’s easy for an engineer to think of the immediate effects of the crack, which were already accounted for in design. But it’s easy to not look into the long term damage that could result, such as rebar deterioration.

      • Jordan O
        October 9, 2018 at 1:42 am #

        Josiah,

        That is part of the point I was working towards with it being a specialized commissioning agent rather than a structural engineer with potentially minimal failures background. While a structural engineer likely brushes off small concrete cracks as expected and nothing to be concerned with, someone more well versed in the building failures side of the industry could weigh other factors that could compound on that crack and lead to a more serious problem. Depending on the severity of the crack, location in the building, surrounding systems (potentially mechanical systems that could leak water or leaky enclosure system), and other factors, having a commissioning agent on site doing periodic inspections could backup owners concerns that might typically be brushed off and proactively fix small issues that might end up more severe.

  8. Abby S
    October 3, 2018 at 10:50 pm #

    In his presentation, Mr. Pirro discussed a case where brackish mixing water was used for the concrete throughout the entire project, which then had to be demolished. I was surprised that such a large error was repeated for all of the concrete mixing on the project. Water quality is an important factor in the performance of concrete, so it surprised me that the use of brackish water either went undetected or was purposely overlooked.

    As Mr. Pirro mentioned, several factors such as water to cement ratio and environmental conditions when curing can greatly affect the performance of the concrete, yet the moisture content is still often thrown out of balance during construction. He also stated that pH levels can greatly affect the concrete reinforcing. This all leads me to wonder what controls or measures are in place for checking the quality of mixing water. The handling of mixing water during the construction process is important, but the quality of the water itself is also critical. In areas where there is not a lot of fresh, clean water to use, especially in developing areas, how does this affect concrete production and what can be done to ensure concrete is still of acceptable quality?

    • Eric I
      October 6, 2018 at 3:52 pm #

      Abby,

      I think you brought up an excellent point when discussing the quality of mixing water in concrete. The case study you mentioned, where brackish water was used as the mixing water, is a seriously shocking mistake. It is such a glaring issue to us but somehow it was used throughout the entire project. This particular instance is obviously an extreme case, as the entire building needed to be demolished, but it does make one wonder how often the water quality actually is checked. On the list of control measures, it is easy to see how water quality may be overlooked, but it is so vitally important to the structural integrity of the concrete. As soon as there are unintended contaminants in the water, the reinforcing is subject to unforeseen levels of deterioration.

      While this is definitely a process error, I’m sure it was the engineers worst nightmare. Controlling the finer details, such as the mixing water quality, can be difficult from the comforts of an office. I think you have asked a very tough question in how are we able to control this. As a structural design professional, the importance of this issue is very apparent but to the contractors, it may not be. I think it all starts with preconstruction meetings and educating the builders. Sharing case studies like this one can show the magnitude and effects of such errors and would probably make everyone involved think twice before taking the easy way out.

  9. Eric I
    October 3, 2018 at 10:10 pm #

    Mr. Pirro’s presentation introduced a more in depth view into a topic of structural engineering that I often overlook. His presentation focused on concrete as a material and provided numerous case studies about what can go wrong and more importantly, how to resolve those situations.

    One of the more interesting graphics he presented to us was the repair cost vs. time graph. The basic idea conveyed was that the preventative maintenance phase, which is early in the life of a structure, is the most economical time to care for a structure. This preemptive approach allows for issues to be addressed before they grow into massive, expensive problems. This general idea seems to be the trend for every building failure type we have discussed so far this semester. One failure example he spoke about showed the entire underside of a reinforced slab that had spalled, corroded and deteriorated to the point of being unsafe for occupancy. More attention to detail in the workmanship and a simple surface repair could have prevented the entire situation. Instead the owner is now faced with a big ticket repair. Building owners seem to hold off on repairs until the extreme case arises so we, as an industry, need to work to change that.

    Another interesting part I enjoyed in his presentation was about the new technology that is coming to light. He spoke about new OSHA regulations that are making the traditional ways of cutting/removing concrete very difficult and expensive. As a response, the use of high pressure water to cut concrete is becoming more common. Along the same lines of new technology, he provided information on his experience with carbon reinforcement to externally strengthen structures. These two items are great examples of the creative solutions engineers have come up with to solve complex problems. As our careers begin, these technologies will advance and new will be created. Things like this could provide unique opportunities and specialties for us if we choose the forensics path.

    • Jackson H
      October 9, 2018 at 8:01 pm #

      The technological advancements that are made in response to new and increasing regulations is interesting. I wonder though “how much is enough?” At what point does the industry say that a certain level of risk is acceptable? At what point do construction companies refuse to accept these new regulations that cut into time, productivity, and profit?

      Although safety is important, it seems unrealistic to believe that we can legislate safety issues away in an industry that often ignores these regulations. New technologies can reduce risk but are often cost prohibitive. I wonder if new regulation eventually prices some companies out of competition.

    • Jackson H
      October 9, 2018 at 8:02 pm #

      The technological advancements that are made in response to new and increasing regulations is interesting. I wonder though “how much is enough?” At what point does the industry say that a certain level of risk is acceptable? At what point do construction companies refuse to accept these new regulations that cut into time, productivity, and profit?

      Although safety is important, it seems unrealistic to believe that we can legislate safety issues away in an industry that often ignores these regulations as much as possible without getting caught. New technologies can reduce risk but are often cost prohibitive. I wonder if new regulation eventually prices some companies out of competition.

  10. Josiah M
    October 3, 2018 at 5:53 pm #

    During Mr. Pirro’s presentation, he spoke a bit about some of the solutions that have been devised to remedy structural issues in concrete. He mentioned everything from removing deteriorating concrete and rebar entirely to applying FRP systems to strengthen them. I think the most interesting solution that was mentioned was running current through rebar to combat the effects of corrosion.

    As Mr. Pirro described it, inducing a current in the rebar eliminates the “battery effect”. This solution recognizes that there is an electrical potential between different portions of the rebar cage, which causes current flow from one section of rebar to the next. The more negative portion of the rebar acts as a cathode, while the positive portion is the anode. The anode portion of the rebar is the portion that will corrode. To remedy this, current is run through the rebar cage, the result is that the entire cage has the same electrical potential effectively stopping corrosion.

    I thought this was interesting because it wasn’t necessarily a structural solution to a structural problem. It took a bit more creativity and research into what causes corrosion to devise this fix.

  11. rgstanza
    October 3, 2018 at 2:55 pm #

    I found the FRP systems used for strengthening concrete beams very interesting. To be able to retrofit a structure and add more strength to a concrete beam by adding FRP sheets with fireproofing, instead of going through the process of adding rebar and pouring additional concrete, seems like a much faster and less taxing process. By saving time and effort, both the owner and contractor benefit. However, I wonder what the trade-offs are as far as durability is concerned when using FRP sheets.

    The PCA reading discusses the durability of concrete and how it is resistant to the environment, chemicals, and abrasions. By adding FRP sheets instead of concrete, I think that you may lose many of the durability benefits that concrete provides. For instance, a journal from the University of Cambridge discusses how the fibres in FRP sheets are corrosion-resistant in the sense that they do not rust, however, the glass and synthetic polymers do break down and hydrolyse, especially when in an alkaline environment such as the surface of concrete. (Burgoyne 4, http://www-civ.eng.cam.ac.uk/cjb/papers/cp83.pdf).

    So, while you gain the benefit of saving time and effort with FRP, you might also lose out on the durability that is provided with concrete and rebar. I wonder how this is evaluated when deciding whether to strengthen with FRP sheets or with additional concrete.

    • Sierra S
      October 4, 2018 at 8:42 am #

      I was curious about the same thing. When I asked in class how the adhesion of FRP to the concrete is he stated that there have been no issues so far, not saying they aren’t to come. Also, the environment of that application wasn’t discussed. This leaves potential for future problems.

      Within the same article you mentioned above, it discusses a weakness of durability for the FRP. Even though the fibers don’t rust like steel, the resins are able to degrade under exposure to different conditions. A high alkalinity in the concrete could potentially break down the glass and aramid. I am unsure of how a high alkalinity can develop in concrete or how often it occurs. Either way, this is cause for concern.

      Another issue discussed in the article is that even if these resins were to degrade they would not be easy to detect since no indications would be shown on the surface of the material. I am curious if there are any standards out for this product that require certain checks to ensure that the product is performing at its highest capacity. This is also an issue for building owners because if they aren’t able to see any issues then they don’t have a reason to check.

    • Ryan L
      October 5, 2018 at 11:57 am #

      The East Hall’s contractor is currently using FRP on the bldg under construction (not sure the name of it). We took a tour of the dorm right after they had cut the penetrations for utility runs through each of the concrete floors. They had scanned for existing rebar, marked each location, ground the concrete (for floor leveling/sloping) and put strips of FRP in that were about 6″ x 24″ near each penetration.

      They may be a good resource in understanding how they took the unknown break down characteristics over time into consideration when making the design recommendation.

  12. Ryan L
    October 3, 2018 at 11:00 am #

    The introduction on this page references Mr. Pirro’s discussion on the exponential costs associated with conducting preventative maintenance regarding identified concrete issues, and addressing issues as soon as they are identified. This is a common problem across most building systems. I think that rapid deterioration of other building systems along with their direct effect on occupants often puts these issues ahead of concrete repairs.

    From a maintenance perspective, I think concrete is often addressed early only if it is a significant safety hazard (falling object; trip; etc.). There are multiple examples of spalling and exposed aggregate around PSU’s campus, similar to those shown in the slide show above. During our campus investigation, missing flashing or drip edge and ponding areas on concrete surfaces seemed to be prevalent. Knowing that PSU has a significant deferred maintenance backlog, I imagine these issues are known but prioritized significantly lower than other work orders.

    With regard to repairs, we saw multiple areas where proper preparation of the concrete surface was not conducted prior to making the repair, specifically on steps and concrete walk ways. I wonder if these repairs were made knowing they would be short term repairs after a couple of freeze and thaw cycles. Mr. Pirro’s examples of proper preparation show that proper repairs are significant efforts, even when issues are caught early.

    • Smithr
      October 8, 2018 at 3:43 pm #

      I agree Ryan, one of the biggest takeaways from Mr. Pirro’s presentation was preventative maintenance. I totally understand that from a management perspective, hazards and maintenance need to be prioritized and that we are always going to have some issues in any building/campus. It was refreshing to see some quantification on the cost of the concrete repairs in different states.

  13. Smithr
    October 2, 2018 at 2:44 pm #

    To Kevin’s point, this topic could be its own class and in fact much of this presentation was a refresher from my CE 584 class, Concrete Materials and Properties. It is not offered every semester but it is a helpful class to understanding concrete at a graduate level.

    One of the interesting photos that stuck with me from Mr. Pirro’s presentation was the photo of the petrograph that showed cracking in the aggregate of the concrete mixture. This is a pretty unusual failure to see and it was interesting to notice that the cracking went directly across the middle of the aggregate and not in a chord. I would have to imagine that this came down to insufficient Quality Control by the concrete supplier.

    Additionally, many of the photos of Mr. Boothby’s presentation were from the East Halls area of campus, where I worked for roughly the last year. Specifically, there were areas of the covered walkways that showed some significant deterioration. I can confirm that the rebar was less than 2″ from the edge in some of those existing structures. In fact we had to replace one of those sections of covered walkway and our rebar design had to be different from the existing pieces due to coverage.

    • mkev
      October 4, 2018 at 12:13 am #

      Very observant R. In fact, I took some of those east halls photos many years ago. Another batch came from the Music Building. Some of those were repaired and had to be fixed a second time. Lack of rebar cover cover was an all too common feature that resulted in deterioration.
      MKev

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