Concrete Deterioration & Repair – 2016

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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43 Responses to “Concrete Deterioration & Repair – 2016”

  1. Shubham
    October 13, 2016 at 8:17 am #

    “Thermal Shrinkage”
    The ‘Concrete Microstructure, Properties, and Materials’ book by Mehta and Monteiro is quite popular for the study of concrete. I studied about the Thermal shrinkage from the book. Here is the summary of its mechanism.

    We know, solids expand on heating and contract on cooling. Ordinary concrete structures in normal climatic conditions suffer little or no distress from changes in ambient temperature. However, in massive structures (example below), the combination of heat produced by cement hydration and relatively poor heat dissipation conditions results in a large rise in concrete temperature within a few days after placement.
    Subsequently, cooling to the ambient temperature often causes the concrete to crack. Since the primary concern in the design and construction of mass concrete structures is that the completed structure remains a monolith, free of cracks, every effort to control the temperature rise is made through selection of proper materials, mix proportions, curing conditions, and construction practice

    Example:
    Hoover dam, built in 1933, faces the problem of Thermal stresses (shrinkage and expansion). To overcome this there are thin-wall cooling pipes running horizontal throughout the height of the structure. These cooling pipes carry cold water to prevent the rise/ fall of temperature of the concrete core.

  2. Yemi O
    October 13, 2016 at 12:51 am #

    The durability of concrete is always going to be a thing of interest. The cost of repair and rehabilitation of concrete has continued to increase with time and complexity of buildings and the challenge will always be how you can prolong the life of these concrete structures.

    Understanding the effect chemical admixtures have on concrete, the rate at which rebar corrodes, construction techniques, etc. will be vital in pushing this research forward.

    • Prateek Srivastava
      October 13, 2016 at 8:40 am #

      I agree with your thought that durability of concrete will always be the most important question but i feel apart from durability it also depends on how well the workmanship has been and how well the maintenance is neing done.
      Its the principal aim of any civil/structural engineer that his/her created structures should last forever but it requires a lot of effort to do so.

      Secondly, people have to get educated about the basic properties of concrete, as back in my home country India or even in United States, its a general tendency for a labourer to add more water to the cement aggregate mixture just to make it more workable without even giving a thought that how much its going to cost in terms of structural capacity to retain loads. Thereby, the construction of the design as thought does not go in accordance to the technical aspects, leading to failures.

      So educating people atleast who are involved in the construction process about the materials, workmanship etc are essential to prevent failures occurring due to carelessness as there can not be some one monitoring each and every construction processess every time. One of the examples of failures caused due to carelessness in construction was the Fischer parking garage as discussed in class. People should be educate enough to actually acknowledge building failure signs before it actually collapses refering to Fischer parking garage case.
      Thus, durability of concrete/structure is achieved not only by good quality materials but also with the vigilance of people in and around the facility.

  3. Ommar E
    October 12, 2016 at 10:58 pm #

    Concrete as a building material of choice for engineers and owners of buildings and other type of structures proved to be reliable and and resilient. As known to all, it is widely used as a primary structural material in construction due to numerous advantages, such as strength, durability, ease of fabrication, and non-combustibility properties, it possesses over other construction materials. It’s fire resistance properties ranks it among the best building materials if not the best.
    Mr. Pirro affirmed that concrete will continue to enjoy favorable status in the construction industry. However, from the lecture and the discussion, and like most building materials there are issues and concerns that need to be addressed in order guarantee future of this important building material. In addition to what have been already mentioned, I would add inspection by professionals to the mix. Since, it has been shown that signs of deterioration and in many occasions go undetected due to lack of knowledge from owners and end users. So, investing in periodic inspection could actually end up saving owners lots of money in future costly repairs or even law suits when catastrophic failures happen causing loss of lives. This calls for more training and research in non-invasive or destructive testing methods of concrete structures.

  4. Yingzhe You
    October 12, 2016 at 10:41 pm #

    Here is a article I found related to concrete deterioration on Failure Wiki and I’d like share with you all. https://failures.wikispaces.com/Concrete+Bridge+Failures+-+Deterioration+and+Spalling

    It talks about concrete Bridge failures caused by deterioration and spalling. The figures in this article are very similar with those in the lecture. Chloride and moisture penetration can lead to reinforcement deterioration. And a bridge collapse case is also mentioned in the article.

  5. ErikS
    October 12, 2016 at 4:24 pm #

    Bob, thank you very much for coming to present to us; it was a great presentation.

    It always amazes me how much damage something as unassuming as water can cause. Professor Parfitt, Mr. Pirro, and our other guest presenters have discussed over the last few weeks many topics about various failures that, while not all of them many of them include water in some form or another, cause damage to a structure that leads to a failure. The failure may not necessarily be as severe as a collapse of a building or even a section of wall or structure, but it could include leakage to the interior that leads to corrosion of steel studs or masonry veneer anchors, migration of salts via water intrusion corroding steel reinforcing, or moisture intrusion rotting wood sheathing.

    It is shocking sometimes the lack of common sense some designers and contractors use when creating or installing a flashing or roofing detail or interface condition or concrete cover over reinforcing (or lack thereof). Simple corrective action early on with proper installation can make many of the building failures, which plague the construction industry, go away (as well as our consulting and repair careers – so thank goodness there are so many poorly designed and implanted details out there…
    As you mentioned in your presentation the $1, $10, $100 rule applies and is absolutely true. Fix it during design and it costs nearly nothing; fix it early during construction and it cost a little more; fix it late in construction there are change orders and materials that must be demolished to fix the error or oversight; wait until there are errors following occupancy and now not only are you paying for the demolition and repairs of the details you are also paying for professions such as Structural, WJE, SGH, etc. to first assess the condition, then develop a repair procedure, then implement the repairs….costing many, many times more than the initial cost would have been.

    As you stated many of the details and methods that could be used to address the deterioration of the concrete or other materials are rather simple and can be relatively inexpensive; however, the Owner must be willing to pay for it and then contractor install it properly.

  6. Di W
    October 12, 2016 at 11:00 am #

    Bob mentioned a “shotcrete” method in surface repair. I would like to add something that I read from ACI and other articles. There is a way called”dry-mix shotcrete”. Repair material is placed dry or slightly damp into shotcrete machine and mixed with compressed air. The mixture is transported via hose to the exit nozzle where water and admixtures, if any, are introduced. The ingredients are propelled onto the prepared substrate by the force of the compressed air.
    The best application would be large vertical and overhead areas with small bars, No. 6 or less, and minimal congestion of embedded reinforcement. Well-graded aggregate with necessary binders is required. Admixtures are frequently used to shorten set time, and/or allow thicker layer to be built-up in a single pass.

  7. YusufA
    October 12, 2016 at 10:27 am #

    Found another very useful document here by the ‘Portland Cement Association’.
    http://www.cement.org/docs/default-source/fc_concrete_technology/durability/is536-types-and-causes-of-concrete-deterioration.pdf?sfvrsn=4

    It basically highlights the various causes of concrete deterioration just as Mr Piro has clearly laid out.

    The highlighted potential sources of concrete deterioration are:

    1. Corrosion of embedded metals: this is the most common cause of concrete deterioration. Some occur quicker while others are faster. The premature failure however are caused by the presence of cracks and this should be avoided by all means. Adequate cover should also be ensured (likely workmanship error). Other likely causes in the paper as listed below.

    2. Freeze-thaw deterioration:
    3. Chemical attack:
    4. Loss of support
    5. Surface defects
    6. Overload and impact
    7. Restraint to volume changes
    8. Fire/heat to cause a loss of strength and stiffness
    9. Abrasion/erosion

    More information can be found in the document but the most important aspect I can learn is the need for a quick and instant solution to be provided once this is sighted. The effect of this can also be noted in the Tuesday lecture on the Parking garage failure.

    Engineers are usually always aware of a potential failure once sighted but what you do once its noticed is most important to avoid failure or collapse.

  8. Shubham
    October 11, 2016 at 11:04 am #

    Very informative presentation by Bob. Learned about the six causes, including workmanship, for concrete problems and various techniques to tackle them.

    The NDT method, Pachometer for rebar size and placement is a remarkable among others.

    I did not understand what mechanism/concept of Fiber Reinforced Polymer (FRP) helps in Strengthening of Concrete?
    This is quite an impressive, as the ‘Structural’ group applied this in walls of huge cooling tower of a nuclear reactor.

    I learned that faulty workmanship is a cause for many building performance problems and believe that, each firm should develop specifications and promptly adopt them.

    • ErikS
      October 12, 2016 at 3:46 pm #

      Fiber Reinforced Polymer (FRP) plates or wraps strengthens concrete externally with minimal demolition or other damage incurred to the existing concrete structure. FRP wraps essentially adds an external layer of reinforcing around, under, over, or wherever additional reinforcing is required. For instance if there is concern with the flexural capacity of a concrete beam FRP wraps can be applied along the beam soffit to supplement the positive moment bending steel – similarly above connections at a girder or column for negative moment strengthening. This can also be applied to round columns, or cooling towers as it may be, to supplement the existing steel reinforcing.

      As mentioned the benefit is there is little to no demolition, drilling, bending rebar, epoxying bars, and repair of the concrete as would be necessary if conventionally upgrading the reinforcing; however, surface preparation of the concrete is critically important as the only mechanism attaching the FRP wrap is the chemical bond of the epoxy layer. Additionally, as Mr. Pirro mentioned, the epoxy is susceptible to softening due to heat; therefore, additional measures may be required.

  9. Ishan Uppal
    October 11, 2016 at 10:32 am #

    As a student with previous NDT and materials testing lab work experience, I was very much looking forward to Mr Pirro’s lecture.

    The various new concrete testing techniques that Mr Pirro introduced during his lecture were some topics that I, personally, will like to delve into deeper.

    The analogy of anodic cathodic behaviour exhibited by steel reinforced concrete that leads to steel rusting was a fantastic way of understanding the phenomenon. Also the fact that carbon fiber rebars are now being made available in the construction industry speak volumes of how much rust is a problem.

    The pH of concrete being a measure of health of the concrete was a new concept to me. I would like to know more about the actual process of determining the pH value of concrete. Anyone?

    • Alec B
      October 12, 2016 at 1:35 pm #

      Ishan,

      I looked into measuring the pH of concrete. I was able to find an article through Penn State’s online library database that has great information related to measuring the pH value of concrete. The article is very technical with a lot of information on the subject; though overwhelming at first, it may be a great reference for learning more about the pH of concrete and how to determine such a value through testing. The link may be referenced below (after clicking on the link, you should be able to “Download PDF” by clicking on the icon on the top left-hand corner of the webpage). In summary, there are different destructive and non-destructive methods that have been developed to measure the pH of concrete. According to the article, the most common destructive method is extracting a concrete pore solution by applying high pressure. Non-destructive methods include using embedded metal/metal oxide electrodes and fibre optic sensors that permit real-time monitoring of pH fluctuations over time. Unfortunately, no testing method has been standardized yet as of October 2015 when the article was finished being written and revised. The article is filled with helpful figures, graphs, etc. that may help in understanding some of the testing procedures. Also, there are close to 100 references at the bottom of the article that may direct you to some additional research and information if you are interested.

      From: Construction and Building Materials Journal; “Methods for Measuring pH in Concrete: A Review”
      http://ac.els-cdn.com/S0950061815307054/1-s2.0-S0950061815307054-main.pdf?_tid=1fbb985a-90a0-11e6-992e-00000aacb35d&acdnat=1476292988_dd5e49b6a577355be53179d6d9d89e93

      • Ishan Uppal
        October 13, 2016 at 10:28 am #

        Thanks for the link Alec. The article answered a number of questions I had.

  10. Shane M
    October 11, 2016 at 2:36 am #

    This presentation was very insightful. The thing I found the most interesting was affects that pH levels had on the rebar and how much it could change over time. This might have been the first time I ever had someone give a thorough description of the causes of rebar corrosion and concrete deterioration. It would make sense that this type of issue would be common in parking structures located in snowy regions because of the salts used to de-ice the roads. The constant flow of vehicles entering the structures with water and salts on them will aid in the deterioration process. If the structure is not heated, then the freezing and thawing of these waters will also speed up the process until the problem locations are fixed. Are there any measures being taken to combat this issue in concrete structures that are exposed to the elements? Or do design methods specify certain admixtures that delay the chemical reactions?

    • Joe H
      October 12, 2016 at 10:51 am #

      In a quick google search for “parking garage admixtures” I came across a few sites that advertise a variety of admixtures. However, almost all of them have to do with water content, workability, strength, and placement. I was unable to find anything that would alter the pH levels or reduce corrosion as an admixture, so this leads me to believe that there needs to be other measures taken.

      Parking garages are a very difficult matter for this, as owners are rarely concerned about the interior aesthetics of a garage, so there are almost never any finishes on the concrete and it is always exposed. I would suggest that extra care needs to be taken in sealing the floor and providing a way for the salts and other exterior particles brought in to flow to a drainage system, either naturally or forced during cleaning. Because garages are always sloped, this could be taken advantage of to have great control over the runoff and make sure certain areas are more protected than others.

      Admixture sites:
      http://www.euclidchemical.com/markets-applications/new-construction/parking-garages/concrete-admixtures/
      http://premiereadmix.com/parking-garages/

      • ErikS
        October 12, 2016 at 4:04 pm #

        Correct, garage concrete structure deterioration from deicing salts is a major industry headache and without increasing concrete cover to multiples of inches, which is not economical or practical as concrete will still crack and moisture and salts will still migrate to the steel eventually. One major recommendation offered to owners of garages is waterproof, traffic-bearing coatings, as Joe mentioned. They are one of the best methods of managing the runoff from vehicles as they enter garages. The owners often are sold on, due to cost savings, only applying the coatings to the entrance level drive lanes and not the remainder of the garage. This can be problematic as yes, the majority of the water and salts will drop off during the initial entrance to the garage and while driving down or up the initial drive lane, but much of the salts remain on the vehicle until they park at which time they drop off and slowly begin the migration through the slab. Increasing the application area to include the first level drive lane as well as the parking spaces increases the protection level; however, again take a look at the slab under your vehicle after you park after driving through rain and see if when you are on levels other than the main entry level there is still moisture on the slab when you park.

        Any surface applied coating will be an ongoing maintenance item as it will delaminate and flake off and no longer provide the intended protection. The benefit for the owner for only applying the coating to the main drive lane is ease of future maintenance and reducing the cost of lost revenue from parking spacing being out of commission during reapplication efforts. This is a short-sided approach by the owner (and recommendations by consultants, contractors, etc.) for as we have learned time and time again the $1, $10, $100 rule applies here. The relatively low cost, initial application of the coating and the relatively low cost reapplication of the coating regularly will help protect the investment of the concrete slab and far outweighs the costs of repairing the slab, replacing reinforcing, and losing revenue from parking spacing closed for weeks or months during these major repairs.

        Additionally, as Joe alluded to, properly drainage design and regular maintenance such as washing down the drive lanes to minimize the deleterious effects of the deicing salts, is crucial as well. Making sure the vehicle run-off is managed and evacuated from the slabs is a key component of maintaining the durability of your concrete, or other, parking garage or structure.

        • Shane M
          October 13, 2016 at 2:07 am #

          It seems like the best way to prevent corrosion and deterioration would be for the owner to properly maintain the structure, but that just never seems to be in their interest. Maybe sometimes they just lack the knowledge of this issue.

          Joe, if you go into the specialty admixtures you will find the corrosion inhibitors. The product EUCON BCN is a Calcium Nitrite based admixture designed to inhibit the corrosion of steel reinforcement in concrete.

      • Brendan B
        October 13, 2016 at 12:48 am #

        Joe,

        It is unfortunate owners only value the money involved in a project, instead of the aesthetics or longevity of the building. As we learned in Mr. Pirro’s presentation, the $1 $10 $100 rule can be crucial to a building if proper maintenance is not performed. It would certainly be in best interest of the owners to seal the floors with the proper admixtures from the beginning to prolong the life of the structure as well as avoid any risk of failure.

        In regards to your comment on the sloping of parking garages, it would certainly be advantageous if the sloping can be aimed towards the entrance/exit area as cars often idle there while paying the parking garage attendant. Perhaps another solution could be to heat the structure to reduce the freeze thaw cycles effect on corrosion. Either way, the proper care from initial design would contribute the greatest amount towards preventing concrete deterioration.

  11. Joshua Z
    October 11, 2016 at 2:29 am #

    I found Mr. Pirro’s presentation on concrete deterioration to be both interesting and engaging. It’s fascinating to me how many issues concrete can have and how easy it is for a mistake to occur. For example, one of the buildings Mr. Pirro talked about used brackish water to mix the concrete, which trapped chlorides in the concrete and lead to corrosion quickly. Additionally, it’s fairly easy to make an error in the form of design or workmanship. Improper placement or lack of reinforcing steel can be catastrophic. In one of the cooling towers, the engineer forgot to design #6 bars in certain areas of the tower. Consequently, Mr. Pirro’s company had to go in and replace the structure, an issue that cost the owner a great deal of money. Corrosion, time, improper reinforcement and installation, and lack of maintenance can all contribute to concrete failure, and it’s fairly easy for any of these to happen.

    I also found this lecture interesting because it tied into some of the work I did this past Summer. During my internship, I was required to perform a chain dragging test on a parking structure in Massachusetts to locate areas of concern. We were unable to locate any, but the experience gave me a better understanding of some of the topics Mr. Pirro discussed.

    • Ishan Uppal
      October 13, 2016 at 10:47 am #

      I too had a similar experience during my internship where it was very common that concrete being mixed on site was done using brackish water from nearby backwaters. It was during Mr Pirro’s lecture that I realized the mistake being committed.

      This incident goes to prove how important workmanship is to the overall health and future life of the structure.

      In areas of high rebar density, it is required that proper vibration be done for proper settlement and penetration of concrete. However poor workmanship at our site resulted in improper concreting and honeycombing.

  12. Brendan B
    October 11, 2016 at 1:14 am #

    Mr. Pirro’s presentation was particularly interesting to me as the company that I interned for this summer was assigned to a project that included investigating an old parking garage to see if it was worth repairing. Unfortunately my company visited the site before I started working so I was unable to see it, but my co-workers showed me pictures and told me about the visit. They said the biggest issue was the corrosion in the rebar. At the time I had no knowledge of concrete deterioration, but they explained how the combination of salt from cars and temperature change worked together to expand the rebar which in turn caused issues such as cracking and spalling. It was certainly nice to listen to Mr. Pirro’s presentation as it helped clarify what I had previously learned about concrete deterioration from this summer.

    • ErikS
      October 12, 2016 at 4:08 pm #

      Brendan, what is even more enjoyable than chain-dragging the slab is rebar tapping the concrete soffit. Did you get to experience that? Walking around with a 4 to 6 foot length (depending on the soffit height) length of steel rebar slowly and methodically tapping the soffit listen for the same delamination sound as you were looking for with the chain. I would highly recommend everyone take the chance in their career to do this as it gives you an appreciation for making sure you concrete is designed and installed properly.

      • Mehrzad
        October 12, 2016 at 10:47 pm #

        Erik,

        Thank you for mentioning rebar tapping and chain dragging. I have not got to do them but chain tapping is also done in bridge decks as a simple yet more labor intensive method (traffic noise will be distributing) as explained in the prevalent non-destructive methods in the following brief presentation file.

        https://www.concrete.org/Portals/0/Files/PDF/Webinars/Donnelly.pdf

        In the more accurate Impact Echo method, the concrete surface is vibrated and locations of shallow and deep delamination spots can be collected. Smaller devices with a similar mechanism can be used in buildings, and I assume forensic structural firms are equipped with such devices.

      • Joshua Z
        October 13, 2016 at 1:04 am #

        Erik,

        I had the pleasure of performing a chain-dragging test on a concrete parking structure this summer. There was no cloud cover and no shade of any kind anywhere. We also tapped the soffits as you mentioned. My coworker and I spent about 3 or 4 hours out there trying to find imperfections and issues with the concrete that weren’t already visible. We were not able to find any. As frustrating as it was, it gave me a newfound appreciation for the design of concrete and definitely made me realize the importance of proper design and installation.

  13. Yemi O
    October 11, 2016 at 1:07 am #

    I enjoyed Mr. Pirro’s presentation last week. Seeing how many ways concrete could deteriorate and also ways to tackle this was quite informative. Poor workmanship and material quality almost always seem to take a huge chunk of the blame with regards to this topic. However, i found it interesting that an owners decision in the early stages can play a huge part in the repair/deterioration in the future. Use of different types of reinforcements such as the mentioned FRP can be the difference between a $1000 and $10000 expense and good discretion has to be made early on to compensate for this.

    I am always very eager to learn about concrete as a material and how we can continue to test its limits to push even more boundaries. However, and still thinking along the lines of concrete repair and restoration, research has shown concrete to be utilized much more differently in the near future, in the sense of having a considerable potential with regards to things such as Eco-efficiency and reducing the energy consumption of buildings.

    This might be important and will be very interesting to see the discovery of new ways concrete could deteriorate or fail.

  14. MichaelB
    October 10, 2016 at 9:11 pm #

    I greatly appreciated Mr. Pirro’s presentation.

    It was intersecting to see parallels with his presentation and Emily’s presentation on water penetration. Both topics dealt with building issues caused by both design errors and bad workmanship. As Mr. Pirro mentioned concrete has a very long history in human construction and the industry has a pretty good understanding of how to work with the material. Despite this issues still happen today such as missing critical reinforcement in tension areas around columns.

    I thought the cooling tower case was also interesting. I would think owners or managers of large projects such as nuclear power plants could be convinced to use methods similar to the one used on Mr Pirros project in new construction. Power plants like to have control over all aspects of their facility to keep power being generated and being able to pin point malfunctions such as rust in a cooling tower would expedite repairs.

  15. Ommar E
    October 10, 2016 at 8:45 pm #

    Mr. Bob Pirro’s lecture about concrete and the challenges of repairing it when it deteriorates was very crisp and informative. It revealed that although concrete is a millennia old construction material owners or the general public for that matter have difficulties in identifying the signs of its deterioration and when intervention is required. To add to the complexity of the issue, modern concrete embeds steel bars, strategically, to compensate for concrete weakness in tension. Together, they join forces to make one of the world most common building materials better known as reinforced concrete. A formidable building material if designed, and installed correctly. The difficulty in recognizing the need for repair led to, often, late stages intervention by the experts in the field and sometimes was too late to salvage anything. Also, as Mr. Pirro, mentioned, sometimes the design itself was the cause of the failure. It was very interesting to know that one of the cases of building failure led to changes in the codes regarding punching shear. I believe that advancements in additives and other components of concrete are promising in terms of providing preemptive measures to preserve concrete strength throughout its life span. Since most of these developments happened relatively recently, a couple of decades or so, the jury is still out in finding how effective they would turn out to be.

  16. Rebecca M
    October 10, 2016 at 8:03 pm #

    I found last week’s presentation on the evaluation and repair of concrete, and more specifically, the problems associated with it, to be extremely enlightening. Learning how concrete behaves and interacts with its surroundings is monumentally important when considering the lifetime of structure and becomes vital for understanding repair work.
    One thing I found most interesting was the cause of corrosion. I’ve always believed that it was the moisture alone getting down to the rebar that caused cracks, spalling, or even worse in concrete but in reality it is the mixture of moisture, oxygen, and chlorides together that lowers the pH enough to ruin the passivating layer surrounding the rebar.
    Of the touched upon methods to repairing these causes of problems in concrete, the FRP systems stood out the most. The idea of strengthening concrete by applying carbon fiber sheets raises a few questions such as, how costly is carbon fiber as a concrete repair solution? Can FRP systems be a more long-term solution if it were added during the placement of concrete? Knowing that concrete is particularly sensitive to the environment it’s in, does adding the carbon fiber increase the longevity by protecting it as well as adding strength?

    • Yamile R
      October 12, 2016 at 7:45 pm #

      Rebecca:
      According to what I’ve read, FRF has a higher initial cost, a lower modulus, suffers strength degradation with time and the stress-strain behavior is linear elastic to failure.

      Apparently, FRP has lower shear strength than steel reinforced concrete, and lower modulus of elasticity that cause cracks to open wider; and the depth to neutral axis is smaller so the shear can transfer across the compression zone easier.

  17. Yingzhe You
    October 10, 2016 at 5:48 pm #

    Thanks Mr. Pirro for the great lecture. As a civil student, what I usually learn about concrete is the designing method and our focus is mainly on the calculation part. From this lecture, I had a better understanding of concrete failure. The pH change of concrete can be very common in the failure cases of concrete which may lead to the corrosion of rebar.
    He also mentioned the collapse caused by workmanship. We’ve reviewed several cases caused by the faulty workmanship since the beginning of this semester, and I’m wondering can we draw a conclusion that the construction part usually causes more problems than other parts (designing, etc.).
    The comparison of the cost of repair for a parking garage is very interesting. The correct decision made by the owner may save a huge amount of money. I can still remember the failure case and the appropriate decision made by the owner. A museum was built near the seashore in my hometown when I was kid. But it opened for less than one year time and then closed because of the corrosion of exterior masonry wall. Although I was really disappointed at that time, I now think they made a correct decision for repairing at the very beginning and minimized the loss

  18. YusufA
    October 10, 2016 at 5:28 pm #

    A very interesting topic and presentation. I have particularly in the past found concrete as an area of interest. It has been widely researched however and needs to leave some room for newer sustainable materials as the industry’s focus.

    Having said this however, hardly would there be any building that has no concrete in either its un-reinforced or reinforced form therefore much attention is still needed in its handling. As mentioned by Mr Piro in his presentation, Poor Workmanship once again is one of the major factor which leads to the failure of concrete as in many other construction failures. This needs to be attended to via supervision

    Looking over the ‘investigation of deteriorated concrete’ presentation by Prof. boothby, I could not help but notice that The Freezing and Thaw effect is one which is most common. It almost feels as if it can not be avoided to exposed concrete. I believe having a proper concrete curing process as well as using a good quality of concrete would reduce the extensive failure of such concrete and avoid it leading to a structural failure or corroded reinforcement bars.

  19. Prateek Srivastava
    October 10, 2016 at 3:24 pm #

    Mr. Pirro’s lecture on Concrete Evaluation and Repair Techniques was a holistic one, as it covered from the basics as to what concrete is, how concrete structures are build and how they are repaired.

    He coupled his presentation with pictures of his own professional experiences which made the lecture more interesting.

    He told about the pH of the concrete which is responsible for the failure in most of the cases. As, the concrete is basic in nature so any exposure with the environment leads to chemical reactions which turn the nature of concrete to acidic thus leading to spalling and other concrete deterioration.

    He also discussed about usage of Petrographics which was new to me. His description about the repair and maintenance of cooling towers using titanium rings and letting the current pass through them supports for the maintenance measures according to the structure/site we are taking in consideration.

    He also talked about punching shears which are seen commonly these days resulting from poor quality of materials and workmanship.

    Overall, his lecture was interesting and his presentation skills were good enough to take notes from.

  20. Yamile R
    October 10, 2016 at 2:58 pm #

    Pirro’s presentation was very interesting. We learn about the different deterioration mechanisms, the process and techniques to assess it and how a repair is done in different cases.

    This presentation was of particular interest to me, since I come from a town that is very exposed to saltpeter, due to the closeness to the ocean; and most of our buildings are construct with reinforced concrete and CMU. So we encounter daily a myriad of cases with corrosion and deterioration.

    One thing that surprises me, is how the ignorance of building owners could result in severe failures. They do not realize that once the concrete shows deterioration, it starts worsen very quickly, resulting in a total collapse or a very high cost repair.

  21. Di W
    October 10, 2016 at 1:41 am #

    This lecture illustrated me a lot. It was one that I was interested in most because I have learned about concrete for more than three years but I have no experience about how to repair concrete. It was very good to learn about several way of surface repair such as you should make your repair layout as a whole part but not separately. And I would very like to see the “shot concrete” if I have an opportunity.
    I have a question, how do we guarantee the strength of the repaired concrete?

  22. Joe H
    October 9, 2016 at 5:22 pm #

    One of the biggest things that stuck out to me was his description of chlorides and carbonation seeping to the rebar. From how he described the process, it seems almost inevitable that the concrete will eventually deteriorate. So, how long is the concrete intended to last? Are there preventive measures that can be taken to make the concrete last longer? I know that he said the titanium is often used as a solution, not as a preventive measure due to the cost. Perhaps there is a cheaper option that can be used to slow down the deterioration?

    • MBologna
      October 12, 2016 at 3:18 pm #

      Joe,

      I also got the impression that you can not hold off moisture from reaching the reinforcement forever. Knowing this it is even more impressive to think of how long ancient structures such as the Pantheon have survived. I guess what really helps in these ancient structures is they are built as domes and arches where all the structure is in compression and there is no steel to deteriorate.

      I thought it was interesting how Mr. Pirro mentioned that the industry has changed its stance on protecting rebar from corroding. As Alec mentioned in an earlier comment I think FRP will be interesting in the future.

      An article on Penn State Library’s database, “Construction and cost analysis of an FRP reinforced concrete bridge deck”, compared two bridges that were virtually identical except that one was built with conventional steel rebar and one was built with FRP rebar. The article concluded that right now FRP rebar has a higher material cost but it can introduce savings in labor. Although from what I understand from the article the savings on labor costs were mainly gained from using a prefabricated FRP top grid system that greatly reduced construction time. A prefabricated steel grid would have the same reduced construction time but Wisconsin does not allow conventional prefabricated steel grids as top reinforcing due to fears of corrosion.

      The article did mention potential cost savings in the long term as the FRP rebar will not corrode but they could not measure this as the bridges were built fairly recently.

    • MichaelB
      October 12, 2016 at 3:19 pm #

      Joe,

      I also got the impression that you can not hold off moisture from reaching the reinforcement forever. Knowing this it is even more impressive to think of how long ancient structures such as the Pantheon have survived. I guess what really helps in these ancient structures is they are built as domes and arches where all the structure is in compression and there is no steel to deteriorate.

      I thought it was interesting how Mr. Pirro mentioned that the industry has changed its stance on protecting rebar from corroding. As Alec mentioned in an earlier comment I think FRP will be interesting in the future.

      An article on Penn State Library’s database, “Construction and cost analysis of an FRP reinforced concrete bridge deck”, compared two bridges that were virtually identical except that one was built with conventional steel rebar and one was built with FRP rebar. The article concluded that right now FRP rebar has a higher material cost but it can introduce savings in labor. Although from what I understand from the article the savings on labor costs were mainly gained from using a prefabricated FRP top grid system that greatly reduced construction time. A prefabricated steel grid would have the same reduced construction time but Wisconsin does not allow conventional prefabricated steel grids as top reinforcing due to fears of corrosion.

      The article did mention potential cost savings in the long term as the FRP rebar will not corrode but they could not measure this as the bridges were built fairly recently.

  23. Mehrzad
    October 9, 2016 at 1:14 am #

    This lecture was interesting in categorizing concrete failures under one fundamental group of causes comprising of design/materials/construction defects, and two secondary groups of damage (overload, fire, impact, chemical spill) and deterioration (reinforcement corrosion, erosion, freeze and thaw cycles, sulfate attack).

    The efforts over the past decades to produce higher-strength / more green concrete with less impermeability and more desirable strength developments have resulted in increasing usage of (1) distinct mineral and chemical admixtures in the traditional constituents of concrete, (2) recycled materials as aggregates, and (3) incorporation of modern strengthening procedures such as FRP and fiber reinforcements. This entails more careful evaluation of properties of the new or rehabilitated concrete together with strict construction controls to ensure compliance with their tested values in the lab. This specially is important when mineral admixtures are added as there are failure case studies due to improper blend of blast-furnace slag with the ordinary cement in site, high alumina contents leading to rapid full strength gain in a few days yet leaving a porous concrete with significantly lower strength later on, slow strength development as a result of many mineral admixtures’ influence in reductions of the hydration heat and delays in strength gain, etc.

    Bob mentioned he had seen more punching shears in the recent years. They are probably due to lack of strength development as a consequence of poor construction or inadequate detailing at the critical perimeter location.

    • philr
      October 12, 2016 at 1:50 pm #

      I would think that the expanded seismic requirements in the recent building codes that require more or continuous development of rebar across columns would lessen the amount of punch shear that is currently being seen.

      • Mehrzad
        October 12, 2016 at 10:57 pm #

        Phil,

        Be more careful with designing and developing your FRP rebars for seismic ductility performance though 🙂 The brittle and elastic nature of the rebar at ultimate rupture may pose ductility inadequacies.

  24. Alec B
    October 6, 2016 at 9:57 pm #

    I found this morning’s presentation particularly interesting as Mr. Piro covered a topic that I have been exposed to over the summer at my internship. I was fortunate enough to perform a site survey of a pre-cast concrete parking garage in need of serious repair work; my experience served as a great background to today’s topic, and Mr. Piro’s talk improved my understanding greatly.

    I was particularly interested in Mr. Piro’s discussion of using carbon fiber and other fiber-reinforced polymers to strengthen existing concrete structures and to help in the repair of concrete structures. I did some additional research on this topic. Copied below are two links for your reference if you’d like to learn more about carbon fiber repairs and FRP applications in strengthening concrete. One link directs you to a video that demonstrates the strengthening of a concrete beam through the use of one company’s FRP product. The other link is to a STRUCTURE magazine article that discusses the “Strengthening of Concrete Structures Using FRP Composites.” One of the items I found interesting in the STRUCTURE article is the mentioning of a repair code introduced by ACI in 2013, Code Requirements for Evaluation, Repair and Rehabilitation of Concrete Buildings (ACI 562), which is the first performance-based standard developed for the repair of existing concrete buildings.

    https://www.youtube.com/watch?v=3CO9rMbZuKo

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

  25. philr
    October 6, 2016 at 2:01 pm #

    Good presentation today. I am surprised that there are not more rebar coatings that can be applied to mitigate the corrosion issues.

    Secondly, on the cooling tower / titanium ribbon retrofit, if the intent was to run a current through the rebar, is not all of the rebar connected electrically through the structure? If so, then would there be any advantage to finding one end of the rebar and putting a current on it…or applying current at several distinct points? Why was it really necessary to cut 11 miles of groves in the structure to attach to every bar?

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