Let the Bakers Bake
October 8, 2012
When was the last time you bought a cake? How did you order it? Maybe you told the baker you wanted a chocolate layer cake with pink roses on it for a little girl. If you were getting fancy, maybe you ordered it with buttercream frosting. If you were ordering a special cake, like a wedding cake, maybe you even tasted a sample of the cake before you ordered it. However, did you ever tell the baker how many eggs to use, or what brand of flour to use? Even if you did, the baker probably would have ignored you and made the cake the way he knew it should be made.
You can probably already tell where I am heading with this. In the concrete industry purchasers of concrete frequently tell concrete producers not only what kind of concrete they want, but also how to make it. Maximum water-cement ratios, minimum cement contents, target combined aggregate gradings and limits on materials selection force a concrete producer to make less-than-optimum concrete. If you are an engineer or specifier, take the following true/false test.
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Decreasing the water-cement ratio is the best way to improve the durability of concrete. T/F
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Concrete using straight cement is better than concrete containing fly ash because fly ash is just a filler. T/F
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Concrete should not be pumped, because in order to pump concrete we must compromise the quality of the concrete. T/F
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Increasing the air content of concrete is the best way to improve freeze-thaw durability. T/F
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Concrete should not be placed at over a 6” (150mm) slump. T/F
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Fly ash should not replace more than 25% of the cement in a concrete mix. T/F
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Concrete with a water-cement ratio less than 0.40 will be durable. T/F
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The best concrete mixes follow the ACI 211 tables. T/F
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Concrete mix designs shouldn’t be changed without a resubmittal. T/F
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Concrete over 90 minutes old must be discarded because it has gone bad. T/F
Did you respond “True” to any of the above statements? If so, then I don’t think you are qualified to design concrete mixes. Every one of these statements is either false or true only under certain conditions and cannot be generalized. Too many current specifications contain references to statements similar to those above. The time has come for specifiers to get out of the kitchen and let the bakers bake.
Concrete production has changed dramatically over the past 20 years. It is a full-time job just to keep up with the variables that today’s concrete producer must consider. Think of the following issues:
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Depletion of resources
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New materials, such as pozzolans, admixtures, mineral fillers and manufactured aggregates
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Environmental considerations affecting concrete production, such as process water
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Sustainability issues, such as cradle-to-grave life cycle assessment
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Competitive requirements requiring increased productivity of men, materials and equipment
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Long term durability of concrete
How can any engineer with only a 1 semester course in materials think that he (or she) is qualified to specify how a concrete mix is made? Engineers already have too many demands placed on them. Design requirements, life safety issues, governmental regulations, risk management and ever-decreasing fees for design services make it impractical for a designer to spend the time to micro-manage the concrete mix design process. Engineers are bakers, too. They should spend their time doing what they do best and leave concrete mix design and production to the concrete producers.
If you think that I am just rehashing the NRMCA P2P (Prescriptive to Performance) efforts, I hope that you will read this article through to the end.
How did we get to the point where designers felt they needed to control the concrete ready mix industry? Hundreds of years ago, the architect was considered the “master builder” and knew not only how to design the aesthetics of a building, but also was well versed in structural design and construction methods. Over the centuries people specialized and became architects, engineers and contractors. In the early 1900s concrete production started to change from an on-site, low volume process to more of the current ready-mix operation we see today. Ready-mix producers eventually realized that they were spending more money on production and delivery equipment than they were on the materials they actually delivered. Many producers considered themselves truckers and that concrete was only the materials they were trucking. It didn’t help that concrete was such a forgiving material that it could be grossly abused and still perform acceptably. With the increased notion of owners and purchasers accepting the lowest bid, a practice which predominates in the U.S., engineers who understood concrete better than many producers started adding specification requirements to limit the bad practices of some concrete producers. (Please don’t think that I am bad-mouthing all early concrete producers. I am certain that many of them were highly quality conscious. I am talking about concrete producers who didn’t understand the material, but produced it without regard to proper techniques.)
If we come back to the present day, it becomes obvious that the current system of designing and producing concrete in the U.S. is broken. Designers include inappropriate specifications in order to protect themselves from low-bidding, ignorant concrete producers. At the same time they perpetuate outdated notions to protect themselves from a future recurrence of a problem that happened to them 20 years ago. This limits the capabilities and creativity of concrete producers to come up with appropriate solutions. At the same time, there are still concrete producers that don’t understand basic concrete technology. They use mix designs that they inherited from their predecessors without knowing why things were set up as they were. This applies not only to small concrete producers, but also some larger ones as well. I have even seen a division of a multi-national concrete producer where the person in charge of quality control shouldn’t be designing concrete for driveways, much less high-rise office buildings. My only salvation in making this statement is that anyone reading this blog entry is probably not the person I am talking about.
At this point I don’t know if I am St. George, trying to slay a dragon, or Don Quixote tilting at windmills. For the sake of argument, let’s say that I lean a little more to being St. George, swinging his ancient sword. Like any sword, mine cuts two ways. Not only must designers get out of the mix design business but concrete producers need to get into the mix design and quality control business.
The late Ken Day was a good friend and former competitor of mine. For those that didn’t know him, Ken was an Australian, the originator of the ConAd software that is the basis for Command Alkon’s COMMANDqc program (https://commandalkon.com/product/commandqc/ ), and a self-proclaimed “concrete evangelist”. Ken took great delight in telling people how much better Australians are at producing concrete than we are in the U.S. I don’t know that they are actually better at it than we are, but they certainly operate under a different paradigm than we do. In Australia concrete producers are responsible for their own concrete testing. They don’t have the luxury of pointing their finger at the testing lab and blaming poor testing, because they are the testing lab. Producer testing labs must be accredited by the National Association of Testing Authorities, http://www.nata.com.au/, and I assume that on some projects there is also random quality assurance testing as well. While this may seem here in the U.S. like the “fox guarding the henhouse”, this same approach is followed in most European countries and many South and Central American countries as well. It is primarily here in the U.S., where we have a “cops and robbers” mentality, that we don’t require concrete producers to do their own testing. My father used to scoff at the idea that a third party lab can perform quality control. He said, “The only person that can control quality is the one doing the work.” Everything else is quality assurance.
At this point I am going to go positively medieval and throw down a gauntlet. I challenge the concrete design, construction and production industry in the U.S. to move into the 21st century and to insist that concrete producers learn about their own material, become responsible for their own quality control, and to shift specifiers out of the mix design business. I am 57 years old and I want to see this happen before I retire, which hopefully won’t be for another 20 years or so.
This idea obviously isn’t anything new. There are already initiatives underway to make it happen. I have been on the NRMCA’s P2P committee (http://www.nrmca.org/P2P/ ) almost since the day it began. ACI has Committee 329, “Performance Criteria for Ready Mixed Concrete” (https://www.concrete.org/committees/directoryofcommittees/acommitteehome.aspx?committee_code=C0032900 ). I have been told the ASCE has a group promoting the use of performance specifications, but I couldn’t track anything down using a Google search. If you know the name of the committee, please post it.
Let the bakers bake!
