When I first started this blog almost 3 years ago I posted an article entitled “If I Ruled the Concrete Industry”. The article presented 5 changes that I felt needed to be made to the concrete industry. Responses that I received to my most recent post on the fact that concrete producers are not being sent concrete tests as required by the Building Code have pushed me to recognize that the 5 changes I suggested are really symptoms of the same thing, at least here in the U.S. That conclusion is that in the U.S. we are operating under an inappropriate paradigm when it comes to designing, specifying, manufacturing, constructing and testing with concrete. We need to change the paradigm so that the entire design and construction industry takes a more professional approach to the design and use of concrete. Continue reading
If you were to walk into an Engineer’s office and tell him to reduce the reinforcing steel in a structure or to cut back on the design strength he would probably think your were crazy (or part of the Mafia). However, many Engineers, Owners, Contractors and Laboratories routinely violate the Building Code and possibly endanger workers and the public. It is time to put an end to this unsafe practice and comply with the Code. What heinous crime am I referring to that endangers the public? It is the practice of not providing concrete test results to the concrete producer.
I had really planned on stopping the section with my last entry on “Statistical Overdesign by EN-206” but quickly realized there are still a bunch of bits and pieces about this topic still floating around that need to be pinned down. Since the series started there have been updates on ACI 318 and EN-206. Also, there are considerations for other documents, including ACI 301, “Specifications for Structural Concrete” and ASTM C94, “Specification for Ready Mixed Concrete”. Continue reading
At the American Concrete Institute Fall 2015 Convention in Washington D.C. I delivered a presentation entitled “Particle Packing from a Rock’s Perspective”. ACI has just posted the presentation on YouTube at http://youtu.be/JamUGG3-DSg. If you are looking for a stuffy presentation filled with facts and figures, this presentation isn’t for you. If you want to find out what rocks think about particle packing, drop by and meet Rocky. Hey, its only 12 minutes long. What can you lose?
My past couple of posts have been about statistical overdesign using ACI 318, so I thought this time I would discuss the overdesign technique used in EN-206. After all, EN-206 uses a similar statistical method to ACI 318, right? Wrong! What started out as a simple 2 hour exercise in paraphrasing EN-206 has turned into a major effort involving about 20 people on 3 different LinkedIn groups. One of my favorite sayings has come to be, “If you want to make God laugh, tell him your plans.” My only consolation from this blog post is that God must have gotten a real belly laugh. Continue reading
When determining the required average compressive strength, f’cr, by ACI 318, the Structural Concrete Building Code, the Code cites the preferred option of using 30 consecutive tests to determine the sample standard deviation, then to use that standard deviation to calculate the overdesign above specified strength, f’c. Fortunately the Code recognizes that not every concrete producer will have 30 consecutive tests for every combination of materials and provides options for other alternatives. In my last blog post we looked at determining required average compressive strength using 30 tests. In this post I would like to examine the other options. (NOTE: There are many details in ACI 318 that are not covered in this post. This post just covers one aspect of ACI 318. If you must develop a concrete mix in compliance with ACI 318 it is strongly suggested that you first obtain a copy of that document. Copies are available from ACI at http://www.concrete.org .) Continue reading
The first question most people ask about concrete is, “How strong is it?” Yes, there are other important characteristics about the concrete, but strength is usually the most important one. In fact, most “hidden concrete”, such as footings, columns, beams and slabs, really is not affected by durability concerns. The primary function of the concrete is to provide support. If we don’t need to worry about maximum water/cementitious ratios for durability concerns, there are other ways to design mixtures just for strength. When concrete has a prior performance history the primary way we determine the cementitious content of concrete is through the use of statistical overdesign techniques, such as are in ACI documents. Continue reading
It sounds so easy to say, “Design a concrete mix using a water/cement ratio curve”, but it isn’t. Finally in this mix design series we are talking about concrete and not just components. However, there are a number of steps we have to go through before we cast our first trial batch. Continue reading
Have you ever started a project, then realized that the only way you can begin your project is to do 3 other projects first? Sitting down for the third time to write an article on water/cement ratio curves, I am reminded once again how concrete imitates life. Another thing I have discovered is that when I have trouble writing an article, it is usually because I don’t understand what I am writing about, even if I think I do. I have been having a problem writing about water/cement ratio curves because they aren’t just about paste and water and cement, as I have previously implied, but about an entire concrete mix. Continue reading
As we continue on our discussion of “Concrete Mix Design: Art and Science” I would like to move on to a discussion of “paste”. We have already discussed paste near the beginning of this series (http://www.commandalkonconnect.com/2013/07/15/concrete-mix-design-art-and-science-paste/) and, after rereading it, it is a pretty good start, but I would like to add a few things to the discussion. Continue reading