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Heading: 1.2.2Concrete testing
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While the discussion about "Concrete Test Reports" is in full force, a building in Cologne collapsed with 2 people killed. This probably due to the early strength of certified prescription concrete.
Are there more people scared about the poor status the civil concrete industry still is in, in general? If the, what I considered "simple" testing of concrete strength, causes so much fundamentally good dialogue on this site, I could block the ARI system by asking "how about "Durability" testing.
Yes I questioned why we compare a nicely vibrated sample put 28 days in water with the reality of a site. Are we putting bridges under water 28 days before we use them? But whom am I.

It is time we get further inspired by the refractory concrete industry I came from, stop Prescription and move to Performance and Procurement needs.

If we agree on what is CEMENT and what is a BINDER I might still take back my words that we are still dealing with supplier imposed pseudo technological tools such as WCR and 28 days strength.

As with refractory concrete, keep the mix secret and agree on testing methodology, but not by the usual endless consensus way practiced in Europe and North America. Just by verifiable best proven practice of some wise men who's integrety is not questioned as I do in many cases here.
Let us not waste a good crisis to get it right this time.


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Boudewijn Piscaer


BP
You may have over-simplified this.
Concrete is only part of the equation - remember forming and shoring design and installation also play a role in a building under construction.
I go back to my earlier comments that there are cylinders for acceptance, which are cured ideally at 100% humidity and 73 F.
Then there is concrete in-place, which is subject to the environment. Other reliable means of strength checking should be used while the concrete is still young to get accurate strength data of in-place concrete.
Prescription concrete is used when a buyer will not permit the concrete provider to create his own formulas. This is very common in North America esp. where a government agency is purchasing the material. In free market circumstance, the contractor submits a mix design for the engineer to review, and then it is the contractor's responsibility to insure the early strength is adequate for form or shoring removal as the work progresses.
However it doesn't matter if it is prescription or performance concrete - if the early strength for some reason is inadequate, there is chance for failure or collapse. All concrete must be properly produced, placed, and cured to perform at early ages and for the life of the structure
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Roy Keck


BP - I appreciate the points you and others are trying to make. Rather than placing blame on a particular group of concrete professionals, let us understand why cylinders cured in an idealized environment are used to verify design strength. In the early days of structural concrete design, the design formulae were developed empirically in a laboratory. Knowing that field conditions could hardly duplicate laboratory conditions, engineers solved the problem the old fashion way: throw in sufficient safety margin. Over a century of structural concrete construction has shown that "laboratory" cured cylinders work.
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Teck Chua
 
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