Slump of Concrete is irrelevant?

Most obviously, to cover the cases where 1) such admixtures are either not being used, or 2) are being used where conditions still require some limit to the water/cement ratio of the enhanced mixture, 3) these anmixtures are not accepted by the client according to job specifications.

There are other properties than strength (i.e. 28 day compressive strength) to consider. Please consider that these requirements as well.

I agree that there are many other requirements. But I want to see ideas and justification as to why SLUMP is still tied to STREGTH.

Yes, traditionally this was used as an indicator of the water/cement ratio, which IS directly related to final stregth (all of which is compressive or flexural when talking concrete), and may still apply in some situations. But very few Ready Mix plants produce just the basic rock, sand, cement, and water mixes unless specifically asked. They will throw fly ash in as a cost savings over cement. That will change the slump.

I should have been more direct in stating commercial/public application were some type of admixture is almost always called for.

To be a little more clear of my position-

I believe slump can be an important indicator as to initial set, workability, and final finish quality, all of which are directly related.

Its value as a water/cement indicator is obsolete and should not be specified as such.

In a non-public or non-commercial setting it will not likely be tested for and therefor is also worthless.

You may be able to ascertain workability, etc., but you can not accurately tell the slump 'just by looking at it' and nobody will ever convince me otherwise. You are at the mercy of the plant and/or the driver and his gauge to tell you what it is.

Hopefully, the plant is honest, and giving you what you pay for.

I still believe that the Slump Test is relevant on the job site. For instance, when I was a Resident Engineer on a project site, the specs called out that the ready-mix plant had to provide the batch ticket with each truck load. These tickets had to show the quantities of all of the constituent materials used to make that concrete load, including the plant's calculation for W/C Ratio.

All too many times these batch tickets didn't arrive with the truck, so instead of sending the driver and the load packing undelivered I had to rely on the Technician to conduct a Slump Test as some sort of measure of conformance to the specs.

I don't like to rely on the use of slump meters that are provided on ready-mix trucks too much, unless the plant can show me, by submission of written documentation, that the meters have been satisfactorily calibrated very recently, otherwise I find that they they should only be used as an approximating tool.

I have another opinion that any admixture that affects the true Slump should only be added at the jobsite at the Resident's Engineer expressed approval, otherwise admitures like water reducers or Mid-Range to High-Range superplasticizers (not to0 mention heat or severe cold factors) that are added at the plant can and tend to mask the real unalterated Slump value by the time the load reaches ther job site......how can you not derive whether or not the driver has added water to the batch during transit?

Adding my 2 Cents.........

Signed,

CaptMoosie, LPE, PhD

Civil, Environmental, Structural, & Transportation Engineer

Now thats the kind of discussion I was looking to generate!

Slump tests are a good indicator of batch to batch consistency.

I personally require that all batch weights be documented on the ticket, when I have the power, if it is not already written into the specs or specials.

It is just a quick calc to see if the w/c ratio is in line.

Hi CaptMoosie,

Well said Sir! I agree with your sentiments, it may be a bit out of date but as an R E myself I was charged with quality control and the last thing I needed was a low strength cube test at 7 days and the possibility of a 'duff' slab to be cored or worst still cut out. Actually the good 'ol slump test was respected by the gangers as much as the engineers and in a cold climate a watery mix was slower to cure and ran the risk of frost damage.

So , yes as a site control mechanism use the slump test.

Massey.

Dear Uncommon & Massey,

I'm glad to note that we're all on the same page about this Slump issue, irregardless of where we are! Also glad to note that we're not old "Fossils" after all in our thinking.....sometimes the old ways are still the best ways!!

Beers & cheers for all! (Bitters anyone? LOL). Have a great day gents!!!