Concrete Sampling 2

[canon252]

Hi,
I kindly would like to ask about concrete sampling for compressive strength, I have to cast 1200 m3 in one day as one batch to pour a water treatment sedimentation tank ... how many 15x15cm cubic sample I should cast to represent the 1200 m3?
I will highly appreciate if you kindly inform the ACI reference.
I Think that the specifications of sampling say that I should pour 24 cubic for each 50m3 of concrete but not sure, and this info missing something.

 

[bimr]

Specifications for Structural Concrete, ACI 301-96, requires obtaining at least one composite sample for each 100 cubic yards, or fraction thereof, of each design mixture of concrete placed in any one day. Composite samples are obtained in accordance with "Standard Practice for Sampling Freshly Mixed Concrete," ASTM C 172. Strength tests are conducted on each sample.

Slump tests are required for each composite sample and whenever consistency of the concrete appears to vary. If air entrainment is required, air-content tests are also required for each composite sample.

http://www.concreteconstruction.net/concrete-articles/how-often-should-fresh-concrete-be-tested.aspx

 

[cvg]

ACI 318 is a bit different

Building Code Requirements for Structural Concrete (ACI 318-08)

5.6.1 — Concrete shall be tested in accordance with the requirements of 5.6.2 through 5.6.5. Qualified field testing technicians shall perform tests on fresh concrete at the job site, prepare specimens required for curing under field conditions, prepare specimens required for testing in the laboratory, and record the temperature of the fresh concrete when preparing specimens for strength tests. Qualified laboratory technicians shall perform all required laboratory tests.
5.6.2 — Frequency of testing
5.6.2.1 — Samples for strength tests of each class of concrete placed each day shall be taken not less than once a day, nor less than once for each 150 yd3 of concrete, nor less than once for each 5000 ft2 of surface area for slabs or walls.
5.6.2.4 — A strength test shall be the average of the strengths of at least two 6 by 12 in. cylinders or at least three 4 by 8 in. cylinders made from the same sample of concrete and tested at 28 days or at test age designated for determination of f’c

 

[canon252]

Thank you very much for the valuable infirmation. But, to sumurize this, can anyone advice me how many cubic block of 15x15cm i should test for the 1200m3 if it will be tested in one batch?

 

[cvg]

would not recommend 15x15cm blocks, use standard 6 inch diameter x 12 inch long cylinders

 

[canon252]

Blocjs us the most familier un my country ^_^

 

[dik]

In these environs, air is tested from each load until the engineer is comfortable with something less.

Dik

 

[bimr]

The frequency of sampling depends on what is specified in the contract and what is specified in the building code. Suggest you read the contract and building code.

Lacking those documents, the standard specifications for concrete call for at least one composite sample for each 75 cubic meters. The building code specifications call for at least one composite sample for each 115 cubic meters.

http://www.engr.usask.ca/classes/CE/898/t2/b/notes/PCA/Chap.16/Chap16.pdf

 

[BigH]

Canon252 - I can sympathize with your "cubes" vs others "cylinders" - which are the matter of choice in US/Canada. Britain has always used cubes and as a result almost all commonwealth countries also use cubes.

I am not sure of any "code" requirements - you might find it under British Standards somewhere - but on several jobs I have been on:

1. Currently, we take 1 set for up to 10 m3; 2 sets for up to 40 m3, 3 sets for up to 80 m3 and then 1 set every 50 m3 after that.
2. On a large dam where we were casting sets for up to 1500 m3 placements, we took one set for every 50 m3 and then after we felt confident of the concrete - we took at every 100 m3.

Following 1 above, if you were to place 55 m3, then you would take 3 sets. We normally tried to do this on a random number basis. Say determine how many transit mixers will be used in the the placement, determine the number of sample sets required and then go to a table of random numbers to ascertain which transit mixer to test.

Hope this helps.

 

[canon252]

Dear Friends,
Thank you very much for the kind reply ... hope this thread was helpful.
I have visit a laboratory which doing concrete tests in my city, they told me that sampling frequency to be as follows;

For raft foundation:

For >50m3 ==> 3 cubic for 7 days test
==> 12 cubic for 28 days test
+
For 50-100m3 ==> 3 cubic for 7 days test
==> 12 cubic for 28 days test

>>> i.e. if we have 99 m3, we should prepare 30 cubic (15 for the fisrt 50m3 + 15 for the second 50)

+ For 100-150m3 ==> 3 cubic for 7 days test
==> 12 cubic for 28 days test

+ 3 cubic for each additional 50m3



For Other Structures:

For >60m3 ==> 3 cubic for 7 days test
==> 12 cubic for 28 days test
+
For 60-80m3 ==> 3 cubic for 7 days test
==> 12 cubic for 28 days test


+ For 80-100m3 ==> 3 cubic for 7 days test
==> 12 cubic for 28 days test

+ 3 cubic for each additional 20m3

 

[BigH]

Canon252 - I think that you better review what you were told. It is not how many cubes or how many cylinders you take per se, it is the number of set samples. Don't think of the number of cubes or cylinders but of the number of "sets" - which I gave you in my earlier post for a couple of projects I have been on here in Asia.

Normally, in North America, a set consists of 3 cylinders (taken at the same time from the same truck - a composite of a number of small samples taken from the truck at different intervals). One cylinder is tested at 7 days and two cylinders are tested at 28 days. The Compressive strength "result" as reported would be the average of the two 28-day compressive strengths.

In Asia, I have found that generally 6 cubes or cylinders are taken from one composite sample from one truck. Three would be tested at 7 days and three at 28 days - the average of the 28 day compressive strengths is the test "result".

Now, due to the use of fly ash in the mix which is commonly occurring these days, some specifications are not calling for a 28-day characteristic strength but are, in fact, calling for a 90-day characteristic strength as being the acceptance strength. In cases one would cast sufficient cubes or cylinders to cover a 7 day strength (to have an early idea of what the strength will likely be at the required test date), a few would be tested at 28 days as this is a better result for fly-ash cement substitutions and then two or three cubes or cylinders would be tested at 90-days for the acceptance. We have also taken additional cylinders to determine 180 and 365 day test results - especially for low cement content conventional concrete. (note: Our contractors have used both 25 or 30% fly ash and also 50% fly ash substitutions for cement in the last 5 years.)

To summarize, I don't understand what you have just written - it sound like you are taking 3 sets of cubes - 1 cube in a set for 7 days and 4 in a set (?) for 28 days. What you have written is very strange. I have never seen anyone take one set consisting of 3 cubes/cylinders for 7 days and 12 cubes/cylinders for 28 days - from one sampling set. You need, in my view, to review what they have told you. For a set to be valid, all the cubes or cylinders must be from the same transit mixer. You should revisit what you were "told".