Concrete Sampling 1

[sachin-rangari]

I would like to know how to do sampling for a continuous work. I am in a railway project where thousands of foundation are to be done. Each day around 10 foundations (20 meter cube of concrete) are being done. Should I do sampling for each day separately or should i consider for whole project??? The concrete is obtained from same RMC plant.

 

[Ron]

20 cubic meters of concrete is not a lot, so not enough for full-time sampling program. Sampling should be done each day,

A common specification for sampling is one set of specimens for each 100-150 cubic meters of concrete but not less than one set per day of placement.

What does your specification require?

 

[sachin-rangari]

Thank you Ron,

Now, my question here is, should i take only one sample for 5 days of concreting (that would be 100 cubic meters considering 20 cubic meters of concrete each day) or should i take 1 sample for each day. The latter one would not be economic.

 

[dik]

In these environs, if you had concrete being placed over 5 days, you would have a minimum of 5 sets of concrete samples. Many codes or standards stipulate the rate of sampling. You would also have slump tests and, unless waived by the EoR, air content testing for each set of samples (3 cylinders for each set of samples).

Dik

 

[cvg]

one per five days? why are you making cylinders? if it is for acceptance testing, than you really should have at least one per structure or location and also any time you change mix design, take another

 

[jgailla]

You should take at least one sample per day.

 

[sachin-rangari]

Dear All,

Thank you for response. I want to follow the 1 sample per day criteria. Please can anyone refer a code for the above said criteria. Which code to follow and which code has it defined clearly??

 

[dik]

cvg:
I said a minimum of 5 sets... apologies cvg, your response was to another message, and I missed that.

Dik

 

[zelgar]

A minimum of 1 sample per day is considered GEP (Good Engineering Practice). Even if the mix is the same for each day, you'll get some differences due to temperature, humidity, and human error. For any type of QA/QC a minimum testing frequency of 1/day is standard.

 

[dik]

OP:
In Canada, CSA Standard A23.1-14 stipulates under Clause 4.4, 'Quality Control' the frequency of testing. It's pretty much as noted above and closely reflects the requirements of the ACI Code. My copy is at the office and when I return Friday, I'll scan the relative Clause and post it to you.

 

[dik]

The following is from my Project Notes and closely reflects the requirements of CSA A23.1:

CONCRETE QC

WATER SHALL NOT BE ADDED TO THE CONCRETE MIX ON SITE UNLESS APPD IN WRITING BY THE CONCRETE SUPPLIER AND AUTHORISED BY THE ENGINEER

PROVIDE HISTORY OF CONCRETE MIX USE IN ACCORDANCE WITH CSA A23.1

TESTING SHALL BE IN ACCORDANCE WITH THE REQUIREMENTS OF CSA A23.1 UNLESS NOTED OTHERWISE

A MINIMUM OF THREE CYLINDERS SHALL BE TAKEN FOR EACH STRENGTH TEST, ONE CYLINDER FOR 7 DAY STRENGTH AND TWO CYLINDERS FOR 28 DAY STRENGTH

TEST CYLINDERS SHALL BE 6" DIA X 12" HIGH U/N

SLUMP TESTS SHALL BE TAKEN WITH EACH SET OF CYLINDERS TAKEN FOR STRENGTH TESTING

AIR CONTENT TESTS SHALL BE TAKEN FROM EACH LOAD UNLESS A REDUCED FREQUENCY IS AUTHORISED IN WRITING BY THE [OWNER | CONSULTANT | ENGINEER]

CYLINDERS FOR STRENGTH TESTS AND A SLUMP TEST SHALL BE TAKEN FROM AT LEAST EACH THIRD TRUCK

A MINIMUM OF THREE CYLINDERS FOR STRENGTH TESTS, AND A SLUMP TEST SHALL BE TAKEN EACH DAY FOR EACH DIFFERENT TYPE OF CONCRETE MIX DESIGN

WHERE THE FREQUENCY OF TESTING ABOVE WILL PRODUCE LESS THAN THREE TESTS FOR A GIVEN CLASS OF CONC, TESTS SHALL BE MADE FROM AT LEAST THREE RANDOMLY SELECTED BATCHES

IF LARGE VOLUMES OF CONCRETE ARE BEING SUPPLIED (OTHER THAN BY TRUCK), THERE SHOULD BE A MINIMUM OF THREE CYLINDERS TAKEN FOR STRENGTH TESTING, ONE AIR TEST AND ONE SLUMP TEST FOR EACH 100 CUBIC METRES OR PART THEREOF

CARE SHALL BE EXERCISED IN PROTECTING THE TEST CYLINDERS FROM DAMAGE

TEST CYLINGERS SHALL BE PROPERY CURED

IF TEST RESULTS SHOW A LARGE 'SCATTER' OF DATA, ADDITIONAL TESTING SHOULD BE PRESCRIBED

THE TESTING AGENCY SHALL FORWARD A COPY OF ALL TEST RESULTS DIRECTLY TO THE [OWNER | CONSULTANT | ENGINEER] AT THE TIME THE TEST RESULTS ARE FORWARDED TO THE CONTRACTOR

IF CONCRETE SPECIFIED IS IN EXCESS OF 35 MPA, THE CLIENT SHALL ARRANGE FOR THE GEOTECHNICAL CONSULTANT TO REVIEW THE CONCRETE BATCH PLANT

FOR TESTING MASONRY GROUT, REFER TO NOTES ON MASONRY CONSTRUCTION

Dik

 

[cvg]

should i take only one sample for 5 days of concreting

DIK - I wasn't commenting on your reply, the OP said 1 sample, which is entirely inadequate for 5 days of work on up to 10 structures per day. Even 1 sample per day is probably inadequate. I would suggest:

minimum of the following:
at least 1 set per mix design, and
at least 1 set per structure, and
at least 1 set per day

So if you are doing 10 foundations per day, theoretically you may be taking 10 sets of cylinders, 1 for each structure

 

[dik]

Correct cvg... I misunderstood you. I usually don't read the other postings until some time after I've commented.

Dik

 

[wannabeSE]

Frequency of testing can be found in section 5.6.2 of ACI 318-11.

 

[BigH]

I've skimmed the above. The OP says that he is doing many footings . . . presumably the concrete is coming from one plant. I would say that he should do 1 set of samples per day for each grade of concrete. In other words, he may be placing 10 foundations of 2 to 3 m3 each - all the same grade (or class if you prefer) of concrete all from the same concrete batching plant; then 1 set of cylinders (or cubes - depending on country) should be done.

Sadly, I've seen specs that were written to say that each "placement" must have a set of samples taken. So if, for instance, one is placing concrete v-drains and he does one of 2 cubic metres and skips 20 m of length of the same drain as he had done that section a week earlier and does another of 2 cubic metres all from the same transit mixer, then they would have to do two sets. Ridiculous.

 

[dik]

This is a short paper I put together a few years ago...

The information is based on the codes in effect at the time it was written.