Spot Sampling of Fresh Concrete per EN 12350-1

[BigH]

For my British mates although the Canucks, Yanks and others can add their 2 cents or twopence to the thread.

ASMT C 172 requires sampling of fresh concrete to be a composite sample whereby the initial 10% and last 90% of the discharge is ignored and not used.

EN 12350-1 permits spot or composite sampling (thinking specifically for slump). Section 4.2 states that the composite sample, as per ASTM C 172 let the first and last part of the mixer to be disregarded in sampling. For spot sampling, it doesn't actually specify that the initial part of the discharge is to be disregarded. Yet, as per the reference seen in :

https://qaqcconstruction.com/2017/0...ixed-concrete-at-the-field-bs-en-12350-12009/

suggests that it must be disregarded.

I am looking for "practice" experience for spot sampling.

 

[TigerGuy]

BigH,

Of all the projects you have attended, how often have you seen the testing staff actually follow ASTM C172? I feel that I have followed it, on rare occasions. Typically, I see the discharge aimed into the wheelbarrow and the pour resumed.

 

[BigH]

TigerGuy - you are very correct . . . in Malaysia, I was able to get the Contractor to actually do composite samples. Here it is first out of the mixer truck but sometimes I need to nitpick the Contractor. Probably the worst I've seen is that they take 9 cubes (here they use cubes for some reason) - and then test them as a "test result" - but for a while until I noted it, they would take three cubes from three different transit mixers - so no wonder the variations within each set of three per a specified day of testing (i.e., 7, 28, 90) were all over the place. The main purpose of my question was the issue of "spot sampling" that EN permits . . . Fortunately, all concrete testing is per ASTM except for, and get this, testing of hardened concrete (compressive strength) which follows EN and not ACI. Cheers

 

[TigerGuy]

I had some nut called me and accused my company of fraudulent test reports, because we would accept and test cylinders molded by the contractor. His reasoning was that we couldn't certify everything to standards. I told him that we only certify the part we handle.

I'm sure we could share thousands of stories about how standard procedures aren't followed in real life. It keeps life interesting.

 

[Ron]

In C172, You're supposed to obtain a composite sample from the middle 1/3 of the delivery. This is absurd. Slump must be sampled early so that loads may be accepted or rejected.
If C94 is followed, the first part of the load should be the same as the last part of the load. Why is conflicting with its own committee requirements? Welcome to standards development in ASTM

 

[BigH]

One thing I've noticed Ron - today, slumps are so much higher than when we were youngsters - all the slumps on our project are in the 150 to 200 mm range - for large placements, we end up with running rivers and hard to control vibration . . . I prefer 100 mm slumps in large "mat" like foundations. Workers an work within the formwork rather than from above. I also noticed in the past that the slump at the beginning of the placement is typically but not always lower than in the middle - I've seen them having to shovel down the first part of the discharge but in the middle it ran "like water" . . . You are right, of course, in that many times "standards" conflict with each other . . .

 

[Ron]

BigH...always an issue! I agree. Slumps have slumped! I remember holding contractors to a 4" (100mm) slump while they bitched at me. So what. Concrete was better and cracks were fewer. I kind of miss those field days and yelling matches on site! The younger guys don't understand that. They want to stay out of conflict with the contractors. My philosophy has always been that is the contractor is not complaining about the technician, he's probably not doing his job!

 

[BigH]

Ron - talk about yelling matches and confrontations, I was on a job in Vancouver and the main contractor and his excavation subcontractor got into it - really into it. I thought they were actually going to come to blows - hot is too cool of an adjective!. This happened at about 1500 h. Yet, at 1730, they both went out for a beer together! Work is work; outside of work is outside of work. Cheers

 

[TigerGuy]

I've been called some colorful names over the years over the slump result. If they want to yell at me, I kick the base and measure it again. Then I ask them which result they like better.

I won't yell at anybody on the job site, but I can be really ornery if they want to start trouble.

 

[Keith_1]

As a super for a GC I would never tell them when I was going to pull a sample, in my experience after you make them tear down a sheerwall or column or two the shell guys get it into their heads not to add a bunch of water. Once everyone understands that they can either do it right or do it over, things run smooth.

On occasion the tech "decided" that his sample was bad and needed to take another one a few minutes later.

This is not following the standard to the letter, but it accomplished the intent.

The only issue I have ever had from the plant were trucks that were late, and the batch expired. Which to be fair was not the drivers fault 99% of the time.