ASTM C172/C172M Sampling Freshly Mixed Concrete

What is the max time between obtaining the first and final portions of a composite sample?

15 min

What type of sample is required for C172?

Composite samples unless otherwise stated.

What types of containers can be used to obtain the concrete sample?

Metal pan; wheelbarrow; flat, clean nonabsorbent mixing board

What should you protect the C172 sample from?

Sun, wind, other sources of rapid evaporation, contamination.

Minimum Sample Size of Concrete

1 cubic foot

What is the minimum size sample for molding strength test specimens?

1 cubic foot

What are the effects of wet-sieving on test results?

1. Causes the loss of a small amount of air due to additional handling 2. The air content of the wet-sieved fraction of concrete is greater than that of the total concrete because the larger size aggregate which is removed does not contain air. 3. The apparent strength of wet-sieved concrete in smaller specimens is usually greater than that of the total concrete in larger appropriate size specimens.

Sampling Process from Revolving Drum Truck Mixers or Agitators

1. Collect the sample by repeatedly passing a receptacle through the entire discharge stream or by completely diverting the discharge into a sample container. 2. Collect two or more portions taken at regularly spaced intervals during discharge of the middle portion of the batch. 3. Do not take more than 15 min 4. Combine them into one composite sample for test purposes

Sampling Process from Stationary Mixers, Except Paving Mixers

1. Collect two or more portions taken at regularly spaced intervals during discharge of the middle portion of the batch. 2. Obtain in less than 15 minutes 3. Combine into composite sample for testing purposes.

C172 Performance checklist

1. Ensure that all water and admixtures have been added 2. Sample the concrete at two or more regularly-spaced intervals during discharge of the middle portion of the batch 3. Repeatedly pass receptacle through entire discharge stream or completely divert discharge stream into sampling container 4. Transport samples to a place of testing. Combine and remix to form a Composite sample 5. Obtain composite samples within 15 min from eh start of sampling 6. Minimum size of sample used for strength tests shall be 1 cubic ft 7. Start tests for slump, temperature, and air content within 5 min after obtaining final portion of composite sample 8. Start molding specimens within 15 min after fabricating the composite sample 9. Protect sample against rapid evaporation and contamination

When sampling from a stationary or revolving drum mixer, how many portions are collected and when is it taken during discharge?

1. In two or more portions of concrete 2. At regularly spaced intervals 3. From the middle of the batch

How are the sample portions obtained from the discharge stream of a stationary or revolving drum mixer?

1. Repeatedly pass a receptacle through the entire discharge stream 2. Completely divert the discharge stream into a sample container

Sampling Process from Continuous Mixer

1. Sample after the discharge of at least 5 cubic ft of concrete. 2. Collect two or more portions taken at regularly spaced intervals during discharge of the middle portion of the batch. 3. Do not take more than 15 min 4. Combine them into one composite sample for test purposes

Sampling Process from Paving Mixers

1. Sample the concrete after the contents have been discharged. 2. Obtain samples from at least 5 different portions of the pile 3. Combine them into one composite sample for test purposes. Avoid contamination with subgrade material or prolonged contact with an absorptive subgrade.

What are the five types of Mixers are covered in the C172 practice?

1. Stationary Mixers 2. Paving Mixers 3. Revolving Drum Truck Mixers 4. Continuous Mixers 5. Open-Top Truck Mixers

How long should you wait after obtaining the composite sample from a Continuous Mixer to begin tests?

2-5 minutes

At what point in the construction process should sampling be performed for C172?

As the concrete is delivered from the mixer to the conveying vehicle used to transport the concrete to the forms

What action is required after the individual concrete samples have been transported to the place where tests are to be performed?

Combine and remix the samples with a shovel

What should you do directly after collecting your sample?

Combine and remix with a shovel the *minimum amount* necessary to ensure *uniformity* and must meet the constraints of the tests following collection.

Sampling process from Open-Top Containers/Truck Mixers/Agitators

Depends on what is most applicable under the given conditions but: 1. Sample after the discharge of at least 5 cubic ft of concrete. 2. Collect two or more portions taken at regularly spaced intervals during discharge of the middle portion of the batch. 3. Do not take more than 15 min 4. Combine them into one composite sample for test purposes

What portion of the batch discharge should you sample from a Stationary Mixer, Except Paving Mixers?

Do not obtain portions of the sample from the very first 10% or last part of the batch discharge (after 90% has been discharged).

Can concrete samples from a mixer be obtained before any water or admixtures are added to the mixer at the job site?

No, must be obtained after water or admixtures are added.

How should you collect the sample from a Continuous Mixer?

Perform sampling by passing a receptacle completely through the discharge stream, or by completely diverting the discharge into a sample container.

How should you collect portions from a Stationary Mixer? What should you do if the discharge of the concrete is too rapid?

Perform sampling by passing a receptacle completely through the discharge stream, or by completely diverting the discharge into a sample container. If the discharge of the concrete is too rapid to divert the complete discharge stream, discharge the entire batch of concrete into a container or transportation unit and then accomplish the sampling in the standard manner. Do not restrict to flow of concrete that may cause segregation.

When sampling, how should you regulate the rate of discharge from a Revolving Drum Truck Mixer or Agitator?

Regulate by the rate of revolution of the drum and not by the size of the gate opening.

What is the Sample Size dictated by for ASTM C127? What is the minimum?

Sample size is dictated by the maximum aggregate size. Minimum of 1 cubic feet.

What are the time constraints when collecting a sample?

The elapsed time shall not exceed 15 min. between obtaining the first and final portions of the composite sample.

Purpose of sampling by the C172 practice

To obtain representative samples to test compliance with quality requirements of the specifications.

What should you start molding specimens for the strength tests?

Within 15 min after fabricating the composite sample.

When should you start tests for slump, temperature, and air content?

Within 5 minutes after obtaining the final portion of the composite sample.

When the concrete contains aggregate larger than that permitted for a particular test method, the sample of concrete must be ____ before making the test.

wet-sieved