How to Sample Fresh Concrete for Field Test ? ASTM C 172

The sampling procedure of fresh concrete to conduct field tests is as per ASTM C 172. The concrete samples that are obtained from a mixer that is stationary or paving or truck mixers, or from the agitated and non-agitated concrete mix can be sampled by this method. 

Collecting Fresh Concrete Sample; Image Courtesy: NPCA -https://precast.org/ 

The procedure of sampling involves the following step:

1. Collect the composite concrete sample from the middle portion of the batch that is discharged.
2. Collect the sample of sufficient quantity not less than 1 cubic foot.
3. The sample must be collected after 10 % of the concrete has been discharged and before 90 percent of the concrete has been loaded.
4. Collect the sample at least twice. Mix both together to get the final sample.
5. Collect the samples randomly.
6. Do not perform sample collection based on factors like appearance, convenience, etc.
7. The concrete is mainly sampled when it is transported from the mixer. Some test recommends having sampled at the discharge of the concrete pump line. 
8. A significant change in characteristics is shown by testing concrete samples collected from the discharge point of the pump.
9. Pumping characteristics changes the concrete properties like air content, consistency, or even the potential strength.
10. Collect the concrete from the pump to a container without causing segregation - control flow and regulate discharge ( Reduce the drum revolution - do not adjust the gate opening size)

Point to Remember while Sampling Fresh Concrete at the Site

1. The Time-lapse between the first and last portions of the composite sample is 15 minutes.
2. The slump test must be conducted within 5 minutes after obtaining the composite sample.
3. Molding of concrete strength specimens must be performed within 15 minutes after preparing the composite sample.

Quantity of Sample of Concrete Field Tests

The quantity of sample collected for field tests must be not less than 1 cubic foot. Always perform the tests in the space where the concrete composite sample is made. 

When it is required to test the strength, air content, and temperature, ASTM C 172 recommends collecting samples in larger amounts to take all the tests.

To test routine field tests on concrete-like air content, slump, and temperature, ASTM also allows smaller sample quantities.

Review the sampling procedures that apply to each mixer type outlined in ASTM C172 and implement quality sampling for your site.