Sampling of Fresh Concrete
To ensure it is representative of the whole truck load, a standard sample consists of scoopfuls taken from different parts of the batch and collected in bucket.
Scoopfuls must be taken through the moving stream, as the load is discharged, sampling the whole width and depth (not just the top part). The size of sample taken should be 1.5 times the estimated volume required for testing.
The whole operation of sampling of fresh concrete can be divided into three steps as given below.
- Step-1 (collection of samples in increments)
- Step-2 (Preparing composite sample)
- Step-3 (Recording sample information)
Step-1 (Collection of Samples in Increments)
Fresh concrete samples can be collected from the mixer at the time of discharging or after concrete is discharged on site.
While sampling from a mixer, then divide the batch into different parts and take sample increments form those parts. Avoid taking samples from the first and last part.
If it is a continuous mixer, then one batch is regarded as the discharge of concrete during one minute. So in case of continuous mixer, take sample increments at equally spaced time intervals. For example if 3 increments have to be taken, then take increments after 15 sec, 30 sec and 45 sec. if more increments have to be taken then the time interval is to be chosen accordingly.
If the batch of fresh concrete has already been discharged on site, then collect the samples from not less than five well distributed positions. Avoid taking sample from the edge of the mass, as segregation may have occurred there.
Step-2 (Preparing Composite Sample)
Place all the increments collected as described in step-1, on a non-absorbent plate and mix them uniformly with the help of a shovel.
After mixing the increments thoroughly keep this composite sample in an air tight container, so that it is protected from the effects of atmosphere/environment.
Step-3 (Recording Sample Information)
The following information about the sample must be recorded before dispatching it to test.
- Date and time of sampling
- Method of sampling
- Mix proportions
- The location of the sample batch after placing
- Temperature and weather condition