SAMPLING OF CONCRETE

SAMPLING OF CONCRETE

Taking concrete samples at the point-of-placement rather than the point-of-delivery is always 

preferable. Special situations may occur which create difficulties in sampling and transporting 

samples taken from the point-of-placement. When this occurs, sampling at the point-of-delivery is 

satisfactory but only after running correlation tests between the 2 sampling locations. (Caution: 

The correction factors developed between the 2 sampling locations may vary due to changing 

conditions such as air and concrete temperature changes, pumping distances, etc. Perform 

correlation tests several times throughout the day.)

If necessary, modify sampling procedures to fit a specific situation. If the slump test result is 

outside of the slump range, correct before placing the concrete in the work. Make corrections as 

follows: 

Slump too low: Add water in measured amounts to bring the slump within the specified range. 

Record the added water on the Certificate of Compliance. 

Slump too high: Add additional cement by full bag to bring the slump within the specified range. 

Provide cement from the same manufacturer as the original batch. Record the added bags of 

cement on the Certificate of Compliance. 

After the addition of water, cement, or air-entraining admixture, remix the batch for 50 revolutions 

at mixing speed to insure adequate dispersion ofthe materials throughout the batch. Retest to 

verify compliance with the Specifications. If the concrete is placed in the work, report both tests 

on the Weekly Concrete Report(Form 2448) with a notation of the amount of water, cement or air-entraining admixture added. The number of revolutions at mixing speed shall not exceed 150 per 

Specification 2461.4C. Mix the concrete at agitating speed for all revolutions over 150. 

Obtain samples for strength tests by the same procedure as for slump or air test, except obtain the 

sample from the middle half of the load wheneverpossible. If the sample is transported to a 

different location for specimen fabrication, remix the sample to ensure uniformity. The following 

sections provide procedures for sampling from various mixers. 

Start slump, temperature, and air content tests within 5 minutes after obtaining the sample of fresh 

concrete. Start strength tests within 15 minutes of obtaining the sample.
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Guide to Sampling Concrete

Concrete Manual