Quality of fresh concrete is verified by collecting specimen. It is assumed that these specimens fully represent the concrete cast at the construction site and represent its quality.

Collection of Specimen
• Every specimen should be collected from separate batches or separate truck-mixers.
• The specimen should be collected at the concrete delivery point of the construction site from the truck-mixer chute; after the initial 15 % of truck-mixer load is discharged but before the final 15 % of the load is yet on the truck.
• The specimen collected from the truck-mixer chute should represent not any particular part of the flowing concrete but it’s whole.
• Date and time of the specimen collection should be recorded. If necessary, the temperature of the fresh concrete and the ambient temperature should also be recorded

Preparation of Specimen
• At all phases of the specimen collection and transport phases, concrete should be protected from contamination, water access, water loss and temperature variations.
• Concrete specimen have to be filled into moulds in even layers not thicker than 10 cm. 15 cm or 20 cm cubes should be filled in two and15/30 cylinders should be filled in three layers.
• The impacts of the compacting bar have to be distributed evenly on the horizontal cross section of the mold. Care should be taken while squeezing the initial concrete layer that the rod should not hit the bottom of the mold and for subsequent layers that it should not penetrate into the layer beneath.
• Each layer should be poked with the compacting bar at least 25 times. After pressing, the lateral surfaces of the mold should be hammered with a mallet until the vacancies generated by the compacting bar are filled
• Excess concrete overflowing from top surface of the mold should be wiped off by a cutting motion to be applied by a steel trowel or a surfacing trowel and the surface of the concrete should be leveled carefully.
• Specimens should be labeled clearly and durably, not to give any damage to the specimen. Specimen records (date and time of collection, concrete strength class, construction site code, name of the facility, truck-mixer registry plate, consignment note no.) should be kept carefully.

Safeguarding of Specimen at the Construction Site and Their Transport
• Specimen should not be moved, and be kept at the place they have been collected in molds, secure from external effects, shocks, vibrations and drying until they attain the necessary hardness (not to be less than 16 hours and not to exceed 3 days)
• Specimen should be kept at a medium to provide a temperature of 20 ± 2° C or alternatively 25 ± 2° C in hot climatic conditions, safe from airstreams and humidity loss (under wet cloth or plastic cover or in a closed case)
• Specimen have to be protected from excessive temperature variations and humidity loss during the transport process.
• Hardened test specimen can be safeguarded in wet sand or wet sawdust or can be put in a watertight plastic mold filled with water

Curing of Specimen
• Concrete specimen after their removal from the molds have to be cured in water (or in 95 % humid medium) at 20 ± 2° C until the start of the test.

There are two alternative sampling methods for concretes produced according to TS EN 206-1 standard. The Initial Production covers the production period until at least 35 test results are obtained. Permanent Production designates the production carried out after obtaining at least 35 test results within a period not exceeding 12 months.

For determining the minimum specimen collecting and test frequency for concrete; the frequency demonstrated in Table 1 that demonstrates the greatest number of specimen for Initial or Permanent production should be chosen. Specimen should be collected after water and chemical additives are mixed in the concrete, in compliance with the specimen collection procedures. However, in case it has been verified during preliminary tests that plasticizers or super plasticizers do not have adverse effects on the concrete strength, collecting specimens before adding such additives for adjusting the consistency may be permitted.

In case the difference between the minimum and maximum values of the test results obtained from two or more specimen prepared from the same fresh concrete sample deviate from the mean value more than 15 %, the test results are rejected, except for cases when there is an satisfactory reason that justifies that any one of the test results should be invalidated.