The Structural Concrete EHE referred to in Article 89. No tests of concrete information to the estimation of concrete strength by testing specimens witness The EHE is noted that in case you need to estimate the strength of concrete of a certain part of the work, witness the concrete may be removed from the structure to evaluate this resistance. This requirement appears to exist or risk of damage or because they refine the time of stripping, mold release or descimbrado or control testing of concrete with acceptable results. However, the EHE does not define a procedure for conducting this evaluation, which should take into account correction factors which provide the differences between the concrete evaluated upon receipt and placed concrete in the structure, due to factors such as compaction and curing. Witnesses give us direct information on in-situ concrete, which is the final result of the quality of concrete provided by the supplier and the proper execution and curing by the constructor.
However, these results are not directly comparable with those obtained from standard cylindrical specimens, as set out in the EHE. The cylindrical specimens measuring the quality of concrete on site, in full ideal compaction and cured for 28 days prior to the completion of compression test. The concrete structure will have been cured by a different procedure, almost always unfavorably than standard storage conditions, and has possibly been placed with a lower degree of compaction. Effects may also occur settlement of concrete placed on site. This can cause cores extracted from the bottom of walls or pillars differ up to 15% -30% of those taken from the top. With this in mind we can detect defects such execution witnesses by removing elements of concrete in appropriate areas.