EN 206 Conformity Testing for Concrete Strength in Compression

Abstract

Concrete strength in compression is the common characteristic used in the design of concrete structures. However, in general, there are two different types of concrete specimens specified for the determination of concrete strength in compression. They are the standard 150mm diameter by 300mm length cylinders and the standard 150mm cubes. In the case where the maximum size of coarse aggregate is less than 40mm (1½ in.), 100mm diameter by 200mm length cylinders and 100mm cubes may be adopted. Cylinder specimens with aspect ratio (length/diameter) of 2 are likely to be closer to the uniaxial compressive strength as end friction effects at the platens tend to induced a more complex state of stress compared to that of a cubical specimen with aspect ratio of unity. Hence, the two types of test specimens do not provide the same measured strength for the same concrete. For the purpose of conformity testing, the consistency of test results is of greater interest than the magnitude of the measured strength of the concrete specimens. This paper reviews the issues concerning the two types of specimens, (cylinder or cube) and the size of the specimen in relation to maximum size of coarse aggregate used. Some experimental data for compressive strength at 3 strength classes for which slightly over 100 batches produced over several consecutive calendar months were tested. Three types of specimens, 150mm diameter by 300mm cylinders, 150mm cubes and 100mm cubes were adopted for testing at the age of 28- days. Maximum size aggregate of 20mm and CEM I cement were used for strength classes of C32/40, C50/60 and C65/80 achieved with added silica fume. The findings of these test regimes are summarised with recommendations for conformity testing based on EN 206 and its complementary British Standard BS 8500.