ARE CURRENT CONCRETE STRENGTH TESTS SUITABLE FOR HIGH-STRENGTH CONCRETE

Some important factors are investigated that may have an effect on compression test results of high strength concrete, including the size and shape of the test specimen as well as the mould material. Compression tests were performed on 6 different specimen types with a total of 360 specimens cast from 18 different high strength concrete mixtures (f'(c) = 82-117 MPa). The compressive strengths of the different specimen types were compared and conversion factors between them were established. The comparative results indicate that for each 50 mm increase in cube size there is a similar to 5% drop in the compressive strength. It was also found that the concrete strength of 150 mm x 300 mm cylinders was, on average, 94.5% of the 150 mm cube strength. Moreover, plastic moulds yielded concrete with a strength lower than that of the concrete cast from iron moulds, and the reduction in compressive strength due to the plastic moulds increased with increasing mould size.