ARE CURRENT CONCRETE STRENGTH TESTS SUITABLE FOR HIGH-STRENGTH CONCRETE

Some important factors are investigated that may have an effect on com pression test results of high strength concrete, including the size an d shape of the test specimen as well as the mould material. Compressio n tests were performed on 6 different specimen types with a total of 3 60 specimens cast from 18 different high strength concrete mixtures (f '(c) = 82-117 MPa). The compressive strengths of the different specime n types were compared and conversion factors between them were establi shed. 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 cylind ers was, on average, 94.5% of the 150 mm cube strength. Moreover, plas tic moulds yielded concrete with a strength lower than that of the con crete cast from iron moulds, and the reduction in compressive strength due to the plastic moulds increased with increasing mould size.