Experimental study on the influence of the shape and size specimen and the type of cement used on the conversion factors of compressive strength of concrete specimens

Compressive strength test of concrete is one of the most important tests for controlling the quality of concrete in construction structures and, moulds with different shapes and dimensions (cubic and cylindrical) are used to provide experimental specimens based on the workshop conditions and the regulations of the relevant codes and standards. The purpose of this research is to investigate and determine changes in the conversion factors for the strength of specimens with different shapes and dimensions for C35 and C45 concretes made with different types of cement. In this research, 425-1, 2, and 5 cements were used for the preparation of specimens. A total of 162 cubic and cylindrical specimens with dimensions (200 × 200 × 200) mm, (150 × 150 × 150) mm and (150x300) mm at the age of 3, 7 and 28 days have been tested for compressive strength. The results of this study show that in addition to the shape and size of the samples, the type of cement used also affects the strength and conversion factors for the strength of the specimens with various shapes and sizes. The results also show that the difference in conversion factor for strength obtained with the corresponding conversion factors provided by the Iranian National Building Code, Part 9 at the age of 3 and 7 days of the specimens is maximum and is minimum at the age of 28 days.