Effect of Specimen Shape and Size on the Strength Properties of High Strength Concrete

Abstract

High strength concrete is currently a common construction material and its compressive strength is most basic and important material property in structural design. In this paper we investigate the influence of the shape and of the size of the specimens on the compressive strength of high strength concrete. We use cylinders and cubes of different sizes for performing stable stress-strain tests. This value was kept constant throughout the experimental program. Our results show that the post-peak behavior of the cubes is milder than that of the cylinders, which results in a strong energy consumption after the peak. This is constant with the observation of the crack pattern: the extent of micro-cracking throughout the specimen is denser in the cubes than in the cylinders. Indeed, a main inclined fracture surface is nucleated in cylinders, whereas in cubes we find that lateral sides get spalled and that there is a dense columnar cracking in the bulk of the specimen. Finally, we investigate the relationship between the compressive strength given by both types of specimen for several specimen sizes. The influence of specimen size and shape on the measured compressive strength was investigated for different high strength concrete mixes. Also, the compressive strength can also be determined to be insignificantly affected by changing l/d as the strength of concrete increases. After testing of specimens at 7and 28 days, the results show that the cube specimen is generally stronger than the cylinder specimen and this effect will be gradually decreased when the concrete strength increased. For the effect of the specimen size the results show that the compressive strength increases as the specimen size decreases. This size effect might be ignored as the relationships showed that the effect is relatively small as compared to specimen shape effect.