دانلود رایگان مقاله انگلیسی اثر اندازه نمونه بر روی مقاومت فشاری و خمشی بتن مسلح با مقاومت بالای فیبر - الزویر 2018

ABSTRACT

It is a well-known fact that the size of the sample influences values of mechanical properties of concrete measured during the tests. However, the comparison of results of various researchers clearly shows that the importance of this effect varies for different types of concrete. The paper presents outcomes of extensive experimental study focused on determination of relations between the size of the specimen and results of mechanical tests of high-strength fibre-reinforced concrete (HSFRC) with coarse aggregate (maximum aggregate size 16 mm). The main observed parameter was compressive strength. Six different HSFRC mixes having the expected compressive strength between 100 and 175 MPa were investigated. Cube samples of four sizes – 40, 100, 150 and 200 mm – were examined. The results proved that the size dependence of compressive strength diminishes with increasing strength of concrete. For very high strength materials (more than 130 MPa), the results were almost size independent. Additionally, flexural strength of two high-strength concrete mixes was measured on prismatic specimens of two different sizes. The results indicated that flexural strength of HSFRC with coarse aggregate is size dependent without regard to expected compressive strength. Conversion factors for the tested type of material were proposed for both compressive and flexural strength measurements.

8. Conclusions Based on the results of this investigation of compressive and flexural tensile strength exhibited by various size cubes and beams, the following conclusions are drawn:

⁃ The results of previous studies dealing with size effect on concrete strength measurements have shown that the importance of size effect varies significantly for different mix compositions and strength levels. The only reasonable conclusion is that for each type of concrete, the relation between the size of the specimen and measured strength has to be derived experimentally. ⁃ Compressive strength of HSFRC with coarse aggregate generally decreases with increasing cube size. However, the higher is the expected compressive strength of the material, the lower is the size effect. For very-high strength mixes (C145 and C175), the results were almost independent on the cube size, probably thanks to increase of homogeneity of the mix and reduction of statistical size effect.

⁃ Comparison with results of Graybeal and Davis [12] showed that the relation between expected compressive strength and significance of size effect has opposite tendency in fine-grained and coarse-grained HSFRC, probably because of distinct rate of statistical and deterministic part of size effect as a result of different RVE size in differently grained materials.

⁃ Size effect of flexural strength in HSFRC with coarse aggregate is very similar to other types of concrete. Smaller beams exhibit higher strength, possibly due to surface layer effect.