Experimental Study On Size Effect On Concrete Strength

Size effect is a general property of quasi-brittle materials. Concrete as a quasi-brittle materials, there is also size effect happening. The size effect of concrete strength is affected not only by the property of the material, but also by the size of specimen, which is not a constant value. With more and more concrete materials being widely used, and the increase of structure height and span, the sizes of the concrete structures are also increased. However, the designing concepts, methods and formulas of large-size specimens are also based on the research findings of the small-size specimens currently because of the limitation of understandings and experimental conditions. This will be lack of scientific proof when they are used in modern practical projects. Although we have got some achievements in the research field of the size effect of concrete strength, there is no uniform standard or index to judge the size effect. And we still haven't taken the size effect into account in the codes of conduct so far. According to the above problems, the several main aspects of theoretical and experimental research are as follows:(1) The size effect of concrete compressive strength and splitting tensile strength are considered in this experimental research of this article. The concrete compressive strength test considered cube, prism and cylinder these three specimen form. While the splitting tensile test only considered cube and cylinder these two kinds of specimens.(2) In the size effect test of concrete compressive, four groups of cubes and prism with side length of 150mm,250mm,350mm,450mm,and four groups of cylinders with diameter of 150mm,250mm,350mm,450mm were considered respectively. The results show that size effect exists in all the three forms of concrete specimens of compressive strength and that the concrete compressive strength decrease with the increase of specimens'size. The author also use Bazant's size effect formula and modified formula based on the stress distribution and Carpinteri fractal size effect formula to fitting the experimental results, which fits well.(3) In the size effect test of concrete splitting tensile strength, six groups of cube specimens with side lengths of 150mm,250mm,350mm,450mm,550mm,750mm, and five cylinder specimens with diameters of 150mm,250mm,350mm,450mm,550mm were considered respectively. The result show that size effect exists in the concrete splitting tensile strength and that the concrete splitting tensile strength decrease as its size increase. But no matter what the specimens'form is, when the splitting area reaches 1000mm2, the size effect almost disappears, and splitting tensile strength reaches a constant value. At the same time, using Weibull's statistical size effect theory to analysis experimental results, a good correlation can be found between splitting tensile strength of concrete and splitting area.(4) By comparing the influence of the specimens'form on the size effect of concrete strength, the specimens'form affect the concrete strength, which can be found on the concrete compressive strength test and the splitting test. Although the general trends perform the same, the influences that the different shapes acted at the size effect of concrete strength perform differently.