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УДК 624.04
студент Неверова А.С.
Сибирская государственная автомобильно-дорожная академия (СибАДИ), Омск
Abstract. This article tells about carrying out compression test for concrete. There are two concrete samples for compression test: cube and cylinder. Which one is better? This is explained in the text.
Аннотация: В статье рассматриваются различные образцы для проведения испытания на сжатие бетона: в виде круглых цилиндров и в виде кубов. Обсуждаются достоинства и недостатки различных видов образцов, приводятся основные теоретические положения, позволяющие квалифицированно провести испытания и проанализировать полученные результаты.
Keywords: compressive strength of concrete, compression test, concrete samples, test by cubes, test by cylinders.
Ключевые слова: прочность бетона на сжатие; испытание на сжатие; образцы в виде куба; образцы в виде цилиндра.
IN CARRYING OUT COMPRESSION TEST FOR CONCRETE, SHOULD TEST CUBES OR TEST CYLINDERS BE ADOPTED?
Concrete is one of the most widely used building materials in the world, but people still find it difficult to take samples correctly and manage the testing and certification process. Concrete is used mostly for structural purposes such as foundations, columns, beams and floors and therefore must be capable in taking the loads that will be applied (unless you’re just after a large paperweight!). One of the methods of checking its fit for purpose is to carry out a concrete cube and cylinder test which measures the compressive strength of the concrete and relates directly to the required design strength specified by the designer. Also it is usually a minimum requirement from the client to provide evidence of cube test results to ensure compliance with the designers’ requirements [1].
Compressive strength of concrete is important because the main properties of concrete, such as elastic modulus and tensile strength, are qualitatively and quantitatively related to this property. It is also important because in structural design, load-bearing capacity of structures is related to the concrete compressive strength.
Compressive strength of concrete is ability to resist the influence of external forces, without collapsing. Compressive strength depends on numerous factors: structures, brand and type of cement, water cement ratio, look and durability of large and small fillers, type of a tension, form and sizes of a sample. Concrete has various durability at different power influences: compression, stretching, bend, cut. As is well known, there are two types of standard test specimens used for the determination of compressive strength: cubes and cylinders.
Pic. 1 Concrete samples: a) cube, b) cylinder
Cubes are generally used in Great Britain, Germany and Singapore, whereas the standard specimens in the United States, Australia, France and Canada are cylinders. In Scandinavia, tests are made on both cubes and cylinders. Cubes are either 100 or 150mm in size with aspect ratio of Cylinders have aspect ratio of 2 and are either 100mm high or 150 mm-300mm high. During testing, the planets of the loading machine restrain the lateral expansion of the concrete in parts of the specimen near its ends [2].
Pic. 2 Press for compression test
This restraint is dependent on the amount of friction developed. Under normal conditions, with friction, an element within the specimen is subjected to a shearing stress as well as to compression. With an increase of distance from the platen, the magnitude of the shearing stress decreases and the lateral expansion increases. This shear stress has the confining effect of increasing the axial load for failure. The restraining effect of the platens of the testing machine extends over the entire height of the cube but leaves a part of the cylinder unaffected due to this increase in aspect ratio. Therefore, compressive strengths of cubes are expected to be higher than those of cylinders made from the same concrete [3].
Pic. 3 Crack pattern for: (a) Cubes; (b) Cylinders.
Basically, the results of compression test carried out by using cubes are higher than that by cylinders. In compression test, the failure mode is in the form of tensile splitting induced by uniaxial compression. However, since the concrete samples tend to expand laterally under compression, the friction developed at the concrete-machine interface generates forces which apparently increase the compressive strength of concrete. However, when the ratio of height to width of sample increases, the effect of shear on compressive strength becomes smaller. This explains why the results of compression test by cylinders are lower than that of cubes [4].
Pic. 4 Compression test
Both cubes and cylinders are used in Russia. But the results of compression test carried out by using cubes are higher than that by cylinders. Although the results of compression test by cylinders are lower than that of cubes, tests by cubes are more economical.
Научный руководитель – М.А. Ращупкина, канд. тех. наук, СибАДИ; Т.Г. Галкина, канд. филологич. наук, доцент кафедры «иностранные языки» СибАДИ, Омск.