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In order to investigate the dimensional effect of concrete cubic compressive strength, a series of compression tests were performed on 135 groups of cubic specimens with three different strength grades and three different aggregate mixtures. The strength grades of specimens included C20, C40 and C60, and the side lengths of specimen included 100 mm, 150 mm and 200 mm respectively. Test and analysis results show that the strength grade influences the dimensional effect of concrete cubic compressive strength greatly. The value of dimensional effect degree of 200 mm cubic specimens with strength grade C40 and C60 are about 1.61 times and 1.85 times of cubic specimens with strength grade C20. The dimensional effect is influenced greatly by the coarse aggregate. The dimensional effect degree of concrete is about 2.7 times of the mortar. The fine aggregate affects the dimensional effect much weaker than coarse aggregate. The dimensional effect degree of cement is about 88 percent of the mortar. Furthermore, the computational dimensional effect law equation on the concrete was proposed based on the test results. The predicted results of the proposed equation agreed well with test data.

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135 groups of concrete, mortar and cement prism specimens were manufactured to study the influence of aggregate mixture and strength grade on the dimensional effect of concrete uniaxial compressive behavior. The concrete strength grade included C20, C40 and C60, and the dimension of specimens included 100 mm×100 mm×200 mm, 150 mm×150 mm×300 mm and 200 mm×200 mm×400 mm. The complete stress-strain curves were obtained by rigid support technique. Based on the test results, the dimensional effect of mechanical parameters such as prismatic compressive strength, strain at peak stress and elastic modulus were studied. The results indicate that the dimensional effect phenomenon exists in the compressive strength and strain at peak stress in concrete, mortar and cement. While, the dimensional effect on elastic modulus can be neglected in those materials. The concrete strength grade influences the dimensional effect greatly. The dimensional effect degree on compressive strength and strain at peak stress of concrete with strength grade C60 and side length of 200 mm are about 2.0 times and 1.6 times of the concrete with strength grade C20. The dimensional effect is influenced greatly by the coarse aggregate. The dimensional effect degree on compressive strength and strain at peak stress of concrete are about 2.3 times and 3.0 times of mortar, respectively. The fine aggregate affects the dimensional effect much weaker than the coarse aggregate. The dimensional effect degree on the compressive strength and strain at peak stress are about 75 percent and 65 percent of the mortar. Furthermore, the computational dimensional effect equations were proposed based on the test results. The predicted results of the proposed equations agree well with test data.

A series of compression tests were conducted on 150 groups of cement paste specimens with side lengths ranging from 40 mm to 200 mm. The specimens include cube specimens and prism specimens with height to width ratio of 2. The experiment results show that size effect exists in the cubic compressive strength and prismatic compressive strength of the cement paste, and larger specimens resist less in terms of strength than smaller ones. The cubic compressive strength and the prismatic compressive strength of the specimens with side length of 200 mm are respectively about 91% and 89% of the compressive strength of the specimens with the side length of 40 mm. Water to binder ratio has a significant influence on the size effect of the compressive strengths of the cement paste. With a decrease in the water to binder ratio, the size effect is significantly enhanced. When the water to binder ratio is 0.2, the size effects of the cubic compressive strength and the prismatic compressive strength of the cement paste are 1.6 and 1.4 times stronger than those of a water to binder ratio of 0.6. Furthermore, a series of formulas are proposed to calculate the size effect of the cubic compressive strength and the prismatic compressive strength of cement paste, and the results of the size effect predicted by the formulas are in good agreement with the experiment results. © 2015, Central South University Press and Springer-Verlag Berlin Heidelberg.

The types of concrete investigated incorporated limestone and gravel as the coarse aggregates and natural sand as the fine aggregate. The nominal water-cement ratio varied from 0. 33 to 0. 87. Each set of test specimens consisted of two 102 multiplied by 203 mm and two 152 multiplied by 305 mm cylinders, cured under standard moist room conditions and tested at ages ranging from 3 days to about 8 months.

Compressive strength of concrete specimens with different shapes and different sizes are experimentally studied. The shapes of the specimens included cube, column and prism, while maximum and minimum lateral dimensions are 450 mm and 150 mm respectively. All specimens are cast at the same mix proportion, cured under the same condition, and subjected to strength determination under the same loading condition at 90 days. The concrete grade is 20 MPa. The strength values of the specimens of various types are in good consistency. The relativity can be presented by a kind of experimental formula.

Testing high-strength concrete (HSC) for compressive strength puts into doubt a certain number of concrete testing practices. First, most concrete testing laboratories are equipped with loading capacity machines inadequate for testing 150 × 300-mm (6 × 12-in) specimens, thus limiting HSC specimens to 100 × 200 mm (4 × 8 in) in size. As most designers rely on compressive strengths derived from large specimens, they must be given relations between the different values obtained when smaller specimens are used. Comparative testing reveals that HSC compressive strength values are greater by 5 percent when measured on 100 × 200-mm specimens is as small as, or smaller than, that for 150 × 300-mm specimens.

Scale effect of compressive strength of ordinary concrete and high-strength concrete were investigated through compression experiments on ordinary concrete and high-strength concrete specimens with the strength grade of C20, C40 and C60, and the specimen side length of 100, 150, 200mm. The relationship between the strength grade and scale effect was established. Then, the critical size and critical strength of ordinary concrete and high-strength concrete were obtained. Furthermore, the computational equations of scale effect were proposed. Finally, good agreements have been found between tested data and the computational equations. The test and analysis results show that the scale effect exists in the cubic compressive strength of the ordinary concrete and high-strength concrete. With an increase in the strength grade, the scale effect is significantly enhanced. The scale effect of concrete with strength grade C20 is 55% of the concrete with strength grade C60.

The size-effect phenomenon was investigated numerically and experimentally on both normal- and high-strength concrete cylinders subjected to static and dynamic compression. The tests provided data whose analysis produced evidence on the effect of loading rate and material strength on the size effect for structural concrete in compression. Parallel pretest and post-test computational simulations were used to perform numerical tests of the same specimens and to explore the role of the time dimension on the physical phenomena that contribute to the size effect. Comparisons between test and numerical data assisted and guided the investigators in identifying the governing parameters that define the physical phenomena. Both tests and numerical models proved the existence of a size effect in parameters other than strength such as the modulus of elasticity and the strain at maximum stress.

This paper surveys the available results on the size effect on the nominal strength of structures — a fundamental problem of considerable importance to concrete structures, geotechnical structures, geomechanics, arctic ice engineering, composite materials, etc., with applications ranging from structural engineering to the design of ships and aircraft. The history of the ideas on the size effect is briefly outlined and recent research directions are emphasized. First, the classical statistical theory of size effect due to randomness of strength, completed by Weibull, is reviewed and its limitations pointed out. Subsequently, the energetic size effect, caused by stress redistributions due to large fractures, is discussed. Attention is then focused on the bridging between the theory of plasticity, which implies no size effect and is applicable for quasibrittle materials only on a sufficiently small scale, and the theory of linear elastic fracture mechanics, which exhibits the strongest possible deterministic size effect and is applicable for these materials on sufficiently large scales. The main ideas of the recently developed theory for the size effect in the bridging range are sketched. Only selected references to the vast amount of work that has recently been appearing in the literature are given.

An experimental investigation is reported into the size effect for compressive strength from 36 concrete prism specimens under axial loading and with three different kinds of dimensions of 100×100×300mm, 150×150×300mm, 200×200×400mm. Such parameters as strength grade of concrete and reinforcement ratio are taken into consideration. Three different strength grades of concrete and two different reinforcement ratio are included in those specimens, all tests are undertaken according to ASTM C 39/C 39M-2005. Based on the results obtained, a new size effect law for different kinds of concrete in prismatical compressive strength is suggested and those relative parameters on the size effect are discussed.

81 concrete prism specimens under axial compression were tested to invesgigate the size effect on the axial load stength. Three different kinds of specimens with the dimension 100×100×300mm, 150×150× 300mm, 200×200×400mm were tested. The parameters including compressive strength of concrete and aggregate composition are taken into consideration. Three different strength grades of concrete and three different aggregate composition are included in those specimens. The test method are undertaken according to ASTM C 39/C 39M-2005. Based on the test results, a new size effect law for different kinds of concrete in prismatical compressive strength is suggested and those relative parameters on the size effect are discussed.