The Research On The Size Effect Of Concrete Behavior In Compression And Tension

The mechanical properties of concrete closely relate to its geometric dimension.In order to accurately describe the differences of damage process and mechanicalproperties, the research on size effect is particularly necessary. The research on thesize effect of compression behavior and aggregate composition is still insufficient.Furthermore, the mechanical properties of mortar are generally assumed as a constant.The effectiveness of this assumption has not yet been confirmed by test results. Thenumerical analysis on size effect can effectively solve the limitation of theexperimental investigation and also provide another research method for the study.A series of experimental and numerical analysis research were conducted in thispaper. The following conclusions can be made:1.162concrete cubic specimens were tested in order to investigate the size effecton compressive strength. Test results indicate that the larger the size, the lower theconcrete compressive strength. The concrete compressive strengths with dimension of150mm and200mm are94%and88%of100mm specimens. The size effect ofconcrete is stronger than the mortar and cement. The size effect of mortar and cementare33%and30%of concrete. With the raise of strength level, the size effect comesmore obvious. The size effect in C60concrete is1.8times of C20concrete.2.216uniaxial compression specimens were experimented in order to obtain thesize effect on axial compressive behavior. The experiment result shows that the sizeeffect exists in each kind of specimens. The peak stress, strain at peak stress,ultramate strain of specimens with dimension200mm are85%,104%and110%ofspecimens with dimension100mm respectively. These mechanical paramters of150mm specimens are92%,102%and105%of100mm specimens. The higher thestrength level, the more dramatical the size effect. The size effect of C20concrete is50%of C60concrete. The size effect in concrete is much stronger than the mortar andcement. The size effect on compressive behavior of concrete are about2.7and2.8times of the mortar and cement respectively. Reinforcement can reduces the sizeeffect dramatically. The size effect on compressive behavior of reinforced concrete isabout28percent of concrete.3. The test result of162flexural tensile specimens proves that: the flexuraltensile strength increased with the decrease of specimen size. The flexural tensile strength of concrete specimens with dimension of70mm and100mm are anbout1.15and1.1times of150mm concrete specimens. The extent of size effect for the threeaggregate composition is concrete, mortar, cement, respectively. The size effect ofmortar and cement are30%and24%of concrete. The size effect on flexural tensilestrength of C60specimens is2times stronger than the C20specimens.4. Based on the fully understanding of the size effect theories, the parameters ofsize effect laws were suggested. Also, the computational formulas of size effect wereproposed in this paper. The higher the compressive strength, the larger the critiacl size.The critical size of C40ad C60concrete are1.7and2.1times of C20concrete.5. The two dimensional and three dimensional concrete random aggregate launchprogramm were compiled. Based on the test result and the random aggregate model,the mechanical properties of bonding interface were obtained by a series of numericalanalysis. Also, the relationship between the bonding interface and concre mechanicalbehavior were built in this paper.6. Mesoscopic numerical models of homogeneous and heterogeneous concretematerial are established in combination with elastic brittle constitutive and bothelastic brittle and plastic constitutive model for concrete mesoscopic elements. Thedestruction process and macroscopic stree-strain curves were acquired by numericalanalyze.7. A series of numerical analysis were performed on the size effect of concretecompressive and tensile behavior. Based on the analysis result, the critical dimensionsof size effect on several mechanical parameters were obtained. Furthermore, the sizeeffect law of various concrete mechanical properties were proposed in this paper.