Advanced Materials Research Vols. 261-263

Abstract: Based on the Compressive strength, workability and raw material consumption of concrete, a mathematical model is established for mix proportion design of high performance concrete (hereinafter referred to as HPC) with chlorine ion’s diffusion coefficient and per cubic meter cost as its optimized objectives. Matlab’s Sequential Quadratic Programming method is used for the solution of constrained nonlinear problems, with which the calculation and optimization of mix proportion of concrete are solved satisfactorily. HPC with optimized design can meet all requirements for its type and has obvious economic benefit.

Abstract: After modification, Toufar model was used to calculate the packing degrees of sand mixtures with different particle sizes. For four gradations of sands, the weight ratios of different types of sands with different size ranges, which achieve maximum packing degrees, have been obtained using the modified Toufar model. A strength test of reactive powder concretes (RPCs) with the four gradations of sands was reported. The test results show that the strength of RPC is related to both the maximum grain size and the packing degree of sand mixture. The smaller maximum grain size and larger packing degree of sand mixture can achieve the higher strength of RPC.

Abstract: Using micro-wave heating method, the previous disadvantages of heating slowly and non-uniform are broken through. And plain concrete high temperature loading experiment system is composed of the method and material experiment machine. Many experiments of self-made concrete are carried out from room temperature to 600°C by this system. The strength and critical strain of concrete with temperature are obtained, and through analysis of the compressive stress-strain curves under different temperature, the constitutive relationship is established. The result shows that this constitutive relationship is greatly agrees with experiment. Meanwhile, the phenomenon is analyzed and explained in the progress of experiment.

Abstract: This paper addresses the efficiency of using recycled concrete as an aggregate by systematically presenting results on the influence of fly ash on recycled aggregate concrete (RAC) properties. The percentage of recycled aggregate replacements of natural aggregate used by weight was 50%. Fly ash (FA) was used as 0, 10, 20, 30, and 40% by weight replacement of cement. The results showed that an increase in the W/B decreased the resistance to carbonation depth. Nevertheless, the use of FA as a substitute for cement decreased the carbonation depth of the recycled aggregate concrete. Being analyzed on the basis of Gray Theory, it can be seen that the biggest influence on the depth of carbonation of the recycled aggregate concrete comes from W/B, then the carbonation age and FA content affects the least.

Abstract: A new class of high performance fiber reinforced cementitious composites called Ultra High Toughness Cementitious Composites (UHTCC) is developed in the last few years. It is a pseudo strain hardening material with maximum tensile strain capacity more than 3%, yet the fiber volume fraction no more than 2%. The multiple cracking patterns accompanying pseudo strain hardening behavior are obtained which implies high ductility, energy absorption capacity, and toughness. A remarkable characteristic distinguish it from conventional high performance fiber reinforced concrete is the maximum crack width of multiple cracks which is about 60µm under ultimate tensile load. Such micro-cracks are often small enough to prevent the intrusion of aggressive agents. From a durability point of view this composite can be considered as an effectively uncracked material. The performances of this new material, including the apparent density, the uniaxial tensile property, and the drying shrinkage performance, are experimental studied in this paper.

Abstract: Study on the dynamic behavior of concrete is important, for the sake of seismic design and safety evaluation of mass concrete structures, such as concrete dams, nuclear reactors and so on. There have been a lot of uniaxial strength experiment data of concrete under dynamic loading, but multiaxial data is scarce, for the test of multiaxial strength of concrete under dynamic loading is difficult, while most mass structures work under multiaxial static and dynamic stress states. In this paper a three-dimension failure criterion of concrete under dynamic loading in octahedral stress space was proposed. Then the multixial strength tests of concrete under dynamic loading were carried out with concrete triaxial static and dynamic apparatus system. The selected loading paths consisted of uniaxial compression and tension, biaxial proportional loading compression, biaxial compression with one constant lateral compression and triaxial compression with two constant lateral compressions. In the test the strain rate range is 10^-5~10^-2/s. Based on the test data and the literature data, the characteristic of this failure surface is that it considered the influence of the strain rate and the angle of similarity; it is smooth, convex in meridian and deviatoric plane. The proposed model for nonlinear dynamic analysis and design of mass concrete structures under dynamic loading is useful.

Abstract: The paper discusses the modulus of elasticity of plain concrete for a wide range of compressive strength. A large volume of selected experimental data has been collected from existing literature and then analyzed. Particular emphasis has been given to studying the effects of concrete compressive strength and the type of coarse aggregate on the modulus of elasticity of plain concrete. The adequacy and applicability of the existing models for predicting the modulus of elasticity of high-strength concrete has been critically examined, and a new empirical model is proposed to cover concrete strength up to 125 MPa. The new empirical model seems to perform much better when applied to the published experimental data on normal weight concrete over a wide strength range.

Abstract: Combined with Jones-Nelson-Morgan model applied to ceramics and graphite successfully, the nonlinear constitutive model of concrete is obtained through large number of tests in this paper. The model takes concrete as nonlinear elastic isotropic material. By using strain energy function, it makes the nonlinear mechanics behavior of concrete as the function of strain energy. According to the mechanics behavior of concrete, a simple model is obtained by increasing stress to realize the model calculation program. The model can be extended to the constitutive model analysis of concrete under biaxial stress. The theoretical model conforms to testing results well.

Abstract: Functionally Graded Material (FGM), as a new concept in material fields, has been a research hotspot in recent years, the application of which can improve the stress state of structures. This paper tried to introduce FGM into the concrete material by investigating the factors which have influence on the concrete FGM. In this study, mix proportion parameters of haydite concrete are analyzed by using the Taguchi’s experiment design methodology. Mixtures are designed in a L₁₆ (4⁵) orthogonal array with three factors, namely, “volume fraction of haydite in total aggregate (H/A)”, “water/cementitious material (W/C) ratio”, and “air entraining agent (AE) content”. The mixtures are extensively tested. The experimental results are analyzed by using the variance analysis (ANOVA). The influence degree of three selected factors to performance indexes is obtained.

Abstract: This paper researched the high temperature properties of ceramic concrete though experimental. Test and analysis on the microstructure between the ceramic concrete and ordinary concrete which experience different temperatures using scanning electron microscopy (SEM); and analysis on the high temperature performance of the ceramic concrete using finite element method .The results show that: the C-S-H gel, Ca (OH) ₂ crystals and the interfacial transition zone between aggregate and colloidal and other microstructure have different characteristics, these features can be used to explain the main reasons for changes of the concrete performance indicators after the high temperature and to provide technical basis for the application of ceramic concrete in the high temperature environment.