Advanced Materials Research Vols. 261-263

Abstract: With the mass diffusion module of ABAQUS, the moisture diffusion behavior of recycled aggregate concrete material (RAC) was investigated in this work. The simulation was carried out under the standard drying conditions (Ambient humidity: H=60%; Temperature: T=20°C). The results indicate that: with the dry age grows, the water evaporation begins from the RAC’s surface first, and the water concentration reaches the equilibrium value rapidly; then the evaporation process gradually extends to the interior, but the process is quit slowly. In moisture diffusion process, the water concentration takes on gradient distribution. the calculated value of water concentration matches well with the experiment results, and can provide a theoretical base to the caculation of drying shrinkage stress of RAC.

Abstract: Cementitious coefficient β_t was introduced to reflect the comprehensive effect of fly-ash quality on HFCC strength. On the basis of β_t, actual water-binder ratio [W/(C+β_tF)] and ash-binder ratio K was proposed, and the strength calculation model of HFCC with specific design age was established. On the basis of economy principal, the formula to determine K was founded. Influence of the design strength of HFCC and β_t on K and the content of fly ash was analyzed.

Abstract: The effect of the fly ash content on the properties of the fly ash-coal gangue foam concrete was studied in this paper. Results revealed that: With the increase of the fly ash content, the dry density, the compressive strength and the shrinkage of the fly ash-coal gangue foam concrete decrease; the density of the fly ash - coal gangue foam concrete was influenced greatly by the ratio of water to total dry material. The pore structure and microstructure of the foam concrete was analyzed by scanning electron microscopy, and the results show that most of the pores are fine, closed, and even distributed.

Abstract: An elastoplastic-anisotropic damage constitutive model for the description of nonlinear behavior of concrete is presented. The yield surface is developed in effective stress spaces, which takes into account the hardening effect and better match the experimental data. The stiffness degradation and softening effect are considered in the framework of continuum damage mechanics formulation. The second-order damage tensor is used to characterize the anisotropy induced by the orientation of microcracks. In order to simulate the unilateral effect, the elastic Helmholtz free energy is decomposed into a volumetric part and a deviatoric part. The different behavior under tensile and compressive loadings is modeled by using different variables in effective stress and damage tensor. Numerical results of the model accord well with experimental results at the material and structural levels.

Abstract: In this paper, the freeze-resistance of concrete is studied for the special requirements of the engineering. Through the analysis of the damage mechanism of concrete’s freezing and thawing; researching the effect on freeze-resistance of concrete when to be mixed into active mineral ingredients additive and admixture; proposing the right mix proportioning to fit the request of project; making a good result by testing the property of mixture and the mechnical property of concrete as well as its freeze-resistance.

Abstract: The evaluation of the correct stability factor of tunnel is a critical element in the various design and construction phases of a tunnel excavated in difficult geotechnical conditions. An innovative, and well-applied, procedure for optimize the construction phase management is described in this article. The starting point of this procedure involves the verification of the results of numerical methods obtained from referenced analytical methods. In the first step of the procedure the results obtained through the analytical method are verified by means of a numerical method in order to evaluate the practical consequences in terms of development of deformations and plastic zone. In this manner, the assumed design risk is evaluated for the different methods and the solution that gives the best correspondence with numerical simulation is selected. Finally, residual uncertainties and parametric variations are incorporated in the analysis and Monte Carlo simulation is used to calculate the statistical distribution of the face-stabilizing pressure and the design value is selected on the basis of an acceptable probability of failure.

Abstract: In order to determine the impact resistance of lightweight aggregate concrete (LWC), especially the effect of steel fibers on impact resistance of LWC, a series of drop-weight tests, recommended by the ACI committee 544, have been carried out in the present study. Impact and flexural tests were carried out on lightweight aggregate concrete reinforced with five different percentages of steel fibers 0.0%, 0.5%, 1.0%, 1.5% and 2.0% by volume of concrete. For each volume of fibers, complete load–deflection curves of SFLWC were generated in order to determine the total energy absorbed for each specimen. The addition of steel fibers to concrete has improved impact resistance and also the flexural toughness. The test results showed that a logarithmic relation exists between flexural toughness energy by means of the generated load–deflection curves from the flexural tests and the impact energy by means of drop-weight tests.

Abstract: Mechanical properties at low temperature (-5°C, -20°C and -30°C) including compression strength, flexure strength, splitting tensile strength and modulus of elasticity of concrete with fly ash were investigated. In order to remain the temperature of the specimens unchanged during the test, a new insulation device was designed. In addition, the effects of curing ages on mechanical properties of concrete were studied. The results showed, at low temperature, all of the mechanical properties were improved; as the temperature decreases, the growth ratio increased continuously. The relative growth ratios of compression strength and flexure strength achieved the maximum value when the temperature decreased from -5°C to -20°C, and the relative growth ratios of splitting tensile strength and modulus of elasticity kept increasing during the whole process of cooling. At -35°C, all of the mechanical properties were improved at each curing age.

Abstract: Self-compacting concrete (SCC) is a new style of concrete with high workability. The key techniques of SCC including workability, strength, dimension stability, thermal properties and durability were investigated in this paper. High workability can be achieved at low water-cement ratio by adding superplasticizer. After adding inert powder such as limestone powder, the low strength SCC can be produced. The dimension stability of SCC can be improved by using expansive agent. Mineral and inert admixture can reduce the hydrate heat of binder and avoid temperature crack of concrete. The durability of SCC can be improved by controlling water-cement ratio, adding chemical admixtures and fibre.

Abstract: The properties of hollow partition such as compression strength, impact resilience, hanging capability, sound insulation capability are investigated systematically. The results of experiment indicate that if the content of waste concrete was less than 70% the mechanical behavior of the partition is acceptable. When the content of wastes was appropriate the hollow partition precast with recycled concrete have good physical properties.