The purposes of this study were 1) evaluating the influence of the recycled aggregate on permeability and strength of concrete, and 2) decreasing the permeability and increasing the strength of recycled aggregate concrete. In the experience using five types of recycled aggregates, the influences of recycled aggregate on Clpenetration depth, carbonation depth, tensile strength and compressive strength were measured and compared. After evaluating two ITZs in recycled aggregate concrete, the relations between permeability or strength and ITZs were explained. Moreover, based on the above discussions, the method for decreasing permeability and increasing strength of recycled aggregate concrete could be proposed and proved.
The Plane Element Working Group of the Subcommittee on Structural Performance working for a Ministryof Construction project for the development of new reinforced concrete technology revised design guideline equations for the ultimate strength design of shear walls with a view to estimating the shearstrength of reinforced concrete shear walls without openings that are made of high-strength materials. After conducting a large-scale shear wall test and a finite element analysis modified for application to high-strength concrete, the working group proposed a shear reinforcement limit of 4.1 N/mm2 for panels of shear walls without openings that are made of concrete with a strength of 60 N/mm2. To attain better agreement with the large-scale shear wall test results, the authors have conducted a finite element analysis using a model of mechanical properties of reinforcement as a reinforced concrete element, which was proposed by Hsu, and formulated shear reinforcement limits for concrete strengths ranging from 36 to 100 N/mm2 by parametric analysis
This paper presents an experimental study for the investigation of the effect of the circumferentialcrack caused by impulsive uplift load on the dynamic lateral resistance of reinforced concrete (RC) column. First, the impulsive uplift test was carried out for the miniature RC column model (10cm square section and 30cm height), and the horizontal circumferential crack was occurred in the specimen. Second, the horizontal static and high speed (2.0m/s) loading tests were executed in order to examine the lateral resistance of damaged specimen and compared with no-damaged specimen, respectively. The experimental results show that the circumferential crack due to impulsive uplift load reduces about 10-17% on the lateral resistance and about 15%-, 40% on the lateral deformability of RC column.
Using mortar specimens associated with self-compacting concrete and normal concrete incorporating ground granulated blast-furnace slag (ggbs), the strength development for various curing temperatures supposing cold regions was researched. The experimental results revealed that the strength development is varied by the incorporation of ggbs, its specific surface area and replacement level, and the difference between self-compacting concrete and normal concrete. Thus suggesting the method for evaluating the effect of ggbs to the strength development of ggbs-concrete quantitatively, the influences of mixture proportion and curing temperature to the strength development of such concrete were investigated.
In this study, in order to establish the mix proportion principle of concrete containing large quantity of coal ash with constant portland cement content, properties of fresh concrete, compressive strength and carbonation were measured and discussed. As a result, the relationship between mix proportion and properties of fresh concrete was clarified and equi-potential line on compressive strength and carbonation rate could be calculated on the basis of the experimental results. And the mix proportion principle of this concrete and procedure of mix design could be shown.
In this paper we describe an experimental study of the expansive concrete filled steel tube using for the brace member of the energy dissipative braced frame structure. The results of the compression test of the expansive concrete in the tube may be summarized as follows : (1) The expansive concrete with Water/ (Cement+Silica fume+Expansive admixture) =30% and Ex/ (C+S+Ex) ≥55% has a very high expansive capacity. (2) The apparent axial initial stiffness of the expansive concrete with W/ (C+S+Ex) =30% in the tube is as same as the Young's modulus of the usual concrete without the expansive admixture. Finally, we showed the compression design strength and condition of this brace member with the expansive concrete filled tube
This paper presents numerical analyses of reinforced concrete beams subjected to axial compression. A rigid-bodyspring model is used to represent concrete material as an assemblage of rigid particles interconnected along their boundaries through flexible interfaces. The material is discretized into a large number of random particles using Voronoi diagrams in order to reduce mesh bias on the fracture conditions. Rather than averaging the effect of reinforcing over a regional material volume, reinforcing material is explicitly modeled. Mesh construction is greatly facilitated since the material discretization is semiautomated and each reinforcement can be positioned irrespective of the concrete material. Numerical results agree well with experimental observations in terms of loading capacity, crack patterns, concrete strain, and steel strain. The model predicts an increase of shear carrying capacity in RC beams due to axial compression. The rate of increase of shear carrying capacity is investigated through analyses of RC beams with the different span-depth ratio.
The pullout behavior of steel fibers has a significant influence on the overall mechanical properties of steel fiber reinforced concrete. The embedment length of steel fiber is one of the principal factors which influence the pullout properties of a single fiber. In this study, therefore, the effect of embedment length of fiber, being the principal factor, was examined experimentally. The effect of the matrix concrete strength for both high strength and normal strength and that of the fiber geometry were examined as well. From the experimental results a pullout model is derived taking the embedment length as a parameter.
A method for estimating macrocell corrosion rate of existing reinforced concrete member with joint and bending cracks was proposed and was verified in this study. First, the model, which replaced macrocell in reinforced concrete with the equivalent electric circuit, was constructed. Significance of this model was to estimate the macrocell corrosion rate that was otherwise impossible to measure in existing concrete member. Especially, the substitution values to this model were only potential, polarization resistance and concrete resistance that were measurable by non-destructive tests. The model was then verified using mortar specimen with joint or bending cracks, and also using existing reinforced concrete members.
The accuracy of tensile strengths of concrete obtained by the uniaxial tension test proposed by the authors was investigated, comparing with simulation results which were calculated by using finite element models combined with fictitious cracks and bi-linear tension softening curve. The following were clarified. The application of notches is reasonable procedure, because the missleadings in observing tensile strength of concrete is insignificant in spite of high stress concentration in elastic region due to the presence of notches. It is indispensable to eliminate a secondary flexure which usually occurs during the uniaxial tension test, because the reduction of the observed tensile strength caused by the secondary flexure sometimes reaches 20%. The results show the reliability of the proposed uniaxial tension test.