Reinforcing bars embedded in concrete tend to corrode due to salt attack under marine environments. Corrosion of bars might be often caused with phenomenon of macro-cell. Cathodic protection has been, so far, applied to control the corrosion of reinforcing bars in RC members. In order to make clear the mechanisms of macro-cell corr osion and the effect of cathodic protecti on, laboratory tests were carried out. Testing concrete specimens contained two reinforcing bars which were buried at upper area of specimens and at lower area of ones, respectively. Lower zone of the concrete specimens were immersed in water. Testing results indicated as follows: (1) reinforci ng bars under wetting condition were anode and reinforcing bars under drying one cathode, (2) current density of macro-cell between two bars increased according as the potential difference increased and electric resistance of the concrete between two bars decreased, and (3) cathodic protection was effective to prevented macro-cell corrosion of reinforcing bars in concrete. Furthermore, it was presumed that corroded iron might be reduced to metal iron due to the protection current.
In order to establish the evaluation method of the effect of the water supply curing we proposed the estimation method of influence of curing condition on the compressive strength development behaviors of concrete using ordinary portland cement. This method evaluates the strength development behaviors of concrete under various moisture conditions by the volume of hydration products calculated in consideration of the influence of water retaining condition on the hydration velocities of cement. In this study, the applicability of this method for concrete using various portland cements was investigated. As a result of the investigation, the general estimation method applicable for various portland cements was established in consideration of the difference in hydration velocities and the influence of water retaining condition due to the kind of cement.
In this paper, MPS method was applied to fluid an alysis of self-compacting concrete. MPS method is one of the particle method, and it is suitable for the simulation of moving boundary or free surface problems and large deformation problems. The constitutive equation of self-compacting concrete is assumed as bingham model. In order to investigate flow Stoppage and flow speed of self-compacting concrete, numerical analysis examples of slump flow and L-flow test were performed. In addition, to evaluate verification of compactability of self-compacting concrete, numerical analys is examples of compaction at the part of CFT diaphragm were performed. As a result, it was found that the MPS method was suitable for the simulation of compaction of self-compacting concrete, and a just appraisal was obtained by setting shear strain rate of flow-limit πc and limitation point of segregation.
Drying shrinkage of coarse aggregate is one of principal indexes to evaluate drying shrinkage of concrete. However, testing of drying shrinkage of a coarse aggregate particle has not been commonly conducted. We carried out measurement of drying shrinkage of a coarse aggregate particle using wire strain gauges and discussed the variation in the measurement. We found that variation among particles in drying shrinkage strain of coarse aggregate is intrinsic and much bigger than test result due to the simplified unidirectional strain measurement under the assumption of ignoring multi-axial strain field. Strong relationship between the mean value of drying shrinkage strain of coarse aggregate and drying shrinkage strain of concrete prism specimens was observed, which indicates that measured drying shrinkage strain of aggregate particles intrinsically contains large variation, however the mean value is an effective index to estimate drying shrinkage of concrete.
The durability of cementitious material can be effectively improved by reducing permeability and by changing cement hydrates due to car bonation reaction. This paper describes the examination results about the mechanism of pore reductio n during the curing with CO2 gasses of new cementisious materials containing low heat Portland cement, γ-2CaO.SiO2 and pozzolanic admixtures. As a result, it was provided that the pore of the mortar containing the pozzolanic admixtures and γ-2CaO.SiO2 got small, because the pozzolanic admixtures would accelerate the reaction of γ-2CaO.SiO2 and CO2 gasses.
In case of that column diameter is restricted by the narrow construction space, Concrete filled steel tube column is used. Authors developed new arrangement of bars that the range of longitudinal reinforcement ratio is from 14.8% to 24.7% and the longitudinal reinforcements are reinforced by spiral reinforcement. For the confirmation of the damage form and the deformation performance of the column with new bar arrangement at the earthquake, static reversal cyclic loading test was carried out. The parameters are longitudinal reinforcement ratio, shear span ratio and strength ratio. As the result, the damage form showed different trends due to longitudinal reinforcement ratio, shear span ratio and flexural strength and shear strength ratio. And specimens with the new bar arrangement had a good ductility with rotation angle of the column more than 1/10 and no rapid decline of strength. And, it is possible to evaluate ultimate bending capacity by considering the damage situation at maximum load.
Properties of aggregate are not taken into account in current codes for drying shrinkage of concrete although the drying shrinkage is affected by the properties of aggregate. Aggregate restrains cement paste from shrinkage so that the drying shrinkage of concrete is controlled by drying shrinkage and Young's modulus of aggregate itself. The effect of the aggregate properties on drying shrinkage of concrete can be calculated by composite model in which concrete consists of cement paste and aggregate. Several different kind of coarse aggregate were used in order to verify a 3-phases composite model for drying shrinkage. Drying shrinkage and Young's modulus of cement paste, aggregate and concrete were measured. It was verified that drying shrinkage of concrete can be estimated accurately by the composite model associating with both drying shrinkage and Young's modulus of aggregate.
A new two-layer anchor-infill assembly structure for the post-installed anchor is introduced with the analytical model to simulate its pull-out deformational response. The post-installed anchor is such that used in strengthening techniques for reinforced concrete structures. The properties of the infill material used for post-installed anchor are characterized by nonlinear interfaces. Because of the mechanical properties of the infill layer the existing pull-out model of deformed bars is not applicable in this case. Interfacial de-bonding is examined using energy criterion and strength criterion. The effect of the interface properties such as stiffness and strength on the pull-out behavior of a post-installed anchor is investigated. Using sensitivity analysis, the effect of these parameters on load-displacement curve, shear stress distribution, de-bonded length and damage to the surrounding concrete is clarified. Then, the optimum combination of these parameters is presented. It is confirmed that the elastic modulus of infill should be large to reduce the pull-out displacement and the increase of the shear strength of infill makes the pull-out load larger.