Crack extension due to rebar corrosion is one of serious problems in concrete structures. It is well known that the mechanisms of crack nucleation and extension can be theoretically analyzed by applying fracture mechanics to concrete. For diagnostic purpose of the concrete structures, a rational model is in demand for predicting the deterioration process of rebar corrosion. Thus, an application of fracture mechanics to spalling cracks due to rebar corrosion is studied. Crack extension is observed under electrolytic corrosion of rebars. To analyze crack extension, the linear elastic fracture mechanics is applied. The critical stress intensity factor is determined from bending tests of notched beams, taking into account acoustic emission (AE) activity. Based on the maximum circumferential stress criterion, crack trajectories are analyzed by employing the two-domain boundary element method (BEM). Taking non-isotropic distribution of pressure due to corrosion product, crack trajectories of spalling cracks are simulated in reasonable agreement with those observed in the experiment.
In order to evaluate a bond splitting strength of lap splices with high-strength concrete of 60 MPa grade, pure bending tests of eighteen simple beam type specimens were conducted. Bond splitting strength was applied to the bottom longitudinal bars of beams which cause the bond splitting failure in the side-split mode. As a result, the bond splitting strength of lap splices showed a tendency to decrease as the length of lap splices became longer. And the bond splitting strength of lap splices increased in proportion to the increase in the ratio of transverse reinforcement. Furthermore, the bond splitting strength of lap splices equation for high-strength concrete of 60 MPa grade proposed based on the past bond splitting strength equation. By the verification to this experiment and past experiment data, this equation was able to confirm the adaptability.
This paper presents an experimantal study on the dynamic flexural toughness of post-tension prestressed reinforced concrete beams. The elastic plastic behavior and the flexural toughness of the pretension prestressed concrete beam, the pretension prestressed reinforced concrete beam and the post-tension prestressed reinforced concrete beam were evaluated and compared by the static and high speed loading tests. Under the static loading condition and the same flexural strength of beams, the ultimate deformation of the post-tension prestressed reinforced concrete beam is clearly larger than those of the pretension prestressed reinforced concrete beam and the pretension prestressed concrete beam. On the other hand, although the order of the ductility in case of high speed loading test is not different from that of static loading test, the ultimate deformations in the high speed loading became smaller than those of the static loading.
Recently, the research on the meshless method which is considered as a new numerical analysis technique has been developed in many engineering fields. Within these meshless methods, the free mesh method (FMM) proposed by Yagawa has been applied in many engineering fields by efforts Yagawa's grop. The purpse of this research is to apply this FMM to the tesion softening analysis of concrete. In this analysis, the crack band model has been used as a crack model. Also, in incremental analysis, the dynamic equilibrium equation has been used in order to analyze the problem in case of unstable phenomena such snapback. As numerical examples, the direct tensile tests of concrete bars and the bending tests of concrete beams are analyzed and the results became excellent.
In this paper, the early age creep under autogenous shrinkage condition of 100 N/mm3 class highstrength concrete was investigated. According to the experimental studies, 1) The relationship of compressive strength and tensile strength, compressive young's modulus, tensile young's modulus were analyed. And mechanical properties of early age concrete were evaluated by compressive strength development. 2) Specific creep both compression type and tensile type can evaluated to the limit of 40% of stress-strength ratio. And elastic strain for early age concrete was very importance. 3) Specific creep strain was evaluated simply exponential function. And tensile creep was proportional to compressive creep.
This paper describes a model for predicting the leaching degradation from the concrete in contact with water. The degradation mechanism was considered based on the degradation condition of the specimens obtained by electrochemical acceleration tests and diffusion tests, and the model was proposed. Analyzing the test results obtained from diffusion tests were carried out using mass transport equation. In the case of diffusion coefficient are 1E-12 [m2/sec] for non degraded region and 1.7E-10 [m2/sec] for degraded region, the computed result was close to the test result and showed the appropriateness of the model.
The purpose of this study is to make clear the law governing flow of water forced to seep into concrete under pressure. Further, based on the results of the study, fundamental data on materials for watertight concrete, selection of mixture proportions, and cross-sectional design of watertight concrete members are furnished. Noting that the ratio of seepage water forced into concrete differs depending on the degree of water pressure and varies between approximately 1.0 and nearly 2.0 times in volume, flow of water in concrete is divided into Darcy seepage flow in case of low water pressure and osmotic diffusion flow under high water pressure. Next, analytical studies are made of these flows, and equations of seepage coefficients are indicated for Darcy seepage flows and a diffusion coefficient calculation formula for osmotic diffusion flows. It is proposed that watertightness of concrete be evaluated by the former in case of water pressure less than about 0.15 MPa and by the latter in case of higher water pressure. Based on the results, the effects of using various chemical admixtures are evaluated by seepage and diffusion coefficients. Further, a method of checking watertight concrete member thickness is tentatively proposed as a part of studies on safety at the serviceablility limit state.
Reinforced concrete is an excellent composite system combining both steel and concrete However, when a crack is formed in concrete both water and oxygen can easily approach to the surface of steel in concrete, and this causes corrosion of steel reinforcement The corrosion reduces the performance of reinforced concrete structure. This paper aims to evaluate the corrosion rate of steel in concrete quantitatively, in chloride environment The results show that corrosion rate of reinforcing steel bar can be predicted numerically by applying different chloride boundary conditions to cracked portion and other surfaces. The effect of temperature is also examined by both experiment and computer simulation
The electrodeposition method for rehabilitation of cracked reinforced concrete, based on the electrochemical technique, is presented here. There are some studies on application to marine structures, however, trials on terrestrial structures of this relatively new method have not been carried out yet. So, in this paper, it was evaluated by considering (1) the possibility of electrodeposition method as a means of repair for cracked concrete structure on land, (2) the effectiveness of this method on the concrete property, and (3) the desalination and the repassivation effects of the method. The restults indicate that electrodeposits formed on the concrete surface and able to close the concrete crack and to coat the concrete surface. In addition, the investigations show that the electrodeposition method affects the properties of concrete and has an effect of desalination and re-passivity of reinforcing steel.
This paper reports about experimental results carried out in order to obtain data about the failure behavior of concrete column reinforced with strands which have higher tensile strength and lower bond strength with concrete than usual deformed bars. The following things about failure behavior was made clear, 1) cracking locally, 2) distance from neutral axis and strain in the cross section are not in proportion, 3) residual displacement in small, 4) energy Absorption per each hysteresis loop is small, 5) yield displacement is large. And if both ends of each strand were anchored firmly, ultimate bending strength can be calculated by the way of calculating it which distance from neutral axis and strain in a cross section are in proportion is suppposed.