In this paper, the authors have proposed the stress function which can be applied to explain the crack mechanism for concrete structures by expanding materials or swelling of reinforcing bars due to corrosion. The analytical model is an infinite elastic plate under uniform compressive stresses with a circular hole which has radial cracks at the edge. Applied loads are uniform loads in the direction of cnlarging the diameter at the boundary of the hole. The function can express a process zone with smooth finite stress concentration at tips of the cracks.
A new approach in the classification of the resulting failure mode, whether shear, bond splitting or flexure, for reinforced concrete columns is presented. Particular emphasis is placed on the analysis of the strain distribution in the main reinforcement based on the truss and arch model theory. Failure mode prediction from the proposed alternative method is compared with results from several series of column experiments. The proposed method is shown to provide a high level of precision in classifying failure modes with the proper consideration of the presence of inner rows of main bars and the effect of axial loading.
A new retrofitting system for wall type bridge pier has been developed. Significant feature of this system is that pier wall can be efficiently confined by hoop-tension of multi-cylindrical steel segments with less number of tie-boltings than the ordinal steel jacketting method. The experimental result indicates that new system ensures more significant improvement in ductility capacity. This paper finally proposes practical design formula for ductility capacity assessment of bridge piers retrofitted by the present system.
This paper proposes a method estimating the long term movement phenomena of ions under various environmental conditions. According to this method, the quantity and direction of the movement of ions can be theoretically simulated. Special features include : considering (1) coexistence ions, (2) internal electrical potential. The formulas used in this method are based on the Nernst-plank formula, Debye-Mickel theory and electrical neutralization. The simulated results were confirmed by examination of the actual concrete exposed to seawater for 15.5 years. As a result, the validity of this method was confirmed.
The chemical potential of unfrozen water and frozen water content were measured by the modified electric method in some range of lowest temperature. We used a thermal mechanical analyzer (TMA) and measured the dilation under freezing and thawing cycle. The rate of frozen water content under both super cooling and depression of melting point was described statisically. The relation between the radius of capillary pore and depression of melting point was shown statistically. Subsequently we proposed the method to estimate the amount of frozen water by the temperature and pore structure taking account of the thick of unfrozen water layer. The dilation that is calculated from freezing of supercooled water shows the similar tendency to the one that measured by TMA. Consequently we proposed the modified mechanism of frost damage. The rapid growth of ice crystal under supercooling makes rapid flow and large hydraulic pressure of unfrozen water. The large hydraulic pressure cause frost damage of Concrete.
The strength development caused by carbonating low heat cement mortar was compared with those of ordinary portland cement and blast-furnace slag cement mortars. The variation of the strength development of low heat cement mortar under various curing conditions was investigated. The low heat cement and blast-furnace slag cement mortars were easily carbonated than the ordinary portland cement mortar. The strength of the low heat cement mortar treated by the carbonation was higher than that of the blast-furnace slag cement mortar treated by it. However, the strength developments of these types of mortar largely varied according to the starting time and period of the carbonation reaction. The strength of mortar was measured and the distribution of pore in and the specific surface area of the hardened cement paste were studied and elucidated that the total pore volume in the hardened low heat cement was remarkably reduced and the specific surface area of it was increased by the carbonation.
A method was contrived for establishment of the average stress-strain curve. Strain values corresponding to the specified stress were averaged out from the relative stress-strain curves to estimate the average ascending branch. The established average stress-strain curves were applied for the evaluation of the damaged concrete. Tests of several types of limited cyclic loadings, namely damage, were conducted on specimens to determine the shape change of each type of stress-strain curve under compression.The obtained diagrams of the average stress-strain curves subjected such loadings were presented Observation of the average stress-strain curves showed that, even in a small damage, the concrete would change the ascending branch of the stress-strain curve to the downward than that obtained from monotonically loaded reference concrete specimens. These findings imply the possibility to estimate the magnitude of damage by means of the shape change on the average stress-strain curve. The results, indieated in this paper, demonstrated the ability of the average stress-strain curve for detection of the damage applied to the concrete.
This paper reports about experimental and analytical results carried on in order to obtain data for judgment if we can improve the durability of reinforced concrete by stopping, delaying or suppressing the progress of corrosion of reinforcing steel in neutralized concrete by surface treatment after the considerable progress of neutralization of concrete. Experiments of 16 month-accelerated corrosion test and 11 year-outdoor and indoor exposure tests for test specimens of reinforced concrete treated with various surface finishing matherials after 5 month-accelerated carbonation were carried on. Suppressive effects of surface finishing materials on corrosion of reinforcing steel in neutralized concrete have been quantitatively evaluated both by power law and by the general parabolic law involving a constant term concerning time. A concept of equivalent ratio of corrosion weight loss causing crack is proposed based upon these suppressive effects of surface finishing materials.
This paper deals with theoretical study on suppressive effects of surface finishing materials on corrosion of reinforcing steel in neutralized concrete experimentally confirmed by accelerated corrosion test and outdoor and indoor exposure tests. Theoretical modeling has been made on the progress of corrosion of reinforcing steel in neutralized concrete and the influence of surface finishing materials, by combining unsteady-state diffusion theory with equivalent electric circuit theory of corrosion reaction. It was found that suppressive effects of surface finishing materials on the corrosion of reinforcing steel can be well explained by the time delay in reaching very near the surface of reinforcing steel of vapor and oxygen due to the diffusion-shielding functions of surface finishing materials against vapor and oxygen, and that the progress of corrosion influenced by surface finishing materials generally obeys the power law.
The post-cracking behavior of a steel fiber reinforced concrete is important because it affects the crack width which influences the durability of the structure. In this study the deformational behavior of a steel fiber reinforced concrete subjected to uniaxial tension and shear was investigated experimentally by applying a load to a specimen with a discontinuous plane for a crack. In the experiment the effects of the fiber inclining angle to the crack plane and the fiber geometry were investigated. High-strength concrete was used in the specimen. From the experimental results models for load-displacement relationships were obtained considering the fiber inclining angle as a parameter.
This research features the anchorage system for fiber sheets in the strengthening of reinforced concrete structures. This anchorage consists of steel angles and anchor bolts. Two series of tests are performed with an objective of investigating the influence of the anchorage method on the bond strength and failure pattern. The one is the bond test between steel plates and fiber, the other is tensile test using a new type of specimen, which represents a corner part of a column with wall or a beam with slab, that were strengthened with CFRP sheets. Experimental results show that the rigidity of the angle plate and anchor bolt very much influences the bond strength of CFRP sheets. By using angle plate strengthened with rib, the bond strength of CFRP sheets is further increased. Replacing the angle plate and the anchor bolt to beam element model, the relationship between the strength and deformation of the angle plate at bond slip failure is evaluated by elastic calculation.
The relationship between a) the adsorption characteristics of the dispersing components in polycarboxylate-based AE high-range water-reducing agents onto various type of fine particles and b) the fluidity of a paste of the fine particles, was studied. The results of the study indicated that as the relative surface area of the same type of fine particle increases, the adsorption amount of the dispersant per unite weight of fine particle increases, but the adsorption amount per unite surface area of the particle remains constant. This result suggests that it is possible to estimate the amount of dispersant required for dispersing particles whose relative surface area are different, such as blast furnace slag and limestone fine particle. It is also believed that the lower surface tension of the paste water after adsorption saturation reduces the viscosity of the fine particle paste, thereby increasing the paste's fluidity.