In this research two kinds of experiments were performed from a basic point of view to prevent reinforcing bars embedded in concrete being corroded by covering the surface of concrete with using Metallized Zinc and Zinc Aluminum Coating. One is experiments on corrosive substance separating effect and another is experiments on sacrificial cathodic protection. The results of tests show that the corrosive substance on reinforcing bars can be expected to be avoided by spraying suitable metals over the surface of concrete, and that sacrificial cathodic protection can be expected to be protected for corrosion by using Metallized Coating on condition of maintained the water content of the concrete, anode/cathod area ratio under 5 and adjustment of the consumption of it.
The small specimens have been in general used in non-destructive testing of concrete. However, there may be significant differences in the quality of concrete between the specimens and in situ concrete because of the difference in the methods of compacting, curing of concrete and moulds, etc. In this paper, non-destructive test techniques, such as measurements of ultrasonic pulse velocity through the concrete, the thermography and the radiography were used to detect regions of defects of in situ concrete up to the age of 2 months from immediately after compacting of the concrete. The specimens used in this investigation were four reinforced concrete beams with a nominal height of 1 200 mm, a web width of 500 mm and a length of 1 200 mm. The effects of defects were simulated by casting with three conditions : well compacted concrete with man-made defects ; no compaction ; and not well compacted concrete. Plywood panels and permeable panels for the concrete form were used.
Series of studies on application of β-1, 3-Glucan (Curdlan) for viscosity agent to super workable concrete have been reported. The purpose of this study is to make clear about the poperties of β-Glucan by comparing the solubility, viscosity and other characteristics in cement system with conventional viscosity agent, cellulose ether. As a result, it is confirmed that β-Glucan exists in the form of independent swollen calcium gel particles and they have negative electric charge on their surface. It indicates that β-Glucan has the ability of increasing the viscosity of cement slurry, and furthermore it is suggested that β-Glucan partly contributes to increasing the fluidity of the cement slurry.
To predict the compaction behavior of fresh concrete by means of vibrating table, an analytical evaluation method was proposed. It is based on a few assumptions that fresh concrete is expressed by Newtonian fluid and compaction is accomplished by discharging air bubbles from the fresh concrete. This method was applied to the compaction tests of a fresh concrete for roller compaction during vibration by means of vibrating table, then efficiency of the method was confirmed.
In this study, reinforced concrete column members were tested during static and dynamic horizontal loading under low axial load ; the effect of strain rate on strength, deformation and mode of failure was investigated. The results obtained in this study could be summarized as follows : 1) The maximum strengths during dynamic loading were about 1.15 times greater than those during static loading. The ratios of maximum strengths during dynamic loading to those during static loading decreased with increasing hoop ratios ; the ratios were also different with the change in the main reinforcement ratio. 2) For flexural failure, the drift angles at yielding of main reinforcement increased, and the drift angles decreased at the maximum strength during dynamic loading. For shear failure, the drift angles of yielding of hoop during dynamic loading decreased compared to those during static loading. The drift angles of maximum strengths were almost the same during static and dynamic loading regardless of crack patterns and modes of failure. 3) During static loading the mode of failure was shear failure ; during dynamic loading the change from shear failure to the bond splitting failure was also observed.
In this study, the methods of evaluation of deflection and minimum tension bar ratio of reinforced concrete member under bending moment, which are very important in limit state design, are examined analytically. That is, at first the evaluation method of crack spacing on the basis of the relationship of moment-curvature, mechanism of occurrence of crack and bond characteristic between reinforcing bar and concrete is proposed analytically. Then the evaluation method of load-deflection of RC beams under bending moment, in which the influence of tension zone of concrete is taken into consideration, is also proposed. Besides, the evaluation method of minimum reinforcing bar ratio which is able to apply for the different material strengths is proposed in order to prevent brittle failure of reinforced concrete beams.
There are two main purposes in the present study. One is to examine the effect of specimen size on the stress-strain curves of concrete under uniaxial and triaxial compressive stress states. The other is to grasp quantitatively the cracking pattern of specimens from the data analysis of the size distribution of concrete fragments of the tested specimens after failure. It is found that the effect of specimen size on the deformation behavior of concrete under triaxial compression is more remarkable than that under uniaxial compression. Based on the data analysis, a model of compressive cracking pattern is proposed. Discussion is also carried out on the size effect in the compressive deformation behavior of concrete, spotlighting the dissipation energy at cracking.
In this paper, the following conclusions and summary can be made : 1) An energy absorption of concrete specimen with unit size of (10 × 10 × 10 cm) is examined from the experimental data under triaxial compression, and then a characteristic equation to evaluate energy absorption after failure of concrete is suggested. 2) An energy absorption of concrete specimen with different shapes and sizes is also considered from the experimental data. 3) A length of failure zone inside the concrete specimen with different shape ratio becomes longer with an increase in the confining pressure. 4) An energy absorption capacity per unit volume decreases with an increase in the size ratio of concrete specimen. 5) Applying the results obtained from items 1) through 4), concrete-filled tubular steel columns are analyzed, and analytical results are compared with the experimental data.
This paper reports the effect of coating the concrete surfaces with mortar of high nitrite content on corrosion protection of reinforcing bars within concrete containing chlorides. Accelerated corrosion tests in a glass house and outdoor exposure tests were conducted over a period of 5 years. Specimens were made with using concrete containing 0.3-4.0 kg/m3 chlorides. Reinforcing bars were embedded with different cover depths in the specimens, the surfaces of which were coated with mortar of high nitrite content. The measurement of the half-cell potentials indicated that, starting from those with thin cover, the corrosion?inhibiting environment gradually surrounds the bars in the specimens as the nitrite ions permeate the concrete. Weight losses by corrosion of the reinforcing bars were embedded in the specimens with mortal of high nitrite content were less than those of specimens uncoated or coated with polymer cement mortar. It was confirmed that the mortar coating with high nitrite content is effective in protecting reinforcing bars from corrosion in concrete in which chloride ions have already penetrated.
Polymer dispersions have been used in polymer-modified mortars for many years, and are also being used as sealers for bed concrete of mortar or tile finished exterior walls. This study mainly deals with the stability of polymer films formed with polymer dispersions in alkali environment, and the influence of alkali on the physical properties of the polymer films in polymer-modified mortars. The conclusions obtained are summarised as follows : (1) Homopolymers containing ester linkage and copolymers containing vinyl acetate are less stable in alkali environment, because their chemical structures are altered by the alkali. (2) Polymer films formed with polymer dispersions are used as sealers are apt to deteriorate compared with polymer films in polymer-modified mortars. The reason for this may be explained to be due to the difference of exposure conditions of the polymer films to concentrated alkali such as in pore solution.
In this paper, the influence of curing time and water-cement ratio on hardened cement paste is approached by both experimental and analytical method. Compressive strength and pore size distribution of hardened cement paste with various water-cement ratios and curing time is measured. The model for strength development based on the assumption that strength is related to contact area between a hardened cement particle and adjoining one. The model for the influence of water-cement ratio is based on the assumption that is related to an increase of apparent cement volume caused by aggregation of fine cement particles. The analytical results of strength development and pore structure of hardened cement paste obtained agreed well with experimental results.
Recently, several mineral admixtures and superplasticizers are used to improve concrete property. However, the interaction between cement, mineral-admixture and superplasticizer retards the setting and hardening of concrete. In this paper, a model to explain concrete setting mechanism due to W/C and superplasticizer is proposed to estimate the settig time. The effect of blast-furnace-slag and fly ash is also considered.