Shigeyoshi Nagataki

Evaluation of AgNO 3 Solution Spray Method for Measurement of Chloride Penetration into Hardened Cementitious Matrix Materials

Recently the number of reinforced concrete structures damaged by chloride attack has increased. It is important to establish a simple method for measuring chloride content in concrete. Observation of discolored area after spraying certain indicator solutions on a fractured surface of the specimen has been considerd as one of these methods. For example UNI (Italian Standard) has recommended such a method for chloride contents using AgNO3 solution. The authors have examined the chloride content at the color change boundary and measured the electrochemical properties of steel bars in the discolored area to clarify the engineering significance of this method.

Evaluation of the AgNO3 solution spray method for measurement of chloride penetration into hardened cementitious matrix materials

Recently, the number of reinforced concrete structures damaged by chloride attack has been increasing. Therefore, it is important to establish a simple method for measuring chloride content in concrete. Observation of the discoloured area after spraying certain indicator solutions on a fractured surface of the specimen has been considered as one of these methods. For example, UNI (Italian Standard) has recommended such a method for chloride contents using AgNO3 solution. The authors have examined the chloride content at colour change boundary and measured the electrochemical properties of steel bars in the discoloured area to clarify the engineering significance of this method.

Condensation of Chloride Ion in Hardened Cement Matrix Materials and on Embedded Steel Bars

It is shown that condensation of the water-soluble chloride ion in concrete and on embedded steel bars is surprisingly significant in concrete structures submerged in seawater. That is, the chloride ion concentration of the pore solution in these concrete structures can be a great deal higher than the surrounding seawater. Also, the chloride ion concentrations of the solution on steel bars can exhibit much higher, and these concentrations are closely related to the electrochemical property of steel bars. Also, the formation of Friedels salt is confirmed to be closely related to the binding of intruded chloride ion in materials with cement matrix.

Prediction of Carbonation Depth of Concrete With Fly Ash

This paper reports the accelerated carbonation test results in order to investigate the effect of replacement ratio of fly ash, initial curing period in water, and air content on the carbonation phenomena in concrete. Using these test results, equations for the prediction of carbonation depth of concrete with and without fly ash are proposed, and these effects are also evaluated by these equations. Furthermore, the accelerated carbonation test results are compared with natural exposure test results for 15 years, and a method to predict the carbonation depth of concrete with and without fly ash exposed to natural indoor conditions is proposed. Concrete with fly ash is affected by initial curing period in water rather than concrete without fly ash from the viewpoint of depth of carbonation and compressive strength. The higher the fly ash content of concrete is, the deeper is the depth of carbonation. Depth of carbonation can be evaluated by compressive strength of concrete cured in water for 28 days, irrespective of the fly ash content of concrete. Carbonation depth of concrete with and without fly ash naturally exposed indoors can be predicted by the equation obtained by the accelerated carbonation tests.

Evaluation of Fly Ash for Controlling Alkali-Aggregate Reaction

Mortar using Pyrex as an aggregate were made using water-binder ratio of 50 percent, replacement ratio of fly ash from 0 to 30 percent by weight and an alkali content of 1.2 percent per weight of cement. Eight fly ashes were used as supplementary cementing materials. These mortars were cured at a temperature of 40 degrees Centigrade and a relative humidity more than 95 percent, and the expansion of these mortars was measured. The concentration of soluble alkali ion in fly ash immersed in the solution containing sodium hydroxide and calcium hydroxide was also determined. By studying effects of physical properties, chemical and amorphous silicon dioxide in fly ash, a method to evaluate the expansion of mortar containing fly ash was proposed based on amorphous silicon dioxide, the replacement ratio and particle diameter of fly ash.

A RATIONAL REPAIR METHOD FOR DETERIORATED REINFORCED CONCRETE MEMBERS

The purpose of this study is to establish a rational repair method for deteriorated concrete structures. The bond strength and the durability between the repair material and the old concrete are estimated and the flexural behaviours of the repaired reinforced concrete beams are discussed by both experiment and analysis. The repair materials selected are high early strength concrete, polymer modified mortar, resin concrete and steel fiber concrete.

A STUDY OF MIXTURE DESIGN AND QUALITY CONTROL METHODOLOGY FOR HIGH FLY-ASH CONCRETE

A mixture of fly ash and cement with a water to powder ratio close to the optimum moisture content has the characteristics of a wet powder immediately after mixing. After a few minutes of vibration compaction, however, the wet powder becomes fluidized and can be adequately compacted. By using this fluidization phenomenon in the manufacting process, the water to powder ratio and cement can be reduced. This in turn improves the quality and cost efficiency of high fly ash concrete. In this study, the authors investigate methods of mixture design and quality control for such high fly ash concrete. The work demonstrates that an optimum mixture can be determined through flow tests on fly ash, while the quality of high fly ash concrete can be controlled in terms of fluidization time.

PREDICTION OF CARBONATION PROCESS IN CONSIDERATION OF HYDRATION OF CEMENT AFTER INITIAL CURING

本研究では, 初期養生以降のセメントの水和の進行が中性化速度に対してどの様な影響を及ぼすかを明らかにするため, 実験的および解析的検討を加えた. その結果, 乾燥や水分の供給を受ける場合のセメントの水和進行予測手法と中性化進行予測手法とを組み合わせることにより, 促進試験中のセメントの水和の影響を考慮した中性化進行予測が可能となった.

ACOUSTIC EMISSION FROM REPAIRED REINFORCED CONCRETE BEAMS

The acoustic emission behaviors of repaired reinforced concrete beams under flexure load was studied. Useful correlation was established between the acoustic emission activity and crack growth in the repaired reinforced concrete beams. Three different acoustic emission activities were observed during the flexural loading. Flexural crack initiation, flexural crack propagation and slip between repair material and old concrete were identified by monitoring the acoustic emission. The zone of slip initiation and development can be identified from the acoustic emission event-location plot, showing major acoustic emission concentration areas. Repetitive loading showed that the Kaiser effect was not valid after slip was happened at the connected face between repair material and old concrete. Flexural crack growth acoustic emission burst event signals were found to be of higher amplitude compared with those due to the slip. The accumulated number of burst events of these highamplitude emissions, monitored by the use of a high threshold, showed good correlation with the crack growth in the beam.