Osamu Senbu

DETARIORATION AND PREVENTIVE EFFECTS OF FINISHING MATERIALS AGAINST CARBONATION AND CORROSION OF REINFORCING BARS IN CONCRETE BASED ON TWENTY YEAR OUTDOOR EXPOSURE TEST USING MODEL BUILDING

This paper reports the results of twenty years outdoor exposure test using a model building consisted of concrete specimens with various finishing materials. According to the results, it was observed high correlation between the deterioration degree of chalking and the degree of crack in the finishing material. The carbonation preventive effects in the coating finishing materials exposed to outdoor for twenty years were confirmed. It was also confirmed that corrosion preventive effects in the finishing materials meant the effects to delay the corrosion progress of reinforcing bars in concrete with the finishing materials.

Diffusion of moisture and chloride ions in repaired concrete subjected to complex deterioration factors

Repairing a reinforced concrete structure reduces various deterioration factors, such as chloride ions, and extends its service life. However, short-term redeterioration has frequently been reported in repaired concrete. Although many researchers have tried to find the cause of short-term redeterioration in repaired concrete, the mechanism remains unclear. In this study, experimental investigation was conducted into the causes of short-term redeterioration in repaired concretes subjected to chloride-induced damage and complex deterioration (chloride-induced damage and frost damage) environments. According to the results, the complex deterioration environment increases the ingress of chloride ions into concrete to a greater degree than the chloride-induced damage environment. A patch material with frost resistance and dense structure, such as polymer cement mortar, reduces the transfer of chloride ions and moisture. These characteristics protect repaired concrete from short-term redeterioration.

EFFECT OF CONSTRUCTION METHODS ON FROST RESISTANCE OF CONCRETE APPLIED BLAST-FURNACE SLAG FINE AGGREGATE

According to previous reports, it was reported that concrete applied Blast-furnace slag fine aggregate （BFS） observed excessive bleeding was found remarkable scaling in upper area of concrete specimen. It was carried out some construction methods which were effective in decrease of bleeding amount, such as re-vibration, using water percolation mold, and investigated the effect of the construction methods on frost resistance of concrete applied Blast-furnace slag fine aggregate. The obtained experimental results were as follows: 1）Water percolation mold improved the frost resistance of BFS concrete regardless of the replacement ratio of BFS. 2）Revibration did not improve the frost resistance of BFS concrete. 3）Revibration at 30 minute and 90 minute after placing of concrete decreased the voids under steel rods because of bleeding. 4）Revibration decreased air content in hardened concrete. However, it was not observed the difference on the following spacing factor and bubble distribution of concrete between revibration and no revibration. 5）Water percolation mold improved the decrease of air content in hardened concrete. 6）Water percolation mold and revibration decreased the amount of scaling by improvement of solidity in concrete.高炉スラグ細骨材（BFS）を用いたコンクリートについて、ブリーディングの大きいコンクリートに対して効果的と考えられる打込み後の再振動及び透水型枠の使用が耐凍害性に及ぼす影響について検討した。実験により、透水型枠を使用することで、コンクリート内部の気泡に影響を与えていたブリーディングが減少するため、内部の気泡組織が粗大化しないこと、余剰水の排出により組織の緻密化を図れることがわかった。また、BFSを用いたコンクリートに30～90分の間で再振動を行うと組織は緻密化するが耐凍害性は低下し、これは気泡間隔係数だけでは説明できないという結果を得た。

RESISTANCE TO FROST DAMAGE AT EARLY AGE AND STRENGTH DEVEROPMENT AT LOW-TEMPERATURE ON CONCRETE USING VARIOUS RECYCLING MATERIALS

This paper reports the results of the experiment on resistance to frost damage at early age and strength development at low-temperature on concrete using various recycling materials.Results show compressive strength to prevent frost damage at early age can be set at 5N/mm2, which is equal with normal concrete in any case. Low-temperature strength development of concrete using high-strength artificial aggregate, electric arc furnace oxidizing slag aggregate and normal eco cement is equal with normal concrete.

A COMPARATIVE STUDY ON THE INDEX TO EVALUATE THE REGIONAL FROST DETERIORATION HAZARDS

There are many previous studies on the index of regional frost deterioration hazards for concrete. However, it is sometimes pointed out that the evaluated results are different from each index. This report deals with the comparison of the famous indexes in Japan, and it makes clear the features of these indexes. According to the results, high correlation between each index is observed.