Reinforced concrete specimens with pre-induced cracks were subjected to a long-term exposure test in order to observe the development of rebar corrosion under the condition of cold rural districts. After 42 years exposure, inspection results showed that the time at which the rebar would start to corrode was affected by the crack width and that the rebar corrosion rate was under about 0.004 mm/yr. Based on the above-mentioned inspection results and the past references, deterioration prediction of concrete structures was carried out. As the result, it is considered that bearing capacity and durability of concrete structures are not seriously hampered by rebar corrosion.
A theoretical method based on upper bound theorem to analyze ultimate strength of reinforced concrete columns is proposed. A yield line which crosses the extreme compression edge of a member end is assumed. As the angle of the yield line is varied, the yield line and the strength of the smallest strength are considered to be the predicted solutions, when a yield criterion of reinforced concrete sections considering interaction of combined forces being used. The predicted solutions by the proposed method show good correlation with test results of 26 reinforced columns. The method is also compared with conventional methods. By these examinations, the usefulness of the method is shown. Additionally, it is cleared that the amount of reinforcements has a great influence on the angle of yield lines.
A theoretical method based on the upper bound theorem to analyze ultimate strength of reinforced concrete shear walls is proposed. A yield line which crosses the extreme ompression edge of the bottom end of a shear wall is assumed. As the angle of the yield line is varied, the yield line and the lateral strength of the smallest lateral strength are considered to be the predicted solutions, when a yield criterion of reinforced concrete sections considering interaction of combined forces is used. The predicted solutions by the proposed method show good correlation with test results of 41 reinforced shear walls.
The tensile stress and shearing stress on the interface between the GRC casting forms and the concrete of the reinforced beam during fires were calculated by finite element method. Two types of GRC casting formworks were selected to improve joining performance between GRC and concrete. One was putting embossment and the other was burying wire net on the inside surface of GRC casting formworks. Fire resistance test was carried out on reinforced concrete beams covered with these GRC casting formworks and also to the reinforced concrete beam without GRC formwork. From these tests it was recognized that GRC formwork in which wire net was buried showed good joining performance between GRC and concrete. GRC formwork which has embossment on inside surface showed a little separation because the ascent of the temperature of the steel showed lower than in the other specimens and this fact was confirmed by the inspection of the specimen after the heating test but it was not so serious. It can be considered that RC beams using GRC permanent formworks have the similar degree of fire resistance properties with the conventional RC beam without formworks.
The effects of cement characters on the performance of superplasticizers for concrete was investigated by the fluidity tests using cement pastes with combinations of six kinds of cements and six kinds of superplasticizers. Based on the results, two parameters, i. e. critical dosage and dispersing ability, were proposed. There was a minimum value of superplasticizer dosage to show the dispersing effect, which named as the critical dosage. Less than the critical dosage, superplasticizer did not work. Over the critical dosage, the fluidity of cement paste increased proportionally to the dosage. The increment of fluidity per unit dosage of superplasticizer was named as the dispersing ability. In the relationship with cement characters, the critical dosage was closely related to hydraulic reactivity of cement at early age. The dispersing ability was related to alkaline sulfate amount in cement in the case of polycarboxylate-type superplasticizer.