Electrochemical properties of embedded steel bars in the various materials were evaluated in view of the chloride attack. The measured items were (1) anodic polarization curve, (2) polarization resistance, (3) resistance of material, and, (4) potential. Also, the meanings of the measured values were investigated. The conclusions were as follows ; (1) Using resin as coating materials for concrete as well as for steel bars, electrochemical properties of the embedded steel bars were improved. The properties, however, were getting worse gradually. (2) Concrete mixed with blast furnace slag cement showed excellent properties among the concrete used. (3) There were many difficulties in evaluating the measured values, especially the potentials.
Form release agents are applied to the form contact surfaces to prevent bond and thus to facilitate stripping. Experiments have been performed to clarify the performances of form release agents that are made for the experience. Tests for following items are performed : (1) Maximum compressive loads applied at a steel core embedded in concrete. (2) Maximum tensile loads applied at the form vertically. (3) The compressive strength of mortar which contains release agent. (4) Chemical analysis of the cement paste which is in contact with form release agent. (5) Distribution of the bubbles at the concrete surface which was contact with a form. Based on the limited number of test, several oils and aditional agents are recommended.
The pore solution compositions of motar specimens which were made by changing reactive aggregates, water-cement ratios, and alkali contents were investigated. The specimens were stored under the open (non-sealed) environment like mortar bar methods (ASTM C 227, JIS A 5308). Then the pore solution compositions were compared with those stored under the sealed condition. At the same time, the restrained expansions of motar specimens which were made by same mix proportion and stored under the open condition were measured, and we correlated the expansions with the pore solution compositions. The following results were obtained : 1) The pore solution compositions of open stored mortar specimens were the same composition as those of sealed stored mortar speciments. 2) Alkali ion and hydroxide ion concentrations in pore solutions of open stored mortar specimens rapidly decreased with the passage of time, however the pH did not decrease less than 12 even at 6-months age. 3) Alkali ion and hydroxide ion concentrations in pore solutions showed good correlations with the expansion.
To investigate the long-term alteration behavior of concrete, two ways of experiments were conduced. First, the analytical techniques were proposed on the experimentally synthesized hydrates. The thermal analysis, chemical analysis and analytical electron microscopy were taken on the several mixtures of hydrates, and the reliability of these methods were confirmed. Next, these evaluation methods were applied on the concrete structures deteriorated by sea water, by alkali-aggregate reaction or by neutralization. The sea water erosion and alkali-aggregate reaction are more destructive than the neutralization, though the well-manufactured concrete structure is proof against the various expected environmental conditions even its hydrated phase was completely carbonated.
It is possible to predict detectable defects diameter in the inner parts of mortar and concrete, from relations between echo-height from defect and scattered echoes from both fine and coarse aggregates ; the relations can be evident by making use of a longitudinal probe with a central frequency of 1 MHz and a double crystal probe with a 1 MHz. An A-scope has been generally used for ultrasonic testing (UT), whose users need the technical knowledge and experience for interpretation or analysis of the echoes received. If the imaging of defects is realized by the B-scope, users of the UT do not need the technical knowledge and experience. The joint reseachers have succeeded in imaging defects and embedded bars by the use of the B-scope.
Trial underwater concretes were prepared by mixing ultra high-fineness slag (Blaine area of around 14 000 cm2/g) with ordinary Portland cement (OPC). Strength development and segregation resistance properties of the concrete under the coexistence of some kinds of segregation controlling agents were studied for laboratory and concreting in site tests. As the results, the underwater concretes composed of the ultra high-fineness slag are found to be applicable to the actual use. The concrete's major features are (1) a good segregation-resistance property which leads to the reduction of the dosages of segragation controlling agents, (2) a good pumpability, (3) a high self-leveling property, and (4) good mechanical properties.
The facts that chlorides and sulfides fixed inside concrete are dissociated in the form of ions as carbonation progresses and migrate toward the interior of the concrete, an uncarbonated zone, so that parts of very high concentration are formed locally, and that alkali metal ions also migrate have been disclosed through area analyses by an electron probe microanalyzer. As a result of these analyses, it was shown that there is a possibility for deterioration of concrete structures to occur because the action of carbonation releases corrosive factors which had been fixed in the interior even in cases where penetration of corrosive factors does not occur from outside.
This paper discloses 1) that expansive properties due to alkali-silica reaction, diffusion properties of oxygen and infiltration properties of chlorine differ for the direction of concrete placement and the direction perpendicular to it, 2) that when the placement height of a lift becomes great, these properties will differ markedly between upper and lower parts of the lift even when placement is in the same direction. It is also pointed out that the causes of these ununiformities are 1) that continuous capillaries in the vertical direction and voids at the undersides of aggregate particles are formed due to segregation accompanied by bleeding immediarely after placement and 2) that the constitution of the concrete has greater porosity at the upper part due to rising of segregated water the greater the height of placement.
In principle, lap splices of large-diameter deformed bars in reinforced concrete are not acceptable. Accordingly, the main methods used in joining these bars are welded splices and many kind of mechanical connections. However, these methods are accompanied by problems about quality contorol, need for special skills, etc. To solve these problems, a lap splices with splint-bar reinforcement was developed. In this report, results of flexural and shear-flexural strucutal experiments on reinforced concrete members containing the joint method developed are explained. It was shown that beams or columns with short lap length possess sufficient strength and ductility for practical use.