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In order to establish durable design of concrete structures, to estimate the service life of the bridges and to obtain data indicating whether the prestressed concrete bridges need repair, the durability of 267 prestressed concrete bridges in service for ten to thirty years in north- east district of Japan was investigated. Furthermore, results of investigation in north-east district were compared with those of Kyushu district. Characteristics of the deterioration of respective parts of prestressed concrete bridge are described from the viewpoints of materials and structures. The results establish the influence of moisture on efflorescence and cracking of superstructures and the influence of frost damage as in snow and cold regions. Furthermore, effective countermeasures for improving durability of concrete structures are discussed and proposed.

At the early stages of development, RCD concrete often tended to be inferior in strength and durability to any other conventional dam concrete because RCD concrete had the properties of stiff consistency and lean mixture. In this research, a laboratory test was conducted to determine its optimum sand percentage, sand ratio and optimum mixture proportions in order to improve durability of RCD concrete. In addition, a field test was conducted to determine the optimum lift height and optimum compacting method. Furthermore, a new construction method was developed to improve durability of RCD concrete that any existing RCD concrete can be strengthened by casting one of the conventional types of dam concrete on the upstream or downstream slope of the dam. Hence the proposed method in combination with the recommended mixture proportions and construction method has enabled one to rebuild many of the dams and to keep then in serviceable condition for a long time.

The degradation of samples of cement pastes, mortars and concretes in acidic solutions (pH 2-4) ha s b een investigated over relatively short periods, e.g. -72 hours at 25°C. The degradation rate of the cementitious material is taken as the rate of alkali leaching at constant pH; the latter is obtained directly from the amount of acid required, as function of time, to maintain the pH at a preset value. The data allow the calculation of apparent rate constants, the magnitude of which is expected to be related to the durability of the materials investigated in acidic environments. Paste degradation rates were obtained at two W/C (0.35 and 0.45); the role of several additives (silica fume, superplasticizers, air entraining agents) and the influence of solution composition (pH, ionic strength, other electrolytes) were investigated. Kinetic data were also obtained for the acid reaction rate of several mortar and concrete samples of varying mixture compositions and in the presence of S0,-2. Under the conditions of this study, the acid degradation rate appears largely controlled by H+ diffusion through the leached zone of the matrix. The diffusional rates values are moderately influenced by changes in mixture compositions, in reasonable agreement with expectations from greatly enhance the acid degradation rate, an effect zone and the related studies. Sulfate ions which can be understood from pH gradients in the leached activity coefficients of the H+ in the presence of sulfates.

In this study, the applicability of the automatic temperature control method instead of the ASTM C 672 test, for the determination of the scaling resistance on various kinds of concrete specimens was examined, because the automatic control method will be profitable from the viewpoint of the elimination of labor such as the transfer of specimen in every required cycle. The scaling damage obtained from this modified method was almost equivalent to that of the conventional ASTM test method. Using this automatic method, the characteristics of scaling were investigated using the bottom or side surface of the specimen for the test surface instead of the conventional top surface. In addition, the effects of air content, water cement ratio, de-icing salts, curing condition and use of a permeable sheet were also studied. The relation between the mass of scaled-off particles and the visual rating was also obtained. Through the examination of the characteristics of scaling, the automatic temperature control method of modifying the conventional ASTM method was judged promising for assessing the scaling resistance in the presence of de-icer salts.

The durability of cement-stabilized specimens in various aggressive media were studied by means of the Koch and Steinegger test over 56 days at 20°C. Prismatic lxlx6cm samples of normal portland cement (OPC) and normal portland cement with 80% ground granulated blast furnace slag (OPC/BFS) addition, were prepared mixing them with water containing 5,000 ppm Pb2+ (OPC samples), 15,000 ppm Pb2+ (OPC/BFS samples) or 50,000 ppm Cd 2+. Those specimens were immersed in the aggressive solutions tested: a buffered AcH/Ac- medium, a NaCl 0.45M + Na2SO4 0.03M solution (SO4= and Cl- concentrations equivalent to those of the sea water) and deionized water as reference. In addition, the concentration of toxic metals in the aggresive media. was measured I Changes into microstructure and flexural strength were evaluated by X-ray diffraction (XRD) and mercury intrusion porosimetry (MIP). The pore fluid solution extracted from specimens and the leachate solutions were analyzed for Pb2+, Cd2+, Ca2+, Na+,K+, SO4 and Cl-ions. Results show that normal portland cement and blast furnace slag blended cements are durable matrices in saline medium similar to sea water, but undergo an acid attack with formation of a porous degradation coating and dissolution of toxics metals in the acid medium of AcH/Ac- buffer solution.