AbstractsThis paper describes the history and new trends in the development of chemical admixtures in Japan. PC (polycarboxylic acid)-based agents are the main products in the superplasticizer market. A low-stickiness type PC-based superplasticizer has been developed based on the conventional PC-based superplasticizer. The flowing speed of concrete with low stickiness type PC-based superplasticizer is faster than that with the conventional PC-based superplasticizer. By addition of a new viscosity agent consisting of a mix of anionic and cationic surface active agents, the three dimensional reticulation structures is formed in fresh cement paste and the viscosity of the cement paste can be increased and segregation can be prevented. The hydration of cement in sludge water is controlled by addition of a set-retarder, and the specific surface area of cement does not increase while a large amount of unreacted alite remains in the sludge water. Recycling of concrete at ready mixed concrete plants is possible without adversely influencing the properties of concrete when sludge water with the set-retarder containing gluconate salt is used. The slurry type and powder type calcium aluminate based accelerator (CA) and calciumsulfoaluminate based accelerator (CSA) for shotcrete have been developed. In the case of CA, the final setting time of the mortar is accelerated by increasing the dosage. By adding of CSA, both the initial and final setting times of mortar are shortened with increased dosages.
Fracture prediction and fatigue detection techniques in ceramic composites were examined. Composites with an electric conduction path were fabricated with ceramics having different electrical resistivity, using calcium fluoride powder as the insulating matrix and silicon carbide whiskers as the conducting additive. When a bending load was applied to the test piece, the electrical resistivity of the composites increased up to fracture. When the test pieces were repeatedly loaded below the fracture limit, there was a gradual increase of electrical resistivity before fracture. These phenomena suggested the possibility of predicting fracture and detecting fatigue in ceramic composites. The movement of whiskers disconnecting the conduction path and leading to an increase in electrical resistivity was confirmed by scanning electron microscopy observation.
Two-dimensional computer simulations were conduct ed on percolative structure in which second phases of various aspect ratios were arranged in a matrix phase. The second phases were randomly arranged in an array with two different computational programs; one pro hibiting an overlap among second phases and the other allowing the overlap. From the simulation prohibiting the overlap, it was predicted that a continuous path was formed at less amounts of the second phase with higher aspect ratios.In the simulation allowing the overlap, a continuous path throughout the array was formed by arranging the second phase of an aspect ra tio of 100 with less than 4% in the array. These results agreed well with the conduction path formation in hot pressed ceramic composites consisting of an insulator matrix and electrically conductive whisker additives.
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