The studies reported were concerned with the application of high-strength concrete to structural members as related to some aspects of their design, construction and behavior. With regard to construction, tests were performed on the consistencies and strengths of concretes of low water-cement ratios using superplasticizers. The superplasticizers used were the 5 brands being marketed in Japan. The influence on consistency of fineness of cement was also studied. In examinations made by design calculations, monorail piers were used as case studies. The relation between concrete strength and cross-sectional dimensions, and quality of reinforcing bars required when applying high-strength concrete to structural members were investigated. In structural tests, the stresses, bending strengths and ductilities of model piers using high-strength concrete were studied.

In order to consider the workability of superplasticized concrete, it is necessary first to evaluate rheologically the effect of a superplasticizer on fresh cement paste. The authors conducted a series of experiments measuring the resist-ances met by a sphere in motion at various constant speeds in cement pastes, and calculated their rheological constants. It is indicated that the rheological constant of a paste to which superplasticizer has been added is completely different from that of plain paste and also different from pastes with conventional chemical admixtures, and as a result, the superplasticizer can be rheologically defined. Further, in order to clarify the reason for the comparatively rapid slump loss after superplasticizing, the variations in rheological constants due to elapse of time after mixing of cement paste are measured, and it is found that when the addition of the superplasticizer is delayed, the increase in the yield value (rheological constant) is hastened, and it is thus substantiated that the rate of slump loss of concrete is increased when the timing of superplasticizer addition is delayed.

SP-68 A collection of 30 papers from 11 countries. Principal topics: water-reduced and high-strength concrete, physical and mechanical properties of concrete using superplasticizers, freeze-thaw durability, energy conservationand by-product utilization, slump loss and rheology, surface phenomena, and special applications.

Generally the flow of fresh concrete is assumed to represent distortion as a Bingham body. In this study, in order to clarify the effects of chemical ad-mixtures on the flow of fresh concrete, rheological values such as the plastic viscosity and yield value (shearing stress) of fresh paste and mortar with superplasticizer were experimentally investigated both with and without vibration, Four types of chemical admixtures, sulfonated naphthalene-formaldehyde condensates, sulfonated melamine-formaldehyde conden-sates, poly-condensed aromatic sulfonate and a conventional water reducing agent (modified lignosulfonate) were used, and various water/cement ratio, sand/cement ratio, and consistencies, with and without chemical admixture, were selected for the mix pro-portions of test samples. The apparatus used in this study was designed to conduct experiments on the rheological phenomenon of fresh concrete under vibration. The frequencies of vibration em-ployed were 0, 100, 120, 150 and 180 Hz with accelerations of 0, 2, 4 and 6g. The plastic viscosity and yield value of vibrating cement paste and mortar through which a sphere moves can be calculated from Stokes's law. The results obtained have provided useful in-formation for identifying the fundamental rheological properties of the plasticizing concrete.

Previous workers have shown that the air-void system in air-entrained concrete containing a superplasticizer tends toward larger bubbles. This effect leads to spacing factors larger than the 0.2 mm normally accepted as a requirement for durability. Nevertheless, concretes containing such admixtures generally have been found to be frost-resistant. The present work is an attempt to understand the reasons for durability when the accepted 0.2 mm spacing factor requirement is not met. The distribution of air-void sizes in air-en-trained concretes made with and without a naphthalene sulfonate type superplasticizer were examined, using a new microprocessor-based Rosiwal linear traverse apparatus. The individual chord intercepts available with this system were fitted to a zeroth-order logarithmic distribution function, and the parameters of the fitted function were related to frost resistance as tested for by ASTM: C 666, procedure A. Concretes containing the superplasticizer were frost-resistant, despite spacing factors in excess of 0.2 mm. The most frequently encountered chord lengths in superplasticizer-con-taining concrete did not change relative to equal slump refer-ence concrete.