Feature analysis of fly ash (FA) was carried out for five different FA (equivalent to JIS Class II) having varied levels of alkali-silica reaction (ASR) suppression effect. The purpose of this study was to identify the chemical and physical characteristics relating ASR suppressing effects. The equipment used was a scanning electron microscope (SEM) combined with, backscattered electron (BSE) detector, energy dispersive X-ray spectrometer (EDS) and electron backscattered diffraction (EBSD). Authors classified FA particles into six phases quantitatively by feature analysis and gave particle size distribution and specific surface area of each phase. The classified particles as mullite dispersed in Si-rich glass matrix showed a strong negative correlation with 14-day expansion of mortar bar evaluated by ASTM C 1260. Judging from the results obtained in this study, specific surface area of Si-rich glass accompanying mullite crystals is revealed to be the key for the ASR suppressing effect of FA.
This paper describes the method for quality control of the cementitious materials used in radioactive waste disposal facility in Japan. The influence of the fly-ash quality and the methods of the early-age curing on the fresh properties, mechanical properties and the effective tritium diffusion coefficient is investigated. In addition, the applicability of nondestructive test for quality control of these cementitious materials is also investigated. The test for the those investigation are done in the simulated actual conditions during construction and exposure environment of the disposal facilities. Test results indicate that the variability in the quality of fly-ash has no remarkable influence on the property of the cementitious materials in this case, and that the compressive strength can be calculated from the surface strength tested with the rebound hammer of the nondestructive test.
Three large size specimens composed of a combination type self compacting concrete in the range of slump flow 45-76cm were manufactured 21 years ago. The concrete was placed without compaction. These specimens have been exposed to nearshore for 11 years, after that, these were exposed to 20km inland for another 10 years. Then the authors measured the properties of the concretes such as strength, porosity, carbonation depth, and chloride ion diffusivity. As a result, the porosity of the concretes was almost constant depending on neither slump flow nor flow distance. Then, it was found that the combination type self compacting concrete was more durable than conventional concrete with the same W/C. Thus, the carbonation depth of the self compacting concrete was 15-80 percent and the chloride ion diffusion coefficient was 1-10 percent of conventional concrete, respectively.
This study focused on relationship between frost damage resistance and air-void system in concrete. Analysis using 200 concrete experimental data shows that entrained air content in fresh status tend to decrease during hardening process, which appears significant in concrete using fly-ash with moderate heat portland cement. As a result, correlation between durability factor representing frost damage resistance and entrained air content measured after hardening is higher than that measured in fresh status. This tendency is more remarkable in concrete using fly-ash with moderate heat portland cement than using normal portland cement. Spacing factor in concrete does not mean identical air-void size distribution as being affected by entrained air content and specific surface. Hence even with the same spacing factor values, concrete containing air void less than 0.15mm diameter tends to show better frost damage resistance.