STUDY ON UTILIZATION OF FLY ASH PRE-MIXED SAND AS FINE AGGREGATE FOR CONCRETE

－Examination on carbonation of concrete and storage period of the fine aggregate－

Abstract

 The harvesting of river and ocean sand, which are used as fine particulates in the manufacturing of concrete is restricted due to environmental safety concerns, which is why crushed sand is now used instead. However, crushed sand has problems stemming from its large fineness modulus. On the other hand, due to recent changes in social conditions, the ratio of thermal power generation in Japan has increased. Furthermore, for reasons involving the long-term stable supply of resources, it is predicted that the amount of coal-fired thermal power generation will continue to increase, and therefore the amount of fly ash (hereinafter “FA”) generated in the process will also continue to increase. For this reason, in consideration of the environment, measures must be taken to effectively utilize FA.
 One of two possible solutions to the problem mentioned above is to mix FA into the sand (hereinafter “FAS”) when mixing the concrete in order to supplement crushed sand’s insufficient amount of fine particles. We investigated about carbonation property of concrete using FAS by accelerated carbonation test and X-ray diffraction analysis. As a result, the following conclusions were drawn.

 1) When we compared carbonation depth and carbonation rate coefficient of concrete using the FAS and mixed sand, at the same water cement ratio, carbonation depth and carbonation rate coefficient were common to standard curing and atmospheric curing, and there was no pronounced difference.

 2) In 50% of water cement ratios, as a result of having examined the influence that a keeping period of the FAS gave to carbonation property, a keeping period was the comparison of the carbonation rate coefficient of concrete in seven days and 90 days and, as for the remarkable difference, was not admitted.

 3) About concrete after the accelerated carbonation test end as a result of XRD analysis, in the sample of the center, because quantity of Ca(OH)₂ was smaller than concrete using mixed sand, concrete using the FAS was able to confirm consumption of Ca(OH)₂ by the pozzolanic reaction of the FA. In addition, in samples of the surface sections, concrete using FAS had a smaller quantity of CaCO₃ than concrete using mixed sand.