The Evaluation of Quality and the Effective Utilization of Fly Ash

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To find the effective usage of fly ash, Charasteristics of fly ashes, mechanical properties of fresh and hardened concrete, and frost resistance of concrete with various types of fly ashes produced in Japan were evaluated in this study.Test results are as follows.(1) Quality of fly ash depends on the type of coal , burning temperature in the furnace and its particle size. Irrespective of the type of fly ash smaller size particles contain more glassy content, less carbon content and more spherical particles. As a results, fly ash with particle size smaller than 25 m improves workability of concrete and pozzolanic activity of fly ash. Therefore it is suitable for mineral admixture in concrete.(2) The water-fly ash ratio of the water-fly ash slurry, which takes 20 seconds to flow out of P type funnel (W20), is an useful index to evaluate workability of mortar and concrete containing fly ash.(3) Concrete with air content of about 4.5% by volume, during casting, has good frost resistance even if strength of the concrete decreases with an increase in fly ash content. However, the frost resistance of fly ash concrete which is cast after agitating for 60 min. is remarkably low. This is due to air loss of fly ash concrete during agitating is significant.(4) Small air void in concrete is reduced by agitating. Therefore, even with the same air content, the spacing factor becomes larger compared with that of concrete cast immediately after mixing. When water-cement ratio is decreased, the spacing factor of concrete becomes smaller due to an increase in small air void.(5) Frost resistance of concrete can be evaluated by the spacing factor except for the case of no air-entrained concrete with fly ash.