PURPOSE:To easily and accurately judge the compatibility of coal ash with an air-entraining agent and to increase the efficiency of the coal ash when the coal ash is used as an admixture for cement and concrete. CONSTITUTION:Coal ash having a specific surface area of =2.5m2/g, preferably, =2.0m2/g of BET specific surface area is selected as an admixture for cement and concrete and then the selected coal ash is used as the admixture for producing cement and concrete. By this process, the amount of air-entraining in coal ash can be detected unconditionally and accurately. As a result, coal ash suitable for an admixture is obtained and accordingly a fly ash cement and a concrete which are admixed with the coal ash become obtainable.
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