The Evaluation of Quality and the Effective Utilization of Fly Ash

为了寻找粉煤灰的有效利用途径，本研究对粉煤灰的特性、新拌混凝土和硬化混凝土的力学性能以及使用日本不同类型粉煤灰的混凝土的抗冻性能进行了评价。测试结果如下：(1)粉煤灰的质量取决于煤的种类、炉内燃烧温度及其颗粒大小。无论何种粉煤灰，粒径较小的颗粒含有较多的玻璃质含量、较少的碳含量和较多的球形颗粒。结果表明，粒径小于25 m的粉煤灰改善了混凝土的和易性，提高了粉煤灰的火山灰活性。因此，它适用于混凝土中的矿物掺合料。(2)水-粉煤灰浆体从P型漏斗（W20）流出所需时间为20秒的水-粉煤灰比是评价含粉煤灰砂浆和混凝土和易性的有用指标。(3)掺量4.5%左右的混凝土，在浇筑过程中，混凝土强度随粉煤灰掺量的增加而降低，但仍具有良好的抗冻性能。而搅拌60 min后浇筑的粉煤灰混凝土的抗冻性很低。这是由于粉煤灰混凝土在搅拌过程中的空气损失是显著的。(4)通过搅拌减少混凝土中的小空隙。因此，即使在相同空气含量的情况下，与拌合后立即浇筑的混凝土相比，间距系数也会变大。当水灰比减小时，由于小空隙的增加，混凝土的间距因子变小。(5)除不掺粉煤灰的掺气混凝土外，混凝土的抗冻性可用间距系数来评价。

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.