Review on the Role of Ultra-fine Fly Ash on the Performance of Concrete

Fly ash is mainly the solid waste emitted by coal-fired fossil fuel power stations, which is collected through the flue gas emitted. At present, the comprehensive utilization of fly ash has been widely promoted and applied in actual production. The application of fly ash to concrete can not only improve the strength of concrete, but also save cement. However, its hydration rate is slow, and the incorporation of concrete will reduce the early strength of concrete. In order to improve the activity and other properties of fly ash, ultrafine fly ash with small particle size is obtained by grinding fly ash. Ultrafine fly ash has finer particle size than fly ash and larger spherical shape than original fly ash. Water demand decreases, density increases and activity increases. It can better fill the cement void, improve the internal compactness of concrete, and improve the interface structure of materials. Research has shown that adding 10% to 20% fly ash can achieve better performance than conventional concrete. For higher fly ash content, the strength decreases with the increase of fly ash content.