A Review of the Research on the Mechanical Properties of Ultrafine Fly Ash Recycled Concrete

Abstract

Fly ash is a solid waste from coal-fired power plants, and its massive discharge puts pressure on the ecological environment. Using fly ash in concrete can improve strength and reduce cement usage, but its early strength is relatively low. By grinding to produce ultrafine fly ash (particle size<10 μ m or specific surface area>600 m ²/kg), its activity can be significantly enhanced, the compactness and interfacial structure of concrete can be improved, and it has a certain water reducing effect. At the same time, the recycling of construction waste has also received much attention. Recycled aggregates replace natural aggregates to produce recycled concrete, which is both environmentally friendly and resource efficient. Research has shown that a moderate amount of fly ash (20%~40%) can improve the later strength and workability of concrete, but excessive dosage can lead to a decrease in performance. Ultra fine fly ash further optimizes the performance of concrete due to its finer particle size and higher activity. For example, adding 10% to 30% ultrafine fly ash can significantly improve compressive strength and enhance fluidity. In addition, adding ultra-fine fly ash to recycled concrete can delay slump loss and improve resistance to sulfate attack, but the carbonation resistance will decrease with increasing fly ash content. This review is systematically based on existing knowledge, discussing fly ash concrete and fly ash recycled concrete, and then focusing on the more advanced ultra-fine fly ash recycled cement, providing a comprehensive overview of its evolution and benefits.