There are many factors that affect the activity of fly ash and are very complex. The main controlling factors include: chemical composition (mainly glass phase); glass structure; chemical and physical defects of the activation point in the glass (including those produced by grinding); water The role of the chemical reaction medium; the particle size distribution of the particles. The more processes on the fly ash production line, the finer the fly ash produced, and the higher the fly ash price. But in general, it can be divided into two categories; one is chemical, which mainly involves the number and composition of active substances that participate in and promote pozzolanic reactions; the other is physical, which mainly affects the hydration process and hardening of cement The cement stone structure formed later.
1. Chemical factors
Since the silica-alumina glass phase is the main source of the activity of fly ash, the factors that reduce the number of glass bodies, such as large loss on ignition and many crystalline phases, are unfavorable to the activity. In addition, in the composition of the glass phase, the roles of different elements are not the same. Oxides are the most common components in fly ash, and are also the main components of hydration products. However, under different age and temperature conditions, the degree and importance of oxides participating in hydration reactions are different. For example, iron can reduce the melting point of ash, which is conducive to the formation of glass microbeads. However, because iron oxide has an extremely poor ability to participate in hydration reactions, it is generally believed that excessive iron oxide content is not good for activity; a small amount of alkali metal oxides can promote hydration. The reaction is carried out, but when using active aggregate, the high content of potassium and sodium oxides in fly ash will promote the reaction of alkaline aggregate, thereby destroying the stability of concrete; a small amount of sulfur trioxide in fly ash has It is beneficial to the formation of hydrated calcium silicate and the formation of hydrated calcium sulfoaluminate (ettringite) that contributes to the early strength, but too much ettringite expansion will cause volume stability problems, so the content of sulfur trioxide should not be high at 3%.
2. Physical factors
The main factors affecting the activity of fly ash are particle morphology, microstructure and other physical factors. For different types of fly ash, the smaller the water requirement of the standard consistency, the higher the activity; the lower the carbon content, the higher the activity; the smaller the fineness, the higher the activity; in terms of particle morphology, spherical glass in fly ash The more, the higher the activity of fly ash. From the microstructure characteristic E, the fly ash with short-chain silicon-oxygen tetrahedral structure has higher activity.
The specific surface area of fly ash can reflect the particle composition and structure of fly ash to some extent. The finer particles of fly ash have a larger specific surface area; the calcium-rich glass body has a dense structure and a small corresponding specific surface area; there are many porous glass bodies. Holes, the corresponding specific surface area is large.
Post time: Mar-15-2022