tailieunhanh - Precast concrete materials, manufacture, properties and usage - Chapter 4

FLY ASH - Vật liệu này, còn được gọi là tro nhiên liệu nghiền thành bột hoặc PFA, là một sản phẩm của thế hệ điện từ đốt than nghiền thành bột. Đó là chủ yếu quan tâm đến những quốc gia có hình thức sản xuất điện, nhưng ngay cả ở một số nước không nhất thiết phải sử dụng ở khắp mọi nơi bởi vì chi phí vận chuyển. Nó có một hành động mang lại lợi ích trong nhiều ứng dụng trong bê tông tại chỗ xi măng pozzolanic (có hiệu lực dài hạn trong sự. | 4 FLY ASH This material also known as pulverised fuel ash or PFA is a by-product of electricity generation from pulverised coal firing. It is mainly of interest to those countries having this form of power production but even in some of those countries it is not necessarily used everywhere because of transport costs. It has a beneficial action in many applications in in situ concrete where its pozzolanic long-term cementitious effect in the presence of lime and water and exotherm control properties as well as its ability to give ordinary Portland mixes an improved sulphate resistance have been used to advantage. As far as precast concrete product properties are concerned these benefits are of little value because of early strength requirements generally small sections being cast and good compaction respectively. What is of interest to the precaster are the following questions a Does the addition improve the early 0-10 minute old handling properties b Does the addition improve the early strength 6-18 hours old c Has the product better surface appearance and arrisses d How are other relevant properties affected e Does one get less wear and tear on machinery and plant This chapter divides into several parts the first part dealing with a description of fly ash and the remaining parts dealing with specific process studies of applications researched by the author. There is one matter to note before proceeding however and that is a criticism constructive of the terminology cement replacement . Depending upon how one defines the control mix the mix not containing fly ash any addition of ash to the mix is a replacement of the cement and or the aggregate. The only factor that is of interest is that of the concrete being Copyright Applied Science Publishers Ltd 1982 economical to produce as a function of materials price the total cost of production and the number of rejects. PROPERTIES OF FLY ASH Fly ash is a light slate grey to dark grey or brown powder extracted from .