To give full play to the pozzolanic activity, morphological water reduction effect and micro-aggregate filling effect of active admixtures and inactive admixtures, and improve the quality and performance of concrete, admixtures must have a finer particle size and larger than cement Specific surface area.
The average particle size of silica fume itself is 0.1-0.2 microns, and the specific surface area is greater than 15000㎡/kg. It does not require fine grinding. Other active and inactive admixtures require fine grinding or sorting to meet the requirements of concrete admixtures.
Processing procedure of concrete admixture
Raw material →Drying → Pre-crushing and grinding → Sorting → Stockpile → Transport
Tips: The key to the processing of concrete admixtures is grinding and sorting.
Main processing equipment
The specific surface area of concrete admixtures is generally above 400-450㎡/kg, or even higher (such as limestone powder and quartz powder with an intermediate particle size of 2-4μm, equivalent to 750㎡/kg). The specific surface area of cement is 330～380㎡/kg. Since the fineness of the admixture is finer than that of cement, there are two types of equipment suitable for the production of concrete admixtures:
Drying-Ball mill-Powder selection system
Vertical mill system
Which processing system should I choose when processing admixtures?
First of all, it is necessary to determine whether drying, pre-crushing or pre-sorting processes are required according to the type, particle size and moisture content of the admixture. Then according to factors such as the nature of the blended raw materials, the size of the particle size and the fineness of the finished product, a reasonable selection of the grinding and powder selection process and the type of the mill. Finally, the model and quantity of the equipment of the admixture grinding system are determined according to the type and production capacity of admixture grinding.
- Fly ash, desulfurized gypsum, phosphorous slag and other raw materials with an average particle size of less than 1 mm and a moisture content of more than 8% are suitable for fine grinding after drying using a ball mill and fine powder separator combined system.
- Slag, limestone, tuff and other raw materials with large particle size and moisture content less than 5-8% are suitable for vertical fine grinding system.
The vertical fine grinding system integrates drying, grinding and powder selection. Compared with the traditional drying-ball mill-powder selection system, it has the advantages of small area and low comprehensive processing cost. It should be preferred.
How to produce good concrete admixture
1, Choose qualified admixture raw materials
The raw materials of the admixture must first pass the radioactivity test, and try to choose the raw materials with high content of useful mineral components and low content of harmful substances such as moisture, soil, and chloride ions.
2, Choose fine grinding equipment with low energy consumption
For admixture materials with low moisture content such as slag, a vertical fine grinding system that integrates drying, grinding and powder selection can be used, and the power consumption is only 55-75% of the ball milling process. For example, the specific surface area of the same finely ground slag admixture is 450㎡/kg, and the power consumption of the ball mill system is 70-90KW/T, while the power consumption of the vertical fine grinding system is only 40-50KW/T. The vertical mill has obvious energy-saving advantages and accounts for The land area is small, so it is widely used.
3, Minimize the raw material cost of the admixture
The raw materials of the admixture should be obtained nearby and try to use nearby waste materials, such as marble scraps, limestone carving waste, broken ceramic glass, etc., to minimize the purchase and transportation costs of admixture raw materials.
4, Reasonably control the grinding and fine grinding of admixtures to reduce processing costs
Generally, raw materials that have been calcined at high temperatures, such as blast furnace slag, steel slag, broken glass ceramics and other raw materials, have a high cost of fine grinding. The specific surface area can be ground to 400-500m2/kg. If further grinding, the energy consumption is too high and uneconomical.
For easily-grindable admixture materials such as fly ash and limestone, in order to give full play to its pozzolanic activity, morphological water-reducing effect and micro-aggregate filling effect, the fine grinding specific surface area should be 550-750m2/kg.