Fly Ash for concrete admixture

Fly Ashis  the Tiny particles coming from the combustion of fuel (mainly coal). Its particle size is generally between 1-100μm. Also known as fly ash or soot. The fine solid particles in the ash content of the flue gas produced by the combustion of the fuel. Such as fine ash collected from flue gas in coal-fired power plants. The fly ash is formed by the coal powder entering the furnace at 1300～1500℃, after being subjected to heat absorption by the hot surface under suspension combustion conditions, and then cooled. Due to the effect of surface tension, most of the fly ash is spherical, with a smooth surface and small pores. Some of them are stuck together by colliding with each other in the molten state, and become honeycomb composite particles with rough surfaces and many corners. The chemical composition of fly ash is related to coal composition, coal particle size, boiler type, combustion conditions and collection methods. The emission of fly ash is directly related to the ash content in the coal. According to Chinese coal consumption, burning 1 ton of coal will produce about 250-300kg of fly ash. If a large amount of fly ash is not controlled or treated, it will cause air pollution, and it will block the river when it enters the water body. Some of the chemical substances cause harm to organisms and humans.

Fly ash mainly contains silicon dioxide (SiO2), alumina (Al2O3) and iron oxide (Fe2O3), etc., and has been widely used in the manufacture of cement and various lightweight building materials. In addition, fly ash can also be used as floating beads and as fertilizer and trace compound fertilizer. In industry, iron, carbon, copper, germanium and scandium can be recovered from fly ash. The density is 1.5 g/cm3.

Application

1. Fly ash can be used as an admixture for cement, mortar, and concrete, and becomes a component of cement and concrete. Fly ash is used as a raw material instead of clay to produce cement clinker, making sintered bricks, and autoclaved aerated concrete , Foam concrete, hollow bricklaying, sintered or non-sintered ceramsite, paving roads;

After fly ash is mixed into concrete, it can not only replace part of the cement, reduce the cost of concrete, and protect the environment, but it can also complement the short and long lengths of cement, balance and synergize, and improve a series of performances of concrete. Fly ash concrete has obvious technical and economic advantages. benefit.

Improve the workability of fresh concrete

The workability of fresh concrete is affected by the volume of the slurry, the water-cement ratio, the gradation, shape, and porosity of the aggregate. The obvious benefit of adding fly ash to fresh concrete is to increase the volume of the paste. A large amount of paste fills the pores between the aggregates, wraps and lubricates the aggregate particles, so that the concrete mixture has better adhesion. Cohesion and plasticity.

2. Inhibit bleeding of fresh concrete

The incorporation of fly ash can compensate for the lack of fines in the fine aggregate and interrupt the continuity of the bleeding channel in the mortar matrix. At the same time, fly ash, as a substitute for cement, will make the water consumption of concrete different under the same consistency. The degree of reduction, so the use of fly ash is beneficial to prevent bleeding of fresh concrete.

3. Improve the late strength of concrete

Experimental data show that after adding fly ash to concrete, as the amount of fly ash increases, the early strength (28 days ago) gradually decreases, while the later strength gradually increases. Fly ash has a three-fold effect on the strength of concrete: reducing water consumption, increasing cement content and increasing strength through long-term pozzolanic reactions.

Because fly ash has a huge specific surface area and strong adsorption capacity, the fly ash particles can absorb the alkali in the cement, and react with the alkali to consume its quantity. It can avoid alkali aggregate reaction.

4. Reduce the heat of hydration of concrete

Adding fly ash can reduce the amount of cement, and fly ash hydration heat is very small, thereby reducing the heat of hydration, so the temperature rise of concrete during construction is reduced, which can significantly reduce temperature cracks, which is suitable for large-volume concrete The project is particularly advantageous.

5. Improve the durability of concrete

Fly ash added to concrete has a great influence on its freeze-thaw durability.

6. Cost reduction

Adding fly ash can reduce the amount of cement by about 10% to 15% under the condition of the same strength level, thus reducing the cost of concrete.

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