What is fly ash loss on ignition?
Fly ash is fine ash produced during the combustion process of coal-fired power plants and is widely used in building materials, cement admixtures and other fields. andFly ash loss on ignitionIt is one of the important indicators to measure its quality and directly affects its engineering application performance. This article will introduce in detail the definition, influencing factors, detection methods and related standards of fly ash loss on ignition.
1. Definition of fly ash loss on ignition
Fly ash loss on ignition (LOI) refers to the mass percentage lost after complete combustion of combustible substances and volatile matter in fly ash at high temperature (usually 950℃±25℃). The higher the loss on ignition, the more unburned carbon content or impurities in fly ash, and the worse its quality.
2. Factors affecting the loss on ignition of fly ash
Loss on ignition is mainly affected by the following factors:
| Influencing factors | Specific instructions |
|---|---|
| Coal burning type | Different coal types have different combustion efficiencies, which affect the content of unburned carbon. |
| combustion temperature | Insufficient combustion temperature results in incomplete combustion of carbon. |
| Collection method | The collection efficiency of electrostatic precipitator or bag dust collector affects the purity of fly ash. |
| Storage conditions | Long-term exposure to humid environments may cause fly ash to absorb moisture and gain weight. |
3. Detection method of fly ash loss on ignition
The detection of loss on ignition usually refers to the national standard "GB/T 176-2017 Cement Chemical Analysis Method". The specific steps are as follows:
| step | Operation content |
|---|---|
| 1. Sampling | Take an appropriate amount of fly ash sample and grind it to uniform fineness. |
| 2. Drying | The samples were dried at 105°C ± 5°C to constant weight. |
| 3. High temperature burning | Place the dried sample into a muffle furnace at 950°C ± 25°C for 1 hour. |
| 4. Cooling and weighing | Take it out and cool it, weigh it, and calculate the mass loss percentage. |
4. Relevant standards for fly ash loss on ignition
According to "GB/T 1596-2017 Fly ash used in cement and concrete", the loss on ignition limit of fly ash is as follows:
| Fly ash type | Loss on ignition limit (%) |
|---|---|
| Grade I fly ash | ≤5.0 |
| Grade II fly ash | ≤8.0 |
| Grade III fly ash | ≤15.0 |
5. The impact of loss on ignition on the application of fly ash
Excessive loss on ignition will cause the following problems:
1.Reduce concrete strength: Unburned carbon will absorb the water-reducing agent and affect the workability and strength development of concrete.
2.Increase water demand: The porous structure of carbon particles will absorb more water, resulting in increased water demand for concrete.
3.Affects durability: High carbon content may cause concrete to carbonize faster and reduce durability.
6. How to reduce the loss on ignition of fly ash
1.Optimize combustion process: Improve coal combustion efficiency and combustion temperature, and reduce the generation of unburned carbon.
2.Improve collection system: Use efficient dust removal equipment to reduce the mixing of impurities.
3.sorting processing: Remove high-carbon particles through air separation or flotation.
By controlling the loss on ignition, the quality of fly ash can be significantly improved, allowing it to play a greater role in the field of building materials.
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