The unburned organic matter of fly ash is mainly charcoal. We know that charcoal has strong adsorption, which is why the undisturbed ash is commonly known as unified ash, that is, ash that has not been sorted. The carbon content of this ash is relatively high, and the adsorption of admixtures is very high. The adsorption of fly ash can be compared through cement and fly ash pure slurry test and loss over time. In the process of concrete production, it can be solved by adjusting the proportion of fly ash and adjusting the amount of admixtures.

Studies have shown that the finer the fly ash, the higher the activity, the activity contribution rate of the particle size below 10 microns is 100%, and the particle size above 100 microns is basically inactive, and it only has a filling effect and a morphological effect in concrete. Therefore, if we want to exert the pozzolanic effect of fly ash in concrete, we must try to use high-quality fly ash. If we use fly ash only to improve the workability of concrete, fly ash of lower quality can be used. In concrete production, if the fly ash is too fine, we should pay attention to whether the water consumption of concrete increases, whether the adsorption of admixtures increases, etc., and adjust in time to ensure the fluctuation of the state and final strength of the concrete.

Side effects of fly ash production process

Fly ash was first classified into different grades of ash. With the development, in order to increase the benefits of fly ash, the power plant has obtained more high-quality ash by grinding the system ash. The ground ash cannot be used because the spherical structure of the fly ash is destroyed and the workability of the concrete is improved, but in fact it is the opposite. The spheroid is ground into several small spheroids, which basically does not affect the improvement of the workability of concrete, and at the same time can increase more secondary chemical reactions and increase the strength.

Second, in order to increase the combustion value of coal-fired power plants, power plants often add oils and fats to the coal-fired coal to support combustion. However, it is the burning charcoal of these combustion-supporting oils and fats that exists in a large amount in the concrete, especially in the mixing plant using polycarboxylic acid admixture, the concrete produced is relatively serious with floating black ash. The fly ash sampled at the site can be put into a small bucket and water is added for stirring. If there is a lot of black ash of oil and grease, it means that the fly ash has a lot of combustion-supporting substances added, or the quality of the coal itself is not good.

In actual production, it can be solved by reducing the content of fly ash, reducing slump or adjusting the adaptability of admixtures, but the final solution is to solve the problem of fly ash material and solve the problem caused by excessive combustion-supporting substances. fundamental.

Third, in order to prevent sulfur and nitrate from polluting the air, the power plant will carry out desulfurization and denitrification treatment. Usually, urea and ammonia are cheaper to deal with, which is often improperly controlled, resulting in the occurrence of ammonia in concrete when it encounters water. Concrete bubbling releases ammonia gas, and concrete has a pungent odor. In the author’s experience, a similar situation occasionally occurred. The main body of a certain floor of a high-rise concrete was poured very late. When the workers went to work the next morning, many workers were choked by the inexplicable pungent smell and could not go to the construction. , there is no way to wait for the smell to slowly dissipate until about 10 am. There is also a more serious case. After the workers poured the concrete, the eyes of all the workers who poured the concrete the next day were damaged by some kind of gas stimulation to varying degrees. After investigation, the fly ash factory was poorly managed, and the ammonia substances used for denitration and desulfurization were investigated. accident caused by leakage.

Finally, the inspection of fly ash is very important. It is enough to control the fly ash by simply observing the color depth, adding water and stirring to see the color of the floating ash, and judging the quality of fly ash by sieving and analysis. quality. In the production process, a series of unfavorable problems caused by the quality decline of coal ash can also be solved by adjusting the mixing ratio. In the later period, contact the manufacturer to adjust the quality of the fly ash product and restore it to the normal state of use.

How to identify desulfurized ash?

Since desulfurization ash is a gypsum-based product formed by fine ash and calcium oxide in the soot, its appearance is lighter in color and more delicate in hand than fly ash. And because it contains calcium oxide, put it into a container, add water and stir, drop into the phenolphthalein solution to make it alkaline, and the phenolphthalein turns red. And because of calcium oxide (lime), the reaction between lime and water is an exothermic process, and the water temperature will rise. And because the main component is gypsum, this ash will harden in the air for a few days. Desulfurized ash is currently mainly used as a setting modifier for cement, but in many cases, fly ash suppliers also transport it to mixing plants and use it as “fly ash”. Using phenolphthalein test, this method can only identify whether it is desulfurized ash, but cannot identify whether this ash can be used.

Countermeasures for Retarding Concrete Structure Caused by Desulfurized Ash

If the concrete using desulfurized ash is retarded for more than 48 hours, the later strength may be reduced (the calcium sulfite content in the fly ash is different, and the impact on the strength is also different). To bear the load of this layer, but also to bear the load of the upper layers. After 28 days, the strength is not qualified and the reinforcement cost is higher.

If the amount of desulfurized ash is small and the retarding time of the concrete is not long, the project can wait for the concrete to be cured to 600 ℃·d, and use non-destructive testing such as rebound to identify whether reinforcement treatment is required. This requires technicians to carefully record the daily temperature to provide a reliable basis for calculating the ℃·d value.

Desulfurization ash that causes serious retardation of concrete should be removed from the warehouse as soon as possible, because this ash is very sticky and will harden over time, making it difficult to clear the warehouse.