High calcium fly ash concrete is an important research direction in the field of green building materials. The application of high-calcium fly ash with industrial waste residue properties in the concrete industry can not only solve its difficult problem, but also reduce the energy consumption required for cement-based materials and reduce environmental pollution. As an ideal concrete admixture, high calcium ash has aroused the research and discussion of many domestic scholars. Li Xiaobing studied the effect of high calcium ash on the mechanical properties, impermeability and frost resistance of cement concrete by changing the content of high calcium ash. The test results show that the early strength of high calcium ash concrete has obvious advantages, and its impermeability and frost resistance are better than those of conventional concrete. Better results. Zhao Hui studied the influence of fly ash quality on various properties of concrete, and found that the compressive strength of high-calcium ash concrete is better than that of low-calcium ash concrete at the same age, and the anti-carbonation and chloride ion penetration effects are better. At present, the processing technology and technological innovation of high-calcium ash lag behind low-calcium ash, resulting in insufficient understanding of high-calcium fly ash. In order to explore whether high-calcium ash can be well used in the field of building materials, this paper mainly discusses its application in modern concrete based on the quality of high-calcium fly ash, construction key points and specific test cases.

1. Quality of high calcium fly ash

High-calcium fly ash is mostly powder collected from flue gases after lignite and sub-bituminous coal have been pulverized and burned. Its color is mostly light yellow or light gray. The higher the carbon content, the darker the color. Therefore, the carbon content of fly ash can be preliminarily determined from the color. In addition, compared with low calcium fly ash, high calcium fly ash has lower water requirements, higher activity, lower loss on ignition and self-hardening characteristics.

Because the calcium oxide content of high-calcium fly ash is ≥ 10%, the existence of high free calcium oxide content will bring problems such as poor volume stability to cement or concrete. The free CaO contained in it has a large expansion in the later stage of cement hydration, which inhibits the increase of concrete strength. Therefore, when using high calcium fly ash as a cement admixture or concrete admixture, the dosage should be well controlled, and the dosage should generally not exceed 20%. In addition, when using high-calcium fly ash, attention should also be paid to controlling its fineness, because the activity of high-calcium fly ash mainly comes from the glass bead particles inside it. In order to ensure that the activity of cement-based materials is not lost, In practical engineering, the sieve residue of 45μm high calcium fly ash is required to be controlled at 7% to 12%.

2. Construction key points of high calcium fly ash

2.1 Before construction

1) The carrying environment should be dried and waterproofed to ensure the dryness of the carrying environment; if the fly ash is not used for a long time, it should be placed in a sealed environment to prevent agglomeration.

2) Accurately calculate the quality of high calcium fly ash required for mixing concrete, preferably with a low water-cement ratio.

3) Before the high calcium fly ash is used, the relevant personnel should be arranged on site to test the fineness, loss on ignition and water demand of the fly ash used.

2.2 Under construction

1) After adding high-calcium fly ash, the concrete dry mix should be fully dry-mixed to ensure the uniformity of high-calcium fly ash in the dry mix. After adding water, the mixing time should also be longer than that of conventional mixed concrete. more than 30min.

2) When the content of high-calcium fly ash is too large, it will cause the concrete to be retarded, and the demolding time will be appropriately delayed.

3) Considering the instability caused by high calcium fly ash to the concrete, the maintenance process should pay attention to constant temperature and humidity.

2.3 Precautions for adding water reducing agent

1) Before adding the superplasticizer, its type should be determined to maximize the workability and durability of the high-calcium fly ash concrete, and the adaptability of the superplasticizer to the high-calcium fly ash should be tested.

2) On the basis of determining the design mix ratio and the type of water-reducing agent, the test personnel should determine the optimal water-reducing agent content through the test again to ensure the economy of concrete.

3. Conclusion

(1) The content of high calcium ash should be controlled in practical applications, generally not exceeding 20%, and it can be used with a reasonable water reducing agent.

(2) High calcium ash should ensure that the environment it is in is dry before use, and pay attention to constant temperature and humidity during the curing of the prepared high calcium fly ash concrete.

(3) The addition of high-calcium ash will cause slight retardation of concrete, and the loss of concrete strength is lower than that of low-calcium fly ash.