Factors affecting the amount of air-entraining agent
1. The impact of materials on air-entraining amount:
(1) The cement has large fineness and high alkali content, and the air-entraining amount is uniform. Reduced; at the same dosage, the air entrainment volume of Portland cement is greater than that of ordinary cement, slag cement, and pozzolana cement; the air entrainment volume is reduced by about 1%
(2) Adding fly ash or slag fine powder, Zeolite powder, etc., has a small air entrainment capacity;
(3) Coarse aggregate (referring to gravel) has a large diameter and a small air entrainment capacity;
(4) Natural sand entrainment The air volume is greater than that of artificial sand; the more particles of fine aggregate (referring to natural sand) with a particle size of 0.15-0.6mm, the greater the air entrainment volume;
(5) Pebbles have a greater air entrainment volume than gravel;
2. The effect of temperature on air entrainment volume: When the concrete temperature is high, the air entrainment volume is large. For every 10℃ increase, the air content can be reduced by 20%-30%.
3. The impact of stirring on the air entrainment volume: Mechanical stirring has a larger air entrainment volume than manual stirring; if the stirring time (3 minutes is appropriate?) is too long, the air entrainment volume will be small, and if the stirring time is insufficient, the air entrainment volume will also be small.
4. The influence of slump on air entrainment volume: The greater the concrete slump, the greater the air entrainment volume.
What are the factors that affect the fluidity of concrete mixtures?
1. The fineness modulus of the sand. The sand is coarse and does not flow. The sand is too fine and has low strength. Adjust it according to the proportion.
2. Water-cement ratio, type and amount of admixture; The agent must be compatible with the cement. A high dosage will cause bleeding easily, and a low dosage will not be effective
3. Air content. If the air content is too small, the concrete will die. If the air content is too high, the strength will be low
4. Admixtures, fly ash containing glass molecules can enhance fluidity, but the ability to improve strength is worse than mineral powder
There are many factors that comprehensively affect the performance of concrete, which must be coordinated Only by adjusting the ratio can the strength and workability of the concrete be well guaranteed
Factors affecting the frost resistance of the material
The water-cement ratio The water-cement ratio affects the various properties of concrete properties (strength, durability, etc.) are important factors. Under the same good molding conditions, the water-cement ratio is different, and the density and pore structure of the concrete are also different. As excess free molecules gradually evaporate during the hardening process of concrete, a large number of open pores are formed. The capillary pores cannot be completely filled by cement hydration products until they are connected with each other, forming a capillary connected system with this pore structure. The concrete has high permeability and water absorption, so it is most likely to be damaged by freezing. Therefore, when considering air-entraining agents, we must also consider the water-cement ratio. When the air content is the same, the radius of the bubbles decreases with the decrease of the water-cement ratio, the pore structure is improved, and the frost resistance of coagulation is improved. When the age and curing temperature are constant, the strength of concrete depends on the water-cement ratio and compactness. During the cement hydration process, the water-cement ratio has a direct impact on the porosity of the hardened cement slurry, and the change in porosity affects the compactness of the concrete, thereby affecting the pore volume of the concrete. At this time, the increase in pore volume is due to the enlarged and connected capillary pores of the concrete, which reduces the reserve pores that buffer frost heave pressure, resulting in greater expansion pressure after the concrete is frozen. Especially after being subjected to repeated freeze-thaw cycles, concrete will suffer severe structural damage. Therefore, in order to improve the frost resistance of concrete, the water-cement ratio must be strictly controlled. If necessary, manual intervention may even be required, such as adding air-entraining agents to implement "artificial hole creation." In terms of improving the frost resistance of concrete materials, there are two main technical means: one is to provide a buffer cavity for frost heave damage, and adding air-entraining agents is the most important basic means; the other is to enhance the frost heave resistance of the material itself, Control smaller water-cement ratio and higher compressive strength.
The penetration of air-entraining agents is controlled through dosage control. In addition to the dosage control of the air-entraining agent product itself, there are also other related admixture product dosage controls, because concrete construction projects During the construction process, admixture products are widely used, and there are many varieties, so we try to use them within a scientific range when using them. Xinxiang CITIC Chemical recommends that you try to test small batches at the beginning of use, because of different environmental humidity. Temperature will affect the performance of air-entraining agents and other admixtures. It will be more reassuring to test it, so as to better avoid the probability of problems during batch use
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