1. Cement ratio
The main raw material of foam concrete is cement. Because foamed concrete is mostly cured at room temperature, and a large amount of foam is added, these two factors determine its higher cement ratio. This is fundamentally different from aerated concrete. Due to the autoclaved aerated concrete, it mainly relies on the hydration reaction of fly ash and lime under high heat and pressure to produce gelation, and cement is auxiliary. However, when foam concrete is produced at room temperature, the active micro-aggregate will not quickly produce hydration reaction, and its solid foam still depends on the cementing effect of cement. Therefore, the mixing ratio of foam concrete must be cement as the main body, and high cement Ratio. Under normal circumstances, the amount of cement should account for 50% to 100% of the total amount of dry materials, and 50% should be the lowest limit for its normal temperature curing. When pouring on site, the proportion of cement should account for more than 80% of the total dry materials. For normal temperature foamed concrete with a density below 600 kg/m3, the proportion of cement should not be less than 70% of the total material. When the density is below 400 kg/m3, the ratio at room temperature should account for more than 90% of the total dry material, preferably 100%.
The low cement ratio must be based on the premise of ensuring product strength, and the cement ratio should be reduced on the basis of meeting product performance. It can be reduced as much as possible, and the stability during pouring (pouring) should be considered. Too low cement content is Will cause collapse. Can not deviate from the technical requirements to reduce the proportion of cement.
The cement ratio design should consider the following factors:
① The type of cement. Cement types with high early and late strength (such as dual-fast Portland cement) can appropriately reduce the proportion of cement, and cement types with low late strength or low early strength should increase the cement proportion;
② Strength grade of cement. High-strength grade cement can reduce the proportioning amount, and low-strength grade cement should increase its proportioning amount;
③ The quality of cement. For the famous brand new dry-process rotary kiln cement of large factories, the proportion can be appropriately reduced, while the proportion of cement with a large amount of vertical kiln cement or mixed materials should be appropriately increased;
④ Density and strength requirements of the product. Low density or higher strength requirements should increase the cement ratio, high density or lower strength requirements can reduce the cement ratio;
⑤ Initial growth temperature. The initial curing temperature after pouring (pouring) is lower (<25°C). The proportion of cement should be increased. When the initial curing temperature is high (25℃～45℃), the proportion of cement can be appropriately reduced. If steam curing or autoclave is used, it is still strong to reduce the proportion of cement;
⑥ Variety and activity of active micro-aggregate (admixture). The use of high-activity micro-aggregates can reduce the proportion of cement (such as ultra-fine slag), while the use of low-activity micro-aggregates (such as secondary fly ash) can increase the proportion of cement.
2. Active micro-aggregate ratio
When curing at room temperature, especially at low temperature, no active micro-aggregate should be designed or less designed in the formula, because it affects the initial setting of the slurry. If the dosage is large, it may cause collapse. In general, the addition of active microaggregates with a cement content of less than 10% has no major impact on coagulation and can be proportioned. In summer normal temperature production, the highest mixing ratio is about 30% of the cement. During steam curing, the highest mixing ratio is about 60% of the cement. The ratio is related to the type of active micro-aggregate. When using slag When powdered, the high value can be used; when the first grade fly ash is used, the middle value can be used; when the second grade fly ash is used, the lowest value can be used. When it is mixed with high efficiency reducer, it can also increase appropriately.
Foam concrete construction is generally not suitable for large-volume active micro-aggregates, because it is mostly constructed at room temperature, and there are many other factors that affect the stability of slurry pouring. Therefore, the maximum amount of active micro-aggregate should be designed to be less than 20% of the cement.
In consideration of cost reduction, many producers often want to use a large amount of active micro-aggregate, especially fly ash, which is still not enough to add 50% of the total proportion of dry materials, which is not feasible under normal temperature curing. It is difficult to guarantee stable pouring (pouring). There have been some reports and papers on room temperature foamed concrete with a large amount of fly ash (more than 50% of the total dry material ratio), but according to our experience, this is not easy to achieve at room temperature.
3. Lightweight aggregate ratio
Lightweight aggregates are characterized by high porosity and therefore high water absorption rates, low density and large volume per unit weight. Therefore, its addition has the greatest impact on the water absorption and density of the product, and also has a great impact on the thermal conductivity. When designing its ratio, the following points should be noted:
① It should not have much adverse effect on the water absorption rate of the product. It is best to choose light aggregates with low water absorption (such as waste polystyrene particles), and not use light aggregates with high water absorption (such as expanded perlite). When the water absorption rate of light aggregate is high, its proportion should be reduced, or it should be subjected to hydrophobic sealing pretreatment;
② It should be able to minimize the density of the product. When selecting lightweight aggregates, the lower relative density should be the first choice, and the lower is the best;
③ It is beneficial to reduce the thermal conductivity of the product. The lighter aggregate with the lower thermal conductivity is more preferable. It is recommended to use waste polystyrene foam plastic particles;
④ The proportion of lightweight aggregates should meet the requirements of product density, strength, and thermal conductivity as the standard. To achieve coordination and unity in these three aspects, one cannot only consider unilateral needs. The larger the proportion of light aggregate, the worse the strength, but the lower the density and thermal conductivity. Density and thermal conductivity require a larger proportion of light aggregates, while strength requires a lower proportion of light aggregates. This is a big contradiction in proportions. Therefore, these aspects should be coordinated and unified.
4. Heavy aggregate ratio
Foamed concrete with a density below 700 kg/m3 generally does not use heavy aggregates, which are mostly only used for high-density foamed concrete. The influence of heavy aggregate ratio on product performance and process is:
① The greater the proportion of heavy aggregates, the worse the stability of pouring (pouring), the more likely it is to cause heavy aggregates to sink and cause collapse; if heavy aggregates are not used or the proportion of heavy aggregates is smaller, pouring (pouring) ) The more stable; considering the stability of pouring (pouring), the proportion of heavy aggregate should be small rather than large;
② The larger the particle size of the heavy aggregate, the worse the pouring (pouring) stability, because the larger the particle size, the easier it is to sink; when designing the ratio, a smaller particle size should be selected while meeting the technical requirements;
③ The proper proportion of heavy aggregate is beneficial to improve the strength of the product. From the perspective of product strength, it is beneficial to mix a certain amount of heavy aggregate.
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