Proportion of Various Materials in Foam Concrete Construction

1. Cement ratio

The main raw material of cemento espanso è cemento. Because foamed concrete is mostly cured at room temperature, e viene aggiunta una grande quantità di schiuma, these two factors determine its higher cement ratio. This is fundamentally different from aerated concrete. Due to the autoclaved aerated concrete, si basa principalmente sulla reazione di idratazione delle ceneri volanti e della calce ad alto calore e pressione per produrre gelificazione, and cement is auxiliary. Tuttavia, when foam concrete is produced at room temperature, the active micro-aggregate will not quickly produce hydration reaction, e la sua schiuma solida dipende ancora dall'effetto cementante del cemento. Perciò, the mixing ratio of foam concrete must be cement as the main body, e un elevato rapporto di cemento. In circostanze normali, the amount of cement should account for 50% A 100% della quantità totale di materiali secchi, E 50% should be the lowest limit for its normal temperature curing. Quando si versa in cantiere, la percentuale di cemento dovrebbe rappresentare più di 80% del totale dei materiali secchi. Per calcestruzzo espanso a temperatura normale con densità inferiore 600 kg/m3, la proporzione di cemento non deve essere inferiore a 70% del materiale totale. Quando la densità è inferiore 400 kg/m3, the ratio at room temperature should account for more than 90% del materiale secco totale, 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 (versando) 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. Tipi di cemento con elevata resistenza iniziale e tardiva (come il cemento Portland dual-fast) può opportunamente ridurre la percentuale di cemento, e i tipi di cemento con bassa resistenza finale o bassa resistenza iniziale dovrebbero aumentare la proporzione del cemento;

② Strength grade of cement. High-strength grade cement can reduce the proportioning amount, e il cemento a bassa resistenza dovrebbe aumentare la sua quantità proporzionale;

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. I requisiti di bassa densità o resistenza più elevata dovrebbero aumentare il rapporto di cemento, requisiti di alta densità o resistenza inferiore possono ridurre il rapporto di cemento;

⑤ Initial growth temperature. La temperatura di polimerizzazione iniziale dopo il versamento (versando) è inferiore (<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;

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⑥ Variety and activity of active micro-aggregate (mescolanza). L'uso di microaggregati ad alta attività può ridurre la percentuale di cemento (come scorie ultrafini), mentre l’utilizzo di microaggregati a bassa attività (come le ceneri volanti secondarie) può aumentare la percentuale di cemento.

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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. Generalmente, 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. Perciò, 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 (versando). There have been some reports and papers on room temperature foamed concrete with a large amount of fly ash (più di 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. Perciò, 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, forza, 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. Perciò, 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 (versando), 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, versando (versando) ) The more stable; considering the stability of pouring (versando), 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 (versando) stabilità, 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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