Decrypt the Amount of Cement in Foam Concrete

2020-10-28 13:56:12

What are the raw materials of foam concrete?

The main components of foamed concrete are cement, fly ash, silica fume, fiber, etc. Some proportions have more cement content, and some proportions have less cement proportions, so specific problems must be analyzed in detail. Because foamed concrete is mostly cured under normal temperature conditions, and a large amount of foam is added, these two factors determine that its cement ratio will be higher.

What is ALC?

ALC is the abbreviation of autoclaved lightweight concrete, which is a kind of high-performance autoclaved aerated concrete (ALC). ALC board is made of fly ash (or silica sand), cement, lime, etc. as the main raw materials, and is cured by high-pressure steam to form a porous concrete sheet (containing processed steel reinforcement). ALC board can be used as wall material and roof panel. It is a new type of building material with superior performance. ALC board first appeared in Europe, and Japan, Europe and other regions have more than 40 years of production and application history. At present, the production technology and production equipment of domestic manufacturers are mainly imported from Japan and Germany.


Foam concrete is fundamentally different from ALC. Because ALC adopts autoclave, it mainly relies on the hydration reaction of fly ash and lime under high heat and pressure to produce gelation. Cement is an auxiliary material.

While foam concrete is produced at room temperature, the active microaggregate will not quickly produce hydration reaction, and its solid foam still depends on the cementing effect of cement. Therefore, the mixing ratio of foamed concrete must be cement as the main body, and high cement Ratio.

Under normal circumstances, the amount of cement should account for more than 30% of the total amount of dry materials, and 30% should be the minimum use amount for its normal temperature curing. When pouring on site, the proportion of cement should account for more than 60% 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 conventional proportion should account for more than 90% of the total dry material.

The following factors should be considered in the design of cement ratio:

(1) The variety 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 (such as 42.5, 52.5, etc.) can reduce the proportioning amount, and low-strength grade cement should increase its proportioning amount;

(3) The quality of cement. For large plants’ new dry-process rotary kiln cement, the mixing ratio can be appropriately reduced, while for small plants, shaft kiln cement or cement with a large mixing ratio 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.

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