The principle of foam concrete
1. Formation of foam concrete
Foamed concrete is a new type of lightweight, heat-preserving, heat-insulating foam made by using a physical and mechanical method to prepare a foaming agent aqueous solution into a foam, then adding the foam to a slurry made of cement, water, etc., uniformly mixing, pouring, and curing. material. Because it contains a large number of closed pores, it shows good physical and mechanical properties, that is, light weight, heat preservation, heat insulation, sound insulation and other functions.
Foam is a dispersion system composed of small air bubbles, separated by a thin liquid film between the bubbles. Due to the surface tension of the liquid, the surface of the liquid has a tendency to shrink automatically, so the pure static liquid cannot produce a large amount of foam after being stirred. In a pure static liquid, two bubbles will join together without hindrance when they collide, and finally all the bubbles will burst. However, if a substance that can reduce the gas-liquid interfacial tension is dissolved in the liquid to form a critical layer that is different from other liquids in composition and has a certain mechanical strength, then when two bubbles collide, this The critical layer can be used as a "buffer layer" to prevent bubbles from bursting. The foaming agent liquid is blown by powerful high-pressure air to form a large number of independent bubbles with extremely strong surface tension.
2. The structure of foam concrete
The prepared foam is added to the slurry composed of cement, water, etc. and mixed uniformly to become a foamed concrete mixture, and the bubbles of the foam become bubbles that are separated from each other. The wall of the bubbles is composed of the particles of the foam slurry and water. The shape of the pores of the foam concrete is different from that of the aerated concrete. Instead of forming an ellipsoid, it will deform to become a polyhedron under the action of the capillary. The finer pores in the mixture are distributed more evenly and in size
The smaller the size, the higher the strength of the foamed concrete.
Raw materials of foam concrete
The foaming agent is a non-polluting strong foaming agent with good foaming ability and good affinity with water. It can produce a large number of uniformly divided independent and closed bubbles in the cement slurry. Stable foam sacs show strong three-dimensional tension and special toughness, support the foam cement slurry to maintain the original state of the pores before the final setting, and use mechanical pumps to transport without defoaming and collapse during construction.
The quality of the foam is identified by indicators such as toughness, expansion ratio and bleeding; the toughness of the foam is the characteristic that the foam will not be destroyed in the air within a specified time, and it is often determined by the sinking distance of the foam in a unit time; Foam ratio is the multiple that the volume of the foam is greater than the volume of the foaming agent aqueous solution, and the bleeding volume refers to the volume of the foaming agent aqueous solution produced after the foam is broken. When the foam quality meets the following indicators, it can be used to produce foam concrete: ①The sinking distance of the foam after 1h is not more than 10mm; ②The bleeding volume of 1h is not more than 80ml ③The multiple of the foam is not less than 20. Therefore, choosing a good-quality foaming agent combined with the correct construction process is a prerequisite for producing high-quality foamed concrete.
Cement is the main material of foamed concrete. Generally, ordinary Portland cement is the main material. The amount and grade of cement are different according to the concrete bulk density required by the design. Generally, the bulk density of foam concrete is 300～1200kg/m3. In common use, if the project requires higher cushion strength, the amount of cement and strength grade should be appropriately increased when the foam concrete is made, and a little medium sand should be added to meet the design requirements.
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