Foam concrete is a chemical or physical method that introduces air or nitrogen, carbon dioxide gas, oxygen, and other gases into the concrete slurry according to the application requirements. After reasonable curing, it forms a large number of small closed pores and has considerable strength. This article discusses the physical production of foam concrete, and the principle is that the foaming agent and water are mixed into a foaming solution in a particular proportion, which is foamed by a foam concrete machine. Then the foam is added to cement, blended with pulverized coal. In the mud made of ash or other materials, a cement slurry containing a large number of closed pores is prepared by stirring, and after specific curing molding, a lightweight concrete product is finally formed.
Foam concrete products have the advantages of a lightweight, heat insulation, fire resistance, convenient construction, etc. Due to the large number of small micro-bubbles, the density of lightweight concrete products is small, and the density is often 300-1200kg/m3, which generally reduces the self-weight of concrete products. 25% or so; at the same time, a large number of closed microbubbles, with good thermal performance, with thermal insulation, its thermal resistance is about ten times that of ordinary concrete, so foam concrete as a high-quality building insulation material A wide range of applications.
Through the observation of the foam concrete production process, the following problems mainly exist in the lightweight concrete mixing:
(1) Foam and gelling material mixing problem
Foam concrete with a density of about 200-300kg/m3, the total volume of foam can account for 70%-80% of foam concrete, while cement and other cementitious materials have high density and small foam density, and the density of the two varies greatly. It will float on the aqueous solution of the cementitious material, and the two will not be easily mixed.
(2) Aggregate and slurry separation problem
When making some special foam concrete products, it is necessary to add a certain amount of aggregates in foam concrete, such as EPS particles, ceramic particles, perlite, and other materials. These aggregates are small in density, brittle, and difficult to be mixed with cement slurry. Mixing, if it is unevenly mixed with the cement slurry or the amount is different, the aggregate and cement slurry will produce segregation during the mixing process or the subsequent conveying process, resulting in poor concrete strength and even scrap.
(3) Bubble breakage problem
A key point in the production of foam concrete is the proper application of foam. Only rich and delicate foam can be used to make high-quality foam concrete. However, in actual production, in addition to the foam quality of the foam, the foam will be mixed with the concrete slurry. The stirring action destroys it, so the time that the foam participates in the stirring must be strictly controlled. If the stirring time is short, the foam and the mud are not sufficiently mixed, the stirring time is long, the foam loss is large, the concrete collapses seriously, and the density of the concrete product cannot be guaranteed.
(4) Mixer wall contamination problem
Compared with ordinary concrete mixing, foam concrete is more likely to stick to the wall. There is a dead angle between the mixing arm and the mixing drum in the mixing machine, the light material throws the sticky wall, the host discharge is insufficient, and the mud remains agglomerated. After a period of accumulation, it will be concentrated in the mud in the later stage, and it will easily sink and cause the bottom foam to rupture and cause the collapse phenomenon after pouring.
2 Treatment plan
After a long-term exploration of foam concrete production, summed up the experience and lessons, if you want to mix high-quality foam concrete, you need to check from the following points:
(1) Choosing the right mixing equipment
Most of the foam mixing equipment on the market uses a horizontal mixer, and the horizontal mixer is divided into a single-shaft mixer and a two-shaft horizontal mixer. The single-shaft mixer stirs smoothly, the foam is not easy to break, but the mixing speed is slow, and the stirring efficiency is low; the mixing speed of the mixing materials of the twin-shaft mixer is fast, the stirring efficiency is high, but the stirring is relatively intense, and the foam breakage rate is high. The two mixing main engines have their characteristics. Considering the production efficiency problem, the twin-shaft mixing main machine is selected. To minimize the damage to the foam, it is necessary to select a suitable stirring speed for the twin-shaft mixing and configure the inverter for the equipment. The frequency conversion of the stirring speed is verified by practice. When the stirring speed of the main machine is about 25r/min, the concrete can be stirred.
(2) The internal structure of the mixer
In the actual production process of the foam, in the early stage, the cementing material is mixed with water. The material of the stirring stage is characterized by fine and vicious, strong, cohesive force and difficult to disperse; then the foam is added to the foam concrete mixing stage, and at the moment of adding the foam, Due to the low foam density and strong buoyancy, it is difficult to mix with the viscous cement slurry, so the mixer is required to force the kneading action. The internal structure of the mixer producing foam concrete should be different from the ordinary concrete mixer. It is necessary to arrange the position and angle of the mixing arm reasonably so that the mixing force is mainly based on the mixing, taking into account the cutting, not only making the cement slurry and the foam evenly mixed but also reducing the cement. With the slurry and the slurry, the twin-shaft mixer has advantages in terms of mixing efficiency and enhanced mixing. At the same time, the internal structure of the mixer is to avoid the problem of dip. The gap between the mixing arm and the mixing drum should be as small as possible. The bucket door should be designed at the lowest point of the mixing drum, and the size should be moderate. Because the fluidity of the foam concrete is better, the bucket door is too. The small club will leave more dead ends, and it will take a lot of effort to seal the door.
(3) Feeding sequence
Through actual production, it is also found that the order of material addition has a great influence on the stimulating effect. If cement is added first, or water and cement are added at the same time, it is easy to cause agglomeration, slurry or pulp, because cement and other gelation When the material is in a semi-dry state, the possibility of getting on the mixing drum or the stirring arm is greatly improved. It is more difficult to stir it evenly, and the uniformity of the cement slurry itself is deteriorated, thereby affecting the lightness of the next step. Stirring production of quality concrete. According to the experience of on-site mixing, add a certain amount of water according to the ratio, and then add cement, fly ash additive, etc., and then add foamed foam after mixing evenly, so that it is not easy to produce agglomeration, and the mixing speed of foam and mud Fast, the mixing efficiency is also very high.
(4) Selection of foaming agent
In addition to the above points, stirring high-quality foam concrete requires good foam stability, so choose a good foaming agent. Although the foaming agent is used less for other materials, it is produced. The key link of foam concrete. The foam produced by the good quality foaming agent has a tough liquid film and good mechanical strength and is not easily broken or excessively deformed under the squeeze of the slurry. Besides, it has self-water retention, and the moisture on the liquid film is not easily lost under the action of gravity and surface tension. The thickness and integrity of the foam liquid film can be maintained for a long time so that the foam can be broken for a long time. At the same time, the liquid film is not easily broken in the slurry body, and it is difficult to form a communication hole. Besides, the cementitious material is the main source of foam concrete strength. The foam obtained by some foaming agents has excellent stability. Still, after adding the cementing material, it will reduce the strength of the concrete and even lose the strength, so it is also necessary to use the prepared foam. The foaming agent that does not adversely affect the cementitious material.
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