The influence of foaming agents for concrete on the quality of foamed concrete is exceptionally critical. A right cement foaming agent can make high-quality, foamed concrete. There are many types of cement foaming agents. We focused on the kinds of glue chemical foaming agents and their application fields.
The foam produced by Tongrun's animal protein cement foaming agent has excellent stability and can be used in low-temperature environments. The height of one-time pouring is more than twice that of similar cement foaming agents. It is an indispensable foaming agent for foam concrete for cast-in-situ wall and wallboard. Many experiments have found that the foaming performance of animal-based foaming agents is better than that of foaming agents of the same level, with long stabilization time, fine foam, and low moisture content of the foam. It is an indispensable material for making high-quality foamed concrete.
Lightweight concrete high-performance foaming agent method
First, the more uniform the foam, the better, the bubble diameter should be the same size
The narrower the ideal pore size distribution of the stomata is, the better, that is, the pore size of the stomata is required to be as consistent as possible, and the difference should not be too significant. The corresponding requirement is that the foam should be uniform and not different in size. The bubble diameter of the foam cannot be the same but should be similar, the range of bubble diameter should be as small as possible, and the difference between the maximum bubble diameter and the minimum bubble diameter should not be too significant. The pores formed by the foam are uniform, which can prevent the compressive stress from concentrating at the giant cells and reduce the compressive strength. If the size of the foam is uneven and the weight is focused on the giant bubble, it is straightforward to cause it to become a weak link, and it will crack first under pressure.
2. The higher the foam stability, the better, and the longer the stabilization time, the better
Foam with excellent stability has a tough liquid film and good mechanical strength, and it is not easy to be broken or deformed excessively under the squeeze of the slurry. Also, it has self-water retention, and the water on the liquid film is not easy to be lost under the action of gravity and surface tension. It can maintain the thickness and integrity of the liquid film of the foam for a long time so that the foam can stay for a long time without breaking.
There are three effects of foam stability on stomata:
One can make most of the foam do not disappear after the initial setting of the slurry is fixed in the foamed concrete to form air holes. Poor foam stability, most or a small part of the foam burst after pouring, the formation of few pores, and even soon after flooding, the slurry collapsed, which is commonly known as mold collapse, resulting in complete casting failure.
2. Foam with excellent stability, the slurry is not natural to deform too much under extrusion, there is a specific resistance to pressure to keep itself approximately spherical, and can eventually form spherical pores with good pore shape;
3. Foam with excellent stability, the liquid film is not easy to rupture in the slurry, and it is difficult to form the communication hole created by the gas through the rupture. Therefore, it finally builds the ideal closed-hole—the worse the foam stability, the fewer closed cells, and the more connected cells. Thus, the balance of the foam should not be based on the standard of not collapse only after pouring, but should be found on the three indicators of non-collapse after pouring, the stomata formed approximately spherical and disconnected from each other.
We know that any cementing material, including cement and magnesite, has an initial setting time, especially for the most widely used ordinary portland cement, which is mostly delayed by 45 minutes. If the foam has poor stability, glue, and other cementitious materials have not yet set, and the foam has collapsed, the foam will not be able to form pores in the concrete. In general, the minimum requirement for foam stability is to make the foam stabilization time longer than the initial setting time of the gelling material by 10-20 minutes. Because the initial setting time of various gelling materials is not consistent, the requirements for foam stabilization time are also different. In general, the foam stabilization time for fast gelling materials can be shorter, and the foam stabilization time for slow gelling materials should be as long as possible. Even if the same kind of gelling material has a different temperature, its initial setting time is different, and the change is quite significant. For example, ordinary silicon cement may set in less than 40 minutes in summer, and it will not set in 80 minutes in cold winter below 5 ° C. Therefore, it is impossible to have a uniform specific standard for the stabilization time of the foam, and it should be determined according to the situation. To adapt the foam to the needs of various conditions of use, it should be allowed to stabilize as long as possible. In general, the stabilization time of the foam should meet the following requirements;
1. When used in Portland cement without setting accelerator, the stabilization time should be more than 60min; the ideal maximum is more than 3h;
2. When used in fast-setting cement such as sulphoaluminate cement, high alumina cement, iron aluminate cement, fast setting Portland cement, the stabilization time should be more than 30min, preferably more than 60min;
3. When used in magnesium cement, the foam stabilization time should be higher than 40min, preferably higher than 80min;
4. When used for gelling materials doped with a large amount of filler or active waste residue such as fly ash, the foam stabilization time should also be extended. The more significant the amount of padding or active waste residue, the longer the foam stabilization time.
The specific foam stabilization time should be determined through a small test. The principle is that the mold does not collapse after pouring, the pores are not connected after formation, and the policy of excessive deformation is not determined. The significant law is that the longer the stabilization time, the better.
3. The larger the bubble diameter, the better. It should be above 1mm.
The pores have the same requirements for the pore size, as well as the requirements for the bubble diameter. Many producers and some experts have misled the pursuit of a fine foam with a pore size of 0.1mm. It is because physical foaming cannot make a foamed concrete if the foam diameter is large and the foam stability is poor. The same raw materials and formula, the same equipment and technology, only change the foam diameter, the compressive strength of foam concrete with 1mm foam diameter is at least 20% higher than that of foam concrete with 0.1mm foam diameter. Therefore, it is wrong to pursue a large bubble diameter of more than 0.1mm, which is a misunderstanding in the production of foam concrete and should be corrected.
Fourth, the lower the foam bleeding rate, the better, avoid using milky foam.
As mentioned earlier, foams are divided into milky foams with more water and less foam and creamy foams with more water and less foam. The milky foam is unqualified and inferior and cannot be used.
After the foam is confident, it gradually exudes water. Its bleeding includes two parts:
1. Bleeding of foam liquid membrane. This part of the water is secreted from the liquid film. It is the water that the liquid film emits under the combined action of gravity drainage, surface tension drainage, and fluid membrane destruction drainage. The thicker the liquid film of the foam, the higher the bleeding; the faster and more the foam collapses, the higher the bleeding.
2. Inter-bubble water between foams. This part is water that does not form a bubble liquid film. The worse the foaming performance of the foaming agent and the foaming machine, the more inter-bubble water cannot create a foam liquid film. They are water that does not become air bubbles.
When the bleeding rate of the foam is very high, it will be as thin as floating juice, flowing randomly and cannot be piled up, and the amount of water in the foam is large. When this foam is added to the cement slurry, the cement slurry becomes very thin. Still, the foam is minimal, the volume of the mud is small, and the density of the foamed concrete is very high, which is not technically desirable.
Therefore, milky foam cannot be used. The appearance of the foam that meets the technical requirements should be sponge-like fine vesicles, piled up like white clouds and like bouncing cotton, and will not flow randomly. The water content of this foam is minimal. The foam liquid membrane bleeds little, the foam is not comfortable to rupture, there is little water between the bubbles, and the amount of bubbles is significant, and most of the volume is bubbles. What needs to be emphasized here is that the sponge-like foam must be small bubbles with a bubble diameter of less than 1mm, not large bubbles of several millimeters or even tens of millimeters. Giant bubbles are easy to pile up, and they are like white clouds, but because the bubble diameter is too large, it is also unqualified.