Cement foaming agents are mainly used for making lightweight foam concrete products such as CLC blocks, thin partition boards, foamed cement insulation boards, foamed cement ground roadbed toilet backfill, and roof insulation. Because of its lightweight, heat insulation, heat insulation, fast construction, time and labor, and labor and cost reduction, it has been widely promoted in the market.
The foaming agent for lightweight concrete is an essential material for making foamed cement.
The foaming agent for cement is an admixture that can reduce the surface tension of the liquid and produce a large amount of uniform and stable foam, which is used to produce foamed concrete. The cellular concrete foaming agent is a kind of substance that can cause its aqueous solution to generate a large amount of foam when mechanical force is introduced into the air. This kind of content is a surfactant or a surface-active material. The essence of the foaming agent is its surface activity. Without surface activity, it cannot be foamed, and it cannot be a foaming agent. Surface activity is the core of foaming.
The foaming agent in a broad sense and a narrow sense
There are two types of blowing agents. One is a broad-spectrum foaming agent, and the other is a narrow-scale foaming agent. In the broad sense, a foaming agent refers to all surfactants or surface-active substances whose aqueous solution can produce a large amount of foam when air is introduced. There are no strict requirements on the technical properties such as the expansion ratio and the stability of the foam. It only indicates that it has a particular ability to generate a large number of foams. It is not clear whether the produced foams have practical uses.
The narrowly defined foaming agent refers to those that can not only produce a large amount of foam but also have excellent properties. It can meet the technical requirements for the foaming of various products and used to produce actual surfactants or surfactants. Its foaming ability is particularly strong, the foam volume per unit volume is large, the foam is very stable, it can not be defoamed for a long time. The foam is beautiful, and it has excellent compatibility with the use medium, such as cement.
Here we mainly introduce the narrow sense of cement foaming additives. The narrow sense of cement foaming agent is primarily divided into the following three aspects.
1 Surfactant cement foaming agent
Surfactants have good surface activity and are excellent reagents for preparing foaming agents. As amphiphilic substances, the physical and chemical properties of surfactants depend on their molecular structure. Under the same concentration conditions, the stronger the hydrophilic effect of the polar group, the more excellent the solubility of the surfactant in water, and the better the foaming performance; but because the surface film layer of the foam contains more water, the drainage speed is faster, and the foam is stable. Wanting sex. Also, because the properties of surfactants in concrete and their properties in aqueous solutions often differ significantly, the compatibility of surfactants and cement particles is an essential factor determining the performance of foamed concrete.
Rosin resin foaming agent is the earliest and most popular surfactant foaming agent. Its main varieties are rosin soap and rosin thermal polymer. The chemical structure of rosin soap is relatively complicated. It is an anionic surfactant. The production process is simple, and the cost is low. Its most significant advantage is that it has excellent compatibility with cement and can react with calcium ions in cement to form insoluble salts. It has foam stability. A specific strengthening effect, but the rosin soap needs to be heated and melted during use. Its foaming factor and foam stability are very general, which can be selected when the technical requirements of foam concrete are not high. The production of rosin thermal polymer is based on toxic phenol as raw material, and its performance is roughly equivalent to that of rosin soap. Still, its production cost and price are relatively high, and there are hidden safety hazards and environmental problems.
In recent years, people have been working on the research of the compounding of different surfactants. The research on the compounding of anionic and cationic surfactants has shown that the activity and viscosity of the compounding system are significantly improved compared with single-component systems. The active electrical effect can slow down the drainage speed inside the foam and increase the stability of the foam, thus denying the view that the anionic and cationic surfactants may be inactivated after compounding.
2 protein cement foaming agent
The foaming principle of protein foaming agents is the degradation of proteins. The cleavage of peptide bonds in protein macromolecules will generate easily soluble protein-small molecules. With the increase of protein-small molecules in solution, the number of hydrophobic groups gradually increase, which will reduce the surface tension and form the interface. Also, since hydrogen bonds are formed between special groups in the molecule, strong hydrogen bonding can ensure that the solution forms a strong foam liquid film so that the foaming agent generates a stable foam. However, protein foaming agents are susceptible to denaturation due to the external environment, such as temperature and acidity, which is an essential factor affecting the development of protein foaming agents.
Protein foaming agents can be generally divided into animal protein foaming agents and vegetable protein foaming agents. Animal protein foaming agents are usually made from keratin of cattle, sheep, and other animals as raw materials and a certain amount of reagents such as sodium hydroxide, magnesium chloride, and hydrochloric acid are added to it in proportion to a dark brown viscous liquid prepared at a specific temperature. Animal protein foaming agent has high foam strength, excellent stability, and other characteristics, and has been widely used in industrialized countries such as Japan and the United States.
Plant protein foaming agent is prepared from natural polymer materials through complex chemical changes. This foaming agent is usually a pale yellow transparent liquid, which is soluble in water and is hardly affected by water hardness. It is non-toxic, odorless, has strong foaming ability, and has lavish and dense foam. With the same amount of foaming stock solution, the foaming amount of the vegetable protein foaming agent is significantly better than that of the animal foaming agent. At the same time, the price of the vegetable protein foaming agent is lower than the animal protein foaming agent. This is why the most commonly used plant foaming agent is currently on the market.
Animal protein foaming agent and vegetable protein foaming agent can be mixed, which is also currently recognized as the best cost-effective foaming agent. The compounding of animal and plant foaming agents, on the one hand, reduces the cost of the foaming agent, on the other hand, it also solves the problems of the low foaming factor of the animal protein foaming agent itself, and the weak foam stabilization effect of the plant protein foaming agent. The compounding of the two protein foaming agents must be a way out of the current protein foaming agents. This is also one of the most popular blowing agents on the market.
3 protein-surfactant composite cement foaming agent
The protein-surfactant composite foaming agent further enhances its surface activity by changing the interfacial tension of the solution. The interface adsorption mechanism in the mixed system is mainly displacement and solubilization. Galvez-Ruiz et al. Studied the foaming effect of protein-surfactant composite foaming agents, and the results show that the situation at the interface between protein and surfactant can affect the stability of the foam. The more molecules of active agent adsorbed on the membrane, the stronger the elasticity and the higher the density. Therefore, the gas in the foam will not quickly diffuse through the liquid membrane to the outside, and the foam can exist stably for a long time. In China, people in the industry have studied the effects of alkyl benzene sulfonate and other substances on the foaming effect of foaming agents. Studies show that when 0.2 g of alkylbenzene sulfonate is added to 30 mL of foaming liquid. Both the liquid foamability and foam stability were significantly improved.
When the foaming factor was 16.7, and the foam stabilization time was more excellent than 3 h. In foreign countries, composite foaming agents were studied earlier. For example, liquid foaming agents composed of alkali metal sulfonic acid alkali metal salts and hydrolyzed protein developed in the United States and mixed foaming prepared by adding an appropriate amount of cationic surfactant in Japan. Agent. This type of foaming agent has stable performance, long foam-stabilizing time, and excellent compatibility with other media such as cement, but its current price is high. This is the reason that restricts the large-scale application of this type of cement foaming agent.
In summary, we analyzed the types of cement foaming agents in light concrete and their various performance characteristics. Different types of cement foaming agents have different application scenarios. You can choose a foaming agent with the highest cost performance according to the actual situation. If the requirements for foam are not high, you can choose a vegetable protein foaming agent. If it is a foamed cement finished product such as a light partition board or block, you can choose an animal foaming agents or animal and plant compound. Foaming agent to complete. At the same time, manufacturers of light foam concrete finished products are welcome to cooperate with them. Tongrun has been committed to the development and application of various additives for light foam concrete.