There are many kinds of foaming agents used in foamed concrete, which can be summarized into four types according to their development stages: rosin soap foaming agent, synthetic foaming agent, protein foaming agent, compound foaming agent, etc.
The foaming agent of rosin soap is one of the earlier foaming agents, which mainly USES rosin soap and hot polymer as the main material. At first, it is mainly developed and applied as the aerating agent of concrete mortar, and later it is also used as the foaming agent of foamed concrete with expanded functions.Its production process is simple, low cost, foam multiple and foam stability is poor, need to be heated and dissolved in use, more trouble.However, the foam has good compatibility with cement and fly ash slurry, and can react with its calcium and magnesium ions to form insoluble salt, thus increasing the stability of the foam.
Surfactant has good surface activity and is a good reagent for preparing foaming agent.As amphiphilic substances, the physical and chemical properties of surfactants depend on their molecular structure.Under the same concentration, the stronger the hydrophilic action of polar groups, the higher the solubility of the surfactant in water, and the better the foaming performance.However, because of the water content in the foam surface layer, the drainage speed is fast and the foam stability is poor.In addition, because the properties of surfactant in concrete and its properties in aqueous solution often differ greatly, the compatibility between surfactant and cement particles is an important factor determining the performance of foamed concrete.
The foaming principle of protein foaming agent is protein degradation.The breaking of peptide bonds in protein macromolecules will generate small soluble protein molecules. With the increase of small protein molecules in the solution, hydrophobic groups gradually increase, resulting in a decrease in surface tension and the formation of an interface.In addition, due to the formation of hydrogen bonds between special groups in molecules, strong hydrogen bond action can ensure the formation of high strength foam liquid film in the solution, so that the foaming agent to generate a stable foam, the natural state of complete defoaming time of more than 24h.However, protein foaming agent is easy to be denatured by the external environment such as temperature and acidity, which is an important factor affecting the development of protein foaming agent.
The compound foaming agent is researched and synthesized to solve the limitation of single component foaming agent.Generally, it consists of two parts: foaming agent and stabilizing agent.Foaming agent usually choose foaming ability or stability of good surfactant;Foam stabilizers are generally colloidal substances, which increase the viscosity of the foam, enhance the surface strength of the liquid film, and delay the rupture time of the liquid film to increase the stability of the foam.The compound methods are mainly complementary, synergistic, synergistic and functional.
Foam quality evaluation index
Most of the foaming agents abroad are protein foaming agents, and their technical standards and testing methods are relatively mature.Domestic foaming agent is still in the development stage, the relevant departments have not issued the relevant national technical standards and regulations of foaming agent.The stability of foam refers to the durability of foam generation, that is, the length of foam existence "life".On the one hand, the durability of the foam itself is determined by the quality of the foaming agent.On the other hand, when the foam is mixed with the concrete slurry in the external environment, it can maintain the properties of non-cracking and non-collapsing, and has no adverse impact on the condensation and hardening process of cementitious materials. It is not only related to its own properties, but also depends on the influence of external factors.Foaming capacity is also known as foaming multiple, refers to the foam volume is greater than the volume of the foaming agent solution multiple.
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