Foaming agent is one of the key technologies for preparing foam concrete. Its performance directly affects the air content and fluidity of the fresh slurry and the volume stability of the cast body. And ultimately affects the apparent density and strength of the hardened slurry.
The foaming principles of foam concrete include physical foaming and chemical foaming. Physical foaming uses the surface activity of the foaming agent to prevent the bubbles introduced during the mixing process from merging, overflowing and disappearing, while chemical foaming generally refers to the use of chemical reactions of substances to produce gases, which are wrapped inside the concrete to form a large number of pores. .
The chemical foaming agent only needs hydrogen peroxide and aluminum powder.
There are four main types of physical foaming agents: rosin, synthetic surfactants, proteins and composites [4].
(1) Rosin is the first generation of foaming agents, mainly including rosin soap and rosin thermopolymers.
(2) Synthetic surfactants are second-generation foaming agents. This type of foaming agent has the advantages of easy foaming and high foaming multiples, but there are Disadvantages include thin bubble walls, poor foam stability, and great impact on concrete strength.
(3) Protein is the third generation foaming agent. This type of foaming agent is divided into plant protein and animal protein. Plant protein foaming agents include tea saponin type and saponin type; animal protein foaming agents include hydrolyzed animal hoof horns, hydrolyzed waste animal hair and hydrolyzed blood glue.
(4) Composite type is the fourth generation foaming agent. This type of foaming agent is no longer a single component, but is composed of multiple functional components. Become.
Because protein-based foaming agents have satisfactory foaming multiples and good foam stability (can be used for a long time without defoaming, most complete defoaming times are longer than 24 hours ) and other outstanding advantages, the foaming agents currently used in developed countries are basically protein-based. Due to the late start of domestic foaming agents, they generally have fewer functions and poor stability, resulting in low strength of the foam concrete products prepared.
In recent years, domestic researchers have done a lot of research work and are committed to developing foaming agents with excellent performance. Wang Cuihua et al. [5] used cow hoof horns as the main protein raw material, and in the presence of an appropriate amount of Ca(OH)2 and a small amount of NaHSO3, synthesized a protein-based foaming agent with a foaming multiple of 14 and a stable foaming time of 90 minutes. Shi Xingbo et al. [6] also successfully prepared protein foaming agents using pig trotters powder, and used a new model combined with mineral material foaming to prepare a series of products with different densities (581-772) kg/m3 and compressive strength. (3.0-6.0) MPa foam concrete blocks. Yin Bing et al. [7] hydrolyzed NaOH and human hair, and then neutralized it with dilute hydrochloric acid to prepare an XK animal protein foaming agent with a foaming multiple of 30 and a stable foaming time of 6 hours. The foaming agent has excellent performance. Li Junwei [8] studied the foam stability of activated sludge protein foaming agent. This foaming agent is a newly developed protein foaming agent in recent years. It is a chemical method for treating excess sewage sludge in sewage treatment plants. The resulting product has excellent foaming properties. Ding Qi [9] prepared an SDS foaming agent by compounding a sodium dodecyl sulfate solution with a mass concentration of 3.5% and a saponin solution with a mass concentration of 10% in a volume ratio of 3:7. The foaming agent has stronger foaming ability than a single foaming agent and improves foam stability.
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