Research progress of foam concrete

1.1 Composition materials

1.1.1 Foaming agent

Foaming agent is an agent that forms closed pores or connected pore structures by promoting the generation of foam. Under specified prerequisites, it uses chemical reaction changes or physical methods (stirring, compressed air, etc.) to process, so that the foaming agent solution can produce a large amount of uniform and stable foam without a long time [4]. Therefore, it can be seen that not all substances or reagents that can produce foam can be used as foaming agents.

There are various types of foaming agents, and the most frequently used ones are: animal protein foaming agents, rosin acid soap foaming agents, petroleum aluminum sulfonate foaming agents agents etc.[5]. Domestic scholars have continued to conduct in-depth research, and different product types of foaming agents have emerged, such as: U-type foaming agent, CLY-99 hydrophobic foaming agent, CON-A type foaming agent, CCW-95 solid foaming agent, etc.

In China, research on high-performance foaming agents has never been interrupted. For example, Wang Cuihua [6] synthesized a foaming agent for protein-based foam concrete using cow hoof horn as the main protein raw material in the presence of quantitative Ca(OH)2 and NaHSO3. Shi Xingbo et al. [7] combined mineral material foaming and surfactant foaming to form a new form, using pig trotter horns as raw materials to make a series of foam concrete blocks. Ma Zhijun et al. [8] conducted a compounding study to observe the modification effect of surface active substances on the foaming and foam stabilizing properties of the foaming agent mother liquor. They found that the foam performance of the protein foaming agent was greatly improved after compounding, and its foaming and foam stabilizing performance was also particularly significant. At present, Eva Kuzielová et al. [9] studied the effect of activated foaming agent on foam concrete, examining the relationship between foam stability, volume density, microstructure, compressive strength, foaming agent concentration and microwave and ultrasonic treatment. Experimental findings The relative reduction in pore size in samples prepared with lower concentrations of microwave- and ultrasonic-treated foaming agents improved the compressive strength of the samples.

There are two important factors in whether a bubble is stable. One is whether the liquid is separated from the foam, and the other is whether the gas diffuses through the liquid film. To determine whether the foaming performance is excellent, it is generally based on three important factors: the sinking distance of the foaming agent, the amount of water bleeding, and the foaming multiple. Taking these three important factors as indicators, the greater the settlement distance and bleeding amount of the dilute foaming agent solution and the smaller the foaming multiple, the worse the foaming performance. Specifically, the subsidence distance and bleeding volume of the foam after 1 hour of high-quality foaming agent are not greater than 10 mm and less than or equal to 80 ml respectively, and the foaming multiple should be greater than or equal to 20 [10]. Up to now, my country has not developed a consistent testing method for foam quality issues. The industry generally determines testing methods based on actual conditions.

1.1.2 Admixtures

At present, there are two major categories of admixtures. One type is chemical admixtures, which are chemicals with organic or inorganic compounds as the main components and the dosage is no more than 5% of the mass of cement; the other type is mineral admixtures, which are chemicals in which cement in concrete is replaced by mineral powder part, the most common mineral additives include fly ash, granulated blast furnace slag powder, etc. [11].

In the process of making foam concrete, we need to add different admixtures in order to achieve special properties such as workability. For example, the water-cement ratio of foamed concrete and the thermal stress of cement hydration are large, so water-reducing agents are added to relieve the pressure; foamed concrete has poor durability when cracked, so expansion agents are added to improve durability; The strength development rate of concrete is slow, and a certain amount of activator is added to the mixed fly ash to speed up the rate; the tensile strength of foam concrete is low, and fiber materials are added to improve its shortcomings.

In recent years, admixtures have gradually attracted the attention of researchers and have been studied in depth. Niu Yunhui et al. [12] focused on the relationship between four kinds of admixtures and the major properties of foam concrete. These four admixtures are: polycarboxylate water-reducing agent, accelerating setting agent, PP fiber and foam stabilizer. , the results show that the foam concrete obtained by coupling these admixtures to each other is beneficial to solving problems such as cracks and formwork collapse when the foam concrete is used as a load-bearing wall during on-site pouring. Hu Lu [13] believed that silicone waterproofing agents would affect the compressive strength and water absorption of foam concrete, and therefore conducted experimental research on this admixture. After the foamed concrete test block was coated with emulsion-type silicone, it was found that compared with the uncoated part, the compressive strength of this part was enhanced and its water absorption rate was also significantly reduced. Cong Ma et al. [14] studied the effects of three waterproofing agents, PT, CS, and SP, on the performance of foam concrete. The results showed that the waterproofing agent had almost no effect on the foam stability and dry density of low-density foam concrete. By adding waterproofing agents, it can resist compression. The strength can also be improved, and the optimal improvement condition is that the content of the waterproofing agent is about 1.0%. As the content of the waterproofing agent increases, the strength retention coefficient RS increases significantly. In addition, its application can reduce the hygroscopic water content. E.K. Kunhanandan Nambiar and K. Ramamurthy[15] studied the impact of fly ash substitution on the strength and density of foamed concrete by comparing it with a mixture without fly ash, and proposed that fly ash substitutionThe process of mixing them with the rapid agitation of a foaming machine to produce tiny foam with a homogeneous diameter, or the process of blowing the foam into a foaming cylinder under the action of compressed air. Stirring is the process of mixing raw materials and water evenly in a cement mixer. Mixing foam is the process of mixing the foam and uniform slurry in a cement mixer. Molding is the process of transporting the slurry to the construction site for use or placing it in a mold for curing.

The specific steps of the mixed foaming method are: directly mix the base material and the surfactant. The surfactant plays its role in the slurry mixing process, and then Foam appeared, and a large number of cavities in the concrete gradually formed. Among them, the surface tension of the foam can withstand the pressure exerted on it by the slurry. After the initial setting of the slurry creates pores, the skeleton formed is stable and solid [26].

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