With the rapid development of the world economy, people pay more attention to energy conservation and environmental protection on the basis of meeting the needs of life, and pay attention to the long-term use of energy. The problem of insufficient energy and energy waste has caused widespread concern in the world, and building energy consumption accounts for more than half of the world's total energy consumption. Winter is a season of rapid energy consumption. People consume energy through heating, air conditioning and coal. Increasing trend year by year. Reducing the total energy consumption of buildings and developing new energy-saving and environmentally-friendly building materials can reduce building energy consumption and save energy. Although the mechanical properties of foam concrete are lower than those of ordinary concrete, they have excellent thermal insulation properties, and can be used as a partition wall or a lightweight load-bearing wall in a low-rise residential building, which has both heat preservation and weight reduction effects. Foamed concrete is usually a lightweight concrete containing a large number of pores by adding a pre-formed foam to a stirred cement-based material and then mixing and mixing until the foam is completely integrated into the slurry, and subjected to agitation, casting and curing processes. The use of foam concrete of different density grades in the non-load-bearing parts of the building can reduce the self-weight. Therefore, the use of foam concrete in the building structure can save the material and reduce the construction cost while meeting the structural requirements.
1 Blowing agent
1.1 Foaming agent foaming mechanism
The goodness of the foaming agent will directly affect the quality of the foamed concrete. The surface activity of the blowing agent is high, so that the surface tension of the liquid is lowered, and the double electron layer is discharged on the surface of the liquid film to surround the air to form a so-called bubble. Surfactants or surface-active substances usually comprise two groups: one is a hydrophilic group that is readily soluble in water, and the other is an oleophilic group that is readily soluble in oily substances. When the surface active material is dissolved in water, the hydrophilic and polar water molecules are attracted to each other and remain in the water, while the lipophilic and polar water molecules repel each other and enter the air.
1.2 Classification of foaming agents
Foam concrete foaming agents mainly include physical foaming agents and chemical foaming agents.
(1) Physical foaming agents.There are mainly five kinds of rosin-based foaming agents, vegetable protein foaming agents, animal protein foaming agents, synthetic surfactants and composite foaming agents.
Rosin-based foaming agent. Rosin-based foaming agent is the most widely used, and its main raw material is rosin. The rosin has a molecular formula of C20H30O2, which is composed of aromatic hydrocarbons, aromatic alcohols, rosin acids, aromatic aldehydes and oxides thereof. The rosin-based foaming agent mainly has two kinds of rosin soap and rosin hot polymer. Rosin soap, low in price, simple in production, stable in foam, moderate in foaming ratio, and has the advantage of being easily soluble in cement slurry. The application of rosin heat polymers is limited, mainly because of its high cost, not easy to produce and produce toxic substances, so it affects its promotion.
Vegetable protein foaming agent. Such foaming agents have been widely used due to their wide range of raw material sources. Plant-based foaming agents have been developed for a long time in China, mainly including tea saponin and saponin. The foam produced by the foaming of tea saponin has a longer stabilization time. In contrast, the foaming ability of saponin is similar to that of tea saponin, but the foam stability is easily affected by environmental factors, so it is not as widely used as tea saponin.
Animal protein foaming agent. At present, animal protein foaming agents are the most used at home and abroad, and their performance has also been affirmed. There are three main categories of animal horns, waste animal hair and animal blood glue. The foam produced by the animal protein foaming agent has a thicker bubble wall, is not easily broken, and the foaming ratio is also in compliance with national regulations, but the foam produced by the foaming agent is also susceptible to environmental influences.
Composite foaming agent. The foaming agent combines the excellent properties of various foaming agents into one body, and is prepared by combining a plurality of components, and it can well solve the problem of poor foam performance caused by a certain component. It has obvious performance advantages compared to the previous foaming agents.
(2) Chemical foaming agents. The process by which a chemical blowing agent produces a foam does not require the use of a foaming device, but rather a spontaneous chemical reaction to produce a foam. Can greatly reduce costs and improve work efficiency. Especially for the production of low-density ultra-light foam concrete, the amount of foam can be better controlled. However, the resulting bubble is poor in stability, and if it is not used, it is easy to cause volume instability or even collapse. And the generated bubbles are too easily affected, resulting in different diameters of the bubbles, which are difficult to control.
2 Preparation and production process of foam concrete
At present, the manufacturing method of the foamed concrete mainly includes the following two methods: one method is to add the pre-generated foam into the stirred slurry, and then mix and stir uniformly. This method is called pre-bubble mixing method. Another method is that the mixing and foaming of the slurry is carried out simultaneously, which is called a mixing and agitating method. This article describes the process flow of the pre-bubble mixing method. Foamed concrete is divided into two types according to the type of process: cast-in-place process and product production process. Both processes are the same on both foamed and pre-formed slurries, the difference being in the way of pouring and curing.
3 Application of foam concrete
(1) Retaining wall. Backfilling with foam concrete after the wall can reduce lateral and vertical loads. Because foam concrete has excellent bonding properties, it does not significantly settle with the increase of peripheral pressure, which can greatly reduce maintenance costs and reduce costs. Foamed concrete can also reduce the soil quality by partially replacing the soil, thereby improving the stability of the embankment slope and achieving certain safety benefits.
(2) Compensation for the foundation. In the construction process, uneven settlement is often caused by the different weights of each building group. At this time, the appropriate foam concrete material can be filled on the foundation of the building's own weight to achieve the effect of compensating the foundation.
(3) Foam concrete blocks. The application of foam concrete blocks started earlier in China and the application is also very extensive. It is most commonly used as wall filling material, which greatly reduces the building's own weight. It can reduce the number of piles and reduce the pile diameter, saving engineering expenses.
(4) Lightweight partition panels. Foamed concrete lightweight partition board. After a large number of experiments, China Building Materials Science Research Institute has successfully developed the production technology of fly ash foam cement lightweight wallboard. The production process of lightweight partition board is based on the use of foam ash and foam cement. Instead of cement, it does not affect the use of partition wall panels, reduces production costs, improves the fluidity of the slurry, and achieves technical, economic and environmental benefits.
(5) Pipeline backfilling. The use of foam concrete filled with a density grade of 600~1100 kg/m3 in sewage pipes, underground pipelines and used oil tanks can effectively prevent the ground from collapsing and have a fireproof effect.
(6) Refractory applications. Foamed concrete has good thermal insulation properties and fire resistance. It can be used in large fireproof factories, as well as in the production of pipe insulation casings and pipe insulation coatings.
(7) Military applications. Foamed concrete is used on the shooting range for live-fire training, because when the bullet enters the target wall, it will be corroded by the soil acid. It will cause environmental pollution for a long time, and the foam concrete can catch the bullet and its alkaline environment. It will not corrode the warhead. In addition, in the construction of anti-riot tunnels, the energy dissipation of foam concrete can be utilized to make the tunnel structure cushioned without being damaged during blasting.
(8) Chemical applications. Foamed concrete is often used for the pouring of the bottom corners of chemical storage tanks. The foam concrete is poured on the bottom of the steel tank bottoms. This ensures that the support of the entire tank bottom is under optimal stress during welding. This continuous support can make the tanks The bottom of the thin box is used, and the convex foundation is also easy to clean. Foamed concrete is used at a density of 800-1000 kg/m3.
(9) Construction of sports grounds and athletic track. Foamed concrete materials can be used on the basis of sports grounds and runways, with a density rating of typically 800-900 kg/m3. The foam concrete is covered with a thin plastic layer and porous asphalt, which can be used as a track and field track. The surface of the foam concrete is covered with artificial turf or gravel and can be used as a playground for various ball activities.
(10) Other applications. Foamed concrete can also be used in backfill grouting, subway tunneling, sandwich components, composite wall panels, roof slopes, support for tank feet, lean concrete filling and insulation filling of firewalls, sound insulation floor filling, decoration Materials and other aspects.