What is foamed concrete?
Foamed concrete is made by using a physical method to make a foaming agent aqueous solution, and then adding the foam to a slurry made of cement, aggregates, admixtures, admixtures, and water. After mixing, mixing, pouring, and natural or Porous concrete made by steam curing. It contains a large number of closed pores, thus showing good physical and mechanical properties and use functions, such as light weight, heat preservation, heat insulation, moisture resistance, sound insulation, etc. Foamed concrete has a huge market in wall and roof thermal insulation projects, lightweight concrete components and products, building floor heating systems, large tunnels, high-grade highways and subway backfill projects, building lightweight cushions, sound absorption barriers, etc. Demand and broad prospects for promotion and application.
There is still a lack of standards and technical specifications for the design and construction of foam concrete at this stage. The application of foam concrete can only be implemented through experience or a large number of tests, which is not conducive to foam concrete quality control and technical development. Study the influence of the composition of raw materials on the performance of foam concrete, explore the correlation between the absolute dry density and compressive strength of foam concrete, establish an empirical formula for absolute dry density and compressive strength, which can not only correctly guide the optimization of the foam concrete composition and the design of the ratio, but also save Financial resources, to simplify the testing and quality control work, and accelerate the popularization and application of foam concrete.
The influence of the design of the ratio of raw materials on the strength of foam concrete
The main components of foamed concrete include cement, foaming agent, aggregate, fly ash, admixture and water. If necessary, other components can be added according to the requirements of use, such as chopped fibers and organic high molecular polymers.
Cement is the main source of the strength of foamed concrete and the primary influencing factor. In order to maximize strength, each foamed concrete with a designed absolute dry density has an optimal cement content. With different raw material systems, the influence of cement content on the strength of foam concrete is not consistent. In the non-clean slurry system, the strength of foamed concrete first increases as the amount of cement increases, and when the optimal cement amount is exceeded, the strength decreases as the amount of cement continues to increase. In the pure slurry system, the amount of cement is relatively fixed, and only the cement strength grade still affects the strength of foam concrete.
Portland cement has a wide range of sources, stable quality, economy and good durability, so it is widely used in the foam concrete industry. The third series of sulphur (iron) aluminate cement has characteristics in foam concrete slurry formation, structural stability, and early strength development. Its application has increased year by year, and its application in some special key projects has been successful.
(2) Foaming agent
There are many foam-producing substances, but not all foam-producing substances can be used as foaming agents. Only the foam produced when mixed with sand (neat) slurry does not break, has sufficient stability, and does not affect the coagulation and hardening of the cementitious material can be used to prepare the foaming agent. By changing the amount of foam added, foamed concrete with different paste densities and absolute dry densities can be made, and the strength of foamed concrete will also vary with the amount of foam introduced. Optimizing the variety of foaming agent and determining the optimal dosage are necessary conditions for the preparation of high-performance foam concrete.
The preparation of foam concrete aggregates is usually divided into three categories: ordinary aggregates, lightweight aggregates and ultra-light aggregates. According to the density and strength requirements of foam concrete, decide whether to use aggregate and which type of aggregate to use. Aggregate types and apparent density have obvious effects on the strength of foam concrete. In order to ensure the density of foam concrete, the structure formed by cement paste can be denser with light aggregate than with ordinary aggregate. The compressive strength of foamed concrete is usually low, and compressive failure usually occurs in a cement-based matrix with a large number of pores. Compared with ordinary concrete, the use of lower density aggregates will significantly increase the compressive strength of foam concrete.
(4) Fly ash
In view of the wide range of sources of fly ash, low price, and certain activity, it has become the preferred admixture for foam concrete. Fly ash can significantly increase the late strength of foamed concrete and improve the molding effect.
(5) Concrete admixture
The commonly used admixtures for foam concrete include dispersants, early-strength agents, accelerators, waterproofing agents, and water-repellent agents. Early strength agents and accelerators can accelerate the formation process and strength development of foam concrete structures, and improve the stability of the slurry structure.
(1) The composition is the primary factor affecting the strength of foamed concrete, which mainly includes cement types and strength grades, aggregate types and absolute dry density, fly ash quality, admixture types and foaming multiples.
(2) Foamed concrete mix design can be based on the fixed raw material weight method and the solid mixture volume method. That is to control the amount of solid components and the ratio of solid components in the foam concrete slurry per unit volume to optimize.
(3) Under the premise of the same composition, ratio and preparation process, there is a good correlation between the compressive strength of foam concrete and the absolute dry density. By detecting the wet density of the foam concrete, and then controlling the absolute dry density of the foam concrete, the purpose of controlling the compressive strength of the foam concrete is achieved.
(4) In the cement-fly ash-foam-water raw material system foamed concrete, adding an appropriate amount of fly ash will help to increase the compressive strength of the foamed concrete, increase the crack resistance, and reduce production costs.
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