The composition of foam concrete

The raw materials required to prepare foamed concrete mainly include: cement, water, and foaming agent. In addition, a certain amount of fillers, aggregates and admixtures can also be added during the preparation process of foamed concrete. On the one hand, this can reduce costs, and on the other hand, it can effectively improve the performance of foamed concrete products. However, as a special type of concrete, foamed concrete not only conforms to the general rules of ordinary concrete, but also has some own characteristics. Its constituent materials should meet the following technical requirements.

Cement

Cement, as the cementing material of foamed concrete, plays a vital role in foamed concrete. Cement is an important source of the strength of foamed concrete. Foamed concrete A large part of the quality depends on the cementing material, namely cement. Different raw material systems and the influence of cement dosage on the strength of foamed concrete are inconsistent. In the non-pure system, the strength of foamed concrete first increases as the cement dosage increases. When the optimal cement dosage is exceeded, the strength decreases as the cement dosage continues to increase. In the paste system, the cement dosage is relatively fixed, and only the cement strength grade still affects the strength of foamed concrete.

Various types of cement can be used to prepare foamed concrete. Since a large amount of foam is generated in foamed concrete, which delays the cement hydration process, it is suitable to use sulfaluminum with a faster setting time. Salt cement, high alumina cement, early-strength Portland cement, magnesite cement, gypsum, etc. However, based on durability considerations, ordinary Portland cement should be used to prepare high-performance foam concrete, especially when used in Walls and other important parts. Moreover, Portland series cement has wide sources, stable quality, economy and good durability, so it is widely used in the foamed concrete industry. The third series of sulfur (iron) aluminate cements have characteristics in the formation of foamed concrete slurry, structural stability, and early strength development. Their applications are increasing year by year, and their applications in some special key projects have been successful.

Foaming agent

It is well known that the foam in foamed concrete plays a vital role in the various qualities of foamed concrete, and foam is composed of individual bubbles. Therefore, the performance of foam is also a manifestation of the collective properties of each bubble. The different properties of foam used in foamed concrete directly determine the specific use range of foamed concrete, so the foaming agent is a key factor affecting the performance of foamed concrete. The decisive factor in evaluating a good foam agent is not the foam stability, but the stability of the foam slurry and its performance after hardening. The quality of the foaming agent has a huge impact on the performance of foamed concrete products. Choose a foaming agent with a small dosage, high foaming multiple, good foam stability, high air sealing rate, low water absorption, and does not affect the strength. Foamed concrete with uniform pore size and good performance is obtained [4].

High-performance admixtures

Unlike ordinary concrete, the compatibility with foam must be considered when introducing admixtures. The admixtures generally used in the production of foamed concrete The material should have: first, the finer the finer, the better, so that it can wrap the foam better; second, the water absorption of the admixture should not be too large, otherwise it will absorb the water in the foam and cause foam breakage. Therefore, finely ground slag, high-grade ultra-fine fly ash, silica fume, etc. are suitable for preparing foamed concrete, while steel slag and other materials with lower activity, rough particle morphology, high density, and certain water absorption are suitable for use in the preparation of foamed concrete. The aggregate may not be suitable for incorporation into foamed concrete. Incorporating fly ash and other admixtures can also improve the workability of the slurry, reduce costs, reduce the shrinkage and cracking of foamed concrete, increase the later strength of foamed concrete, and improve the molding effect, but the dosage should not be too large , and at the same time, a certain maintenance period needs to be guaranteed.

Aggregate

The aggregates used to prepare foam concrete are usually divided into three categories: ordinary aggregate, light aggregate and ultra-light aggregate. According to the density and strength requirements of foamed concrete, decide whether to use aggregate and which type of aggregate to use. Aggregate variety and apparent density have a significant impact on the strength of foamed concrete. In order to ensure the density of foamed concrete, the use of lightweight aggregates can make the structure formed by the cement slurry denser than using ordinary aggregates. The compressive strength of foamed concrete is generally low, and compressive failure usually occurs in a cement-based matrix that contains a large number of pores. The use of lower density aggregates will significantly increase the compressive strength of foamed concrete compared to ordinary concrete. Foamed concrete generally does not use coarse aggregates such as stones. Considering the ability to wrap the foam, the aggregates used are generally fine sand with smaller particle sizes. Generally, the dry density of foamed concrete is 500 to 700kg/ When m3 is above, fine sand needs to be added. Sometimes light aggregates such as ceramsite, zeolite, microbeads, etc. are used. When incorporating, consideration should be given to selecting aggregates with a suitable packing density so that they are close to the density of the slurry to be prepared, which can effectively prevent the settlement of the aggregates.

Fiber

Foam concrete is a type of porous concrete, which has a large shrinkage, especially for foam concrete with a lower dry density without adding aggregates. more worthy of attention. Therefore, adding a certain amount of fiber can control shrinkage. There are many types of fibers available, depending on the dry density levels of foamed concrete and the areas of application. A large number of tests have shown that polypropylene fiber can significantly improve the compressive strength and splitting tensile strength of foamed concrete. The improvement of the compressive strength of foamed concrete by polypropylene fiber varies greatly with the amount of foaming agent. As the amount of foaming agent increases, the improvement of the compressive strength of foamed concrete by polypropylene fiber increases. big. Therefore, for foamed concrete with low compressive strength, adding polypropylene fiber is an effective way to strengthen it; at the same time, polypropylene fiber can significantly improve the shrinkage performance of foamed concrete.

Admixtures

In order to meet the processability and special properties of foamed concrete, some admixtures need to be added. Various admixtures such as high-efficiency water-reducing admixtures are necessary components for preparing high-performance foamed concrete. Adding water-reducing admixtures can evenly mix the foam and slurry at a lower water-cement ratio. New polycarboxylic acids are used in the laboratory. When using salt superplasticizer, the water-cement ratio can be reduced to about 0.2, which can greatly improve the strength of the base material.

In addition to water-reducing agents and foam stabilizers, other commonly used admixtures used in high-performance concrete (such as quick-setting agents, early strength agents, dispersants, waterproofing agents, etc.) are also produced in production. Essential component of foam concrete.

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