Foam concrete refers to the foaming agent's foaming system that introduces air or nitrogen, carbon dioxide, oxygen and other gases into concrete through chemical or physical means according to application needs. (in the slurry) is fully foamed by mechanical means, and the foam and cement slurry are evenly mixed, and then cast-in-place construction or mold molding is carried out through a pumping system. Through reasonable natural curing, it becomes a kind of material that contains a large number of small, closed, and A porous material with evenly distributed pores, it is a building material with the characteristics of light weight, high strength, heat insulation, fire protection and sound insulation, water resistance and shock absorption.
In recent years, both domestic and foreign countries have attached great importance to the research and development of foam concrete, making its application in the construction field more and more extensive. However, because the research results of foam concrete and its application technology are mostly reflected in the form of patents at home and abroad, domestic production of foam concrete lacks complete sets of equipment, complete data and experience accumulation, and lacks theoretical guidance for construction. Therefore, foam The superior properties of concrete are not fully reflected, and problems such as low strength, concrete cracking or water absorption often occur.
Recently, the author has focused on studying some factors that affect the strength of foam concrete and discovered some rules for improving the strength of foam concrete, which will be helpful for making full use of building energy saving and Environmentally friendly new building materials are of great significance.
1 Principle of Preparation of Foam Concrete
Foam concrete is usually made by mechanical or compressed air. The aqueous solution of the foam agent is prepared into foam, and then the foam is added to a slurry composed of silicon-containing materials, calcium materials, water and various admixtures. After mixing, stirring, pouring, molding, and curing, it is a kind of foam with internal content. Lots of concrete with closed pores.
2 Factors affecting the strength of foam concrete
Like ordinary concrete, the strength of foam concrete is not A fixed value, different types of cementitious materials, cement dosage, concrete mix ratio, water-cement ratio, foam dosage (different volume and mass), foaming agent, curing system and the use of other admixtures all affect the foam. Strength of concrete. This article only focuses on the water-cement ratio, mix ratio and selection of admixtures.
2.1 Influence of water-cement ratio
In the preparation of ordinary concrete, the strength of the concrete changes with the shape It increases with the decrease of water-cement ratio, but the situation found in the foam concrete test is different.
1) When the fluidity of the slurry is mainly controlled by the amount of additives (that is, the slurry already has good fluidity), as the water-cement ratio As the intensity decreases, the intensity increases; on the contrary, the intensity decreases. Analysis reason: As the water-cement ratio decreases, the amount of free water in the concrete decreases, and the water absorption rate of foam concrete decreases, effectively increasing the strength of the concrete; but when the water-cement ratio continues to decrease, due to insufficient water demand for cement hydration, the Absorbing moisture in the foam causes the foam to burst, resulting in a reduction in the number of closed bubbles and a decrease in the uniformity of the concrete, resulting in a reduction in strength.
2) When the fluidity of the slurry is mainly controlled by the amount of water, as the water-cement ratio increases, the strength increases; conversely, the strength decreases .
Analytical reasons: The higher molding water-cement ratio ensures good fluidity of the slurry and ensures that the foam is evenly introduced into the cement slurry and evenly distributed. , thereby achieving strength growth. On the contrary, the reduction of water-cement ratio and insufficient fluidity of slurry material will cause uneven distribution of bubbles, thereby reducing the strength of concrete.
Based on the above situation, the impact of the water-cement ratio of foam concrete on the strength is multi-faceted. It should be analyzed based on the specific situation to adjust the water-cement ratio so that The internal material structure of foam concrete is uniform and has many closed independent cells, which is an important way to improve the strength of foam concrete.
2.2 Influence of mix ratio
Cement can be used alone or simultaneously when preparing foam concrete. In addition to mixed materials other than cement (such as silica fume, slag, fly ash, etc.), fine aggregate (sand) may also be used at the same time. The first situation: It is relatively simple to use cement alone. The higher the strength grade and the greater the dosage of cement used, the greater the strength of the prepared foam concrete. Therefore, when you want to prepare higher-strength foam concrete, you need to choose high-strength grade cement. The second case: the introduction of mixed materials will lead to a significant reduction in the early strength of foam concrete, but will have little effect on the later strength. If appropriate strength activator is filled in, the early strength reduction can be effectively slowed down. In actual construction, it is most common to mix mixed materials and sand at the same time. Therefore, there is an appropriate range for the mix ratio of foam concrete, which needs to be determined based on experiments.
2.3 Influence of the dosage of admixtures
Admixtures used in foam concrete mainly include cement strength stimulators , water reducing agent and foaming agent.
2.3.1 Foaming agent
From the analysis of the preparation principle of foam concrete, the use of foaming agent Introduce a large number ofThe pores give it functions such as lightness, sound insulation, heat preservation, and high fluidity that ordinary concrete does not have, which is the basis for the preparation of foam concrete; but from the perspective of structure and mechanics, it also causes the structural density to be greatly reduced, thereby reducing the Strength of foam concrete. So, how to control the dosage of foaming agent to achieve functions such as light weight, sound insulation, insulation and high fluidity, while ensuring that the concrete strength is not lower than the expected target is a new topic in concrete production scientific research.
There are many substances that can produce foam, but not all substances that can produce foam can be used as foaming agents. Only foaming agents with a large enough foaming ratio that the film will not be damaged when the foam and slurry are mixed, with sufficient stability and no harmful effects on the coagulation and hardening of the cementitious material are suitable for the production of foamed concrete.
The influence of foaming agent on the strength of foam concrete is mainly reflected in the size and uniformity of the foam (uniformity of size and distribution), stability of the foam, and Bubble ability, etc. The foaming agent is required to have strong foaming ability, low density, small unit water carrying capacity, firm, fine and evenly distributed foam, and little side effects on concrete.
2.3.2 Cement strength stimulator
Cement strength stimulator is mainly used in cement mixture materials It can reduce the early strength reduction of foam concrete. However, the use of activators tends to reduce the ultimate strength of foam concrete.
2.3.3 Water-reducing agent
Concrete water-reducing agent makes foam concrete even at lower water levels The mixture of slurry and foam can still be successfully completed under the gray ratio, and foamed concrete with uniform foam distribution can be prepared. Therefore, adding an appropriate amount of high-efficiency water-reducing admixture is one of the important means to prepare high-strength foam concrete. However, because water-reducing agents are relatively expensive and some water-reducing agents have opposite effects on certain properties of foaming agents, the type and amount of water-reducing agents must be determined by testing.
3 Ways to Improve the Strength of Foam Concrete
In summary, the mix ratio and water-cement ratio The addition of admixtures and admixtures are the main factors affecting the strength of foam concrete. Choosing an appropriate mix ratio, using high-efficiency water-reducing agents, controlling an appropriate low water-cement ratio, and using high-quality and efficient foaming agents can effectively improve the strength of foam concrete.
4 Conclusion
Foam concrete, also known as lightweight concrete or foamed cement, is a A new type of building energy-saving material that is waste-free, environmentally friendly, energy-saving, low-cost, lightweight, high-strength, non-absorbent, and non-combustible. It can be used as roof insulation, floor heating, ground cushion, internal partition wall and external wall insulation. Foam concrete has not been popularized and applied in China for a long time, and its performance and preparation technology require further research and exploration. Since the preparation of foam concrete is a systematic process, the factors that affect its performance are relatively complex. During the research process, there are Only by focusing on it can you make breakthroughs. I hope some of the ideas in this article on improving intensity can be inspiring to my colleagues. </p
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