The gas expansion of aerated concrete is due to the chemical reaction of aluminum powder in alkaline solution, and this reaction is carried out in the specific environment of aerated concrete with rheological properties. The gas generation reaction of aluminum powder is the expansion of slurry volume. The change of the elastic-visco-plastic properties of the slurry itself is shown as the gradual thickening and condensation of the slurry. The two processes with time are stored in a system. If the consistency of the two processes is consistent, the gas generation process will be stable. Therefore, the factors that affect the two processes will inevitably affect the stability of the pouring process. In order to analyze the stability of the pouring process, the main factors that affect the two processes must be understood first.
1. Factors affecting the gas velocity
(1) The characteristics of the gas generation of aluminum powder.
Because of the difference in production process and quality control, the products of each production plant, even different batches of products in the same factory, will not be identical. Therefore, the actual gas generating characteristic curve displayed in the use of the powder or aluminum powder paste will have different shapes The results show that the relationship between the two curves is different from that of the slurry. The picture,
The gas delivery speed of aluminum powder is basically within the range required by the process, and the expansion rate of slurry falls within the shadow surface in the drawing. In this case, although there is a short concentrated gas delivery time in the early stage of aluminum powder gas generation, it becomes slow later. More aluminum powder will only send gas when the slurry is close to thickening. In this case, the later gas generation process is blocked, Air holding and bubbling may occur, and the pouring is not stable enough.
The gas of aluminum powder is less concentrated, and the gas curve rises slowly, and a large number of gas is produced after the slurry thickening. In this case, the expansion of slurry is slow, and the air hold is serious in the later stage, even the slurry can not expand normally. The bubble inside the slurry is perforated and merged, and even bubbles even sink. The above phenomena are mainly due to the poor composition of aluminum powder particles, although some fine particles, they are larger or mixed with some particles with low activity. If the aluminum powder is too fine, the gas delivery time will be greatly advanced, in this case, if the slurry is too thin. The gas holding capacity is too poor, and serious bubble may occur, even boiling. In some cases, a large amount of gas may occur in the mixer, and the pouring stability will be greatly affected.
(2) Slurry temperature
The reaction rate of aluminum powder is closely related to the temperature. The solution solution will increase the dissolution rate and solubility of reactants and reaction products at higher temperature, which will undoubtedly be beneficial to the reaction. The relationship between the reaction speed and temperature of the aluminum powder can be determined by experiments. The higher the temperature, the earlier the reaction starts, on the contrary, the reaction will be slow and the time is prolonged. Therefore, by changing the slurry temperature, the gas generation and thickening process can be coordinated to a certain extent. Of course, this can only be within a certain range, but not unlimited adjustment, just as the adjustment of the thickening speed of slurry can not be unlimited to adapt to the gas generating speed. If the temperature is increased too much to adapt to the slurry with fast thickening, for example, the temperature of slurry is raised to 60-70 degrees, which may cause the slurry to be more thickened in most cases, and the effect will be counterproductive.
(3) Mixing time
The mixing time of aluminum powder mainly affects the gas generating speed and its coordination with the thickening of slurry, on the one hand, it is the time for aluminum powder to put into slurry; On the other hand, the mixing time of aluminum powder in slurry is needed. The former mainly adjusts the time of aluminum powder to start to send gas by adjusting the contact time between aluminum powder and alkali solution, while the latter is mainly to control the gas generation speed of aluminum powder from the mixing time of aluminum powder. In order to make the aluminum powder gas flow under the appropriate consistency condition. It is clear that an appropriate time should be chosen. Too early, too thin, too late, too thick slurry, aluminum powder gas and slurry expansion are adverse.