As a lightweight thermal insulation material, foamed concrete has been widely used in construction projects. Some problems have also occurred during its application. When applied to thermal insulation components, due to the excessive water absorption of the material, the bulk density increases, but the thermal insulation performance decreases. Quality issues. It is extremely disadvantageous to the durability of foamed concrete.
Influencing factors of water absorption of foam concrete
The water absorption rate of foamed concrete is carried out through two conditions: the penetration of capillary pores and the penetration of connected pores. Capillary pores are interconnected capillary pores formed in the initial stage of cement hardening. One of the reasons for the formation of connected pores is that during the setting process of foam concrete, the liquid film produces uneven diffusion under the dual action of gravity, surface expansion force, and slurry extrusion, resulting in defects in closed foam pores and condensation. After the performance of incomplete pores; another reason is the passage of bleeding caused by bleeding in the case of large water-cement ratio of foam concrete.
The problem of bulk density
The influence of the water absorption of foam concrete on the thermal insulation performance of the material can be measured by the volume water absorption. As the water increases, the bulk density increases, the cell radius becomes smaller, the cell wall becomes thicker, the number of connected pores decreases, and the moisture permeability per unit volume also decreases. That is to say, the change in water absorption caused by the change in the content per unit volume and the resulting change in permeability cancel each other out. Therefore, the volume water absorption rate of foamed concrete with different bulk weights does not change significantly. At the same time, some experimental data also show that the water absorption rate also shows a similar change trend when using other strength grades of cement to make foam concrete.
Quality problems of foam
When the foaming machine is stable and normal, the foam quality mainly depends on the performance of the foaming agent, and its influence on the mass water absorption is mainly measured from three aspects: the pore size, the uniformity of the pore size of the foam and the stabilization time of the bubbles. In fact, the smaller the pore size, the smaller the pore volume. At the same time, the denser the number of layers of the pore walls in the volume, the lower the probability of forming connected pores.
The hydration age of cement
The difference in water absorption of foamed concrete made of different varieties and strength grades of cement at the same bulk density is mainly determined by its hydration age. Under normal circumstances, the foamed concrete of cement products with a short hydration and hardening age The water absorption rate is low.
Auxiliary admixture problem
The industrial wastes such as fly ash or slag with different dosages of general additives in foamed concrete are most commonly mixed with fly ash in practical applications.
Control of foaming quality
At present, the foaming method at home and abroad is to use high-pressure foaming. By applying pressure at the same time, the mixing speed of gas and liquid is accelerated, so that the bubbles are fine and uniform. The foaming machine has a great influence on the quality of the foam, which is mainly controlled by the ratio of air intake and liquid intake.
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