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Influencing factors and evaluation methods of foam stability of cement foaming agent

wallpapers Industry 2020-04-16

Cement foaming agent foam stability refers to the property that the foam can exist for a long time without being destroyed. The longer the foam exists, the better the security, and the less likely it is to burst. The foam destruction process is mainly the process of the liquid film separating the gas from thick to thin until it breaks. The factors influencing the foam stability of cement foaming agent mainly include the following aspects:

1. The thickness of bubble film

If the width of the bubble liquid film is too small, the mechanical strength is low, and the external force resistance is poor. It is easy to break; the bubble liquid film is too thick, the water between the bubbles is too much, resulting in excessive foam bleeding, and the too thick liquid film will accelerate drainage. It is also easy to cause bubble breaking. Therefore, the thickness of the bubble film layer should be kept within a specific range.

2. Viscosity

The strength of the bubble liquid film is the critical factor that determines the stability of the foam, and the power of the liquid film depends on the firmness of the surface adsorption film. Its durability is related to the surface viscosity. The higher the surface viscosity, the longer the life of the formed foam. On the other hand, the higher the thickness of the liquid itself, the slower the speed of the liquid overflowing from the liquid film, thereby enhancing the foam stability.

3. Liquid surface tension

Lower liquid surface tension is conducive to foam formation, but foam stability cannot be guaranteed. Due to the high surface tension of the liquid, the protein foaming agent has a low foaming factor, but the foam emitted has high stability.

4. Surface charge

When the bubble liquid film has the same command on both surfaces, it repels each other, which can prevent the liquid film from being squeezed and thinned to break.

5. Bubble self-healing ability

When the foam liquid film is subjected to external force, the local thickness of the liquid film will be thinned, which is easy to break. When the foaming agent is adsorbed on the surface of the liquid film, it can resist the expansion and contraction of the surface and restore the thickness of the liquid film. Recovery, to achieve self-repair of surface tension.

6. Molecular structure of surfactant

The hydrophobic chain of the surfactant should have a moderate chain length to ensure that the adsorption film formed on the surface of the liquid film has a high viscosity. The hydrophilic group of the surfactant has a strong hydration ability, which can make the foam liquid film flow high Degree of free water becomes poorly bound water, thereby increasing the viscosity of the liquid film. The dry density of foamed cement increases.

The physical and mechanical properties of cement foam products depend mainly on the foam properties of the foaming agent. The performance of the foaming agent is very similar to that of the surfactant. Therefore, the evaluation method of the foam performance of the cement foaming agent can refer to the evaluation method of the surfactant. There are mainly two methods: the foaming height method and the multiple foaming method.

1. Bubble height method (ISO method)

The core of the foaming height method is two technical indicators: the foaming height of the foaming agent and the half foaming time of the foaming agent. The foaming height reflects the foaming ability of the foaming agent. The higher the foaming elevation, the half the foaming time. The longer it is, the more reliable the foaming power of the foaming agent and the better the foam stability.

In China, the foaming height method adopts GB / T 7462-1994 "Determination of Surfactant Foaming Strength Improvement."

ROSS-Miles method", the test principle is: place 50mL of foaming liquid to be tested in the graduated cylinder before

50 mL of the foaming liquid to be tested flowed into the graduated cylinder from a height of 450 mm at a certain flow rate. The solution collided with the liquid surface, mixed with air, and generated foam. The volume of the foam was measured and used as a measure of the foaming power of the foaming agent. After the ROSS-Miles method is used to measure the foaming height, the time required for the foam height to decrease by half is called the half extinction time.

2. Foam multiple methods

This method is also a commonly used detection method at home and abroad. It mainly uses three technical indicators of foaming agent foaming multiple, 1h foam settlement distance, 1h foam bleeding volume to detect the quality of the foaming agent. When testing, first use the foaming device to make the foaming agent into the foam.

The instrument for measuring the sinking distance of foam and the amount of bleeding is composed of a container, a glass tube, and a buoy. There is a hole at the bottom of the container, and the glass tube is connected to the hole of the container. The diameter of the glass tube is 14mm, the length is 700mm, and there is a small faucet at the bottom. The buoy is a round aluminum plate with a diameter of 190mm and a weight of 25g. According to the scale on the upper container, the distance the foam column sinks per unit time is the sinking distance. According to the scale on the measuring tube, the volume of liquid secreted after the bubble burst per unit time is the amount of bleeding.

 


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Tag: cement foami