The principle of foam concrete water reducer

2018-11-21 10:47:08

Foamed concrete is foamed cement. Cement will use some admixtures in the foaming process. These admixtures mainly involve foaming agents, foam stabilizers, water reducers, anti-cracking agents, water repellents, etc. The use of the foam concrete outer edge agent makes the foamed product made more perfect.
Today, let’s first look at how the water reducing agent used in foam concrete products works.
The water reducing agent is an admixture capable of reducing the water consumption of the mixing under the condition that the concrete slump is substantially the same. Water reducing agents are anionic surfactants which are surface active in concrete. The action mechanism is as follows: the adsorption of cement particles on the superplasticizer and the dispersion of the superplasticizer on the cement, and the cement is added into the cement slurry to form a flocculated structure. When the water-reducing agent molecules are adsorbed by the cement particles in the slurry, that is, a diffusion electric double layer is formed on the surface thereof to become a polar molecule or a molecular group, the hydrophobic end is adsorbed on the surface of the cement particle and the hydrophilic end is directed toward the aqueous solution to form An adsorption film of a monomolecular layer or a multi-molecular layer. This reduces the surface tension of the water and releases the encapsulated water molecules in the floc. At the same time, due to the directional adsorption of the surfactant, the cement particles have the same charge on the outward side, which produces a repulsive effect. As a result, the cement slurry forms a non-stable suspension state; the lubricating effect on the surface of the cement particles, the polar hydrophilic end of the water reducing agent faces the aqueous solution, and is often associated with water molecules in the form of hydrogen bonds, plus water The hydrogen bond association between the molecules constitutes a water film on the surface of the cement particles, preventing direct contact between the cement particles and lubricating.

In summary, we can see that the effectiveness of the water reducing agent is mainly as follows.
Dispersion: After cement and water mixing, due to the molecular gravitational effect of cement particles, the cement slurry forms a flocculation structure, so that 10% to 30% of the mixing water is wrapped in the cement particles, and cannot participate in free flow and lubrication. This affects the fluidity of the concrete mix. When the water reducing agent is added, since the water reducing agent molecules can be adsorbed on the surface of the cement particles, the surface of the cement particles carries the same electric charge (usually a negative charge), forming an electrostatic repulsion, causing the cement particles to disperse and disintegrate the flocculation structure. , releasing part of the water that is wrapped and participating in the flow, thereby effectively increasing the fluidity of the concrete mixture.

Lubrication: The hydrophilic group in the water reducing agent is very polar, so the water-reducing agent adsorption film on the surface of the cement particles can form a stable solvated water film with water molecules. This water film has good lubricating effect. It can effectively reduce the sliding resistance between the cement particles, thereby further improving the fluidity of the concrete.

The steric hindrance effect: a hydrophilic polyether side chain in the structure of the water reducing agent, extending in the aqueous solution, thereby forming a hydrophilic stereoscopic adsorption layer having a certain thickness on the surface of the adsorbed cement particles. When the cement particles are close, the adsorption layers begin to overlap, that is, steric hindrance occurs between the cement particles. The more overlap, the greater the steric repulsion force, and the greater the hindrance to the cohesion between the cement particles, causing the concrete to fall. The degree is kept good.

Slow release of graft copolymerization branch: a new type of water reducing agent, which grafts some branches on the molecule of the water reducing agent, which not only provides steric hindrance effect, but also high alkali in cement hydration In the environment, the branch can be slowly cut off to release the polycarboxylic acid having a dispersing effect, thereby improving the dispersion effect of the cement particles and controlling the slump loss.

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