Effect of Polycarboxylate Superplasticizer in Grouting Material

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Effect of Polycarboxylate Superplasticizer in Grouting Material

Water reducing agent is an important part of the grouting material, water reducing agent is the most important quality of the grouting material, is a kind of can maintain the fluidity of the grouting material, significantly reduce the amount of water. Water reducing agent is one of the essential materials for preparing high-performance grouting material. The content of water reducing agent can change the fluidity of the grouting material and improve the workability (in the case of maintaining the same cement dosage and water cement ratio); due to the reduction of the water cement ratio, a series of properties such as strength and durability of the grouting material are improved (in the case of maintaining the same fluidity); or both. The role of adding polycarboxylate superplasticizer to the grouting material is as follows:

1. Dispersion:
After the cement is mixed with water, due to the molecular gravity of the cement particles, the cement slurry forms a flocculated structure, so that 10% to 30% of the mixing water is wrapped in the cement particles, which cannot participate in the free flow and lubrication, thus affecting the fluidity of the concrete mixture. When the water reducing agent is added, the water reducing agent molecules can be adsorbed on the surface of cement particles, so that the surface of cement particles with the same charge (usually negative charge), the formation of electrostatic repulsion, promote the mutual dispersion of cement particles, flocculation structure destruction, release part of the wrapped water, participate in the flow, so as to effectively increase the fluidity of concrete mixture.
2. Lubrication:
The hydrophilic base in the water-reducing agent is very polar, so the water-reducing agent adsorption film on the surface of cement particles can form a stable solvated water film with water molecules. This water film has a good lubricating effect and can effectively reduce the sliding resistance between cement particles, thus further improving the fluidity of concrete.

3. The slow-release effect of the graft copolymer branch:
In the preparation process of polycarboxylate superplasticizer, some branched chains are grafted on the molecules of the superplasticizer. The branched chains not only provide steric hindrance effect, but also can be cut off slowly in the high alkalinity environment of cement hydration, thus releasing polycarboxylic acid with dispersing effect, thus improving the dispersion effect of cement particles and controlling slump loss.
4, steric hindrance:
The hydrophilic polyether side chain in the structure of the water reducing agent is stretched in the aqueous solution, so that a hydrophilic three-dimensional adsorption layer with a certain thickness is formed on the surface of the adsorbed cement particles. When the cement particles are close to each other, the adsorption layer begins to overlap, that is, the steric hindrance effect is generated between the cement particles. The more overlap, the greater the steric repulsion, the greater the obstacle to the cohesion between the cement particles, so that the slump of the concrete remains good.

Key words:

Polycarboxylate superplasticizer