The development and application of polycarboxylic superplasticizer is relatively rapid. Especially in major and key projects such as water conservancy, hydropower, hydraulic engineering, marine engineering, and bridges, polycarboxylate superplastisizer are widely used.
After the cement is mixed with water, the cement slurry forms a flocculation structure due to the molecular gravity of the cement particles, so that 10% to 30% of the mixing water is wrapped in the cement particles and cannot participate in free flow and lubrication, thus affecting the Flowability of concrete mix. When the supreplasticizer is added, the water-reducing agent molecules can be directionally adsorbed on the surface of the cement particles, so that the surfaces of the cement particles have the same charge (usually negative charge), forming electrostatic repulsion, which promotes the mutual dispersion of the cement particles and the destruction of the flocculation structure. , releasing part of the wrapped water to participate in the flow, thereby effectively increasing the fluidity of the concrete mixture.
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 a good lubrication effect and can effectively reduce the sliding resistance between cement particles, thereby further improving the fluidity of mortar and concrete.
The hydrophilic branched chain in the superplasticizer structure stretches in the aqueous solution, thereby forming a hydrophilic three-dimensional adsorption layer with a certain thickness on the surface of the adsorbed cement particles. When the cement particles are close to each other, the adsorption layers begin to overlap, that is, steric hindrance occurs between the cement particles. The more overlap, the greater the steric repulsion, and the greater the obstruction to the cohesion between cement particles, making the mortar and concrete Slump remains good.
During the preparation process of the polycarboxylate water-reducing agent, some branched chains are grafted on the molecules of the water-reducing agent. This branched chain not only provides steric hindrance effect, but also, in the high alkalinity environment of cement hydration, The branch chain can also be slowly cut off, thereby releasing polycarboxylic acid with dispersing effect, which can improve the dispersion effect of cement particles and control slump loss.
Post time: Mar-29-2024