The water reducing agent can mainly improve the strength of the mortar. It is defined as an additive which has water reducing and reinforcing effects, and is called a water reducing agent, without affecting the construction workability of the concrete.
Generally, the water reduction rate is more than 8%, which is called high-efficiency water reducing agent. The water reducing agent has many functions.
After the cement is mixed with water, due to the hydration of the cement particles, the surface of the cement particles forms an electric double layer structure, so that a solvated water film is formed.And the heterogeneous charge on the surface of the cement particles causes the cement particles to associate with each other, so that the cement slurry forms a flocculated structure.
This allows 10% to 30% of the mixing water to be wrapped in the cement particles, which cannot participate in free flow and lubrication, thus affecting the fluidity of the concrete mixture.
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 kind of charge (usually a negative charge).This will form an electrostatic repulsion, causing the cement particles to disperse each other, disintegrating the flocculation structure, releasing the wrapped water and participating 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 the water molecules.This water film has a good lubricating effect, which can effectively reduce the sliding resistance between the cement particles, thereby further improving the fluidity of the concrete.
(3) steric hindrance
The branch having hydrophilicity in the structure of the water reducing agent extends in the aqueous solution to form 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 repulsion of the space, and the greater the hindrance to the cohesion between the cement particles, so that the slump of the concrete remains good.
(4) Slow release of graft copolymerization branch
A novel water reducing agent such as a polycarboxylic acid water reducing agent is grafted with some branches on the molecule of the water reducing agent during the preparation process.
The branch not only provides a steric hindrance effect, but also, in the high alkalinity environment of cement hydration, the branch can be slowly cut off, thereby releasing a polycarboxylic acid having a dispersing action.
This improves the dispersion of cement particles and controls the slump loss.
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