Water-Reducing Agent
Polycarboxylic acid-based water-reducing agents have developed and been applied rapidly. They are widely used in major and key engineering projects such as water conservancy, hydropower, water engineering, marine engineering, and bridge construction.
Mechanism of Polycarboxylic Acid Water-Reducing Agent
When cement is mixed with water, due to the intermolecular forces between cement particles, the cement paste forms a flocculent structure, causing 10%–30% of the mixed water to be encapsulated within the cement particles. This prevents the water from freely flowing and lubricating, thereby impairing the workability of the concrete mixture. When water-reducing agents are added, their molecules selectively adsorb onto the surfaces of cement particles, imparting the same charge (typically negative) to the particle surfaces. This creates electrostatic repulsion, causing the particles to disperse and break down the flocculent structure. As a result, the water previously encapsulated is released and can participate in flow, thereby effectively improving the workability of the concrete mixture.
Polycarboxylic Acid Water-Reducing Agent Main Performance Characteristics
The hydrophilic groups in the water-reducing agent have strong polarity, enabling the water-reducing agent adsorption film on the cement particle surface to form a stable solvated water film with water molecules. This water film has excellent lubricating properties, effectively reducing the sliding resistance between cement particles, thereby further improving the flowability of mortar and concrete.
The water-soluble side chains in the structure of the water-reducing agent extend into the aqueous solution, forming a water-soluble three-dimensional adsorption layer of a certain thickness on the surface of the adsorbed cement particles. When cement particles approach each other, the adsorption layers begin to overlap, creating a spatial steric effect between the particles. The more overlap, the greater the steric repulsive force, which in turn inhibits the cohesive force between cement particles, thereby maintaining good slump stability in mortar and concrete.
During the preparation of polycarboxylic acid water-reducing agents, side chains are grafted onto the molecules of the water-reducing agent. These side chains not only provide spatial steric effects but also, in the high-alkalinity environment of cement hydration, can be gradually cleaved, releasing polycarboxylic acids with dispersing properties. This enhances the dispersion of cement particles and controls slump loss.