Polycarboxylic acid water reducer is composed of carboxylic acid containing unsaturated monomer copolymerization, so that concrete in water reduction, slump protection, strengthening, shrinkage and environmental protection has a good performance of water reducer.
Poly carboxylic acid water reducing agent belongs to the surface active agent, surfactant molecules composed of hydrophilic group and hydrophobic groups in two parts, hydrophilic group, add water, pointing to the solution, hydrophobic groups to air, solid or nonpolar liquids and directional arrangement, form directional adsorption film decreases and the water's surface tension and interfacial tension.
Its basic action mechanism is that when water reducer is added to cement slurry, hydrophobic group in the molecule of water reducer is adsorbed on the surface of cement particle, reducing the surface energy.
Hydrophilic group to aqueous solution, forming a single molecule in the surface of cement particles or multimolecular adsorption film, surface of cement particles with the same charge, show the repulsion, jianshuiji molecules adsorbed on the surface of cement particles space steric repulsion between cement particle dispersion, destroyed the structure of cement flocculation, release a large number of free water, increase the liquidity of concrete mixture.
Polycarboxylic acid water reducer is sensitive to the alkali content of cement, the compatibility of cement and polycarboxylic acid water reducer is considered from the Angle of rheology, there is a good soluble alkali content of cement.
When too low or too high, the compatibility of water reducer and cement will be adversely affected.
In order to meet the index requirements of low alkali cement, some cement manufacturers cannot reach the good value of soluble alkali content in cement. In this way, not only when the content of water-reducing agent is insufficient, but also when the content is slightly higher than the saturation point, serious segregation and bleeding will occur.
High alkali content in cement will shorten setting time and increase early strength.
