Concrete water reducer is the most widely used and most effective mixing material among the concrete admixtures. Its main function is to improve the rheological properties of the concrete mixture. Adding a water-reducing agent to concrete can reduce water consumption, lower water-cement ratio, improve the hardening performance of concrete, increase concrete strength, increase concrete rheology, and save cement consumption. Without changing the ration of various raw materials other than cement and the strength of concrete, adding a certain proportion of concrete water reducing agent can save more than 15%-30% of the amount of cement.
Classification of Concrete Water Reducer
According to the water reducing and enhancing ability of concrete water reducer, it is divided into the following types. Ordinary water reducing agent, also known as plasticizer. Its water reducing rate is not less than 8%, represented by lignosulfonates. Superplasticizer, the water reducing rate isn’t less than 14%, including naphthalene series, melamine series, sulfamate series, aliphatic series, etc. High-performance water-reducing agent, the water-reducing rate is not less than 25%, represented by polycarboxylic acid-based water reducer. It can also be divided into early strength type, standard type and retarded type.
According to the chemicals composition, it is usually divided into lignosulfonate superplasticizer, naphthalene superplasticizer, melamine superplasticizer, sulfamate superplasticizer, fatty acid superplasticizer and polycarboxylate superplasticizer.
Mechanism of Action
Dispersion. After the cement is mixed with water, due to the hydration of the cement particles, and electric double layer structure is formed on the surface of the cement particles to form a solvated water film. In addition, the surface of the cement particles has an opposite charge to cause the association between the cement particles and the cement slurry to form a flocculating structure, so that 10%-30% of the mixing water is wrapped in the cement particles and can’t participate in free flow and lubrication. This will affect the fluidity of the concrete mixture. When the water reducing agent is added, the molecules of concrete water reducers can be directionally adsorbed on the surface of the cement particles, so that the surface of the cement particles is charged with the same kind of electric charge, forming an electrostatic repulsion effect. This can promote the mutual dispersion of cement particles, the disintegration of the flocculation structure, release part of the water that is wrapped and participate in the flow, thereby effectively increasing the fluidity of the concrete mixture.
Lubrication. The hydrophilic group in the concrete water reducer 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, thereby further improving the fluidity of the concrete.
Steric hindrance. The hydrophilic branch in the water reducer 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 approach, the adsorption layer begins to overlap, that is, steric hindrance is generated between the cement particles. The more overlap, the greater the steric hindrance and the greater the hindrance to the cohesion between cement particles, so that the slump of the concrete is maintained well.
The slow-release effect of graft copolymer branch chain. In the preparation process of new water-reducing agents such as polycarboxylic acid concrete water reducing agent, some branched chains are grafted on the molecules of the water-reducing agent. The branched chains can not only provide steric hindrance, but also can be slowly cut off in the high alkalinity environment of cement hydration, thereby releasing substances with dispersing effect, which can improve the dispersion of cement particles and control the slump loss.