Water reducing effect is an important role of surfactant in cement hydration process. Water reducing agent can reduce the unit water consumption without affecting the workability of concrete; or it can improve the workability of concrete without changing the unit water consumption; or it has the above two effects at the same time, but does not significantly change the air content. At present, the concrete water reducing agents used are all surfactants, belonging to anionic surfactants.
After mixing cement with water, hydration reaction occurs and some flocculation structure appears, which is wrapped with a lot of mixing water, thus reducing the workability of fresh concrete (also known as workability, mainly refers to the performance of fresh concrete in construction, that is, in the process of mixing, transportation, pouring, etc., it can keep uniform and dense without stratification segregation). In order to maintain the required workability in construction, the mixing water volume must be increased accordingly. Because the increase of water volume will make the cement paste structure form too many pores, which will seriously affect the physical and mechanical properties of hardened concrete. If these wrapped water can be released, the water consumption of concrete can be greatly reduced. In the process of preparing concrete, adding appropriate amount of water reducing agent can play such a good role.
When water reducing agent is added into concrete, the hydrophobic group of water reducing agent is adsorbed on the surface of cement particles, while the hydrophilic group points to the water solution, forming a monolayer or multi-layer adsorption membrane. Due to the directional adsorption of surfactant, the surface of cement particles has the same sign of electric charge. Under the action of the same-sex repulsion, not only can the cement water system be in a relatively stable suspension state, but also the flocculation structure formed in the initial stage of water addition can be dispersed and disintegrated, thus releasing the water in the flocculation structure and achieving the purpose of reducing water. After adding water reducing agent, not only the workability of fresh concrete can be improved, but also the internal pore volume of cement paste is significantly reduced, the cement paste is more dense, and the compressive strength of concrete is significantly improved due to the large reduction of water cement ratio. The addition of water reducing agent also affects the hydration speed and setting time of cement. These properties are very important in practice.