The role of concrete plasticizer in coagulation principle analysis

Concrete plasticizer refers to an admixture that can reduce the amount of water used for mixing and increase the strength of concrete under the condition that the workability of the concrete is constant and the amount of cement is endless.

The effect of concrete plasticizer on fresh concrete is mainly manifested in the following aspects:

Concrete plasticizer effect

The mechanism of plasticizer impact is primarily due to the adsorption of softener by cement particles and the dispersion of cement particles by water-reducing agents. After the water reducing agent is added to the concrete, it will be separated into macromolecular anions and metal cations (such as Na +, Ca 2+). Macromolecular anions exhibiting vigorous surface activity are adsorbed on the surface of cement particles, causing the cement particles to be negatively charged, and the cement particles are dispersed due to the same charge repulsion. At the same time, because the plasticizer is hydrophilic and the adsorption layer is a solvated film around the cement particles, it can also hinder cement cohesion (space protection effect), so the cement particles and secondary coacervated particles are dispersed and released. The water and air contained in the flocculent aggregates can reduce water.

2. Plasticizing effect

After mixing water-reducing admixtures in concrete, the fluidity can be significantly increased without changing the water-cement ratio, which is called plasticizing of concrete. In addition to the effects of adsorption and dispersion, the plasticizing fact also has the effects of wetting and lubricating impact. Due to these several functions of the water reducing agent, as long as a small amount of water is used, the concrete can be easily mixed uniformly, and the workability of the freshly brewed concrete is significantly improved.

3. Regulating effect

The charged ions dissociated in the cement-water system can be adsorbed on the surface of the cement particles to increase the zeta potential, so the stabilization time of the system is longer. At the same time, such an anion adsorbing membrane and the water film produced by the hydrogen bonding association will also hinder the contact between cement particles and water, slow down the hydration effect, and thus can retard the setting.

• Mechanism of water reducing agent

water-reducing admixtures is a typical surfactant. For any water reducing agent, its molecular structure includes two parts: a polar group and a non-polar group. The extreme group is adsorbed on the surface of the cement particles, which mainly determines the affinity of the water, reducing agent molecules to the mineral components of the cement particles. It appears to affect the chemical and physical properties of the entire water reducer molecule or ion. When the water reducing agent molecules (or atoms) are directionally adsorbed on the surface of the cement mineral component, the non-polar groups face outwards to form a hydrophobic film layer, so the hydrophobicity is affected. At the same time, non-polar groups also affect the affinity of cement particles and the adsorption capacity of polar groups.

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