The Hydration Stage of Polycarboxylate Superplasticizer

The exothermic state during the hydration process of cement varies with its different stages, primarily originating from the dissolution of minerals and the nucleation and growth of hydration products. The initial interaction form of polycarboxylate superplasticizers with cement paste influences the dissolution rate of minerals, the ion concentration in pore solution, and the nucleation and growth rate of hydration products. Polycarboxylate superplasticizers can increase the initial dissolution rate of cement and can form complexes with Ca2+ ions and Al3+ ions.

Upon adding water to cement, rapid chemical reactions begin. During the crystallization nucleation process, hydration is in a stage of extensive nucleation where a large amount of ionic solution envelops the cement particles and a small portion of free hydration products. As it enters the phase boundary reaction process, a significant number of ions pass through the phase boundaries of cement particles and hydration products, causing the continuous growth of hydration products. With the increasing amount of hydration products, C-S-H (calcium silicate hydrate) gel gradually precipitates on the particle surface and forms a hydration product film, leading to increased difficulty in ion migration. In the diffusion reaction process, the formation rate of hydration products is controlled by the speed at which reactants diffuse through the already formed hydration product layer towards the surface of unhydrated particles.

This passage describes the complex interactions between cement and water during hydration, highlighting the role of polycarboxylate superplasticizers in this process and the various stages that occur as hydration progresses.