Cellulose ether HPMC will prolong the setting time of cement paste or mortar and delay the hydration kinetics of cement, which is beneficial to increase the operating time of cement-based materials, improve the consistency of mortar and the loss of concrete slump over time, but it is also possible It will delay the construction progress, especially the mortar and concrete used in low temperature environment.
Generally, the higher the content of cellulose ether HPMC, the longer the setting time of cement slurry and mortar, and the more obvious the delayed hydration kinetics. Cellulose ether will delay the hydration of the most important clinker mineral phases tricalcium aluminate (C3A) and tricalcium silicate (C3S) in cement, but they affect their hydration kinetics in different ways. Cellulose Ether mainly reduces the reaction speed of C3S in the acceleration period, while for the C3A-CaSO4 system, it mainly prolongs the induction period.
Further experiments showed that the cellulose ether HPMC can hinder the dissolution of C3A and C3S, delay the crystallization of calcium aluminate hydrate and calcium hydroxide, and reduce C. S. The nucleation and growth rate of H on the surface of C3S particles has little effect on ettringite crystallization. The technicians of Gomez Chemical found that the DS is the main factor affecting the hydration of cement by cellulose ether. The smaller the DS, the more obvious the delayed cement hydration. Regarding the mechanism of cellulose ether HPMC delaying cement hydration. Sliva et al. believed that cellulose ether increased the viscosity of the pore solution and hindered the rate of ion movement, thereby delaying cement hydration.
However, research by chemical technicians found that the relationship between the delayed cement hydration of cellulose ether HPMC and the viscosity of cement paste is not obvious. The technical staff of Gomez found that the viscosity of the cellulose ether HPMC hardly has any effect on the kinetics of cement hydration. The technical staff of Gomez also found that the cellulose ether HPMC is very stable under alkaline conditions, and its delayed cement hydration cannot be attributed to the decomposition of cellulose ether. Adsorption may be the real reason why the cellulose ether HPMC delays cement hydration. Many organic additives will adsorb to cement particles and hydration products to prevent the dissolution of cement particles and the crystallization of hydration products, thereby delaying the hydration and coagulation of cement. The technicians of Gomez Chemical found that the stronger the adsorption capacity of the hydration product and the cellulose ether HPMC, the more obvious the delay. It is generally believed that cellulose ether HPMC molecules are mainly adsorbed on hydration products, and rarely on the original mineral phase of clinker.Tags: HPMC