Cellulose ether will prolong the setting time of cement paste or mortar net, delay the cement hydration kinetics, which is beneficial to improve the operative time of cement base material, improve the consistency and concrete slump after the loss, but also may delay the construction progress, especially in low temperature environment conditions for the use of mortar and concrete.
Generally, the higher the content of cellulose ether, the longer the setting time of cement slurry and mortar, and the more obvious the delayed hydration dynamics. Cellulose ether can delay the hydration of the most important clinker mineral phases tricalcium aluminate (C3A) and tricalcium silicate (C3S) in cement, but the effect on their hydration kinetics is not the same. Cellulose ether mainly reduces the reaction rate of C3S in the acceleration phase, while for C3A-Caso4 system, it mainly prolonging the induction period.
Further experiments showed that cellulose ether could inhibit the dissolution of C3A and C3S, delay the crystallization of hydrated calcium aluminate and calcium hydroxide, and reduce the nucleation and growth rate of C.S.H on the surface of C3S particles, but had little effect on ettringite crystals. Weyer et al. found that the degree of substitution DS was the main factor affecting cement hydration, and the smaller DS was, the more obvious the delayed cement hydration was. On the mechanism of cellulose ether delay cement hydration.
Sliva et al. believed that cellulose ether increased the viscosity of pore solution and hindered the rate of ion movement, thus delaying cement hydration. However, Pourchez et al. found that the relationship between cellulose ether delayed cement hydration and cement slurry viscosity was not obvious. Schmitz et al. found that the viscosity of cellulose ether had almost no effect on the hydration kinetics of cement.
Pourchez also found that cellulose ether was very stable under alkaline conditions and its delayed cement hydration could not be attributed to the decomposition of cellulose ether. Adsorption may be the real reason cellulose ether delay cement hydration, many organic additives will be adsorbed to cement particles and hydration products, prevent the dissolution of cement particles and the crystallization of hydration products, thus delaying the hydration and condensation of cement. Pourchcz et al. found that the stronger the adsorption capacity of hydration products and cellulose ether, the more obvious the delay.
It is generally believed that cellulose ether molecules are mainly adsorbed on hydration products and rarely adsorbed on the original mineral phase of clinker.
Post time: Dec-09-2021