hydroxypropyl methylcellulose HPMC in Plastering MortarFebruary 2nd 2023
Adding hydroxypropyl methylcellulose to cement can slow down the hydration of cement. So what do you know about its principle? Let’s take a look at hydroxypropyl methyl cellulose to delay the hydration of cement. principle.
1. Hypothesis of ion dyskinesia
We speculate that hydroxypropyl methylcellulose will increase the viscosity of the pore solution, hinder the speed of ion movement, and delay the hydration of cement. However, the lower viscosity cellulose ether in this test has a stronger ability to delay the hydration of cement. Therefore, this assumption is invalid. Pourchez and others also doubt this assumption. In fact, the ion migration or migration time is very short, obviously not much different from the delay of cement hydration.
2. Alkaline degradation
Polysaccharides are easily degraded under alkaline conditions to produce hydroxycarboxylic acids that delay cement hydration. Therefore, the reason for the delayed hydration of hydroxypropylmethyl cellulose may be due to its degradation in alkaline cement slurry to form hydroxycarboxylic acid. However, Pourchez et al. found that cellulose ethers are very stable under alkaline conditions, with only slight degradation, and the degradation products have little effect on the delay of cement hydration.
Adsorption can be the real reason why hydroxypropyl methylcellulose hinders cement hydration because many organic additives will adsorb on cement particles and hydration products, preventing the dissolution of cement particles and crystallization of hydration products, thereby delaying the hydration of cement And condensation. Pourchez et al found that cellulose ether is easily adsorbed on the surface of hydrated products such as calcium hydroxide, C.S.H gel and calcium aluminate hydrate, but is not easily adsorbed by ettringite and unhydrated phase. Moreover, in the case of cellulose ethers, the adsorption capacity of HEC is stronger than that of swollen MC. The lower the content of hydroxyethyl or hydroxypropyl in HPC, the stronger the adsorption capacity: in terms of hydrated products, the adsorption capacity of calcium hydroxide is stronger than CSH. Further analysis also shows that the adsorption capacity of hydration products and cellulose ether is related to the delay of cement hydration: the stronger the adsorption, the more obvious the delay, but the ettringite adsorption of cellulose ether is weak, but its formation Significantly delayed. MUllert’s research also shows that cellulose ether has a strong adsorption effect on tricalcium silicate and its hydration products, which obviously delays the hydration process of the silicate phase. The adsorption amount of ettringite is very low, but calcium The formation of ettringite is significantly delayed because the delayed ettringite formation is affected by the Ca 2+ balance in the solution, which is an extension of cellulose ether. Late silicate hydration continues.
These are the principles of hydroxypropyl methyl cellulose to delay the hydration of cement. We hope that the above knowledge will allow everyone to understand the product’s mechanism of action and use it better.