Cellulose ether can delay the hydration of cement to varying degrees. It is manifested in delayed formation of ettringite, C-S-H gel and calcium hydroxide.

The current mechanism of cellulose ether delaying cement hydration mainly includes the hypothesis that ion movement is hindered, alkali degradation and adsorption.

Silva et al. Hypothesized that cellulose ether increased the viscosity of the pore solution, hindered the rate of ion movement, and thereby delayed cement hydration.

However, in this test, cellulose ether with lower viscosity has stronger ability to delay cement hydration.

Therefore, this assumption does not hold, and Pourchez et al. Also doubt this assumption.

In fact, the time for ion movement or migration is very short, which is obviously incomparable with the delay time of cement hydration.

Polysaccharides tend to degrade easily under alkaline conditions to produce hydroxycarboxylic acids that delay cement hydration.

Therefore, the reason why cellulose ether delays cement hydration may be that it degrades to form hydroxycarboxylic acids in alkaline cement slurry.

But the research of Pourchez et al. Found that cellulose ether is very stable under alkaline conditions.

There is only slight degradation, and the degradation products have little effect on the delay of cement hydration.

I.

Adsorption may be the real reason for delaying cement hydration by cellulose ethers. Many organic additives are adsorb on cement particles and hydration products. Prevent the dissolution of cement particles and the crystallization of hydration products, thereby delaying the hydration and setting of cement.

Pourchez et al. Found that cellulose ether easily adsorbed to calcium hydroxide and C. S. H gel and hydrated calcium aluminate surface.

But it is not easy to be adsorbed by ettringite and unhydrated phase. Moreover, in terms of cellulose ether, HEC has a stronger adsorption capacity than swollen MC.

The lower the content of hydroxyethyl in HEC or hydroxypropyl in HPMC, the stronger the adsorption capacity: in terms of hydration products, the adsorption capacity of calcium hydroxide is better than C. S. H has a stronger adsorption capacity.

Further analysis also shows that the adsorption capacity of hydration products and cellulose ether has a corresponding relationship with the delay of cement hydration:

The stronger the adsorption, the more obvious the delay. However, ettringite has a weaker adsorption on cellulose ether, but its formation is significantly delay.

MUllert’s research also shows that cellulose ether has strong adsorption on tricalcium silicate and its hydration products. Therefore, the silicate phase hydration was significantly delayed, and the adsorption of ettringite was low, but the formation of ettringite was significantly delayed.

This is because the delay in the formation of ettringite is affected by the balance of Ca2 + in the solution, which is a continuation of the delay of silicate hydration by cellulose ether.

Ⅱ.

In the test results of this paper, HEC has a better ability to delay than MC, and cellulose ether has a better ability to delay the formation of calcium hydroxide than C. S. The ability of H gel and ettringite is strong.

This is related to the literature [86. S7lq butyl cellulose ether has a corresponding relationship with the adsorption capacity of cement hydration products, further confirming that adsorption may be the real reason for the delay of cement hydration by cellulose ether.

And the stronger the adsorption capacity of cellulose ether and cement hydration products, the more obvious the delayed hydration products are.

The previous test results show that different cellulose ethers have different effects on the delayed hydration of Portland cement.

The delay effect of the same cellulose ether on different hydration products is different, which indicates that the adsorption of cellulose ether by portland cement hydration products is selective. Cellulose ether is also selective for the adsorption of cement hydration products.

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