1. Heat of hydration

According to the release curve of the heat of hydration over time, the hydration process of cement is usually divided into five stages, namely, the initial hydration period (0~15min), the induction period (15min~4h), the acceleration and setting period (4h~8h ), deceleration and hardening period (8h~24h), and curing period (1d~28d).

The test results show that in the early stage of induction (i.e., the initial hydration period), when the amount of HEMC is 0.1% compared with the blank cement slurry, an exothermic peak of the slurry is advanced and the peak is significantly increased. When the amount of HEMC increases to When it is above 0.3%, the first exothermic peak of the slurry is delayed, and the peak value gradually decreases with the increase of HEMC content; HEMC will obviously delay the induction period and acceleration period of cement slurry, and the greater the content , the longer the induction period, the more backward the acceleration period, and the smaller the exothermic peak; the change of cellulose ether content has no obvious effect on the length of the deceleration period and the stability period of the cement slurry, as shown in Figure 3(a) It is shown that cellulose ether can also reduce the heat of hydration of cement paste within 72 hours, but when the heat of hydration is longer than 36 hours, the change of cellulose ether content has little effect on the heat of hydration of cement paste, such as Figure 3(b).

Fig.3 Variation trend of hydration heat release rate of cement paste with different content of cellulose ether (HEMC)

2. Mechanical properties：

By studying two kinds of cellulose ethers with viscosities of 60000Pa·s and 100000Pa·s, it was found that the compressive strength of the modified mortar mixed with methyl cellulose ether decreased gradually with the increase of its content. The compressive strength of the modified mortar mixed with 100000Pa·s viscosity hydroxypropyl methyl cellulose ether increases first and then decreases with the increase of its content (as shown in Figure 4). It shows that the incorporation of methyl cellulose ether will significantly reduce the compressive strength of cement mortar. The more the amount is, the smaller the strength will be; the smaller the viscosity, the greater the impact on the loss of mortar compressive strength; hydroxypropyl methyl cellulose ether When the dosage is less than 0.1%, the compressive strength of the mortar can be appropriately increased. When the dosage is more than 0.1%, the compressive strength of the mortar will decrease with the increase of the dosage, so the dosage should be controlled at 0.1%.

Fig.4 3d, 7d and 28d compressive strength of MC1, MC2 and MC3 modified cement mortar

(Methyl cellulose ether, viscosity 60000Pa·S, hereafter referred to as MC1; methyl cellulose ether, viscosity 100000Pa·S, referred to as MC2; hydroxypropyl methylcellulose ether, viscosity 100000Pa·S, referred to as MC3).

3. Clotting time：

By measuring the setting time of hydroxypropyl methylcellulose ether with a viscosity of 100000Pa·s in different dosages of cement paste, it was found that with the increase of HPMC dosage, the initial setting time and final setting time of cement mortar were prolonged. When the concentration is 1%, the initial setting time reaches 510 minutes, and the final setting time reaches 850 minutes. Compared with the blank sample, the initial setting time is extended by 210 minutes, and the final setting time is extended by 470 minutes (as shown in Figure 5). Whether it is HPMC with a viscosity of 50000Pa s, 100000Pa s or 200000Pa s, it can delay the setting of cement, but compared with the three cellulose ethers, the initial setting time and final setting time are prolonged with the increase of viscosity, as shown in Figure 6 shown. This is because cellulose ether is adsorbed on the surface of cement particles, which prevents water from contacting with cement particles, thus delaying the hydration of cement. The greater the viscosity of cellulose ether, the thicker the adsorption layer on the surface of cement particles, and the more significant the retarding effect.

Fig.5 Effect of cellulose ether content on setting time of mortar

Fig.6 Effect of different viscosities of HPMC on the setting time of cement paste

(MC-5(50000Pa·s), MC-10(100000Pa·s) and MC-20(200000Pa·s))

Methyl cellulose ether and hydroxypropyl methyl cellulose ether will greatly prolong the setting time of cement slurry, which can ensure that the cement slurry has enough time and water for hydration reaction, and solve the problem of low strength and late stage of cement slurry after hardening. cracking problem.

4. Water retention:

The effect of cellulose ether content on water retention was studied. It is found that with the increase of the content of cellulose ether, the water retention rate of mortar increases, and when the content of cellulose ether is greater than 0.6%, the water retention rate tends to be stable. However, when comparing three kinds of cellulose ethers (HPMC with a viscosity of 50000Pa s (MC-5), 100000Pa s (MC-10) and 200000Pa s (MC-20)), the influence of viscosity on water retention is different. The relationship between water retention rate is: MC-5.

Figure 7 Effect of HPMC content on the water retention rate of mortar