The setting time of concrete is mainly related to the setting time of cement, and the influence of aggregate is not great. Therefore, the effect of HPMC on the setting time of underwater non-dispersible concrete mixture can be studied through the setting time of mortar.
Because the setting time of mortar is affected by water. Therefore, in order to evaluate the effect of HPMC on the setting time of mortar, the water-cement ratio and mortar ratio of mortar need to be fixed.
The experimental results show that the addition of HPMC has an obvious retarding effect on the mortar mixture. The setting time of mortar prolongs with the increase of the amount of hydroxypropyl methylcellulose. In the case of the same HPMC content, the mortar formed under water is better than the mortar formed in air. Medium molding takes longer to set.
When measured in water, compared with the blank specimen, the initial setting time of the mortar mixed with hydroxypropyl methylcellulose was delayed by 6-18 h. The final setting time is delayed by 6-22 hours. Therefore, HPMC should be used in conjunction with early strength agents.
HPMC is a high molecular polymer with a macromolecular linear structure. Its functional group has a hydroxyl group. Can form hydrogen bonds with mixed water molecules. Increase the viscosity of the mixed water. The long molecular chains of HPMC attract each other. Make HPMC molecules entangled with each other. form a network structure. Cover the cement and mixing water.
Because HPMC forms a membranous network structure to wrap cement. It can effectively prevent the volatilization of moisture in the mortar. Hinder or slow down the hydration rate of cement.
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