The setting time of concrete is mainly related to the setting time of cement, and the effect of aggregate is not large. Therefore, the setting time of mortar can be used to study the effect of Hydroxypropyl methylcellulose HPMC on the setting time of underwater non-dispersed concrete mixtures. Since the setting time of mortar is affected by water Therefore, in order to evaluate the influence of HPMC on the setting time of mortar, it is necessary to fix the water-cement ratio and mortar ratio of mortar.
The experimental results show that the addition of Hydroxypropyl methylcellulose HPMC has an obvious retarding effect on the mortar mixture, and the setting time of the mortar is prolonged with the increase of the content of Hydroxypropyl methylcellulose. Under the same content of HPMC, the mortar formed under water is better than the mortar formed in the air. Longer setting times for medium molding. When measured in water, the setting time of the mortar mixed with Hydroxypropyl methylcellulose was 6-18 h delayed at the initial setting and 6-22 h at the final setting compared with the blank specimen. Therefore, HPMC should be used in combination with early strength agent.
HPMC is a macromolecular polymer with a macromolecular linear structure with hydroxyl groups on the functional groups, which can form hydrogen bonds with the mixing water molecules and increase the viscosity of the mixing water. The long molecular chains of HPMC will attract each other, so that the HPMC molecules are entangled with each other to form a network structure, which wraps the cement and mixing water. Because HPMC forms a film-like network structure and wraps the cement, it can effectively prevent the volatilization of water in the mortar and hinder or slow down the hydration speed of the cement.
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