Hydroxypropyl methyl cellulose (HPMC for short) has excellent thickening property and can be used as an excellent anti dispersion agent for concrete. In the past, this material was a fine chemical product in short supply in China, with high cost. Due to various reasons, its application in China’s construction industry was limited.
In recent years, with the continuous development of external wall thermal insulation technology, the continuous progress of cellulose production technology, and the excellent characteristics of HPMC itself, HPMC has been widely used in the construction industry. In the setting time test, the setting time of concrete is mainly related to the setting time of cement, and the aggregate has little influence. Therefore, the setting time of mortar can be used to replace the influence of HPMC on the setting time of underwater non dispersive concrete mixture. Since the setting time of mortar is affected by the water cement ratio and cement sand ratio
For the influence of HPMC on the setting time of mortar, it is necessary to fix the water cement ratio and cement sand ratio of mortar.It can be seen from the experiment that the addition of HPMC has an obvious retarding effect on the mortar mixture, and the setting time of the mortar increases with the increase of the amount of HPMC. With the same amount of HPMC, the setting time of the mortar formed under water is longer than that formed in air.
The long molecular chains of HPMC will attract each other, making HPMC molecules intertwine to form a network structure, and wrapping cement and mixing water. As HPMC forms a network structure similar to a film and wraps the cement, it can effectively prevent the volatilization of water in the mortar and hinder or slow down the cement hydration rate. In the bleeding test, the bleeding phenomenon of mortar is similar to that of concrete, which will cause serious settlement of aggregate, increase the water cement ratio of the top layer slurry, make the top layer slurry shrink greatly in the early stage, even crack, and the strength of the slurry surface is relatively weak. It can be seen from the experiment that when the content is above 0.5%, there is basically no bleeding phenomenon. This is because when HPMC is mixed into mortar, HPMC has film-forming and reticular structure, as well as the adsorption of hydroxyl on the long chain of macromolecule, which makes the cement and mixing water in mortar form flocculent, ensuring the stable structure of mortar. When HPMC is added to mortar, many independent tiny bubbles will be formed. These bubbles will be evenly distributed in the mortar and hinder the deposition of aggregates. This technical performance of HPMC has a great impact on cement-based materials, and is often used to prepare new cement-based composites such as dry mortar and polymer mortar, so that they have good water and plastic retention.
The water demand test of mortar has a great influence on the water demand of mortar when the amount of HPMC is very small.
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Post time: Oct-31-2022