Wet-mixed mortar refers to cementitious material, fine aggregate, admixture, water and various components determined according to performance. According to a certain proportion, after being measured and mixed in the mixing station, it is transported to the place of use by a mixer truck. Store the mortar mixture in a special container and use it within the specified time. The working principle of wet-mixed mortar is similar to commercial concrete, and the commercial concrete mixing station can simultaneously produce wet-mixed mortar.
1. Advantages of wet-mixed mortar
1) The wet-mixed mortar can be used directly after being transported to the site without processing, but the mortar must be stored in an airtight container;
2) The wet-mixed mortar is prepared in a professional factory, which is conducive to ensuring and controlling the quality of the mortar;
3) The choice of raw materials for wet-mixed mortar is large. The aggregate can be dry or wet, and it does not need to be dried, so the cost can be reduced. In addition, a large amount of artificial machine sand produced by industrial waste slag such as fly ash and industrial solid waste such as steel slag and industrial tailings can be mixed, which not only saves resources, but also reduces the cost of mortar.
4) The construction site has a good environment and less pollution.
2. Disadvantages of wet-mixed mortar
1) Since the wet-mixed mortar is mixed with water in a professional production plant, and the transportation volume is large at one time, it cannot be flexibly controlled according to the construction progress and usage. In addition, the wet-mixed mortar needs to be stored in an airtight container after being transported to the construction site, so an ash pond needs to be set up on site;
2) The transportation time is restricted by traffic conditions;
3) Since the wet-mixed mortar is stored on the construction site for a relatively long time, there are certain requirements for the workability, setting time and stability of the working performance of the mortar.
Hydroxypropyl methylcellulose is used as a water-retaining agent and retarder of cement mortar to make the mortar pumpable. Used as a binder in plastering plaster, it improves spreadability and prolongs the working time. The water retention performance of hydroxypropyl methylcellulose HPMC prevents the slurry from cracking due to drying too fast after application, and enhances the strength after hardening. Water retention is an important performance of hydroxypropyl methylcellulose HPMC, and it is also a performance that many domestic wet-mix mortar manufacturers pay attention to. Factors affecting the water retention effect of wet-mixed mortar include the amount of HPMC added, the viscosity of HPMC, the fineness of particles, and the temperature of the use environment.
After the wet-mixed mortar is transported to the site, it must be stored in a non-absorbent airtight container. If you choose an iron container, the storage effect is the best, but the investment is too high, which is not conducive to popularization and application; you can use bricks or blocks to build the ash pool, and then use waterproof mortar (water absorption rate less than 5%) to plaster the surface, and the investment is the lowest. However, the plastering of waterproof mortar is very important, and the construction quality of the waterproof layer plastering should be ensured. It is best to add hydroxypropyl methylcellulose HPMC material to the mortar to reduce mortar cracks. The ash pond floor should have a certain slope leveling for easy cleaning. The ash pond should have a roof with sufficient area to protect against rain and sun. The mortar is stored in the ash pool, and the surface of the ash pool should be completely covered with plastic cloth to ensure that the mortar is in a closed state.
The important role of hydroxypropyl methylcellulose HPMC in wet-mix mortar mainly has three aspects, one is excellent water retention capacity, the other is the influence on the consistency and thixotropy of wet-mix mortar, and the third is the interaction with cement. The water retention effect of cellulose ether depends on the water absorption of the base layer, the composition of the mortar, the thickness of the mortar layer, the water demand of the mortar, and the setting time of the setting material. The higher the transparency of hydroxypropyl methylcellulose, the better the water retention.
Factors affecting the water retention of wet-mix mortar include cellulose ether viscosity, addition amount, particle fineness and use temperature. The greater the viscosity of cellulose ether, the better the water retention performance. Viscosity is an important parameter of HPMC performance. For the same product, the viscosity results measured by different methods are very different, and some even have doubled differences. Therefore, when comparing viscosity, it must be carried out between the same test methods, including temperature, rotor, etc.
Generally speaking, the higher the viscosity, the better the water retention effect. However, the higher the viscosity and the higher the molecular weight of HPMC, the corresponding decrease in its solubility will have a negative impact on the strength and construction performance of the mortar. The higher the viscosity, the more obvious the thickening effect on the mortar, but it is not directly proportional. The higher the viscosity, the more viscous the wet mortar will be, that is, during construction, it is manifested as sticking to the scraper and high adhesion to the substrate. But it is not helpful to increase the structural strength of the wet mortar itself. During construction, the anti-sag performance is not obvious. On the contrary, some modified hydroxypropyl methylcellulose with medium and low viscosity has excellent performance in improving the structural strength of wet mortar.
In wet-mixed mortar, the addition amount of cellulose ether HPMC is very low, but it can significantly improve the construction performance of wet-mixed mortar, and it is a main additive that affects the construction performance of mortar. Reasonable selection of the correct hydroxypropyl methylcellulose has a great influence on the improvement of the performance of wet-mixed mortar.
Post time: Apr-04-2023