One of the biggest differences between dry-mixed mortar and traditional mortar is that the dry-mixed mortar is modified with a small amount of chemical additives. Adding one additive to dry powder mortar is called primary modification, adding two or more additives is called secondary modification. The quality of dry powder mortar depends on the correct selection of components and the coordination and matching of various components. Because chemical additives are more expensive, and have a greater impact on the performance of dry powder mortar. Therefore, when selecting additives, the amount of additives should be given top priority. The following is a brief introduction to the selection method of chemical additive cellulose ether.
Cellulose ether is also called rheology modifier, an admixture used to adjust the rheological properties of freshly mixed mortar, and is used in almost every kind of mortar. The following properties should be considered when selecting its variety and dosage:
(1) Water retention at different temperatures;
(2) Thickening effect, viscosity;
(3) The relationship between consistency and temperature, and the influence on consistency in the presence of electrolyte;
(4) The form and degree of etherification;
(5) Improvement of mortar thixotropy and positioning ability (this is necessary for mortar painted on vertical surfaces);
(6) Dissolution speed, conditions and completeness of dissolution.
In addition to adding cellulose ether (such as methyl cellulose ether) to dry powder mortar, polyvinyl acid vinyl ester can also be added, that is, secondary modification. The inorganic binders (cement, gypsum) in the mortar can ensure high compressive strength, but have little effect on tensile strength and flexural strength. Polyvinyl acetate builds up an elastic film within the pores of the cement stone, enabling the mortar to withstand high deformation loads and improving wear resistance. Practice has proved that adding different amounts of methyl cellulose ether and polyvinyl acid vinyl ester to dry powder mortar can prepare thin-layer smearing plate bonding mortar, plastering mortar, decorative painting mortar, and masonry mortar for aerated concrete blocks And self-leveling mortar for pouring floors, etc. Mixing the two can not only improve the quality of the mortar, but also greatly improve the construction efficiency.
In practical application, in order to improve the overall performance, it is necessary to use multiple additives in combination. There is an optimal matching ratio among the additives. As long as the dosage range and ratio are appropriate, they can improve the performance of the mortar from different aspects. However, when used alone, the modification effect on the mortar is limited, and sometimes even Negative effects, such as adding cellulose alone, while increasing the cohesiveness of the mortar and reducing the degree of delamination, greatly increase the water consumption of the mortar and keep it inside the slurry, which leads to a large decrease in the compressive strength; When mixed with air-entraining agent, although the degree of stratification of the mortar can be greatly reduced, and the water consumption is also greatly reduced, but the compressive strength of the mortar will tend to decrease due to more air bubbles. In order to improve the performance of the masonry mortar to the greatest extent, and at the same time avoid harm to other properties of the mortar, the consistency, layering and strength of the masonry mortar must meet the requirements of the project and the relevant technical specifications. At the same time, no lime paste is used, saving For cement, environmental protection, etc., it is necessary to take comprehensive measures, develop and use composite admixtures from the perspectives of water reduction, viscosity increase, water retention and thickening, and air-entraining plasticization.