With the rapid development of the concrete industry, there are higher requirements for the admixtures used in concrete, especially the performance of water reducing agents. Polycarboxylic acid high performance water reducing agent is the latest generation of water reducing agent, its high water reducing rate, good dispersion performance and plastic retention, so that it can rapidly expand the application field, and gradually replace naphthalene series, melamine and other high efficiency water reducing agent. However, due to the characteristics of molecular structure of polycarboxylic acid superplasticizer, more bubbles are introduced in concrete mixing, and the size is not uniform, which affects the quality of concrete. It is necessary to improve the workability of concrete by adding defoamer to meet the production demand. The combination with polycarboxylic acid superplasticizer requires good compatibility between defoamer and superplasticizer, little influence on the water reduction rate of superplasticizer and workability of concrete.






Defoamer is also known as anti-foam agent, there are many kinds, organic siloxane, silicon and ether grafting, containing amine, imide and amide, with faster defoaming speed, longer foam suppression time, a wider range of applicable media, and even harsh media environment such as high temperature, strong acid and strong base characteristics. It is widely used to remove the harmful foam produced in the production process of latex, textile sizing, food fermentation, biomedicine, coating, petrochemical, paper making, industrial cleaning and other industries. At present, most of the antifoam agents used in concrete mortar are composites of modified polyether and modified polysiloxane as main agents.




Polyether is a class of polymers composed of C-O-C bonds, which are mainly formed by embedding ethylene oxide (EO), propylene oxide (PO) or ethylene oxide butane (BO) on active O-H or N-H bonds using bimetallic catalysts or strong bases as catalysts. Polyether is used as a defoamer mainly by taking advantage of the relationship between its solubility and temperature. For non-ionic surfactants containing EO, the solubility of polyether in water changes from water soluble to water insoluble with the increase of temperature. When polyether exists in water in a certain size of particles, it is in line with the characteristics of the "insoluble foaming medium" this defoamer, therefore, it can act as a defoamer in some media at this time, especially some industries and fields that can not use silicone as a defoamer, such as steel plate cleaning, circuit board cleaning, paper industry and so on. However, in many practical cases, the defoaming ability of polyether is not enough, and the actual defoaming temperature range is large, at this time the polyether defoaming agent polyether shows obvious defects. Therefore, it is necessary to modify polyether, the general modification method is to use the active group and the hydroxyl group on the polyether structure reaction, the unit reaction involved mainly esterification reaction, condensation reaction. The modified substances include fatty acids, coupling agents, fatty alcohols, etc.




The modified polyether defoamer has a wider application range and better effect, which can eliminate the excess large bubbles in the concrete and make the appearance of the concrete more beautiful. At the same time, the pore structure and density of the concrete are improved by reducing the gas content of the polycarboxylic acid superplasticizer.




The change of concrete strength is mainly affected by the gas content of concrete after adding defoamer and air entraining agent. The experiment shows that with the increase of the amount of defoamer, the gas content and water reduction rate of concrete decrease, and in severe cases, water leakage and bottom stripping occur, which makes the workability of concrete worse, so there is an optimal range of the amount of defoamer. In the process of use, we should pay attention to three points: 1. When the antifoam agent is used in the production of concrete with polycarboxylate series water reducing agent, the gas content of polycarboxylate water reducing agent will be reduced, and the concrete paste will be relatively sticky. It is recommended to add air entraining agent after adding the antifoam agent to eliminate the uneven large bubbles in the polycarboxylic acid and introduce uniform small bubbles, which can increase the ease of concrete. 2. The dispersibility of the defoamer with water and admixtures is strong, and it is easy to separate after a long time. It is recommended to stir continuously during this period. 3. The defoamer may reduce its performance due to alkalinity, so please avoid using it when pH value is above 10.