The rapid development of the concrete industry has raised higher requirements for the admixtures used in concrete, especially the performance of water reducers. Polycarboxylate high-performance water reducer is the latest generation of water reducer, with high water reduction rate, good dispersibility and plasticity, which enables it to quickly expand its application fields and gradually replace high-efficiency water reducers such as naphthalene and melamine. However, due to the characteristics of its molecular structure, polycarboxylate superplasticizers introduce a large number of bubbles with uneven sizes during concrete mixing, which affects the quality of concrete. Therefore, it is necessary to improve the workability of concrete by adding defoamers to meet production needs. The compounding with polycarboxylate superplasticizer requires good compatibility between defoamer and superplasticizer, minimal impact on the water reduction rate of superplasticizer, and workability of concrete.
Defoamers, also known as anti foaming agents, come in many types, including organosiloxane, silicon and ether grafted, amine, imine and amide containing ones. They have faster defoaming speed, longer foam suppression time, wider applicability to various media, and even harsh media environments such as high temperature, strong acid and strong alkali. It is widely used to remove harmful foam generated 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 defoamers used in concrete mortar are composite compounds mainly composed of modified polyether and modified polysiloxane.
The modified polyether defoamer has a wider range of applications and better effects. It can eliminate excess large bubbles in concrete, making the appearance of concrete more beautiful. At the same time, by reducing the air content of polycarboxylate superplasticizer, it improves the pore structure and compactness of concrete.
The strength change of concrete is mainly affected by the air content of concrete after adding defoamers and air entraining agents. Experiments have shown that with the increase of defoamer dosage, the air content and water reduction rate of concrete decrease, and in severe cases, bleeding and bottom scraping may occur, resulting in poor workability of concrete. Therefore, there is an optimal dosage range for defoamers.
We should pay attention to three points during use:
1. When using defoamers in the production of concrete with polycarboxylate superplasticizers, the air content of polycarboxylate superplasticizers will be reduced, and the concrete slurry will be relatively sticky. It is recommended to add air entraining agents after adding defoamers to eliminate uneven large bubbles in polycarboxylates and introduce uniform small bubbles, which can increase the workability of concrete.
2. Defoamers have strong dispersibility with water and additives, and are prone to separation after prolonged storage. It is recommended to continue stirring during this period.
3. Defoamers may experience a decrease in performance due to alkalinity, please avoid using them at pH values above 10.
