As the latest generation of high-performance admixtures, water-reducing admixtures are increasingly used in engineering applications, from precast concrete components to cast-in-place concrete, from self-compacting concrete, fair-faced concrete to special concrete requiring rapid setting and early strength. From railways, bridges, hydropower and other fields to municipal and civil construction projects, water-reducing agents are occupying an increasing market share. However, after all, the application time of polycarboxylic acid water-reducing agents is still relatively short. Basic research on its application technology There are still relatively few users. Most of the users rely on past experience or even feeling. There are inevitably some misunderstandings in application and even understanding, but you don’t have to worry.
What are the precautions in the application of water-reducing agents?
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Common descriptions of the performance of polycarboxylic acid water-reducing agents are: high water-reducing rate, very good adaptability to cement, good workability of concrete, no loss of slump in one hour, etc. In fact, the glue The composition of concrete materials is complex and changeable. From the perspective of adsorption-dispersion mechanism, it is impossible for any admixture to adapt to all situations. The polycarboxylic acid admixture has good adaptability to cement compared with Cai series water-reducing admixtures.
Outstanding characteristics of water reducing agents
Compared with other high-efficiency water reducing agents, the molecular structure of water reducing agents mainly has the following outstanding characteristics:
l )The molecular structure is comb-shaped, with more active groups on the main chain and strong polarity. These groups include sulfonic acid group (-SO3H), carboxylic acid group (-COOH), hydroxyl group (-OH), polyoxyalkylene group (-(CH2CH2O)m-R), etc. Each group has different effects on the cement paste. For example, the sulfonic acid group has good dispersion; the carboxylic acid group not only has good dispersion, but also has a retarding effect; the hydroxyl group not only has a retarding effect, but also has a retarding effect. It plays the role of penetration and wetting; the polyoxyalkyl group has the role of maintaining fluidity.
2) The side chain has a hydrophilic active group and the chain is long. Its adsorption form is mainly comb-shaped flexible adsorption, which can form a network structure and has a high steric hindrance effect. , coupled with the electrostatic repulsion generated by the carboxyl group, can show a greater three-dimensional repulsion effect.
3) The degree of freedom of the molecular structure is quite large, there are many parameters that can be controlled during the synthesis of admixtures, and the potential for high performance is great. By controlling the polymerization degree of the main chain, side chains (length, type), functional groups (type, quantity and position), molecular weight size and distribution, etc., the molecular structure can be designed, and a product can be developed and produced that can better solve the problem of concrete water reduction. Admixture products for reinforcement, air entrainment, retardation, water retention and other issues
The main chain of high-performance water reducing agent products contains carboxyl adsorption genes, and the branch chains are often connected with a large number of polyether side chains to provide There is steric hindrance, and polyethers mostly have air-entraining properties. Since the production processes and molecular weights of raw materials used by different manufacturers vary greatly, the amount of air entrainment also varies greatly. From the several high-performance water reducing agent products we tested, the lowest air entrainment capacity is only about 3%, the highest is 6%, and some products even reach 8%.
As a water-reducing agent recognized in the world as having excellent performance indicators, water-reducing agents have shown a series of very excellent characteristics. I hope the editor’s sharing can help you.</p
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