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Water reducer is a concrete admixture that can reduce the amount of mixing water under the condition that the slump of concrete is basically the same. It can significantly improve the performance of concrete and plays a key role in modern concrete production. For example, adding an appropriate amount of water reducer to ordinary concrete can make the concrete easier to mix and pour, while improving its strength.

Different types of water reducers have different ingredients. The main component of lignin-based water reducer is lignin sulfonate; naphthalene-based water reducer is mainly composed of naphthalene or naphthalene homologues sulfonated and condensed with formaldehyde; polycarboxylic acid-based water reducer is a high molecular surfactant with a comb-shaped structure synthesized by solution polymerization and other methods from unsaturated monomers with sulfonic acid groups, carboxyl groups, amino groups and polyoxyethylene side chains.

The main function of water reducer is to reduce water consumption, while the main function of early strength agent is to accelerate the early strength development of concrete, which is suitable for winter construction and other scenes; retarder delays the setting time of concrete and is used for large-volume concrete pouring, etc.; air entraining agent introduces tiny bubbles into concrete to improve the frost resistance and impermeability of concrete. Each admixture plays a unique role in response to different performance requirements of concrete.

Common types of water reducers include lignin-based water reducers, naphthalene-based water reducers, and polycarboxylic acid-based water reducers. Lignin-based water reducers are common water reducers with relatively low prices; naphthalene-based water reducers are high-efficiency water reducers with high water reduction rates; polycarboxylic acid-based water reducers are a new generation of high-performance water reducers with advantages such as high water reduction rates and good slump retention.

The water reduction rate of lignin-based water reducers is generally 8% - 15%; the water reduction rate of naphthalene-based water reducers is 15% - 25%; the water reduction rate of polycarboxylic acid-based water reducers is relatively high, reaching 25% - 40% or even higher. The specific water reduction rate will also vary depending on factors such as product quality, dosage, and compatibility with cement.

Polycarboxylic acid-based water reducers have a high water reduction rate, which can effectively reduce the water-cement ratio of concrete and significantly improve the strength of concrete. It has good slump resistance, which can keep the concrete in good working performance for a long time, and is suitable for long-distance transportation and long-term construction projects. In addition, polycarboxylic acid water reducer has good environmental performance, low pollution in the production process, and meets the requirements of modern green buildings.

The main roles of water reducer in concrete are: reducing water consumption, while keeping the water-cement ratio unchanged, it can improve the strength of concrete; while keeping the strength unchanged, it can reduce the amount of cement and reduce costs. At the same time, it can also improve the working performance of concrete, making concrete easier to mix, transport and pour, and improving construction efficiency. For example, in pumped concrete, water reducer can make concrete have good pumpability and reduce pipe blockage.

Water reducer molecules have hydrophilic groups and hydrophobic groups. When water reducer is added to concrete, its hydrophobic groups are adsorbed on the surface of cement particles, while the hydrophilic groups point to the aqueous solution, so that the surface of cement particles carries the same charge, generating electrostatic repulsion, and the cement particles are dispersed, thereby releasing the water wrapped by the cement particles to achieve the water reduction effect. In addition, the hydrophilic groups of water reducer molecules can also form a stable water film with water molecules, further improving the fluidity of concrete.

Water reducers reduce the water-cement ratio of concrete, making the internal structure of concrete denser, thereby improving the durability indicators of concrete such as impermeability, frost resistance and erosion resistance. For example, using water reducers in hydraulic concrete can effectively reduce the amount of water entering the concrete, improve its impermeability and extend the service life of the concrete structure.

The dosage of water reducer is usually determined based on experiments. Generally speaking, the dosage of lignin water reducer is 0.2% - 0.3% of cement mass; the dosage of naphthalene water reducer is 0.5% - 1.0% of cement mass; the dosage of polycarboxylic acid water reducer is 0.1% - 0.3% of cement mass. However, the actual dosage should take into account factors such as cement type, aggregate characteristics, concrete design requirements, etc. The optimal dosage should be determined through concrete trial mixing to ensure that the concrete achieves the expected performance and the cost is reasonable.

Water reducer can be added to concrete by pre-mixing, post-mixing, and co-mixing. The pre-mixing method is to add the water reducer to the mixer together with dry materials such as cement; the post-mixing method is to add the water reducer after the concrete has been mixed for a certain period of time; the co-mixing method is to dissolve the water reducer in water in advance and then add it to the mixer together with water. The post-mixing method can better play the role of water reducer, especially for polycarboxylic acid water reducer, which can effectively reduce slump loss.

The type and quality of cement have a great influence on the use effect of water reducer. Different cements have different adaptability to water reducers. Cement with good compatibility with water reducer should be selected through tests. The grading and mud content of aggregates will also affect the effect of water reducer. Too high mud content will reduce the effectiveness of water reducer. Therefore, aggregates should meet the requirements of relevant standards, and try to use aggregates with good grading and low mud content.

The possible reasons are excessive water reducer dosage, improper concrete mix ratio, or poor compatibility between cement and water reducer. The solution is to first test the water reducer dosage, and if necessary, appropriately reduce the dosage; readjust the concrete mix ratio to ensure that parameters such as sand ratio are reasonable; if there is a problem with the compatibility of cement and water reducer, try to change the cement variety or adjust the water reducer type to find the best combination through experiments.

The reason may be that the cement hydration speed is too fast, the slump retention performance of the water reducer is insufficient, or the ambient temperature is too high. The measures that can be taken are: choose cement with a slower hydration speed; use water reducers with good slump retention performance, such as slump retention products in polycarboxylic acid water reducers; when constructing in a high temperature environment, take measures such as reducing the temperature of concrete raw materials and shortening the transportation time of concrete. The dosage of water reducer can also be appropriately increased, but it needs to be determined through experiments.

When water reducer and cement are incompatible, there may be excessive slump loss of concrete, abnormal coagulation (rapid coagulation or slow coagulation), "bottom grabbing" phenomenon on the concrete surface (i.e. part of cement slurry is separated from aggregate and hard lumps are formed at the bottom), etc., which seriously affect the construction performance and quality of concrete.

First, conduct an adaptability test of cement and water reducer to screen out a suitable combination of cement and water reducer. If incompatibility problems have occurred, you can try to adjust the dosage and addition method of water reducer, such as post-mixing method; you can also add an appropriate amount of stabilizer to the concrete or adjust the mix ratio of concrete to improve its working performance. If the problem still cannot be solved, you need to consider replacing cement or water reducer products.