In recent years, under the favorable environment of my country's economic boom, infrastructure construction has developed rapidly across the country, and the ready-mixed concrete industry has also flourished. The active phases of water-reducing agents are cement and admixtures (mixed materials). The molecules of (salt) water-reducing agent are artificially formed "comb-like" or "dendritic" structures through "molecular design", and have many branched chains (side chains) with a certain length and stiffness connected to the main chain of the molecule. . There are also sulfonates or other groups on the main chain that can charge the cement particles, which can play the role of conservative water reducing agent. More importantly, once the main chain is adsorbed on the surface of the cement particles, the branch chain will interact with the surface of other particles. The branched chains form planar intersections, which prevent the particles from approaching each other, thereby achieving the effect of aggregation (i.e. water reduction).
What are the raw materials for the synthesis of water reducing agent?
Acrylic acid (AA), sodium methacrylate sulfonate (MAS), ammonium persulfate (APS), polyoxyethylene ethylene Propyl ester macromonomer
Synthesis method: Mix acrylic acid, sodium methacrylate sulfonate, ammonium persulfate, and polyoxyethylene allyl ester macromonomer with deionized water to a concentration of 20%. The aqueous solution. Add the monomer and initiator in batches into a three-necked flask equipped with a stirrer, reflux condenser and thermometer. After the dropwise addition is completed, keep the reaction at 75°C for a certain period of time. After the reaction is completed, use a concentration of 20 % NaOH aqueous solution adjusts the pH value to 7-8 to obtain a yellow or reddish-brown water-reducing agent with a concentration of about 20%
So how to scientifically improve the water-reducing rate of the water-reducing agent?
1. The dosage of JH type high-performance water-reducing agent is 0.4% to 2.5% of the total weight of the gelling material, and the common dosage is 0.8% to 1.5%. A concrete trial mix test should be carried out before use to obtain the best dosage.
2. JH type high-performance water-reducing agent cannot be mixed with naphthalene-based high-efficiency water-reducing agent. When using JH-type high-performance water-reducing agent, the mixer that has used naphthalene series high-efficiency water-reducing agent must be used. Clean the mixer truck, otherwise the water-reducing effect may be lost.
3. When using the JH type high-performance water-reducing agent, it can be added directly as a raw solution, or it can be prepared into a solution of a certain concentration for use, and the addition of the high-performance water-reducing agent itself can be deducted. amount of water.
4. Since the water reduction rate of concrete mixed with JH type high-performance water-reducing agent is relatively large, the slump is highly sensitive to water consumption, and water consumption must be strictly controlled during use.
5. JH type water reducing agent has good adaptability to most cements, but for ordinary cement, the water reduction rate may be low and the slump loss will be large. In addition, the fineness and storage time of the cement may also affect the effectiveness of the PC series high-performance water-reducing agent. At this time, it is recommended to deal with it by appropriately increasing the dosage or compounding other retardant components.
6. After adding JH type high-performance water-reducing agent, the air content of concrete increases (usually 2% to 5%), which is beneficial to improving the workability and durability of concrete. If necessary There may be other special requirements for use in steam-cured concrete.
7. Since the JH type high-performance water-reducing agent has a small dosage and a high water-reducing rate, the use of PC-based high-performance water-reducing agent to prepare various high-performance concretes above C45 can significantly reduce the cost. Engineering cost, with obvious technical and economic benefits; used to prepare C45 and above grade concrete, although the cost of PC high-performance water-reducing agent is relatively high, it can reduce the analysis cost of concrete by increasing the amount of mineral admixtures, which also has Certain technical and economic benefits.
After water-reducing agent is mixed into concrete, the hydrophobic groups of the water-reducing agent are directionally adsorbed on the surface of the cement particles, while the hydrophilic groups are directed toward the aqueous solution, forming a single-molecule or multi-layer adsorption film. Due to the directional adsorption of the surfactant, the surface of the cement particles is charged with opposite signs. Therefore, under the action of opposite polarity repulsion, not only can the cement-water system be in an absolutely stable suspension state, but also the cement can be added with water. The flocculated structure formed in the initial stage aggregates and collapses, thereby releasing the water in the flocculated structure to achieve water reduction.
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