What are the methods for synthesizing early-strength water-reducing agents at room temperature? The following three are recognized in the industry. I hope it will be helpful to you
Large molecule reaction method
This method First polymerize and then esterify, that is, first prepare the early strength with a known molecular weight, and then use a polyether with a known molecular weight to carry out the early strength through esterification at a higher temperature under the action of a catalyst. graft. However, due to the limited product varieties and specifications of early strength, it is difficult to adjust its composition and molecular weight. At the same time, because the compatibility between early strength and polyether is not very good, the esterification process is difficult, and as the esterification reaction progresses, If water continues to overflow, phase separation problems will occur. Early-strength water-reducing agent
If you can choose polyether monool or diol that has good compatibility with early-strength water-reducing agent, you can solve the problem of phase separation. He Jing et al. used reactive polymerization of styrene and maleic anhydride to polymerize, and then sulfonated and esterified the prepolymer to obtain this early-strength water-reducing agent. The water-reducing agent has high dispersion properties and excellent slump retention properties.
Two macromonomer method
In this method, the polymer is first esterified, that is, the biomacromolecule with polymer specificity is first produced through the esterification reaction. (usually methoxypolyethylene glycol methacrylate), and then mix the required reactivity ratios together, and directly use solution polymerization to obtain the finished product. This kind of production process seems very simple, but the intermediate separation and purification process is more complicated and costly. Japanese catalyst company uses short and long chain methoxypolyethylene glycol methacrylate and methacrylic acid to directly copolymerize into a concrete additive containing polyether side chains with excellent slump retention. agent.
Tri-in-situ polymerization and grafting
This method integrates polymerization and esterification, and uses polyether as a reflection medium for the unsaturated reactivity rate of carboxylic acids. , the esterification reaction occurs while the carboxylic acid unsaturated reactivity generates polymers, thereby avoiding the problem of poor compatibility between early strength and polyether. Shawl et al. slowly added the mixed aqueous solution of acrylate reactivity rate, chain transfer agent, and initiator into a solution of methoxypolyethylene glycol with a relative molecular mass of 3000, reacted at 65°C for 46 mln, and then raised the temperature to 130°C, continuously remove water (about 60 mln) under N2 protection, then add a metal catalyst to raise the temperature to 162°C, react for 1 hour, and deepen grafting to obtain the finished product. Although this method can control the molecular weight of the polymer, the production process is simple, and the production is low-cost, it usually only needs to select the reactivity rate of the carboxyl group, otherwise it is impossible to graft, and this grafting reaction is reversible. Balanced reaction, there is a lot of water in the system before reaction, the grafting rate is not high, and it is difficult to control, and the molecular structure design is more difficult.
There is no doubt that the function of the water-reducing agent is to reduce the water flow required by the concrete to exceed the required slump, so that less water can exceed the specified slump. It means that the water-cement ratio of concrete can be effectively lowered, thereby smoothly improving concrete rebound, water density (non-absorbency), and performance. But the key is that it can effectively improve the fluidity of concrete and improve pumping performance. The basic concept is to improve the cohesion structure of concrete, improve the pumping characteristics of concrete, avoid turning it into a dispersed structure over a long period of time, and improve circulation, which has achieved the purpose of reducing water.
Can concrete pumps use underwater concrete without water-reducing agents? This may be possible, but it does not have the same compressive strength level. The compactness of the concrete will be relatively low and the impermeability level will be lower. etc. will also be relatively lower than those with water reducing agent added. Nowadays, with the urbanization, Digital China in the new rural planning requires a lot of concrete. Some construction projects choose to mix concrete on site, and some choose commercial mixing. The concrete mixed on site is usually very little. Water-reducing agents are usually used for commercial mixing, except for multi-story buildings, multi-story construction projects or large and medium-sized engineering projects. Water-reducing agents are usually added to the commercial mix to ensure that the concrete pump can be used at the construction site. When conveying the necessary concrete in the project to the concrete pouring point along the horizontal or vertical pump pipe under the certain underwater concrete working pressure, consider its pumpability. The underwater concrete concrete has certain Compressive strength and usability, and also has very good fluidity. </p
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