Water-reducing admixture is an important concrete admixture that can reduce the water-cement ratio of concrete to the greatest extent and improve the strength and performance of concrete. Water-reducing agents are divided into general water-reducing agents and high-efficiency water-reducing agents. Water-reducing agents with a water-reducing rate of more than 5% and less than 10% are called general water-reducing agents, such as sodium rosinate, sodium lignosulfonate and polyether soap. etc. Water-reducing agents with a water-reducing rate of more than 10% are called high-efficiency water-reducing agents, such as sodium thiocyanate series, naphthalene series, sulfamic acid series, toughened lignosulfonic acid series and polycarboxylic acid series, etc. Among many high-efficiency water-reducing agents, the polycarboxylic acid-based high-efficiency water-reducing agent with a comb-shaped molecular formula has become a popular choice due to its high water-reducing rate, excellent slump maintenance properties, low dosage, and no significant retardation. In recent years, countries around the world have discussed and designed plans as a top priority.
The water-reducing effect is the key effect that surfactants play on the hydration process of concrete. The water-reducing agent can reduce the water demand of the enterprise without affecting the workability of the concrete; or it can improve the workability of the concrete without changing the water demand of the enterprise; or it can have both left and right functions at the same time without being obvious. Change the air content of the superplasticizer. At present, the concrete water-reducing agents used are all surfactants, which should be anionic surfactants.
After concrete is mixed with water, a hydration reaction occurs and a certain flocculation-like structure appears, which encapsulates a large amount of mixing water, thereby reducing the workability of the newly mixed soil (also known as workability, mainly It refers to the characteristics that fresh concrete can maintain uniformity and concrete segregation without layer segregation at the construction site, that is, during mixing, transportation, irrigation and other processes). In order to maintain the required workability at the construction site, the mixing water flow must be relatively increased, because the increase in water flow will produce excessive permeability in the cement stone structure, which will seriously affect the physical properties of the hardened concrete. If If the moisture in such cysts can be drained out, the water demand of the concrete can be greatly reduced. In the process of making concrete, adding an appropriate amount of water-reducing agent can achieve this effect very well.
After adding a water-reducing agent to the concrete, the hydrophobic groups of the water-reducing agent are directionally adsorbed on the surface of the concrete particles, while the hydrophilic groups are biased toward the saturated solution, forming a single-ion or multi-ion layer adsorption layer. membrane. Due to the directional adsorption of surfactants, the surface of the concrete sealant contains the same marked charge. Therefore, under the effect of homogeneous repulsion, it can not only keep the concrete-water mechanism in a relatively stable floating state, but also allow the concrete to release water. The flocculated structure formed in the early stage refines and collapses, thereby draining the water in the flocculated structure, achieving the purpose of water reduction. After the water-reducing agent is added, not only can the workability of freshly mixed concrete be improved, but also because the water-cement ratio in the concrete has been sharply reduced, the internal permeability coefficient volume of the cement stone has been significantly reduced, and the cement stone has a higher density, making the concrete more dense. The tensile strength of soil is significantly improved. The addition of water-reducing agent often affects the hydration rate and initial setting time of concrete. These features are very important in practical use. However, while the water-reducing agent effectively destroys the flocculation structure of the cement mortar body and releases the free water inside, it also weakens the function between the concrete particles and the water. From this point of view, it will always aggravate the bleeding and sedimentation of the mixture to varying degrees. This is the reason why spots always appear on the surface after concrete is poured. In severe cases, honeycomb pockmarks, honeycombs or The main reason for defects such as shrinkage gaps along the ductility of stirrups. </p
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