Superplasticizer is a kind of concrete admixture, which can improve the workability of concrete, reduce construction energy consumption and improve construction efficiency. In the concrete, water reducing agent is added to the mixture of cement particles to get dispersion effect and to optimize the working performance of cement. Under the condition of keep the concrete slump constant, mixing and subtract agent can greatly reduce the unit water use of concrete mixture, reduce the water cement ratio of concrete, the strength and stability of the reinforced concrete. Or in the concrete workability and strength of the same condition, adding water reducer can reduce the unit of cement, save cement. However, the application of superplasticizer in concrete also has some problems, such as the majority of superplasticizer ions being anionic surfactants, lignin sulfonate, naphthalene sulfonate formaldehyde polymer, etc..
According to the water-reducing effect of concrete superplasticizer, concrete superplasticizer can be divided into the following three categories:
(1) Ordinary water-reducing agent, also known as plasticizer, its water-reducing rate is not less than 8%, the main component is lignin sulfonate;
(2) High-effect water-reducing agent, also known as superplasticizer, water reduction rate is not less than 14%, the main component is represented by tea water-reducing agent;
(3) High-performance superplasticizer, water reduction rate is not less than 25%, regarding polycarboxylic acid series superplasticizer as a representative.
At present, the new type of high efficiency water reducing agent has the following five categories:
(1) Polycarboxylate superplasticizer (carboxylic acid water reducing agent): poly carboxylic acid system has a lot of chain between the molecules of water reducing agent of some strong polarity in the main chain anions with surface bonded to a piece of electricity. The formation of hydration film can not only enhance the adsorption force between molecules but also produce space steric effect as well as good plasticizing effect. But this water reducer is expensive, which makes its application be limited to some extent, and make it has strong selectivity to defoaming agent and air-entraining agent. At present, the polycarboxylate superplasticizer with the best comprehensive efficiency is the high performance superplasticizer.
(2) Naphthalene series high-efficient superplasticizer: naphthalene series high-efficient superplasticizer has electrostatic repulsion effect, molecular repulsion between electric charges, just on the cement in the hydration process of its own flocculation has a certain decomposition effect, so that free water drainage it contained would be reduced, and the water reduction effect is obvious. Compared with polycarboxylic acid series superplasticizer, naphthalene series superplasticizer has a relatively mature technology with low price.
(3) Aminosulfonic acid series superplasticizer: aminosulfonic acid series superplasticizer is a non-air-entraining resin type high-efficiency superplasticizer, the water reduction rate can reach more than 25%, which make the concrete workability and durability have significant enhancement. However, the production cost of sulfamic acid series superplasticizer is relatively high. When the molecular weight is too small or too large, it is easy to cause bleeding, segregation and hardening. At present, the research of this kind of water-reducing agent is mostly through modifying aminosulfonic acid and dispersing cement particles, which can effectively reduce the shortcomings in use and expand the market prospect.
(4) Modified lignosulfonate superplasticizer: modified lignosulfonate superplasticizer is made by modifying lignosulfonate. The new modified lignin sulfonate is a high-efficiency water-reducing agent, the water-reducing rate is 1.5 times higher than that of the ordinary water-reducing agent, and the hydration heat and collapse degree of cement are changed to effectively ensure the excellent performance of concrete, and the production cost is low, which is conducive to construction.
(5) Hybrid water reducing agent: water reducing agent is blend by mixing the quaternary copolymer acrylate graft copolymer, contains amino benzene sulfonic acid maleic acid amide and vinyl pyrrole copolymer, and at the same time other copolymer containing sulfonic acid and carboxylic acid based collection to a piece, thus using the functions of their different anion and polarity of functionality, can be used as a super plasticizer all kinds of polymer and copolymer, thereby interacting with cement particles. The production of mixed superplasticizer is complicated, and the optimization of mixing amount needs a lot of experiments.
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