Polycarboxylate superplasticizer is a new type of high-performance superplasticizer with good dispersibility and high water reduction rate, which provides a guarantee for the preparation of high-strength high-performance concrete.The designability of its molecular structure theoretically has unlimited design space for structure and performance. Diversification and functionalization of polycarboxylic superplasticizer can be realized by controlling the main chain structure, side chain length and functional group types.With the continuous improvement of engineering construction technical requirements, polycarboxylate superplasticizer has evolved from the initial type of high water reduction, high slump protection, and then emerged today's polycarboxylate superplasticizer, but mainly presents the following types.
1. Polycarboxylate superplasticizer for preserving slump and superpreserving slump
The synthesis of this kind of superplasticizer is in the process of the synthesis of superplasticizer, through introducing the active unsaturated monomer with the function of protecting slump, a kind of slow-release and slump-preserving polycarboxylic superplasticizer with excellent slump retention ability and certain dispersibility is developed.Commonly used to protect slump type unsaturated monomer with hydroxyl ethyl acrylate (HEA) and hydroxypropyl acrylate (HPA) and so on, this kind of superplasticizer in hydraulic concrete can make concrete 2-3 h slump loss, more than 3 h after the loss of concrete slump faster, in tall building or transport distance remote site, generally require 4 to 6 h no concrete slump loss, and setting time of concrete and the late strength is not affected, can satisfy the requirements of polycarboxylate superplasticizer called super collapse type poly carboxylic acid superplasticizer.
2.Functional polycarboxylate superplasticizer
In actual construction process, sometimes encounter water reducing and collapse cannot have it all, the superplasticizer are usually sold on the market, mainly water reducing and collapse, superplasticizer type protecting slump is poorer, collapse type water reducing rate and low, need to be used proportional distribution, in sand and gravel material good, two kinds of superplasticizer proportional distribution of use not only increased the complexity of the production process, also easy to cause the fluctuation of production quality, these areas generally use superplasticizer with high water reducing rate also have good insurance slump, called functional superplasticizer.
3. Low-shrinkage and reductive polycarboxylate superplasticizer
Concrete shrinkage is a common phenomenon in the process of concrete construction. It is caused by the surface tension of concrete.Compared with ordinary polycarboxylate superplasticizer, this kind of superplasticizer greatly reduces its surface tension, and its net slurry fluidity effect is obviously better than that of ordinary polycarboxylate superplasticizer, and its shrinkage effect is also more superior.
4. Viscosity reducing polycarboxylate superplasticizer
Concrete of high strength concrete construction process, will encounter heavy, slow velocity and so on phenomenon, this phenomenon is easy to cause high pumping concrete wall pipe accident, influence the normal construction site and cause large economic loss, in order to meet the needs of actual construction, a lot of mixing station or building materials company will use a special kind of admixture, viscosity poly carboxylic acid polycarboxylate superplasticizer.
5. Mud-resistant polycarboxylate superplasticizer
Sludge-resistant polycarboxylate superplasticizer is an improver of the third generation of superplasticizer, which is developed for the poor quality of sand and stone in many areas at home and abroad. Its biggest characteristic is that when the concrete raw material contains a certain degree of clay content, it still has a good dispersive energy and does not affect the superplasticizer function of PCEs.At present, the optimization of polycarboxylate molecules mainly include: (1) increase the spatial steric resistance of polycarboxylic acid molecules;(2) cationic active groups were introduced to prepare amphoteric PCEs.(3) synthesis of PCEs without PEO side chain.
With the development of engineering construction, the application of polycarboxylate superplasticizer will become more and more popular.However, at the same time, the development of polycarboxylate superplasticizer is also in a bottleneck stage. On the one hand, due to the cost limitation of the upstream raw materials, polyether or polyester, polycarboxylate superplasticizer cannot be better promoted and applied. Many customers are still using naphthalene or aliphatic series superplasticizer.On the other hand, it is difficult to further improve the water reduction rate and slump maintenance performance of polycarboxylate superplasticizer on the current basis, and many research and development work is just the improvement of the original system, and no new synthetic system is born.
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