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Concrete admixtures
admixture dosage in concrete
2020-08-01
Superplasticizer Monomer
Concrete superplasticizer
2020-08-10

Superplasticizer

Superplasticizers also known as high range water reducers, are additives used in making high strength concrete. Plasticizers are chemical compounds that enable the production of concrete with ca.15% less water content. Superplasticizers allow reduction in water content by 30% or more. These additives are employed at the level of a few weight percent. Plasticizers and superplasticizers retard the curing of concrete.

These additives are employed at the level of a few weight percent. Plasticizers and superplasticizers retard the curing of concrete. Superplasticizer is used where well-dispersed particle suspension is required to improve the flow characteristics (rheology) of suspensions such as in concrete applications. Their addition to concrete or mortar allows the reduction of the water to cement ratio without negatively affecting the workability of the mixture, and enables the production of self-consolidating concrete and high performance concrete. They greatly improve the performance of the hardening fresh paste. The strength of concrete increases when the water to cement ratio decreases.

The superplasticizer can reach more than 20%. Mainly naphthalene series, melamine series and their compound water reducers, of which naphthalene series are the main ones, accounting for 67%. Especially in my country, most superplasticizers are naphthalene series superplasticizers with naphthalene as the main raw material. Naphthalene-based superplasticizers can be divided into high-concentration products (Na2SO4 content <3%), medium-concentration products (Na2SO4 content 3%-10%) and low-concentration products (Na2SO4) according to the level of Na2SO4 content in their products. Content>10%). Most naphthalene-based superplasticizer synthesis plants have the ability to control the content of Na2SO4 below 3%, and some advanced enterprises can even control it below 0.4%.

Naphthalene-based water reducing agent is the most produced and most widely used high-efficiency water reducing agent in China (accounting for more than 70% of the amount of water reducing agent). It is characterized by a high water reducing rate (15% to 25%) and no air entrainment. , Has little effect on setting time, has relatively good adaptability to cement, can be used in combination with various other additives, and is relatively cheap. Naphthalene-based water reducing agents are often used to formulate high-fluidity, high-strength, and high-performance concrete. The slump loss of concrete mixed with naphthalene-based water reducing agent is faster. In addition, the adaptability of naphthalene-based water reducers to certain cements needs to be improved.

The superplasticizer has a strong dispersing effect on the cement, which can greatly improve the fluidity of the cement mixture and the slump of the concrete, while greatly reducing the water consumption and significantly improving the workability of the concrete. However, some superplasticizers will accelerate the loss of concrete slump, and excessive mixing will cause bleeding. The superplasticizer basically does not change the setting time of concrete. When the amount is large (overdose incorporation), it has a slight retardation effect, but it does not delay the growth of the early strength of hardened concrete.

It can greatly reduce the water consumption and significantly increase the strength of concrete at various ages. When keeping the strength constant, it can save 10% or more of cement.

The content of chloride ions is small, and it does not corrode the steel bars. It can enhance the impermeability, freeze-thaw resistance and corrosion resistance of concrete, and improve the durability of concrete.

It is suitable for prefabricated and cast-in-place reinforced concrete in various industrial and civil construction, water conservancy, transportation, port, municipal and other projects.

It is suitable for high-strength, super-high-strength and medium-strength concrete, as well as concrete that requires early strength, moderate frost resistance and high fluidity.

Precast concrete components suitable for steam curing process.

It is suitable to be used as the water reducing enhancement component (ie master batch) of various composite admixtures.

The first generation of superplasticizers—naphthalene-based superplasticizers and melamine resin-based superplasticizers were developed in the early 1960s, and due to their performance compared to ordinary water-reducing agents—developed in the late 1930s Lignosulfonate is a representative-it has a significant improvement, so it is also called a superplasticizer. The second-generation superplasticizer is sulfamate, although it is after the third-generation superplasticizer—polycarboxylic acid in chronological order. The graft copolymer with both sulfonic acid group and carboxylic acid group is the most important third-generation superplasticizer, and its performance is also the most excellent high-performance superplasticizer.

With the continuous improvement of engineering design requirements for concrete, higher requirements have been put forward for the development of water-reducing agents, which require higher water-reducing rates, better adaptability to cement, and higher strength High performance concrete. In the future, my country’s research on water reducers will mainly include the following aspects:

  (1) Research on graft modification of naphthalene-based water-reducing agent and non-naphthalene-based water-reducing agent. Naphthalene-based water-reducing agents are the most used high-efficiency water-reducing agents, but in most cases, naphthalene-based water-reducing agents can only be used after compounding phthalates or other chemical components, and the price fluctuations of industrial naphthalene, so The graft modification of naphthalene-based water-reducing agents has been the next research direction of naphthalene-based water-reducing agents.

  (2) Research on a new synthesis method of sulfonated melamine-based superplasticizer. The high price of melamine-based superplasticizers has always been a difficult problem to solve. Therefore, the use of cheap active monomers to partially replace melamine, optimize the ratio of reaction monomers and the synthesis reaction process, to reduce the cost of raw materials and simplify the production process. The next step is a research direction of sulfonated melamine-based superplasticizers.

  (3) Research on polyacrylic acid superplasticizer and reactive polymer water reducer. Judging from the high-level academic literature published abroad, the research papers on polyacrylic acid superplasticizers in Japan, Europe and the United States are on the rise, and the research results are mainly shown in improving the working performance of mixed concrete and strengthening the mechanical properties of concrete. China’s research on polyacrylic acid superplasticizers is at the preliminary stage, so research should be carried out from the following aspects: reasonable molecular design of polyacrylic acid superplasticizers and optimization of the polymerization process; from polyacrylic acid superplasticizers and traditional reduction Research on the synergistic effect of water agents, thereby further reducing costs; further research on the water reducing mechanism of polyacrylic acid superplasticizers to provide a theoretical basis for synthesis.

  • Compound use of different types of water reducing agents, or copolymerization according to the principles of molecular design.
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