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The Inevitable Trend of Development of Polycarboxylate Superplasticizer
1. Introduction of High Efficiency Water Reducer
Superplasticizer is an important concrete admixture, which is one of the important products of new building material pillar industry. The superplasticizer can not only greatly improve the mechanical properties of high strength concrete, but also provide a simple and feasible construction technology. As naphthalene water reducer has exposed some problems which are difficult to overcome in the development of recent decades, such as the slump loss of concrete prepared with naphthalene water reducer is very obvious, it is impossible to have a higher water reduction rate. naphthalene, the main raw material of naphthalene water reducer, is a by-product of coking industry, and its source is restricted by the iron and steel industry. Since 1980s, non-naphthalene superplasticizers have been actively developed in foreign countries. With rich petrochemical products as raw materials, naphthalene superplasticizers have been overshadowed by extremely high water reduction rate and minimal slump loss, thus creating a new situation of polycarboxylic acid concrete superplasticizer technology and concrete construction technology.
Polycarboxylic acid concrete superplasticizer is the third generation of high performance chemical superplasticizer developed after wood calcium and naphthalene superplasticizer. Compared with traditional superplasticizer, it has the following outstanding advantages:
1) Low dosage (0.2 ~ 0.5%) and high dispersity.
2) Good slump resistance and no slump loss in 60 minutes.
3) When compared with the same fluidity, there is less delay in setting time.
4) High degree of freedom in molecular structure, many controllable parameters in additives manufacturing technology, and great potential for high performance.
5) Because of the absence of toxic substances in the synthesis, formaldehyde does not cause any pollution to the environment.
6) Compatibility with cement and other kinds of concrete admixtures.
7) When polycarboxylic superplasticizers are used, more slag or fly ash can be used to replace cement, thereby reducing the cost.
2. The Important Role of High Efficiency and High Performance Water Reducing Agent in the Development of Concrete Technology
High-efficiency and high-performance concrete water reducer has become the fifth indispensable component in concrete mix because of its small amount of admixture and large effect. The quality of its products can affect the quality, durability and service life of hundreds of billions of dollars of infrastructure concrete projects every year in China, and affect the national economic construction and foundation design. The technological, economic and social benefits of the construction. The important role of high performance and high performance concrete water reducer is mainly reflected in two points:
2.1 Improving the Performance of Concrete and Promoting the Technical Revolution of Concrete Construction.
In recent years, the application technology of water reducing agent has been developed rapidly, which promotes the development of new concrete construction technology. For example: Jinmao Tower, an 88-storey super high-rise building with a building height of 420.5 meters, is constructed by using pumping agent and pumping technology to pump concrete to the top; the Three Gorges Dam project with the goal of 100-year durability design attracts worldwide attention; the smooth construction of Qinghai-Tibet Railway under harsh natural conditions, etc. all put forward concrete performance and preparation technology. The high demand for high technology concrete water reducing agents is indispensable for achieving these difficult technologies. At present, almost all important concrete projects and all concrete mixing stations use various water reducing agents.
2.2 Saving Resources and Protecting the Environment.
The application of high-efficiency and high-performance concrete water reducing agent in concrete promotes the application of industrial by-products (such as ground slag, fly ash and silica fume) and reduces the amount of cement in concrete. In general, it can save about 10% ~ 15% of cement. This means that a project can save thousands of tons of cement and save on it. Resources play an important role in reducing environmental pollution caused by clinker firing.
3. Research Progress of Superplasticizer
3.1 Naphthalene Series and Melamine Superplasticizer
Izumi and other hydrophilic groups, such as hydroxyl (- OH), carboxyl (- COOH), amino (- NH2) and sulfonic acid (- SO3H), were introduced into the naphthalene sulfonic acid - formaldehyde condensate to prepare concrete admixtures for preventing slump loss.
Nicholson et al. mixed lignosulfonate treated by ultrafiltration with naphthalene superplasticizer to reduce slump loss and improve the early compressive strength of concrete. Hamada et al. used air oxidation method to remove part of the sulfonate group, and introduced part of the carboxyl side by side to get desulfonate lignin, and then reacted with naphthalene sulfonic acid, formaldehyde to get water reducer. The water reducer has the characteristics of small slump loss. Mizunuma and other naphthalene water reducers are mixed with unsaturated carboxylic acid-unsaturated carboxylic acid ester copolymers to reduce slump loss of concrete. Yamato et al. used the melamine series superplasticizer and unsaturated carboxylic acid polymer together. When the content of melamine series superplasticizer and unsaturated carboxylic acid polymer was 1.5% in low water cement ratio, the slump of concrete was almost no loss within an hour, which improved the workability and could be used to prepare ultra-high pressure injection concrete.
3.2 Research Progress of Amino Sulfonic Acid Superplasticizer
Sulfonic acid water reducers are usually prepared by condensation of p-Aminobenzene Sulfonic Acid and phenol with formaldehyde. The electrostatic repulsion of sulfonic groups in the chemical structure and the wetting effect of hydroxyl groups play a role of water reducing and dispersing. The slump is smaller than that of naphthalene or melamine water reducers and the dosage is less. Formaldehyde-phenolic sulfonic acid-urea condensate capped with Sulfonates such as aniline, naphthylamine and urea was prepared by Izumi et al. When used as water reducing agent, the condensate has high water reducing capacity and low slump loss, and can be used to prepare high strength concrete. The introduction of polyethylene oxide, polypropylene oxide or polyethylene oxide-propylene oxide block grafting chain into the condensate can reduce slump and increase water reduction rate. Maehama and other formaldehyde.