High-efficiency water reducing agent (also known as superplasticizer refers to an additive that can greatly reduce the amount of mixing water while maintaining the same concrete slump.
The first generation of superplasticizers—naphthyl superplasticizers and melamine resin-based superplasticizers were developed in the early 1960s due to their performance compared to conventional water reducers – opened in the late 1930s. Lignosulfonates are representative – a significant increase and are therefore referred to as superplasticizers. The second generation of superplasticizer is a sulfamate, although in chronological order after the third generation of superplasticizer – polycarboxylic acid. The graft copolymer with both sulfonic acid group and carboxylic acid group is the most important in the third generation of superplasticizer, and the performance is also the best high performance water reducing agent.
The water-reducing rate of the superplasticizer can reach more than 20%. Mainly naphthalene, melamine and water-reducing agents made up of them, of which naphthalene is the main, accounting for 67%. Especially in China, most of the high-efficiency water reducing agents are naphthalene-based high-efficiency water reducing agents with naphthalene as the main raw material. Naphthalene-based high-efficiency water reducer can be divided into high-concentration products (Na2SO4 content <3%), medium-concentrated products (Na2SO4 content 3%-10%) and low-concentration products (Na2SO4) according to the content of Na2SO4 in its products. Content >10%). Most naphthalene-based superplasticizers have the ability to control Na2SO4 levels below 3%, and some advanced companies can even control them below 0.4%.
Types and characteristics of high-efficiency water reducers: types and characteristics of new high-efficiency water reducers Currently, high-strength, high-performance concrete is formulated internationally and internationally, and high-efficiency water reducers are used. These high-efficiency water reducers can be divided into four categories: A Naphthalene; B, poly-carboxylic acid; C, melamine; D, sulfonic acid (AminosuHonic acid).
Naphthalene water reducing agent is the most widely used and most widely used high-efficiency water reducing agent in China (accounting for more than 70% of water reducing agent), which is characterized by high water reduction rate (15%~25%). Gas, has little effect on the setting time, has relatively good adaptability to cement, can be used in combination with other various admixtures, and the price is relatively cheap. Naphthalene water reducing agents are often used to formulate high fluidity, high strength, high performance concrete. The slump loss of concrete with pure naphthalene water reducing agent is faster. In addition, the adaptability of naphthalene-based water reducing agents 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, and at the same time greatly reduce the water consumption and significantly improve the workability of the concrete. However, some high-efficiency water reducers will accelerate the loss of concrete slump, and if the amount is too large, it will bleed. The high-efficiency water reducing agent does not change the concrete setting time substantially. When the dosage is large (over-dosing), it has a slight retarding effect, but does not delay the early strength growth of the hardened concrete.
The application of domestic superplasticizers is becoming more and more common, and the most commonly used varieties are still naphthalene water reducers. Such water-reducing agents have the advantages of low cost and high water-reducing rate, but the problem of slump loss is relatively serious, which directly affects the use effect of the water-reducing agent. How to effectively control the slump loss is a major problem that must be solved to further promote the application of high-efficiency water reducer and new concrete technology.
The reason for the loss of slump is that cement is a kind of hydration-active substance. The addition of water-reducing agent may accelerate the initial hydration process of cement. Secondly, the strong adsorption of cement particles on the water-reducing agent will cause liquid. The effective concentration of the water reducing agent in the phase is rapidly lowered, and the potential is continuously decreased. The combination of retarding components in water reducing agents is currently the most common method for reducing slump loss. However, the composite retarding component brings a new problem, which is the development of the early strength of concrete. Generally speaking, the strength of 1d and 3d is lower than that of concrete without retarding component, and the strength can be gradually caught after 7d. In contrast, the use of a water-reducing agent with sustained release properties, once added, slow release, so that the concentration of the water reducing agent in the system is maintained or continuously increased, can also achieve the ear to reduce the loss of slump, not only The process is simple and does not adversely affect the early strength of the concrete.
(1) Superplasticizer (LS-AS) has excellent performance with low dosage and high water reduction rate. With the increase of dosage, the water reduction rate is greatly improved, but there is a saturation point, after reaching this point. The drop and fluidity are good. After the (saturation) point is exceeded, the increase in water reduction rate is rapidly slowed down, and there is a relatively obvious retardation;
(2) The sulfamic acid-based superplasticizer has good compatibility with cement, and has good compatibility with other types of superplasticizers, but has poor compatibility with lignosulfonate and water repellency. Can not get significant improvement;
(3) The production of sulfamic acid-based superplasticizer (LS-AS) is easy to control, and basically no three wastes are produced. LAS-HP has superior performance: low dosage, high water reduction rate and superior plastic retention performance, especially for low alkali cement. These two series of products have passed the technical appraisal, and have been mass-produced and applied, and achieved good social and economic benefits.
The main component of polycarboxylic acid anti-cracking and waterproofing agent (KH-K) is polycarboxylate water reducing agent and auxiliary polyol, antimony waterproofing component, shrinking component and alcohol modified component, which can reduce the concrete under hydrostatic pressure. Water permeability improves the impermeability of concrete and improves durability.
Polycarboxylate superplasticizers have developed rapidly in recent years due to their superior performance and non-polluting properties, especially in Japan, where the ratio of polycarboxylic acid to naphthalene is more than 7:3. The molecular structure, the principle of action and the behavior of the polycarboxylate superplasticizer are quite different from those of the traditional water reducer. Therefore, correct understanding and rational use are important links to promote the application of polycarboxylate water reducer. The author has accumulated three years of experience in the production and application of LEX-9 series polycarboxylate water reducer, and hopes to benefit from the development of such new water reducers in China.
Research and development direction of high efficiency water reducer
With the continuous improvement of concrete requirements in engineering design, higher requirements are also placed on the development of water reducing agents, which require higher water reduction rate, better adaptability to cement, and can adapt to higher strength. High performance concrete. In the future, China’s research on water reducing agents mainly includes the following aspects:
Study on graft modification of naphthalene water reducer and non-naphthalene water reducer. It can greatly reduce the amount of water and significantly increase the strength of concrete at various ages. When the strength is kept constant, cement can be saved by 10% or more. The chloride ion content is small and does not cause rust on the steel. 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. Suitable for high-strength, ultra-high-strength and medium-strength concrete, as well as early-strength, moderately anti-freeze, and large-flow concrete. Precast concrete components suitable for steam curing processes. It is suitable for the water-reducing reinforcing component (ie, masterbatch) of various composite admixtures.
(1) Naphthalene type water reducing agent is the most effective superplasticizer, but in most cases, the naphthalene type water reducing agent can only be used after compound citrate or other chemical components, plus the price fluctuation of industrial naphthalene. Factors, so the graft modification of naphthalene-based water reducer has been the next research direction of naphthalene-based water reducer.
(2) Research on new synthetic methods of sulfonated melamine-based superplasticizer. The high cost of melamine-based superplasticizers has always been a difficult problem to solve. Therefore, the use of inexpensive active monomer instead of melamine to optimize the ratio of the reaction monomers and the synthesis reaction process to reduce the cost of raw materials and simplify the production process is The next step in the research of sulfonated melamine-based superplasticizers.
(3) Research on polyacrylic acid superplasticizer and reactive polymer water reducing agent. From the high-level academic literature published in foreign countries, the research on polyacrylic acid superplasticizers in Japan and Europe and the United States is on the rise. The research results are mainly in improving the working performance of mixed concrete and strengthening the mechanical properties of concrete. China’s research on polyacrylic acid superplasticizer is in the preliminary stage, so it should be studied from the following aspects: Reasonable molecular design for polyacrylic water reducing agent, optimization of polymerization process; reduction from polyacrylic water reducing agent and tradition The synergistic effect of the water agent is studied to further reduce the cost; further research on the water reducing mechanism of the polyacrylic acid superplasticizer provides a theoretical basis for the synthesis.
(4) The combined use of different types of water reducing agents, or copolymerization according to the principles of molecular design.
Polycarboxylic acid water reducing agent
Sulfamic acid-based superplasticizer
Naphthalenesulfonic acid formaldehyde condensate water reducing agent