What are Admixtures?

Concrete admixtures are added during the process of mixing concrete, accounting for less than 5% of the mass of cement, and can significantly improve the properties of concrete. The characteristics of concrete admixtures are that there are many varieties and small amounts, and it has a large impact on the performance of concrete. It has the characteristics of less investment, quick effect and significant technical and economic benefits. With the continuous progress of science and technology, admixtures have been increasingly used, and admixtures have become the fifth important component of concrete in addition to the four basic components.

Development history of admixtures

1. In the early 1990s, the United States first proposed the concept of high-performance concrete (HPC), which is a successful example of the combination of new superplasticizers and the science of concrete materials.

2. In 1824, British I. Aspdin obtained Portland cement patent, and cement concrete has been widely used.

3. In 1962, Kenichi of the Japanese Ministry of Clothing first used naphthalenesulfonic acid formaldehyde condensate (n10) as a dispersant for concrete, and in 1964, Kao Stone Soda Company of Japan sold it as a product.

4. In 1963, the Federal Republic of Germany developed the melamine sulfonate formaldehyde condensate, and the polycyclic aromatic hydrocarbon sulfonate formaldehyde condensate also appeared.

5. In 1966, Japan first applied high-strength concrete and began to produce prestressed concrete piles.

6. From 1971 to 1973, Germany preferred to develop superplasticizers for fluid concrete, and the vertical pumping height of concrete reached 310m.

7. The development direction is the research of HPC and the use of composite superplasticizer (CSP), to realize the full calculation method design of HPC mix ratio and the design of CSP formula.

Development direction of admixtures

1. Superplasticizer: Modification of naphthalene-based and melamine-based superplasticizers, polyacrylate superplasticizer, polyacrylic acid graft copolymer superplasticizer, sulfamate superplasticizer, sulfonation Ketoaldehyde polycondensate, lignin sulfonate high efficiency, industrial waste production of superplasticizer.

2. Composite admixtures: low-alkali and low-content liquid composite admixtures, composite superplasticizers and their formula design, low-alkali and low-content liquid composite antifreeze, micro-expansion multifunctional waterproofing agent, liquid expansion agent, liquid rapid setting Agent, super retarder

3. Other additives: shrinkage reducing agent, alkali aggregate reaction inhibitor, surface hardener, high-efficiency release agent

Functional classification of admixtures

1. Definition: "Classification, Nomenclature and Definition of Concrete Admixtures" GB8075-87, which is added in the process of mixing concrete to improve the properties of concrete, and the content is not more than 5% of the quality of cement (except for special cases). ^[3]

2. Concrete admixtures are divided into four categories according to their main functions:

A. Additives to improve the rheological properties of concrete mixtures. Including water reducing agents, air entraining agents and pumping agents.

B. Additives to adjust the setting time and hardening performance of concrete. Including retarders, early strength agents and quick setting agents.

C. Additives to improve the durability of concrete. Including air-entraining agents, waterproofing agents and rust inhibitors.

D. Additives to improve other properties of concrete. Includes aeration agents, bulking agents, antifreezes, colorants, waterproofing agents, and pumping agents. ^[3]

Classification of admixtures

1. Early strength agent:

A. Soluble inorganic salts: chloride, carbonate, nitrate, thiosulfate, silicate, aluminate, alkaline hydroxide, etc.

B. Soluble organic matter: triethanolamine, calcium formate, calcium acetate, calcium propionate and calcium butyrate, urea, oxalic acid, amine and formaldehyde condensate.

2. Accelerators: iron salts, fluorides, aluminum chloride, sodium aluminate, potassium carbonate.

3. Air entraining agent: wood resin salt, synthetic detergent, lignin sulfonate, protein salt, fatty acid and resin acid and their salts.

4. Water reducing agent and coagulant: lignin sulfonate and its modification or derivative, hydroxycarboxylic acid and its salt or its modification and derivative, inorganic salt (zinc salt, borate, phosphate, Chloride), ammonium salts and their derivatives, carbohydrates and polyacids or sugar acids, water-soluble polymers (cellulose ethers, melamine derivatives, naphthalene derivatives, polysiloxanes and sulfonated hydrocarbons

5. High-efficiency water reducing agent: naphthalenesulfonate formaldehyde condensate, polycyclic aromatic hydrocarbon sulfonate formaldehyde condensate, melamine sulfonate formaldehyde polycondensate, p-aminobenzenesulfonic acid formaldehyde polycondensate, sulfonated ketoaldehyde polycondensate Polyacrylates and their graft copolymers.

6. Retarder: polymer containing carboxyl group, phosphonic acid group, sulfonic acid group and hydroxycarboxylic acid (salt), organic phosphonic acid (salt) and other organic retarders

7. Aeration agent: hydrogen peroxide, metal aluminum powder, some activated carbon that adsorbs air.

8. Expansion agent: fine iron powder or granular iron powder and oxidation accelerator, lime series, sulphoaluminate series.

9. Binder: synthetic latex, natural rubber latex.

10. Pumping agent: synthetic or natural water-soluble polymer increasing agent viscosity, organic flocculant, high specific surface inorganic materials (bentonite, silica, asbestos powder, asbestos short fiber, etc.), cement admixture (pulverized coal) Ash, hydraulic lime, stone powder, etc.).

11. Flocculant: polymer electrolyte.

12. Colorants: gray to black (iron oxide black, mineral black, carbon black, ultramarine, phthalocyanine blue), light red to deep red (iron oxide red), brown (iron oxide brown, manganese-rich brown earth, burnt brown Soil), green (chrome oxide green, phthalocyanine), white (titanium dioxide), etc.

13. Sterilizers and pesticides: polyhalides, dieldrin emulsions and copper compounds.

14. Moisture-proof agent: soaps, butyl stearic acid, certain petroleum products

15, anti-seepage agent: water reducing agent, calcium chloride.

16. Alkali aggregate reaction inhibitor: lithium salt, barium salt, some air entraining agent, water reducing agent, retarder, pozzolan.

17. Rust inhibitor: sodium nitrite, sodium benzoate, calcium lignin sulfonate, phosphate, sodium fluorosilicate, sodium fluoroaluminate.

18. Grouting additives: retarder, gel, gelatin starch and methyl cellulose, bentonite, thickener, early strength agent, aeration agent.

Admixture highly effective

Admixture is the fifth component of concrete, and admixture can improve the workability of concrete, increase the strength and durability of concrete. The characteristics of concrete admixtures are that there are many varieties and small amounts, which have a large impact on the performance of concrete. Therefore, its variety selection, application technology, and quality control are more important than other concrete components ^[1] .

1. Without changing the proportion of various raw materials, adding concrete superplasticizer not only changes the strength of the concrete, but also can greatly improve the rheology and plasticity of the concrete, so that the concrete construction can be self-flowing, pumping, and no vibration. And other construction methods to increase construction speed and reduce construction energy consumption.

2. Without changing the proportion of various raw materials (dewatering) and the slump of concrete, reducing the amount of water can greatly increase the strength of the concrete. The early strength and the later strength are respectively higher than the concrete without the water reducing agent. Increased by 60% and more than 20%. By reducing water, it is possible to achieve the high-strength concrete marked with C100.

3. Without changing the proportion of various raw materials (except cement) and the strength of concrete, the amount of cement can be reduced. Adding 0.2% to 0.5% of concrete water reducer can save 15 to 30 cement. %the above.

4. Adding concrete high-efficiency water reducing agent can increase the life of concrete more than double, even if the normal life of the building is more than doubled.