Basic Knowledge of Concrete Additives

1. What is concrete additives？

Concrete additives are materials that are added before or during mixing to improve the new properties of fresh concrete and hardened concrete. The amount of admixtures is less than 5% of the cement quality (except in exceptional cases).

2. Concrete additives are divided into four categories according to their functions;

(1) Additives to improve the rheological properties of concrete mixtures, including various superplasticizers, pumping agents and air-entraining agents;

(2) Additives for adjusting the setting time and hardening performance of concrete, including retarders, early strength agents and accelerators;

(3) Additives to improve the durability of concrete, including air-entraining agents, waterproofing agents, rust inhibitors, etc.;

(4) Additives to enhance other properties of concrete, including expansion agent, antifreeze, colouring agent, etc.

3. 27 kinds of admixtures are defined in the standard of concrete admixtures: ordinary water reducer, concrete hardener, retarder, accelerator, air-entraining agent, high-efficiency superplasticizer, retarding high-efficiency water-reducing agent, early strength water-reducing agent, Retarding water reducing agent, air-entraining water reducing agent, waterproofing agent, rust inhibitor, air-entraining agent, expansion agent, antifreeze, colouring agent, quick-setting agent, pumping agent, water-retaining agent, flocculant, thickening agent, shrinkage reducing agent, plasticizer, ground slag, silica fume, ground fly ash, ground natural zeolite.

Ordinary water reducing agent refers to an admixture that can reduce the amount of water used for mixing when the concrete slump is the same.

Early strength agent refers to an admixture that accelerates the early strength development of concrete.

Retarder refers to an admixture that prolongs the setting time of concrete.

The coagulant is an admixture that can shorten the time of mixing and setting.

Air-entraining agent refers to an admixture that can introduce a large number of uniformly distributed, stable and closed tiny bubbles during the mixing process of concrete and can remain in the hardened concrete.

High-efficiency superplasticizer refers to an admixture that can significantly reduce the amount of water used for mixing under the condition that the concrete slump is the same.

Retarding high-efficiency superplasticizer refers to an admixture that has both retarding and high-efficiency water-reducing functions.

Early-strength superplasticizer refers to an admixture with both early-strength and water-reducing functions.

Retarding superplasticizer refers to an admixture with both retarding and water reducing functions.

Air-entraining superplasticizer refers to an admixture with air-entraining and water-reducing functions.

Waterproofing agent refers to an admixture that can improve the impermeability of cement mortar and concrete.

Rust inhibitors refer to additives that can inhibit or reduce the corrosion of steel bars and other metal embedded parts in concrete.

Foaming agent refers to an admixture that has a large number of uniformly distributed pores in the hardened concrete due to a chemical reaction and gas released during the preparation of concrete.

Expansion agent refers to an admixture that can produce an individual volume expansion of concrete due to chemical action during concrete hardening.

Antifreeze is an admixture that can harden concrete at negative temperature and reach sufficient landlord's strength level within a specified time under specified curing conditions.

Colouring agent refers to an admixture that can prepare concrete with stable colours.

The accelerator is an admixture that can only set and harden concrete quickly.

Pumping agent refers to an admixture that can improve the pumping performance of concrete mixtures.

Water retention agent refers to an admixture that can reduce the loss of water in concrete or mortar.

Flocculant is an admixture that can increase the viscosity of concrete and resist cement and aggregates during construction in water.

Thickener refers to an admixture that can increase the viscosity of the concrete mixture.

Shrinkage reducing agent refers to an admixture that reduces concrete shrinkage.

Plastic preservative refers to an admixture that reduces the loss of concrete slump within a specific time.

Finely ground slag refers to the product whose granulated blast furnace slag is dried and ground to reach the specified fineness.

Silica fume is a product with amorphous silicon dioxide as the main component, which is collected by the dust collector after the silicon vapour discharged through the flue is oxidized during the smelting of ferrosilicon alloy or industrial silicon.

Finely ground natural zeolite refers to a product that uses natural zeolite with a specific taste and purity as raw material and is ground to a specified fineness.

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