What properties can be added to concrete admixtures?

Concrete admixtures are materials added before or during concrete mixing to improve the properties of fresh and/or hardened concrete. The following are admixtures with different properties that can be added:

I. Admixtures that improve the rheological properties of concrete mix

Water reducers: including ordinary water reducers and high-efficiency water reducers. Under the condition that the slump of concrete is basically the same, ordinary water reducers can reduce the amount of mixing water, while high-efficiency water reducers can significantly reduce the amount of mixing water. Using the water-reducing effect of water reducers can significantly improve the strength of hardened concrete, or maintain the original strength and consistency to save cement.

Air-entraining agents: Introduce a large number of uniformly distributed, stable and closed micro-bubbles during concrete mixing, and can be retained in hardened concrete. The use of air-entraining agents can improve the frost resistance, impermeability, and crack resistance of concrete. However, it should be noted that air-entraining agents will reduce the strength of concrete, so the dosage should be strictly controlled.

Pumping agents: Admixtures that can improve the pumping performance of concrete mixtures.

II. Admixtures that adjust the setting time and hardening properties of concrete

Early strength agents: Admixtures that accelerate the early strength development of concrete. Commonly used early strength agents include strong electrolyte inorganic salts (such as sulfates, sulfate double salts, etc.), water-soluble organic compounds (such as triethanolamine, etc.), and other composite materials. Early strength agents are suitable for steam-cured concrete and concrete projects with early strength requirements in normal temperature, low temperature, and low temperature environments not lower than -5℃.

Retarders: Admixtures that prolong the setting time of concrete. Commonly used retarders include sugars (such as sugar calcium, etc.), lignosulfonates (such as calcium lignosulfonate, etc.), hydroxycarboxylic acids and their salts (such as citric acid, etc.), and inorganic salts (such as zinc salts, etc.). Retarders can be used to prevent premature setting of concrete and extend the construction operation time.

Accelerators: Admixtures that can make concrete harden quickly.

III. Admixtures that improve the durability of concrete

Waterproofing agents: Admixtures that can reduce the permeability of concrete under static water pressure. The use of waterproofing agents can make concrete impermeable under the action of a certain pressure of water.

Rust inhibitors: Admixtures that can inhibit or reduce the corrosion of steel bars or other embedded metals in concrete. The use of rust inhibitors can prevent steel bars from rusting in the presence of chlorides.

Air-entraining agents (also classified here because they can improve the durability of concrete): As mentioned above, improving the frost resistance and impermeability of concrete by introducing micro-bubbles.

IV. Admixtures that improve other properties of concrete

Expanding agents: Admixtures that can cause a certain amount of expansion in the volume of concrete. The use of expanding agents can compensate for the shrinkage of concrete and reduce the occurrence of cracks.

Coloring agents: Admixtures that can produce concrete with stable colors.

Foaming agents: Admixtures that release gas due to chemical reactions during concrete preparation, which can make concrete form a large number of pores. Foaming agents can be used to produce lightweight and porous concrete.

Anti-freezing agents: Admixtures that allow concrete to harden at sub-zero temperatures and reach sufficient frost-resistant strength within a specified time. When anti-freezing agents are added to concrete mixtures, their anti-freezing components can lower the freezing point of the liquid phase and change the crystal form of ice, thereby avoiding concrete damage from freezing.