Concrete Admixtures

Water reducer refers to the addition of admixtures that can significantly reduce the amount of mixing water under the condition that the slump of concrete is basically the same. As a surface active substance, the molecule of the concrete water reducer is composed of two parts: a hydrophilic group and a hydrophobic group. When the cement is mixed with water, the cement slurry forms a flocculation structure, which wraps a part of the mixing water and reduces the fluidity.

According to the chemical composition, there are mainly lignin series, naphthalene series, water-soluble resins, molasses and composite water reducing agents.

The early strength agent it an admixture that accelerates the early strength development of concrete and has no significant effect on the later strength. The early strength agent can accelerate the hardening process of concrete under the conditions of normal temperature and low temperature load, and is mostly used in winter construction and emergency repair projects. The accelerators mainly include inorganic salts (chlorine salts, sulfates), organic amines and organic-inorganic compounds.

Concrete Retarder refers to the concrete additive that can delay the setting time of concrete and has no adverse effect on the strength development of concrete in the later stage. Retarders are mainly sugars and lignosulfonates. The retarder has the functions of retarding, reducing water, reducing the heat of hydration and strengthening, and has no corrosion effect on steel bars. It is mainly suitable for mass concrete and concrete constructed in hot climates, as well as concrete that needs to be parked for a long time or transported over long distances.

Air-entraining agent refers to the addition of a large number of uniformly distributed micro-bubbles that can be introduced during the concrete mixing process to reduce bleeding and segregation of the concrete mixture, improve workability, and significantly improve the frost resistance and durability of hardened concrete. At present, the most widely used air-entraining agents are rosin thermal polymers, rosin soaps, and alkylbenzene sulfonates. Due to the existence of a large number of tiny, closed and evenly distributed air cells, some properties of concrete are obviously improved or changed.

Antifreeze is an admixture can harden concrete at negative temperatures and achieve expected performance under specified curing conditions. Commonly used antifreezes are chlorine salts, chlorine salt rust inhibitors.

Accelerator refers to the concrete additive that can make concrete set and harden quickly. There are mainly two types of accelerators, inorganic salts and organic substances. After the quick-setting agent is mixed into the concrete, the concrete can be initially set within 5 minutes, and the strength can be produced in 1 hour, and the strength can be increased by 2 to 3 times in 1 day, but the strength will decrease in the later period, and the strength in 28 days is about 80% to 90% of that without mixing. The mechanism of quick-setting and early-strength action of the accelerator is to make the gypsum in the cement turn into Na2SO4, lose the retarding effect, and promote the rapid hydration of C3A, and precipitate its hydration product crystals in the solution, resulting in the rapid solidification of the cement slurry. Accelerators are mainly used in mine shafts, railway tunnels, drinking water culverts, underground projects, and shotcrete or shotcrete projects for shotcrete anchor support.