Boosting Construction Efficiency with Concrete Early Strength Agents

Concrete early strength agent refers to an admixture that can improve the early strength of concrete and is often used in winter or emergency repairs. The early strength agent for concrete has no significant effect on the later strength of concrete. The varieties of early strength agents include calcium chloride, sodium chloride, saltpeter, etc.

Concrete early strength agent main function is to promote the development of early strength of concrete. At present, the commonly used early strength agents in China mainly include chlorides, sulfates, carbonates, and composite early strength agents. As an additive that accelerates the early strength development of concrete, early strength agents are in great demand in engineering, especially in winter construction or emergency repair projects. At the same time, the performance and standardization of its use are directly related to the safety and service life of the entire project.

Concrete early strength agent

Common early strength agents

Chloride-based early strength agents:such as CaCl2, have good effects,such as promoting and antifreeze effects. They are inexpensive and easy to use, with a general dosage of 1% to 2%. The disadvantage is that they can cause corrosion of steel bars. In reinforced concrete, the amount of CaCl2 should not exceed 1% of the cement content and is usually used in combination with the rust inhibitor NaNO2.

Sulfate-based early strength agent:such as sodium sulfate, also known as Yuanming powder, is a white powder with a suitable dosage of 0.5%~2%. It is mostly used in combination, such as NC, which is a composite early strength agent made by mixing and grinding sodium sulfate, sugar calcium, and green sand.

Organic-based early strength agents: Organic-based early strength agents mainly include triethanolamine, triisopropanolamine, methanol, ethanol, etc., with triethanolamine being the most commonly used. Triethanolamine is a colorless or light yellow transparent oily liquid that is easily soluble in water. Its general dosage is 0.02% to 0.05%, and it has a retarding effect. It is not only used alone but is often used in combination with other early strength agents.

Concrete early strength agent

Mechanism of action

Different early strength agents or the same early strength agent mixed into different varieties of cement concrete have different effects. Here, only a few early strength agents are taken as representatives to analyze their working principles.

Chloride-based early strength agent: The main mechanism of action is the interaction between chloride and C3A in cement, generating water-insoluble hydrated chloroaluminate, which can accelerate the hydration of C3A in cement. The calcium hydroxide formed by the hydration of chloride and cement generates insoluble calcium chlorate, which reduces the generated complex salt increases the volume of the solid phase in the cement slurry, forming an internal skeleton system that is conducive to the formation of the cement structure. At the same time, due to the fact that chlorides are mostly soluble salts with salt effects, they can promote the dissolution rate of silicate cement clinker minerals, accelerate the hydration reaction process, thereby accelerating the hardening rate of concrete mixtures and improving the early strength of concrete.

Concrete early strength agent

Sulfate-based early strength agents:such as anhydrous sodium sulfate, dissolved in water, react with calcium hydroxide produced by cement hydration to generate calcium oxide and calcium sulfate. This newly generated calcium sulfate has extremely fine particles and much higher activity than doped calcium sulfate, so the reaction rate with C3A to produce hydrated calcium sulfoaluminate is much faster. Sodium hydroxide is an active agent that can increase the solubility of C3A and gypsum, accelerate the amount of calcium sulfoaluminate in cement, and lead to cement setting hardening and early strength improvement. However, sulfate early strength agents have a certain corrosive effect on the steel bars in concrete, including chloride early strength agents, and attenuate the strength of cement mortar in the later stage. Therefore, the dosage of chloride and sulfate early strength agents is gradually decreasing.

Supplier of Concrete Admixture

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