Current status of concrete low temperature early strength agent

The hydration hardening property of cement determines the early strength of concrete. Under standard conditions, the strength can only reach 20%~30% of the design strength and the strength of 3d reaches 40%. Under the low temperature condition in winter, the strength development rate will become Lower. Concrete early strength agent is an admixture that accelerates the early strength development of concrete, and its content generally does not exceed 5% of the mass of cement. At room temperature (20±3) °C, the concrete with early strength agent can reach the demoulding strength for 10h, usually up to 50% of the design strength at 1d, and the strength of the reference concrete for 28d at 3d.

 In the winter construction or early concrete requirements, the early strength agent can be exempted from additional maintenance measures, which plays an important role in speeding up the construction progress and improving the quality of concrete. At present, traditional early strength components can not meet the requirements of green and high-performance concrete, and the research of early early strength agents is mostly carried out at room temperature, while the research under low temperature (especially 5 °C) environment is relatively rare, and early strength agents Early performance, late strength and mechanism of action at low temperatures are not known. Both nitrate and nitrite have an early strengthening effect, which can promote the formation of hydrated calcium silicate (CSH) and hydration of cement, improve the pore structure of hydration products, and make the mortar structure tend to be dense [8]. It must have antifreeze effect, and nitrite also has good rust inhibition effect. Common early-earners such as triethanolamine are calcium nitrate, calcium nitrite, sodium nitrate and the like.

Triethanolamine is considered to be the most widely used organic early strength agent, and its dosage is generally 0.02% to 0.06%. Appropriate amount of triethanolamine can promote the hydration of C3S after the induction period, not only to achieve the purpose of early strength, but also to make the late hydration products fully grow and compact, so that the late strength also increases. Studies have shown that the incorporation of triethanolamine can increase the strength of concrete 1d by 6~9 MPa. However, in practical applications, the amount of triethanolamine is small, and the optimum dosage is difficult to accurately grasp. If the control is not good, the concrete will be seriously retarded and the strength will be seriously affected. Triisopropanolamine has good dispersibility and superior surface activity, can enhance the activity of hydration to form colloids, and has the functions of accelerating adsorption, wetting and dispersing particles, which is beneficial for accelerating the development of concrete strength and improving strength, and can also improve The compactness and impermeability of concrete. When the content of triisopropanolamine is 0.2%-0.9%, the cement paste has a significant reinforcing effect on the 1d strength, and the coagulation effect is obtained when the amount is more than 1.2%.