How to compound early strength agent with PCE liquid?

Compounding of PCE and early strength components

PCE can be compounded with inorganic salt early-strength agents and organic early-strength agents. According to the dosage of traditional early-strength agent, here means that the dosage of early-strength agent is 0.25%-1.5% of the amount of cementitious material, which can advance the setting time of cement mortar and concrete, and improve the early and super early (within 24h) strength. . However, different dosages and different types of early-strength agents will greatly affect the fluidity and retention of cement mortar and concrete.

?I conducted concrete experiments on the following 6 early-strength admixtures respectively, and compared the PCE solution with 1% content of 20% solids as the benchmark concrete for comparison. The six early strength agents are sodium chloride, calcium chloride, anhydrous sodium sulfate, sodium thiosulfate, sodium nitrite and sodium nitrate, and the addition amounts are 0.25%, 0.5%, and 0.75% of the cementitious material, respectively. Calcium chloride and sodium sulfate are used to make the initial slump smaller, and sodium nitrite and sodium nitrate are not significantly affected. The most significant increase in 3d early strength was sodium thiosulfate, which was enhanced by 151% when the dosage was 0.25%, followed by adding 0.5% calcium chloride, and the enhancement was 147% higher than the benchmark. This group of experiments was made under standard maintenance.

?Since the demand for early strength of concrete structures is mainly for construction in low temperature environments, more research and development focus on lower normal temperature environments. When PCE superplasticizer is not added with early strength components, the early strength of low temperature environment mostly fails to meet the construction requirements. When low concentration (PCE content less than 0.2%) PCE superplasticizer is used, the early strength is 12h to 72h. The long-term strength is not up to the requirements.

?The compound early strength effect of calcium formate is also very significant. When the content of calcium formate is 1%, the strength of 1d is 60% higher than that without doping, and 50% higher than that of 3d, all of which are cured in low temperature environment. Because of its low solubility in water, it was replaced by sodium formate, and the dosage was only 60% of the former.

?In recent years, due to the sharp increase in the market demand for low-concentration PCE admixtures, early-strength coagulants have also successively developed sodium thiocyanate with a dosage as low as 0.03%-0.2% of the cementitious material and a relatively obvious 12-72h early-strength effect. , calcium formate, calcium ammonium nitrate double salt and other materials. Experiments show that the super-early strength of calcium nitrate, sodium nitrate and methyl sodium are higher than that of PCE mother liquor itself. 1% in concrete). The amount of sodium formate is relatively low, about 20kg.

?Triethanolamine can also play an excellent role in improving the early strength of concrete in PCE water reducer. It promotes the increase of 12h strength of PCE concrete. The dosage of optimal early strength in PCE concrete is 0.07% of the amount of cementitious material. .

?In addition, adding an appropriate amount of defoamer, foam control agent, etc., also has a significant effect on improving the early and ultra-early strength of PCE water reducers with large air content. Since the defoamer is easy to cause the concrete slump to become smaller and the slump loss to be accelerated, the meaning of "appropriate amount" is that it does not significantly affect other properties after adding it.

?In low temperature environment, increasing the effective components of PCE water reducer (increasing the percentage of solid content) is an effective and cost-effective measure to improve the early strength of concrete. In more occasions, the construction requirements to improve the early strength actually require the shortening of the initial setting time. The development of a more cost-effective setting accelerator and early strength agent is a major issue in winter construction areas.

At present, sodium thiosulfate and sodium sulfate are still widely used as early strength agents for PCE.