Preparation of an Early Strengthening Agent for Concrete under Low-Temperature Conditions and Evaluation of Its Reaction Mechanism

To solve the common problems of concrete preparation in low-temperature environments, calcium formate (C2H2O4Ca), anhydrous sodium sulfate (Na2SO4), triethanolamine (C6H15O3N), calcium bromide (CaBr2), and triisopropanolamine (C9H21NO3) are selected as early strength agents and mixed with C40 concrete in different dosages under low-temperature environments of 5 oC and 10 oC to develop a high-efficiency low-temperature compound early strength agent based on the effect of single-doped early strength agents. The effects of the compound early strength agent on the early strength of the concrete, the cement paste setting time, and cement fluidity at 5 oC and 10 oC are investigated, and the corresponding reaction mechanism is discussed from the perspective of micro-products. The best compound early strength agent ratio is found to be 2% of calcium formate + 0.08 % of TEA (C6H15O3N). The compound early strength agent effectively promotes the formation of hydration products, such as Ca(OH)2 and C-S-H gel. In comparison with the control group, the strength of the concrete cured for 18 h, 1 d, 3 d, and 7 d under simulated natural conditions at 5 oC increases by 700%, 540%, 11.4 % and 10 %, respectively, whereas at 10 oC, the corresponding values are 991%, 400%, 19.6 % and 11 %, respectively. The strength of the concrete at each age is close to the normal temperature standard of the curing strength. The addition of the compound early strength agent causes a reduction in cement fluidity and initial and final setting times, and also yields a good effect on the porosity of the early concrete.