Effect of complexation of alkanolamine in accelerators on the initial stage of cement hydration

In this study, diethanolamine (DEA) and triethanolamine (TEA) were used to prepare a series of liquid alkali-free accelerators to investigate the different effects of complexation of DEA and TEA in accelerators towards the initial stage of cement hydration. Two types of accelerators respectively containing DEA (dosages of 0, 6, 8, 10, 12%) and TEA (dosages of 0, 0.25, 0.5, 0.75, 1, 8%) were prepared, and after addition, the setting time of cement pastes and compressive strength of mortars were tested. The result showed that the optimum dosage of DEA and TEA in accelerators was 8% and 0.25% respectively, and the early-strength effect of TEA was stronger than that of DEA. The mechanisms of DEA and TEA in accelerators were further revealed in terms of complexation capacity, concentration of Ca2+, and hydration products and microstructure morphology of cement pastes. DEA and TEA complexed with Al3+ in accelerators and promoted the formation of ettringite (AFt) in cement pastes, and the complexation capacity of TEA to Al3+ was stronger than that of DEA, causing that high dosage of TEA in accelerator promoted the formation of AFt more than DEA and covered at the surfaces of C3A and C3S, which inhibited the hydration. DEA in accelerator could promote the hydration of C3S in the initial stage due to the transformation of complex DEA-Al to DEA-Ca. This study aims to interpret the different influences of complexation effects of DEA and TEA in accelerators on the properties of cement-based materials and their working mechanisms.