Abstract

Concrete 3D printing is one promising technique used for future construction. However, a bottleneck limiting this technology's rapid development and practical application is the conflicting requirements for concrete properties before and after printing. Hence, the application of the accelerator and a deep understating of its working mechanism is becoming more and more important. As one commonly used accelerator, triethanolamine (TEA) has the advantage of low dosage and high efficiency to reach a fast setting. However, it is still unclear how the delayed addition of TEA affects the performance of cementitious materials. Besides, it is found that the different types and combinations of sulfate carriers can significantly affect the performance of TEA on cement hydration. However, the combined effect of different sulfate carriers and different addition times of TEA on the hydration process of cement paste is also unclear. The effect of different TEA addition times on the hydration and setting performance of cement pastes containing different types and combinations of sulfate carriers were thoroughly investigated in this study. It is found that, depending on the types of sulfate carriers inside, the different addition times of TEA can significantly affect the hydration and setting performance of cement paste. Specifically, to artificial cement (ArC) prepared with hemihydrate (HH), the different TEA addition times do not affect the setting performance of cement paste. To ArC with the two sulfate carriers of anhydrite (AH) and HH, a flash setting was observed when the TEA was added simultaneously. However, a delayed addition of TEA for just 5 min can make the setting performance back to normal. To ArC with only AH, a longer addition time of 15 min is needed to eliminate the flash setting behavior. This phenomenon could be originated from the competed interaction of sulfate ions released from sulfate carriers and TEA with the aluminate phase contained in the clinker.