Li Peiqing, Chen Deyong, Jia Zhirong, Li Yilin, Li Shuaijun, Yu Bin
School of Civil and Architectural Engineering, Shandong University of Technology, 266 Xincun Road, Zibo 255000, China.
School of Transportation and Vehicle Engineering, Shandong University of Technology, Zibo 255000, China.
Materials (Basel). 2023 Apr 11;16(8):3010. doi: 10.3390/ma16083010.
The setting time of alkali-activated slag (AAS) binders is extremely short, while traditional retarders of Portland cement may be invalid for AAS. To find an effective retarder with a less negative impact on strength, borax (B), sucrose (S), and citric acid (CA) were selected as potential retarders. The setting time of AAS with different admixtures dosages of 0%, 2%, 4%, 6%, and 8%, and the unconfined compressive strength and beam flexural strength of 3 d, 7 d, and 28 d AAS mortar specimens were tested. The microstructure of AAS with different additives was observed by scanning using an electron microscope (SEM), and the hydration products were analyzed by energy dispersive spectroscopy (EDS), X-ray diffraction analysis (XRD), and thermogravimetric analysis (DT-TGA) to explain the retarding mechanism of AAS with different additives. The results showed that the incorporation of borax and citric acid could effectively prolong the setting time of AAS more than that of sucrose, and the retarding effect is more and more obvious with the increase in borax and citric acid dosages. However, sucrose and citric acid negatively influence AAS's unconfined compressive strength and flexural stress. The negative effect becomes more evident with the increase in sucrose and citric acid dosages. Borax is the most suitable retarder for AAS among the three selected additives. SEM-EDS analysis showed that the incorporation of borax does three things: produces gels, covers the surface of the slag, and slows down the hydration reaction rate.
碱激发矿渣（AAS）胶凝材料的凝结时间极短，而传统的硅酸盐水泥缓凝剂对AAS可能无效。为了找到一种对强度负面影响较小的有效缓凝剂，选择了硼砂（B）、蔗糖（S）和柠檬酸（CA）作为潜在的缓凝剂。测试了不同掺量（0%、2%、4%、6%和8%）的AAS的凝结时间，以及3 d、7 d和28 d龄期的AAS砂浆试件的无侧限抗压强度和梁抗折强度。通过扫描电子显微镜（SEM）观察了添加不同添加剂的AAS的微观结构，并通过能谱分析（EDS）、X射线衍射分析（XRD）和热重分析（DT-TGA）对水化产物进行分析，以解释不同添加剂对AAS的缓凝机理。结果表明，与蔗糖相比，掺入硼砂和柠檬酸能更有效地延长AAS的凝结时间，且随着硼砂和柠檬酸掺量的增加，缓凝效果越来越明显。然而，蔗糖和柠檬酸对AAS的无侧限抗压强度和抗折应力有负面影响，且随着蔗糖和柠檬酸掺量的增加，负面影响更加明显。在所选用的三种添加剂中，硼砂是最适合AAS的缓凝剂。SEM-EDS分析表明，掺入硼砂有三个作用：生成凝胶、覆盖矿渣表面以及减缓水化反应速率。
