Ma Feiyue, Chen Liangliang, Lin Zhiwei, Liu Zhuo, Zhang Weichuan, Guo Rongxin
Yunnan Key Laboratory of Disaster Reduction in Civil Engineering, Faculty of Civil Engineering and Mechanics, Kunming University of Science and Technology, Kunming 650500, China.
Broadvision Engineering Consultants, No. 9 Shuangfeng Rd., Kunming 650299, China.
Materials (Basel). 2022 Sep 2;15(17):6096. doi: 10.3390/ma15176096.
Due to the low content of silicon and aluminum in red mud and the low reaction activity of red mud, when it was used to prepare composite cementitious materials, it was necessary to assist other aluminosilicates and improve their activity by certain methods. In this study, it was proposed to add slag to increase the percentage of silicon and aluminum in the system, and to improve the reactivity of the system through the activation effect of sulfate in phosphogypsum. The effects of slag and phosphogypsum contents on the mechanical properties and microstructures of composite cementitious materials were studied. X-ray diffraction analysis (XRD), thermogravimetric analysis (TG-DTG), and scanning electron microscopy (SEM) were used to analyze the effects of slag and phosphogypsum contents on the hydration products, microstructure, and strength formation mechanism of composite cementitious materials. The results show that with the increase of slag, the strength of the composite cementitious material increases gradually. When the slag content is 50%, the 28-day compressive strength reaches a maximum of about 14 MPa. Compared with the composite material without phosphogypsum, the composite cementitious material with 10-20% phosphogypsum showed higher strength properties, in which the 28-day compressive strength exceeds 24 MPa. The main reason for this is that the sulfate in phosphogypsum can cause the composite cementitious material to generate a large amount of ettringite and accelerate the dissolution of red mud and slag, increasing the release of aluminates, silicates, and Ca to form more C-(A)-S-H and ettringite. In addition, a large amount of C-(A)-S-H makes ettringite and unreacted particles combine into a uniform and compact structure, thus improving the strength. When the content of phosphogypsum exceeds 40%, the 28-day compressive strength of the composite cementitious material drops below 12 MPa due to the presence of fewer hydration products and the expansion of ettringite.
由于赤泥中硅和铝的含量较低且赤泥反应活性低，在将其用于制备复合胶凝材料时，需要借助其他铝硅酸盐并通过一定方法提高其活性。本研究提出添加矿渣以提高体系中硅和铝的含量，并通过磷石膏中硫酸盐的激发作用提高体系的反应活性。研究了矿渣和磷石膏掺量对复合胶凝材料力学性能和微观结构的影响。采用X射线衍射分析（XRD）、热重分析（TG-DTG）和扫描电子显微镜（SEM）分析矿渣和磷石膏掺量对复合胶凝材料水化产物、微观结构及强度形成机理的影响。结果表明，随着矿渣掺量增加，复合胶凝材料强度逐渐提高。当矿渣掺量为50%时，28天抗压强度最高可达约14MPa。与不含磷石膏的复合材料相比，磷石膏掺量为10-20%的复合胶凝材料具有更高的强度性能，其中28天抗压强度超过24MPa。主要原因是磷石膏中的硫酸盐可使复合胶凝材料生成大量钙矾石，加速赤泥和矿渣的溶解，增加铝酸盐、硅酸盐和Ca的溶出，形成更多的C-(A)-S-H和钙矾石。此外，大量的C-(A)-S-H使钙矾石与未反应颗粒结合形成均匀致密的结构，从而提高强度。当磷石膏掺量超过40%时，由于水化产物减少且钙矾石膨胀，复合胶凝材料的28天抗压强度降至12MPa以下。
