Effects of carbon nanofibers on hydration and geopolymerization of low and high-calcium geopolymers

This paper discusses the different modifying mechanisms of carbon nanofiber (CNF) on the geopolymers with different calcium contents . First, the rheological and mechanical properties of CNF modified geopolymers with low and high-calcium content are measured. Results show that the modifying effect on rheological properties is more obvious on high-calcium geopolymers. The compressive and flexural strength of low-calcium geopolymers decrease, while the compressive and flexural strength of high-calcium geopolymers significantly improve. Based on XRD , MIP , and SEM analyses, it can be concluded that CNFs help to produce refined hydration products in high-calcium geopolymers, resulting in a denser structure. Promoting hydration can counteract the adverse effect caused by the agglomeration of CNFs. CNFs have a positive effect on high-calcium geopolymers in general. However, hydration reaction rarely happens in the low-calcium geopolymers because of the low calcium content, and XRD results show that CNFs do not significantly promote the geopolymerization reaction. Moreover, the agglomeration of CNFs leads to a decrease in compactness. CNFs negatively affect low-calcium geopolymers. Generally, CNFs can be applied in high-calcium geopolymers to form a denser structure and improve the mechanical properties.