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.