Experimental study of the feasibility of using calcium carbide residue as an alkaline activator for clay-plant ash geopolymer

The use of cement is gradually limited due to its enormous thermal energy consumption and carbon dioxide emissions. The plant ash and calcium carbide residue, as waste by-products, are adopted in this research for clay plant ash geopolymer. The primary purpose of this research is to evaluate the feasibility of calcium carbide residue as an alkaline activator to improve the engineering properties of clay-plant ash geopolymer. Laboratory tests containing the unconfined compressive strength test, atterberg limits, orthogonal experiment and scanning electron microscope (SEM) tests are carried out and the influence factors include the plant ash contents, calcium carbide residue contents, sodium hydroxide contents and curing time. The experimental results indicate that the calcium carbide residue has a significant effect on unconfined compressive strength of clay-plant ash geopolymer and the strength increases with the increasing calcium carbide residue contents. The strength of clay-plant ash geopolymer also increases with the increase in plant ash content and curing time. The optimal proportion of clay plant ash geopolymer is obtained from orthogonal experiment and it demonstrates that the highest strength of sample is achieved from 16% calcium carbide residue, 13% plant ash and 0.8% sodium hydroxide. The brittle strain softening behavior is observed from the stress-strain curves of clay-plant ash geopolymer. With the addition of plant ash and calcium carbide residue, the liquid limit and plastic limit of clay-plant ash geopolymer both increase and the plasticity index decreases. The microstructure of samples is revealed by scanning electron microscope test and it indicates that the main reason of strength improvement is attributed to the formation of gelling substances such as calcium silicate hydrate and calcium aluminate hydrate. Finally, the stabilization mechanism of calcium carbide residue and plant ash is analyzed and discussed in this study.