THE INFLUENCE OF PHOSPHORUS SLAG ADDITION ON MICROSTRUCTURE AND MECHANICAL PROPERTIES OF METAKAOLIN-BASED GEOPOLYMER PASTES

In this study, metakaolin plus different weight percent of phosphorus slag (10-100 wt. %) were used in preparation of geopolymer. The compressive strength, phase analysis and microstructure changes were compared with a metakaolin based geopolymer control sample. Results showed that the substitution of slag up to 40 wt. % instead of metakaolin increase the 28 days compressive strength (14.5 %) compared with control sample. This enhancement of strength is related to coexistence of geopolymeric gel and C-S-H gel or C-A-S-H phase by XRD and FTIR study. In slag containing geopolymer samples some microcracks were observed at microstructure that established by volume change during formation of new phase or mismatching of unreacted particle with geopolymeric gel. These microcrack can dominate at high content of slag (above 40 wt. %) substitution and decrease the strength of samples. These results show that it is possible to produce geopolymer cement from waste phosphorus slages.