Microstructure and mechanical properties of carbon microfiber reinforced geopolymers at elevated temperatures

The present work deals with the effect of carbon microfiber addition on the development of microstructure and mechanical properties of geopolymers at elevated temperature. The carbon microfibers were prepared from recycled inexpensive carbon fibrous wastes by ball milling, and then subsequently incorporated under 5, 10 and 15 wt% loading into metakaoline based geopolymers. The addition of carbon microfibers was found to produce compact structure of geopolymers due to their pore filling characteristics and formation of additional calcium silicate or calcium alumino-silicate and sodium alumino-silicate hydrates. The geopolymer composite of 15 wt% carbon micro fiber was found to maintain the residual compressive strengths of 33.55 and 23.96 MPa at 400 °C and 800 °C, respectively and thus recording a minimum strength loss of 19 and 42%, respectively. This behavior was attributed to decreased thermal stresses and restricted swelling of unreacted geopolymer phases after addition of carbon microfibers.