Influence of Processing Conditions on the Mechanical Behavior of Mineral-Impregnated Carbon-Fiber (MCF) Made with Geopolymer

Mineral-impregnated carbon-fiber (MCF) composites are for the construction industry a promising alternative to steel reinforcement or conventional fiber-reinforced polymer (FRP) composites due to their high mechanical performance over a wide temperature range, corrosion resistance, and high technological flexibility. For an efficient industrial fabrication of MCF, a long-range processing window need to be secured for the reactive impregnation suspensions. In this regard geopolymers offer great potential since - similar to organic thermosettings - they require thermal curing to accelerate polymerization, enabling quickly high early strengths. To this end, the presented article is envisaged to study the impact of curing regimes and processing technology on the microstructure and mechanical properties of MCF. The MCFs were fabricated automated and continuously with a geopolymer-suspension and subsequently treated at elevated temperatures. Moreover, a helical winding was applied around the freshly pultruded bundle to profile the reinforcement surface, increase its "green" strength and handleability as well as its subsequent bond behavior towards concrete matrices. The produced samples were thermally "activated" at 75 degrees C for up to 8 h only, to promote the geopolymerization process. With prolonged curing, a gradual increase in flexural and tensile properties was observed, confirmed by microscopic analyses showing a more reacted matrix microstructure with 8 h of curing time. The applied helical winding yielded a slight decrease in flexural performance, but densified the matrix microstructure of the MCF, proven by mercury intrusion porosity measurements. Finally, uniaxial tensile tests presented that the mechanical properties of such produced MCF reinforcements are in the same range as conventional FRPs.