The effect of short carbon fibers on rheological behaviour and mechanical properties of metakaolin-slag geopolymer binder

Abstract

This study investigates the effects of short carbon fibers addition on rheological behaviour of geopolymer binder and final mechanical strength of prepared composite. The pure geopolymer binder and variously carbon fiber reinforced composites were tested. The pure geopolymer binder was synthesized by alkalination of calcined claystone powder and milled blast furnace slag by potassium silicate solution. The binders reinforced by carbon fibers were prepared under the same conditions. Mixtures were accordingly reinforced by 20 wt% of short and milled fibers, respectively. The effect of fibers length (3 mm and ≤ 0.5 mm) was studied with regard to rheological behaviour of prepared mixtures and mechanical properties of final composites. The rheological properties were determined in accordance to flow properties by rotational rheometry. The final properties were determined by measurements of flexural strength after 3, 28 and 280 days and by means of optical and scanning electron microscopy. The results indicate that milled carbon fibers had a slight effect on flow properties compared to pure binder. In contrast, 3 mm long carbon fibers significantly increased viscosity and noticeably decreased workability by interlocking mechanism of individual fibers. Moreover, it was proved that addition of milled fibers had a low reinforcement effect on composite samples and led only to slight improvement of stress-strain behaviour. On the contrary, the reinforcement by 3 mm carbon fibers improved the stress-strain properties and significantly increase ultimate flexural strength (approximately 5 times) compared to pure geopolymer binder in all studied time intervals.