Effects of Two Different Synthetic Wollastonite Microfibers Produced with Natural and Waste Raw Materials on Engineered Geopolymer Composites

Abstract This study covers the effects of two different synthetic wollastonite microfibers (SWMs) on the properties of engineered geopolymer composites (EGCs) developed with fly ash (FA) and ground granulated blast furnace slag (GGBFS). Firstly, SWMs with two different maximum aspect ratios ( 44 ∶ 1 and 12 ∶ 1 ) were produced by using different SiO 2 sources [silica powder and silica fume (SF)] with the specific production process in the laboratory. SWM with a maximum aspect ratio of 44 ∶ 1 had a high proportion of the needle-shaped particles while SWM with a maximum aspect ratio of 12 ∶ 1 had the rare acicular particles. These microfibers were then used at 3, 6, and 9 wt% in place of FA in FA + GGBFS - based EGC. As a results of characteristics tests, it can be concluded that both SWMs increased the bearing strength and deformation capacity of the EGC by up to 6% of replacement level. The incorporation of 6% SWM with a higher aspect ratio increased the 28 day compressive strength, flexural strength, and midspan beam deflection of the EGCs by 11.2%, 6.5%, and 42.6%, respectively, whereas for the SWM with a lower aspect ratio, these improvements were 4.4%, 3.6%, and 8.2%, respectively. Moreover, the presence of wollastonite in the system was confirmed by X-ray diffraction (XRD) analysis, while thermogravimetric analysis/differential thermal analysis (TGA/DTA) and Fourier transform infrared spectroscopy (FTIR) analyses validated the mechanisms responsible for the observed enhancement in mechanical performance. Accordingly, the improvement in mechanical performance of SWM-incorporated EGCs is governed by physical and micromechanical mechanisms, notably crack-bridging efficiency, interfacial bonding, and aspect-ratio-dependent stress transfer rather than by chemical contributions to geopolymerization. Consequently, SWMs with higher aspect ratios and denser acicular particle structures enhanced remarkably the mechanical performance of the EGCs.