Effect of mixed fibers on fly ash-based geopolymer resistance against carbonation

Abstract

In this study, the resistance of mixed fiber reinforced fly ash-based geopolymer incorporated with different polyvinyl alcohol (PVA) fibers and modified multi-walled carbon nanotubes (MWCNTs) against carbonation was analyzed using the accelerated carbonation test. The resistance enhancing effects of modified geopolymer were investigated using the carbonation depth and compressive strength tests. Meanwhile, X-ray diffraction(XRD), Fourier transforms infrared spectroscopy (FT-IR), mercury intrusion porosimetry (MIP), and field emission scanning electron microscopy(FE-SEM) were used to evaluate the mineralogical phases, geopolymerization process, micropore structures, and microscopic morphologies, respectively. The experimental results showed that the resistance of geopolymer against carbonation decreased compared to that of cement mortar. However, the incorporation of an appropriate amount of modified MWCNTs and PVA fibers can enhance the resistance of the geopolymer against carbonation. Moreover, accelerated carbonation decreases the compressive strength of geopolymers while increasing the corresponding compressive strength of cement mortars. The addition of an appropriate amount of modified MWCNTs and PVA fibers can enhance the compressive strength of geopolymers. The resistance of the modified geopolymer against carbonation is best when incorporated with 0.10% modified MWCNTs and 2.00% PVA fibers. After carbonation, the microstructure of the modified geopolymer becomes loose. Moreover, accelerated carbonation decreased the porosity of the modified geopolymer and increased the proportion of harmful pores.