Physical and mechanical properties and micro characteristics of fly ash-based geopolymer paste incorporated with waste Granulated Blast Furnace Slag (GBFS) and functionalized Multi-Walled Carbon Nanotubes (MWCNTs)

Abstract

Geopolymers are highly durable and have favorable mechanical properties, and are thus regarded as an eco-friendly alternative to traditional ordinary Portland cement binder. In this study, MWCNTs are obtained through a modification method using a compound of nitric acid and sulfuric acid, and are then dispersed using three types of dispersants. Fly ash-based geopolymers are prepared to validate the effectiveness and feasibility of adopting 0.05 wt.%, 0.10 wt.%, and 0.15 wt.% functionalized MWCNTs and substitution ratios of 10 %–40 % of fly ash with GBFS. The structure and dispersity of the functionalized MWCNTs in aqueous solutions are characterized using FT-IR and TEM, respectively. Then, the setting time, water absorption capacity, and mechanical behaviors are evaluated. In addition, SEM-EDS, FT-IR, TG-DSC, 29Si NMR, and XRD are employed to investigate the morphology, elemental components, mineralogical phases, and geopolymerization degree of the gel products. The experimental results show that the functionalized MWCNTs comprise −COOH and −OH groups and can be uniformly dispersed in aqueous solution containing SDS dispersant. Furthermore, geopolymer paste incorporated with 0.1 wt.% functionalized MWCNTs and having 30 % substitution of fly ash with GBFS exhibits a higher compressive and flexural strength and a lower water absorption capacity compared with all other geopolymer pastes.