Study on the effects Nano‐SiO2 and spent catalyst ratios on characteristics of metakaolin‐based geopolymers

Abstract

This study focused on nano‐SiO2 (NS) addition levels (0.5%–2%) and spent catalyst replacement levels (0%–20%) in the geopolymerization reaction and subsequent network formation of metakaolin‐based geopolymers (MKGP), which affect the mechanical properties and microstructure of the geopolymers. The geopolymers had high flexural strength (72.9 MPa), high bulk density (1.37 g/cm3), and low porosity (41.4%) when 0.5% NS was constantly added and the spent catalyst replacement level was 5%. The geopolymer weight loss was due to the structural water evaporation occurring at temperatures ranging from 350°C to 550°C. Therefore, weight loss was slightly higher than 0.5% NS MKGP without spent catalyst (1.25%) at the spent catalyst replacement level of 5% (1.44%). Regarding the chemical shifts in 29Si MAS NMR spectra, when the geopolymer contained 0.5% NS, the peak center of Q4 (2Al, −97 ppm) shifted to an even higher magnetic of Q4 (3Al, −90 ppm). The NS surface, which was in an active and high free‐energy state, reacted with the geopolymerization system, forming chemical interfacial bonding with the binder phase. The MKGP with 0.5% NS content and 5% spent catalyst replacement yielded more favorable mechanical characteristics and microstructure, according to the flexural strength, TG/DTA, and NMR analyses. © 2018 American Institute of Chemical Engineers Environ Prog, 38: 220–227, 2019