Setting and nanostructural evolution of metakaolin geopolymer
type: CreativeWork
description: Geopolymers are being promoted as a sustainable alternative to the ordinary cements mainly because their production is associated with much less CO2 emissions. They also show advantages including compressive strength comparable to portland cements, high temperature resistance, and stability under acid attack. However, before geopolymers can be widely used in practice, certain other behaviors must be understood and controlled, among which is setting, the transition from fluid to solid. Geopolymer setting is repeatedly seen to be substantially accelerated by addition of calcium. The objective of this study is to understand the setting at the nanostructural level for calcium and non-calcium geopolymers using a relatively pure aluminosilicate metakaolin precursor. Prior to probing nanostructural evolution, a combination of water treatment to extract soluble species and solvent treatment to extract water was developed for use to stop the geopolymer formation for early-age geopolymers with and without calcium, allowing enough time for nuclear magnetic resonance (NMR) tests. Additionally, a protocol to quantify structures of early-age geopolymers was developed using NMR deconvolution and validated by intensity analysis of NMR spectra and by quantitative chemical extractions. The nanostructural evolution during formation of geopolymer was investigated and correlated with setting. In the non-calcium mix, aluminum was released rapidly right after mixing and immediately condensed with silicates to form aluminosilicate units with growing sizes on metakaolin surface. Set occurred as the remaining aqueous silicates began attaching to these units to form a gel with an interconnected network structure. The structural connectivity during this evolution, for the first time, was monitored experimentally. Additionally, accelerated setting by calcium was investigated. With calcium, enhanced rate and extent of metakaolin dissolution were observed and were found to decrease Si/Al ratio av…
abstract: Geopolymers are being promoted as a sustainable alternative to the ordinary cements mainly because their production is associated with much less CO2 emissions. They also show advantages including compressive strength comparable to portland cements, high temperature resistance, and stability under acid attack. However, before geopolymers can be widely used in practice, certain other behaviors must be understood and controlled, among which is setting, the transition from fluid to solid. Geopolymer setting is repeatedly seen to be substantially accelerated by addition of calcium. The objective of this study is to understand the setting at the nanostructural level for calcium and non-calcium geopolymers using a relatively pure aluminosilicate metakaolin precursor. Prior to probing nanostructural evolution, a combination of water treatment to extract soluble species and solvent treatment to extract water was developed for use to stop the geopolymer formation for early-age geopolymers with and without calcium, allowing enough time for nuclear magnetic resonance (NMR) tests. Additionally, a protocol to quantify structures of early-age geopolymers was developed using NMR deconvolution and validated by intensity analysis of NMR spectra and by quantitative chemical extractions. The nanostructural evolution during formation of geopolymer was investigated and correlated with setting. In the non-calcium mix, aluminum was released rapidly right after mixing and immediately condensed with silicates to form aluminosilicate units with growing sizes on metakaolin surface. Set occurred as the remaining aqueous silicates began attaching to these units to form a gel with an interconnected network structure. The structural connectivity during this evolution, for the first time, was monitored experimentally. Additionally, accelerated setting by calcium was investigated. With calcium, enhanced rate and extent of metakaolin dissolution were observed and were found to decrease Si/Al ratio av…
author: Chen, Xu
language: en
keywords: Geopolymer, Setting, Nuclear magnetic resonance
date published: 2017-08-10T20:33:08Z
date modified: 2026-07-22T22:24:34Z
provider: University of Illinois - Urbana-Champaign
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: University of Illinois at Urbana-Champaign

PropertyValue
property ID: Handle
value: http://hdl.handle.net/2142/97739