Chemical aspects related to using recycled geopolymers as an aggregate

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Abstract

Despite extensive research into geopolymers’ sustainability, it is essential to investigate largely overlooked end-of-life aspects. This requires investigation of alkalis’ leaching potential from the geopolymeric matrix. To study the viability of geopolymer concrete (GPC) recyclability, migration of alkalis was evaluated for the first time on a microstructural level through SEM/EDX elemental mapping and leaching tests. Macroscale impacts were assessed by investigation of Portland cement (PC)-mortar properties affected by alkalis concentration. Leaching tests indicated alkalis becoming immediately available in aqueous environments, but the majority remained chemically or physically bound in the matrix. This type of leaching accelerated the initial setting of PC-paste. Elemental mapping and SEM/EDX analysis showed a complex paste-aggregate interfacial transition zone. Exchange of Ca and Na, revealed by the maps, resulted in migration of Na into the PC-paste and formation of additional Ca-Si based phases in the geopolymeric matrix. Strength values of mortars with of 25% and 50% recycled aggregates (RA) showed negligible differences compared to the reference. Screening tests indicated low potential for GPC-RA inducing alkali silica reaction. Transport of GPC-RA alkalis and the underlying mechanisms were observed. This phenomenon had minor effects on PC-mortar properties indicating that recycling of geopolymers is a viable reuse practice.
Original languageEnglish
Pages (from-to)361-370
JournalAdvances in Cement Research
Volume30
Issue number8
Early online date6 Nov 2017
DOIs
Publication statusPublished - 1 Sep 2018
Event36th Cement and Concrete Science Conference - Welsh Academy of Music and Drama, Cardiff University , Cardiff, UK United Kingdom
Duration: 5 Sep 20166 Oct 2016

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Geopolymers
Alkalies
Portland cement
Leaching
Mortar
Ointments
Concrete aggregates
Energy dispersive spectroscopy
Scanning electron microscopy
Recycling
Sustainable development
Screening
Silicon Dioxide
Silica
Concretes

Keywords

  • Alkali aggregate reactions; Geopolymers; Recycled material

Cite this

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title = "Chemical aspects related to using recycled geopolymers as an aggregate",
abstract = "Despite extensive research into geopolymers’ sustainability, it is essential to investigate largely overlooked end-of-life aspects. This requires investigation of alkalis’ leaching potential from the geopolymeric matrix. To study the viability of geopolymer concrete (GPC) recyclability, migration of alkalis was evaluated for the first time on a microstructural level through SEM/EDX elemental mapping and leaching tests. Macroscale impacts were assessed by investigation of Portland cement (PC)-mortar properties affected by alkalis concentration. Leaching tests indicated alkalis becoming immediately available in aqueous environments, but the majority remained chemically or physically bound in the matrix. This type of leaching accelerated the initial setting of PC-paste. Elemental mapping and SEM/EDX analysis showed a complex paste-aggregate interfacial transition zone. Exchange of Ca and Na, revealed by the maps, resulted in migration of Na into the PC-paste and formation of additional Ca-Si based phases in the geopolymeric matrix. Strength values of mortars with of 25{\%} and 50{\%} recycled aggregates (RA) showed negligible differences compared to the reference. Screening tests indicated low potential for GPC-RA inducing alkali silica reaction. Transport of GPC-RA alkalis and the underlying mechanisms were observed. This phenomenon had minor effects on PC-mortar properties indicating that recycling of geopolymers is a viable reuse practice.",
keywords = "Alkali aggregate reactions; Geopolymers; Recycled material",
author = "Napoleana Chaliasou and Andrew Heath and Kevin Paine and Juliana Calabria-Holley",
year = "2018",
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T1 - Chemical aspects related to using recycled geopolymers as an aggregate

AU - Chaliasou, Napoleana

AU - Heath, Andrew

AU - Paine, Kevin

AU - Calabria-Holley, Juliana

PY - 2018/9/1

Y1 - 2018/9/1

N2 - Despite extensive research into geopolymers’ sustainability, it is essential to investigate largely overlooked end-of-life aspects. This requires investigation of alkalis’ leaching potential from the geopolymeric matrix. To study the viability of geopolymer concrete (GPC) recyclability, migration of alkalis was evaluated for the first time on a microstructural level through SEM/EDX elemental mapping and leaching tests. Macroscale impacts were assessed by investigation of Portland cement (PC)-mortar properties affected by alkalis concentration. Leaching tests indicated alkalis becoming immediately available in aqueous environments, but the majority remained chemically or physically bound in the matrix. This type of leaching accelerated the initial setting of PC-paste. Elemental mapping and SEM/EDX analysis showed a complex paste-aggregate interfacial transition zone. Exchange of Ca and Na, revealed by the maps, resulted in migration of Na into the PC-paste and formation of additional Ca-Si based phases in the geopolymeric matrix. Strength values of mortars with of 25% and 50% recycled aggregates (RA) showed negligible differences compared to the reference. Screening tests indicated low potential for GPC-RA inducing alkali silica reaction. Transport of GPC-RA alkalis and the underlying mechanisms were observed. This phenomenon had minor effects on PC-mortar properties indicating that recycling of geopolymers is a viable reuse practice.

AB - Despite extensive research into geopolymers’ sustainability, it is essential to investigate largely overlooked end-of-life aspects. This requires investigation of alkalis’ leaching potential from the geopolymeric matrix. To study the viability of geopolymer concrete (GPC) recyclability, migration of alkalis was evaluated for the first time on a microstructural level through SEM/EDX elemental mapping and leaching tests. Macroscale impacts were assessed by investigation of Portland cement (PC)-mortar properties affected by alkalis concentration. Leaching tests indicated alkalis becoming immediately available in aqueous environments, but the majority remained chemically or physically bound in the matrix. This type of leaching accelerated the initial setting of PC-paste. Elemental mapping and SEM/EDX analysis showed a complex paste-aggregate interfacial transition zone. Exchange of Ca and Na, revealed by the maps, resulted in migration of Na into the PC-paste and formation of additional Ca-Si based phases in the geopolymeric matrix. Strength values of mortars with of 25% and 50% recycled aggregates (RA) showed negligible differences compared to the reference. Screening tests indicated low potential for GPC-RA inducing alkali silica reaction. Transport of GPC-RA alkalis and the underlying mechanisms were observed. This phenomenon had minor effects on PC-mortar properties indicating that recycling of geopolymers is a viable reuse practice.

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