University of Hertfordshire

Chemical aspects related to using recycled geopolymers as aggregates

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Original languageEnglish
Article number1700120
Pages (from-to)361-370
Number of pages10
JournalAdvances in Cement Research
Volume30
Issue8
Early online date13 Apr 2018
Publication statusPublished - 1 Sep 2018
Event36th Cement and Concrete Science Conference -
Duration: 5 Sep 2016 → 6 Oct 2016
- Welsh Academy of Music and Drama, Cardiff University , Cardiff, United Kingdom
Duration: 5 Sep 20166 Sep 2016

Abstract

Despite extensive research into sustainability of geopolymers, end-of-life aspects have been largely overlooked. A recycling scenario is examined in this study. This requires an investigation of alkali leaching potential from a geopolymeric matrix. To study the feasibility of geopolymer cement (GPC) recycling, the migration of alkalis was evaluated for the first time on a microstructural level through energy dispersive X-ray (EDX) scanning electron microscopy (SEM) elemental mapping and leaching tests. Macroscale impacts were assessed through an investigation of Portland cement (PC) mortar properties affected by alkali concentration. Leaching tests indicated that alkalis immediately become available in aqueous environments, but the majority remain chemically or physically bound in the matrix. This type of leaching accelerates the initial setting of PC paste. Elemental mapping and EDX/SEM analysis showed a complex paste-aggregate interfacial transition zone. Exchange of calcium and sodium, revealed by the maps, resulted in the migration of sodium into the PC paste and the formation of additional calcium-silicon-based phases in the geopolymeric matrix. Strength values of mortars with 25% and 50% recycled aggregates (RA) showed negligible differences compared with the reference sample. Screening tests indicated a low potential for GPC RA inducing alkali-silica reaction. Transport of GPC RA alkalis and the underlying mechanisms were observed. This transport phenomenon was found to have minor effects on the properties of the PC mortar, indicating that recycling of geopolymers is a viable reuse practice.

Notes

This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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