Abstract
Geopolymers are low-calcium, sustainable cementitious materials. The role of Zn, a known retardant used in Portland cement, in geopolymer systems is not well understood. This study scrutinises the effect of Zn on metakaolin-based geopolymer reaction mechanisms and kinetics, and investigates the incorporation mechanism of Zn in geopolymer gels. Isothermal calorimetry and X-ray diffraction analyses show that substitution of ZnO (20 mol% c.f. metakaolin) significantly hinders reaction, likely due to preferential formation of a Na/K-Zn containing phase. Solid-state nuclear magnetic resonance spectroscopy shows that Zn2+ partially substitutes for Na+/K+ in charge-balancing sites within the geopolymer gel. Setting time and leaching tests show that the retarding effect of Zn on reaction kinetics is significantly greater in Na-activated geopolymers compared with K-activated geopolymers, whereas Na-activated geopolymers exhibit superior fixation capacity to Zn. A lab-scale experiment demonstrates that metakaolin-based geopolymers are promising candidates for the stabilisation/solidification of Zn-rich hazardous waste.
Original language | English |
---|---|
Article number | 106194 |
Journal | Cement and Concrete Research |
Volume | 136 |
DOIs | |
Publication status | Published - Oct 2020 |
Keywords
- Alkali-activation
- Geopolymer
- Hazardous waste immobilisation
- Reaction kinetics
- Retarding mechanism
- Zn leachability
ASJC Scopus subject areas
- Building and Construction
- Materials Science(all)