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Evolution of the microstructure of unconsolidated geopolymers by thermoporometry
Author(s) -
Nguyen Quang Hung,
Hanafi Mohamed,
Merkl JanPhilip,
d'Espinose de Lacaillerie JeanBaptiste
Publication year - 2021
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/jace.17543
Subject(s) - geopolymer , mesoporous material , metakaolin , materials science , porosity , chemical engineering , differential scanning calorimetry , microstructure , mineralogy , composite material , chemistry , compressive strength , organic chemistry , physics , engineering , thermodynamics , catalysis
This paper studies the evolution of the pore size distribution of a fresh unconsolidated geopolymer paste between one day and a week, using thermoporometry. This was made possible by following a careful protocol for sample preparation and for analysis by differential scanning calorimetry. In contrast with nitrogen gas adsorption, this method quantifies directly the amount of water in pores. It also does not require heat and vacuum drying, thus maintaining the fragile pore structure of the unconsolidated paste. Moreover, it was found that, in a typical metakaolin‐based sodium geopolymer with a 10 to 20 hours workability period, the porosity gradually refines during the first week while the mesoporous volume is cut in half. This is probably due to the fact that the geopolymer network was still actively condensing from the activation solution. Part of the pore water never froze and, from mass balance, this residual water was attributed to the water bound in the hydration shell of the sodium counter ions. Only a minor occurrence of covalently bound protons as silanol groups was observed. The results presented here usefully complement data obtained by conventional techniques at later ages on consolidated geopolymers. It supports the growing body of literature on the structural evolution of geopolymers with time.