Abstract
Geopolymers are zeolites like structures based on hydrated aluminosilicates units of SiO4 and AlO4. These units, known as poly(sialate), poly(sialate)-siloxo or poly(sialate)-disiloxo are chemically balanced by the group I cations of K+, Li+, or Na+. Simultaneously, the chemical reaction of formation, known as geopolymerization, governs the orientation of the unit, generating mesoporous structures. Multiple methods can be used for pore structure and porosity characterization. Among them, nuclear magnetic resonance (NMR) relaxometry allows the detection of the porous structure in a completely nonperturbative manner. NMR relaxometry may be used to monitor the relaxation of protons belonging to the liquid molecules confined inside the porous structure and, thus, to get access to the pore size distribution. This monitoring can take place even during the polymerization process. The present study implements transverse relaxation measurements to monitor the influence introduced by the curing time on the residual liquid phase of geopolymers prepared with two different types of reinforcing particles. According to our results, the obtained geopolymers contain three types of pores formed by the arrangement of the OH− and Si groups (Si-OH), Si-O-Si groups, Si-O-Al groups, and Si-O rings. After 48 days, the samples cured for 8 h show a high percentage of all three types of pores, however, by increasing the curing time and the percentage of reinforcing particle, the percent of pores decrease, especially, the gel pores.
Highlights
After mixing a material rich in aluminum and silicon oxides with a strongly alkaline solution a binder is formed which through the geopolymerization chemical reaction passes into a tetragonalSi-O-Al structure, resulting in an inorganic material called geopolymer [1,2,3]
The chemical composition analyzed by X-ray fluorescence (XRF) using an XRF S8 Tiger equipment (Bruker GmbH, Karlsruhe, Germany) shows high silica and alumina content being suitable for geopolymers synthesis
The nuclear magnetic resonance (NMR) measurements were performed first on samples maintained in fresh air at room temperature conditions (21–23 ◦ C; 40–48% air humidity) for 48 days to highlight the residual activator in pores
Summary
Si-O-Al structure, resulting in an inorganic material called geopolymer [1,2,3] Due to their physical [4], chemical, and mechanical properties, geopolymers present high interest in many industrial applications. These materials were developed as high fire resistance materials ideal for civil engineering [5,6], but later multiple fields, such as automotive [7], ceramic [8], metallurgical [9], aerospace [10], etc., started using geopolymers as substitutes for conventional oxide materials or polymers. This self-healing characteristic positively influences the time behavior (durability) of geopolymers
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