Performance of geopolymer composites made with feldspathic solid solutions: Micromechanics and microstructure

Reaction kinetics and microstructure of pegmatite‐based geopolymer composites: influence of calcined clay nature

“…The infrared spectra of the pegmatite and raw clay minerals (ET, TA, MA, and BA) and relevant calcined clays (MK-ET, MK-TA, MK-MA, and MH-BA) are reported in Figure 3. The absorption bands observed on the infrared spectra (Figure 3A) of pegmatite are extensively discussed in previous studies 32,34,37,38,40 The absorption bands which appear in the region ranged to 650 and 500 cm −1 are characteristic bands of feldspathic minerals (O-Si-O-M). The bands at 786 and 877 cm −1 correspond to the symmetric stretch, while those situated in the range between 1200 and 900 cm −1 with the maximum at 1001 cm −1 are ascribed to the asymmetric stretching vibration of the Si-O groups.…”

“…The use of fine feldspathic minerals (granite, trachyte, and pegmatite) combined with a low fraction of metakaolin (15 wt%) was observed to perform well in the development of geopolymeric composites with dense and compact microstructure and flexural strength up to 40 MPa. 32,34,38 The achievement of their high performances has been justified by: (i) the presence of undissolved or incompletly dissolved particles that are activated at their surface and develop high covalent bonds with Si and Al oligomers deriving from a controlled amounts of metakaolin. In addition, (ii) these fine particles act as filler in the network and reinforce the skeleton of the geopolymer 3D structure.…”

“…However, previous studies on designing the metakaolin/feldspar-based geopolymeric composites have been mainly conducted with the calcined kaolin at the range up to 15 wt% 32,34,37,38,40 The properties of the products have been mostly influenced by the type, source, and amount of feldspar and calcined clay and the mechanical and microstructural properties were explained in terms of the incongruent dissolution of the feldspar grains in the alkaline medium which produces a variable amount of semi-crystalline to amorphous (Na, K) 2 O-Al 2 O 3 -SiO 2 -H 2 O gel. 35,38 This study aimed to investigate first the threshold limit in the blend pegmatite/calcined clay to develop high strength composites, and finally compare the effect of different clay sources (kaolinite and halloysite) on the properties of resulting geopolymer materials. The resulting pegmatite/clay-based geopolymeric composites were characterized using isothermal conduction calorimetry (ICC), Fourier transformed infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM).…”

“…In their investigations, to design the feldspathic mineral‐based geopolymeric composites, the ground semi‐crystalline to crystalline minerals have been used at the range up to 60 wt% 36 or 85 wt% 34,37 with metakaolin. The use of fine feldspathic minerals (granite, trachyte, and pegmatite) combined with a low fraction of metakaolin (15 wt%) was observed to perform well in the development of geopolymeric composites with dense and compact microstructure and flexural strength up to 40 MPa 32,34,38 . The achievement of their high performances has been justified by: (i) the presence of undissolved or incompletly dissolved particles that are activated at their surface and develop high covalent bonds with Si and Al oligomers deriving from a controlled amounts of metakaolin.…”

On the role of continuity in statistical nanoindentation of composite microstructures

“…Their results showed clearly defined data assignments for each phase, though this may also be attributed to the morphology of phases in the material's microstructure. 5 SNI and other grid nanoindentation methods continue to be a relevant tool for evaluating cementitious materials as seen in a number of recent studies, 6,[20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38] and this study seeks to improve the reliability of these methods without the use of complimentary microscopy of each indent that has previously been recommended. 39,40 We hypothesize that violations of continuity assumptions (i.e., additional sources of structural compliance, C s ) can have a significant effect on the outcomes of SNI methods in materials where the complexity is on the same scale as the interaction volume of indents.…”