Mineralization dynamics of metakaolin-based alkali-activated cements

Abstract

This paper investigates the early-age dynamics of mineral formation in metakaolin-based alkali-activated cements. The effects of silica availability and alkali content on mineral formation were investigated via X-ray diffraction and solid-state 29 Si magic-angle spinning nuclear magnetic resonance at 2, 7, 14, and 28 days. Silica availability was controlled by using either liquid-(immediate) or solid-based (gradual) sodium silicate supplements. Mineral (zeolitic) and amorphous microstructural characteristics were correlated with observed changes in bulk physical properties, namely shrinkage, density, and porosity. Results demonstrate that, while alkali content controls the mineralization in immediately available silica systems, alkali content controls the silica availability in gradually available silica systems. Immediate silica availability generally leads to a more favorable mineral formation as demonstrated by correlated improvements in bulk physical properties.

PVA‐ and PEG‐assisted sol‐gel synthesis of aluminosilicate precursors for N‐A‐S‐H geopolymer cements

“…All synthesized aluminosilicate precursors approximate the chemical composition of calcined clays (ie, metakaolin) as evidenced by Figure . Moreover, similarities to metakaolin are evidenced in both the 29 Si and 27 Al MAS NMR with a resonances near 110 and ~10 ppm corresponding to Q 4 Si units and Al(VI), respectively (Tables and ) .…”

“…As a result, important morphological differences exist due to their “non‐traditional” cement chemistry, as expected from literature . For example, the presence of mineral phases, such as zeolites, is expected at low silicon and high sodium contents when these samples are subjected to hydrothermal curing conditions …”

“…However, determination of different Q 4 (nAl) sites may be determined based on peak maxima with linewidths of 10 ppm, as described in Ref. [], 29 Si MAS NMR spectra collected herein demonstrates the single‐phase purity of precursors, due to narrower linewidths than reported in literature and high upfield resonances. As seen in Table , uncalcined synthetic aluminosilicate precursors demonstrate peak resonances at −111 ppm that are attributed to Q 4 silicon sites.…”

“…All synthesized aluminosilicate precursors approximate the chemical composition of calcined clays (ie, metakaolin) as evidenced by Figure 2. 33 Moreover, similarities to metakaolin are evidenced in both the 29 Si and 27 Al MAS NMR with a resonances near 110 and ~10 ppm corresponding to Q 4 Si units and Al(VI), respectively (Tables 4 and 5). 46 In addition, the presence of silanol groups in PEG-derived synthetic aluminosilicate powders at low I/O ratios, is similar to the reported residual silanol groups in metakaolin.…”

Low-Calcium, Porous, Alkali-Activated Materials as Novel pH Stabilizers for Water Media

“…It is proven that AAM can contain a certain amount of zeolite, depending on the chemical composition of the precursors and activation solution used as well as from the curing conditions. Zeolite Na-A, hydrosodalite, zeolite X, faujasite, analcime, and other types of zeolites of different sizes and amounts can be found in the structure of AAM as a secondary alkali activation reaction product [7,[20][21][22][23]. Zeolites in the structure of AAM could improve the effectiveness of contamination sorption from wastewater, such as heavy metals [24][25][26], ammonium [27], calcium [25], and fluoride [18].…”