TY - JOUR
T1 - Analytical investigation of phase assemblages of alkali-activated materials in CaO-SiO2-Al2O3 systems
T2 - The management of reaction products and designing of precursors
AU - Xiao, Rui
AU - Jiang, Xi
AU - Zhang, Miaomiao
AU - Polaczyk, Pawel
AU - Huang, Baoshan
N1 - Funding Information:
First, thermodynamic simulation relies on the accuracy and availability of thermodynamic parameters of hydration products (solubility data, ΔfGT, PΘ, etc.). While the up-to-date CEMDATA18.01 [12] has substantially enlarged the cement database, more experimental work are needed to expand the possible thermodynamic solid solutions. In fact, the current simulation results have shown that the accuracy of N-A-S-H regions needs improving for both the reported solid phases and pH because obvious discrepancy between the simulated results and experimental work can be found in these regions. For example, it seems that the metakaolin regions shown in Fig. 8 (d) were predicted to have a considerable amount of AH3 (Fig. 2m-o) and amorphous silica (Fig. 2p-r), which is not supported by the Si and Al NMR data of the alkali-activated metakaolin [77]. Moreover, it may indicate that the predicted amount of N-A-S-H is underestimated due to the lack of thermodynamic data. Therefore, more sophisticated N-A-S-H model is required to enhance the accuracy of Ca-deficient regions in the future. Other solid solutions including M-(C-A-)S-H, AFm and AFt models are also expected to improve the holistic modelling of AAMs.
Publisher Copyright:
© 2020
PY - 2020/9
Y1 - 2020/9
N2 - This study presents an analytical investigation based on thermodynamic simulation aimed at achieving a holistic management of the phase assemblages of alkali-activated materials (AAMs) and gaining insights into the designing of precursors. Gibbs free energy minimization method was conducted on AAMs spanning the compositional envelopes at (metastable) thermodynamic equilibrium. The stability regions and quantities of simulated phases were identified in the SiO2-CaO-Al2O3 ternary contour diagrams, yielding the overall relationships between the chemical components of precursors, phase assemblages and pH in pore solution. The analytical results are in good agreement with the available experimental observations that the main precipitation regions of C-(N-)A-S-H appear at CaO/SiO2 = ~1.0 and relatively low Al regions while N-A-S-H phases generally dominate the Ca-deficient regions of the contour diagrams. Strätlingite mainly occurs at intermediate levels of Si, Al and Ca. Katoite and AFm phases form at Al2O3/CaO = ~3.0 under Si-deficient conditions. The findings also suggest the precipitation regions of a product may span a range of pH of aqueous solution, making it possible to simultaneously control pH and maintain the precipitation amount of the phase. The application of this work in designing precursors can achieve a more precise control of the phase assemblages for AAMs.
AB - This study presents an analytical investigation based on thermodynamic simulation aimed at achieving a holistic management of the phase assemblages of alkali-activated materials (AAMs) and gaining insights into the designing of precursors. Gibbs free energy minimization method was conducted on AAMs spanning the compositional envelopes at (metastable) thermodynamic equilibrium. The stability regions and quantities of simulated phases were identified in the SiO2-CaO-Al2O3 ternary contour diagrams, yielding the overall relationships between the chemical components of precursors, phase assemblages and pH in pore solution. The analytical results are in good agreement with the available experimental observations that the main precipitation regions of C-(N-)A-S-H appear at CaO/SiO2 = ~1.0 and relatively low Al regions while N-A-S-H phases generally dominate the Ca-deficient regions of the contour diagrams. Strätlingite mainly occurs at intermediate levels of Si, Al and Ca. Katoite and AFm phases form at Al2O3/CaO = ~3.0 under Si-deficient conditions. The findings also suggest the precipitation regions of a product may span a range of pH of aqueous solution, making it possible to simultaneously control pH and maintain the precipitation amount of the phase. The application of this work in designing precursors can achieve a more precise control of the phase assemblages for AAMs.
KW - Alkali-activated materials
KW - Calcium (sodium) aluminosilicate hydrate (C-(N-)A-S-H)
KW - Phase assemblages
KW - Pore solution
KW - Thermodynamic simulation
UR - http://www.scopus.com/inward/record.url?scp=85088093481&partnerID=8YFLogxK
U2 - 10.1016/j.matdes.2020.108975
DO - 10.1016/j.matdes.2020.108975
M3 - Journal article
AN - SCOPUS:85088093481
SN - 0264-1275
VL - 194
JO - Materials and Design
JF - Materials and Design
M1 - 108975
ER -