Characterization of calcium-silicate-hydrate and calcium-alumino-silicate-hydrate

calcium silicate hydrate (C-S-H);calcium aluminosilicate hydrate (C-A-S-H);nuclear magnetic resonance spectroscopy (NMR);Carbonation;Ca/Si

Hunnicutt, William ; Struble ; Leslie J.

关键词: calcium silicate hydrate (C-S-H);    calcium aluminosilicate hydrate (C-A-S-H);    nuclear magnetic resonance spectroscopy (NMR);    Carbonation;    Ca/Si;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/45395/William_Hunnicutt.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

The primary objectives of this thesis were to synthesize calcium silicate hydrate(C-S-H) and calcium aluminosilicate hydrate (C-A-S-H) and characterize theirstructures with varying Ca/Si ratios and aluminum content. As a secondary objective,carbonation behavior in synthesized C-S-H was studied. C-S-H was synthesized in thelab using two different methods: the double decomposition of calcium nitrate andsodium silicate solutions, and the direct reaction between calcium oxide and fumedsilica in water. In C-A-S-H the source of aluminum was sodium aluminate or aluminumnitrate. A variety of phases were present depending on the degree of carbonation of theC-S-H or C-A-S-H. C-S-H, C-A-S-H, alumina/silica gel, calcite, aragonite, and vateritewere all observed throughout the course of study. X-ray diffraction (XRD) was thetechnique used to identify these phases. XRD was also used to explore the changes incrystal structure with varying Ca/Si ratios and aluminum content. No significantchanges to the crystal structure were found. The effect of Ca/Si ratio, aluminumcontent, and synthesis method were studied on the molecular scale using 29Si and 27Alnuclear magnetic resonance spectroscopy (NMR). An increasing Ca/Si ratio has theeffect of a shorter alumino-silicate chain length and an increase in aluminum contentincreases the alumino-silicate chain length. Aluminum substitution occurred primarilyin the bridging tetrahedron position, but also in the pairing tetrahedron position.Aluminum uptake was also examined with respect with Ca/Si ratio and was found todecrease with increasing Ca/Si ratio. The changes in chemical environment of theiiialuminum ion with varying Ca/(Si+Al) ratios was also observed by 27Al NMR. It wasfound that as the Ca/(Si+Al) ratio increased, the amount of chemical shielding of the27Al nuclei decreased . Carbonation of C-S-H was also examined and it was found thatthe double decomposition synthesis method allows for more rapid carbonation of the CS-H. The source of increased carbonation rate is the high pH of the solutions.