Study on the Structure of C-S-H Gels of Slag–Cement Hardened Paste by 29Si, 27Al MAS NMR
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In this paper, the 29Si and 27Al MAS NMR techniques were utilized to investigate the structure of C-S-H gels of slag cement-hardened paste. The results show that in the hardened paste of Portland cement, the silicate tetrahedron [SiO4]4− exists in the Q0, Q1 and Q2 states, and the C-S-H gel mainly exists as the dimer (Q1). After hydration for 3 days, Al3+ replaces some of the Si4+ in the tetrahedra and generates an aluminum-containing C-A-S-H gel. As the hydration proceeds, the content of C-A-S-H gel increases gradually. With an increase in the replacement of cement with slag, the content of Q2 (1 Al) in the C-A-S-H gel increases significantly, and the mean chain length of the C-(A)-S-H gel increases. For the slag–cement blend with 50% slag replacement, the mean chain length reaches 4.3, and the Al/Si ratio reaches 0.11. Throughout the hydration stage, three coordination states (AlO4, AlO5, and AlO6) exist in the hardened paste of the slag–cement blends.
This work was sponsored by the National Natural Science Foundation of China (No. 51502080, No. U1704148) and Natural Science Foundation of Henan Province (No. 162300410118).
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