Effect of calcium to silicon ratio on the microstructure of hydrated calcium silicate gels prepared under medium alkalinity. (23rd May 2023)

• Record Type: Journal Article
• Authors: Ba, Haojing; Li, Jiajie; Ni, Wen; Li, Ying; Ju, Yongjian; Zhao, Ben; Wen, Guoping; Hitch, Michael
• Is Part Of: Construction & building materials. Volume 379(2023)
• Publication Date: 2023-05-23
• Subjects: Hydrated calcium silicate gel -- Microstructure -- Calcium to silicon ratio -- Medium alkalinity; Building materials -- Periodicals; 624.18
• DOI: 10.1016/j.conbuildmat.2023.131240
• Languages: English
• ISSNs: 0950-0618

Abstract

Highlights: The presence of Cl - results in a low solution pH and low phase transition temperature. When pH = 11.1–12.8, CSH gels with Ca/Si higher than 0.8 is hard to synthesized. Increases in Ca/Si enhanced the degree of crystallization, agglomerate of CSH gel. Decreases in Ca/Si increased the Q 2 structure and decreased the H2 O/Si of CSH. Medium alkalinity generates CSH gel with low Ca/Si and high mean chain length. Abstract: The hydration of solid waste cementitious materials has a medium alkalinity and low calcium-to-silicate ratio (Ca/Si). Understanding how the hydration products behave in such a system is very important to optimize and create new solid waste cementitious materials. This paper investigates the effect of Ca/Si on the generated CSH gels under medium alkalinity. CSH gels were prepared by the double decomposition method at room temperature, and XRD, SEM, TG-DSC, XPS, and NMR examined the microstructure of CSH gels. Results show that the Cl - concentration in the solution controlled its pH, ranging between 11.1 and 12.8. However, the Ca/Si of C-S-H gels increased with the initial Ca/Si in solution. However, it couldn't increase higher than 0.8 when the CSH was synthesized at a pH of about 12. With the increase in Ca/Si, the agglomeration of CSH gels increased, and the CSH became crystallized, the temperature of β -wollastonite formation enhanced. However, the β -wollastonite formation temperature of CSH gel synthesized under medium alkalinity was lower than that under high alkalinity. The increase in the Ca/Si of CSH gel decreased the Q 3 type tetrahedra formation and increased the Q 2 type tetrahedra formation. The variation of H2 O/Si is related to the amount of Q 2 and Q 3 type tetrahedra in the CSH gel, which is determined by the synthesis method. Medium alkalinity could assist in generating CSH gel with low Ca/Si and high MCL. The results of this study could guide new solid wasted-based contentious materials production.