Effect and mechanism analysis of functionalized multi-walled carbon nanotubes (MWCNTs) on C-S-H gel

The effect and the interaction mechanism of functionalized multi-walled carbon nanotubes (MWCNTs) on C-S-H gel were studied in this paper. Fourier infrared spectroscopy, acid-base titration, Raman spectroscopy and transmission electron microscopy were utilized to analyze the pristine MWCNTs and functionalized MWCNTs, showing that the degree of graphitization of the functionalized MWCNTs reduced. And the surface of the functionalized MWCNTs was grafted with acidic functions which the content was 2.5 × 10−3 mol/g. Afterward, the MWCNTs/C-S-H composite was prepared by well-dispersing the functionalized MWCNTs and the C-S-H. The experimental results showed that for the C-S-H produced with different designed molar ratios of CaO to nanosilica (C/SD), the measured molar ratio of Ca to Si (C/SM) of the C-S-H decreased and the interlayer spacing of the C-S-H increased with the increase of the amount of the functionalized MWCNTs. When C/SD = 0.8, the polymerization degree of the C-S-H decreased and the proportion of the capillary pores increased gradually with increasing the amount of the functionalized MWCNTs. When the values of C/SD were 1.5 and 2.0, the trends the polymerization degree and the proportion of the capillary pores of C-S-H were opposite to those of C/SD = 0.8. The reasons were further analyzed based upon the above experimental results. •The pristine MWCNTs and functionalized MWCNTs were analyzed by FTIR, Raman and TEM.•The effect of the functionalized MWCNTs on the C/S of C-S-H gel was analyzed by SEM and EDS.•The effect of the functionalized MWCNTs on the interlayer spacing of C-S-H gel was analyzed by XRD.•The effect of the functionalized MWCNTs on the polymerization and chain length of C-S-H was analyzed by 29Si MAS NMR.•The effect of the functionalized MWCNTs on the pore size distribution of C-S-H was analyzed by N2 adsorption.