Multi-scale investigation and mechanism analysis on Young's modulus of C-S-H modified by multi-walled carbon nanotubes

How the multi-walled carbon nanotubes (MWCNTs) influenced the Young's modulus of C-S-H was investigated at multi-scale in this paper. The functionalized MWCNTs dispersed by ultrasonication were mixed with CaO and nanosilica to prepare MWCNTs/C-S-H composites with calcium to silicon ratios (C/SD) of 1.5 and 2.0 respectively, and the contents of MWCNTs were 1% and 3% of the total mass of CaO and nanosilica. The Young's modulus of MWCNTs/C-S-H was evaluated by atomic force microscope (AFM) at multi-scale. The effect mechanism of MWCNTs on Young's modulus of C-S-H was analyzed by various testing techniques and homogenization method. The BSE, TEM and N-2 adsorption tests results showed that MWCNTs acted as a bridge to reduce the number of cracks caused by shrinkage of C-S-H. Meanwhile, MWCNTs can reduce the porosity of C-S-H by filling the pores. The AFM consequence illustrated that Young's modulus of C-S-H was increased by MWCNTs at both nano and micro scales. At the nano scale, MWCNTs increased the Young's modulus of C-S-H by increasing the mean chain length (MCL) of C-S-H. At the micro scale, MWCNTs increased the Young's modulus of C-S-H by increasing the Young's modulus of C-S-H globules and reducing the porosity and the amount of cracks.