Effects of Multi-Walled Carbon Nanotubes on Mechanical Properties and Microstructure of Ordinary Portland Cement–Sulfoaluminate Cement Repair Mortar

Multi-walled carbon nanotubes (MWCNTs) with high thermal conductivity and electrical conductivity are frequently considered as ideal nano-reinforced materials for the future. This paper investigated the potential application of MWCNTs in ordinary Portland cement-sulfoaluminate cement (OPC-SAC) repair mortar by analyzing mechanical and microstructural changes caused by MWCNTs. The test results revealed that MWCNTs greatly increased the strength of OPC-SAC binary repair mortar in the early days, and promoted sustained growth of long-term strength. The 10.39%/9.3 MPa increases in compressive strength can be attributed to 0.10 wt.% MWCNTs. MWCNTs promotes hydration of OPC-SAC composites through functional groups and nucleation effects, resulting in more C-S-H gels and AFt crystals. The X-ray computed tomography (X-CT), mercury intrusion porosimetry (MIP), and scanning electron microscope (SEM) results indicate that the nanofibers (MWCNTs) optimize the microstructure and microstructure of the composites. The nanofibers with high aspect ratio results enhance the crosslinking between hydration products, improve complexity (higher D_s) and integrity (more crosslinking sites), and reduce the formation and propagation of microcracks through bridging. The filling effect of nanoparticles refines the pore and reduces the pore volume, especially the volume of medium capillary pores. It is precisely these combined actions that improve the engineering performance of OPC-SAC binary repair mortar.