Mechanical behavior and microstructure of cement composites incorporating surface-treated multi-walled carbon nanotubes

Multi-walled carbon nanotubes after modified by using a H2SO4 and HNO3 mixture solution were added to cement matrix composites. The mechanical properties of the newly formulated composites were analyzed, and the results show that the treated nanotubes can improve the flexural strength, compressive strength, and failure strain of cement matrix composites. The porosity and pore size distribution of the composites were determined by using Mercury intrusion porosimetry, and it is observed that the addition of carbon nanotubes can fine the pore size distribution and decrease porosity. The phase composition was characterized with Fourier transform infrared spectroscopy. It is found that there are interfacial interactions between carbon nanotubes and the hydrations (such as C-S-H and calcium hydroxide) of cement, which will produce a high bonding strength between the reinforcement and cement matrix. The mineralogy and microstructure were analyzed by using scanning electron microscope. It is shown that carbon nanotubes act as bridges across cracks and voids, which guarantees the load-transfer in case of tension.