Surface-treated carbon nanotubes in cement composites: Dispersion, mechanical properties and microstructure

In order to achieve good dispersibility and strong interfacial bonding strength in cement-based composites, multi-walled carbon nanotubes (MWCNTs) were chemically modified by low-temperature plasma. Specifically, pristine MWCNTs (p-CNTs), carboxyl functionalized MWCNTs (c-CNTs) and low-temperature plasma modified MWCNTs (m-CNTs) were incorporated in cement matrix for further reinforcement. The results show that the plasma treatment can efficiently form large amounts of oxygen-containing functional groups on the surface of MWCNTs. The m-CNTs in combination with polycarboxylate superplasticizer show favorable dispersion stability in water, especially in cement pore solution, and exhibit more positive effects on mechanical behavior of cement composites. With the addition of 0.1 wt% m-CNTs, the flexural strength and compressive strength of cement mortars were increased by 37.1% and 17.4%, respectively. Microscopic examination shows that the welldispersed c-CNTs and m-CNTs exhibit more effective crack-bridging behavior in cement matrix. Mercury intrusion porosimeter analysis verifies m-CNTs can bring about lower porosity and improve pore size distribution for cement composites, which is closely correlated with mechanical test results. This work paves an effective way to further use MWCNTs as nano-reinforcing materials in cement composites.