Reinforcing cement with pristine and functionalized carbon nanotubes: experimental and simulation studies

Abstract

In recent years, the addition of carbon nanotubes to construction materials has attracted considerable interest, due to the improvement of mechanical, electrical, and thermal properties of cement. The incorporation of carbon nanotubes into a cement matrix causes an increase of several mechanical properties of up to 170% even with low carbon nanotubes concentrations. The objective of this study is to analyze the influence of the type of functionalization and number of walls of carbon nanotubes on the interaction between these nanostructures and a cement surface and thus, on the improvement of their mechanical properties. Thus, single-walled and double-walled carbon nanotubes were used to investigate the influence of the number of walls. The effect of carbon nanotube functionalization was studied using carbon nanotubes functionalized with carboxyl and carboxylate groups. The experimental results demonstrate that the incorporation of carbon nanotubes into the cement matrix improves the mechanical properties of the resulting material. Functionalized carbon nanotubes perform better than pristine carbon nanotubes. Electrostatic attractions play a central role in establishing strong interactions between the carbon nanotubes and the cement surface. The presence of neutral polar groups on the carbon nanotube surface also improves this interaction. The number of walls seems to be less important.

Oxidation of Carbon Nanotubes for Improving the Mechanical and Electrical Properties of Oil-Well Cement-Based Composites

“…These polar groups increase the ease of dispersion of CNTs in the water used for the preparation of cement, thus also improving the dispersion of the reinforcement in the matrix. Furthermore, the carboxyl groups introduced on the surface of the CNTs can react with the hydrated products of cement (Ca­(OH) 2 and C–S–H), , thus enabling the interaction of the reinforcement with the matrix via the formation of primary or secondary bonds …”

“…Furthermore, the carboxyl groups introduced on the surface of the CNTs can react with the hydrated products of cement (Ca(OH) 2 and C−S−H), 51,52 thus enabling the interaction of the reinforcement with the matrix via the formation of primary or secondary bonds. 53 The improvement of flexural strength and fracture energy is probably related to the well-known bridging effect of CNTs when they have good interaction with the cement paste. 40,54 Furthermore, the presence of carbon nanotubes functionalized with carboxyl and hydroxyl groups could promote the nucleation of cement hydrate products, thus improving the C−S−H gel structure.…”

Acid Treatment in Alkyl-Functionalized Carbon Nanotubes: Soft Functionalization Techniques with Lower Environmental Footprint

“…Chemical functionalization of carbon nanotubes (CNTs) is a process that entails the covalent addition of chemical functional groups (e.g., hydroxyl or carboxyl groups) to the CNT structure, enabling a host of additional properties such as dispersion in a solvent or matrix, − high binding specificity through molecular recognition of elements, and improved antimicrobial ability. , These strategies facilitated the development of many CNT-based technologies and applications, including chemical sensors, , drug delivery, and water purification, − while also improving the function of critical high-volume materials (e.g., resins, cement, and concrete). While functionalization is critical to accessing a vast expanse of material property space, explored and unexplored, the processes of chemical functionalization are characteristically random, are energy- and fluid-consumptive, costly from an operating expense perspective, and ultimately degrade the most desirable CNT properties through disruption of the sp 2 -bonded network. ,− …”

Mechanical Properties of Cement Reinforced with Pristine and Functionalized Carbon Nanotubes: Simulation Studies

“…In our previous research, the interaction between tobermorite and different CNTs was studied through experimental techniques, MD and the finite element method [ 47 , 48 ], obtaining quite promising results. These studies show the relation between the functionalization of the CNT surface, concentration and the type of CNT (single- or multi-wall) and the mechanical properties of the material; and agree with those previously found by Zhao et al [ 49 ].…”