Hybrid n-SiO2/MWCNTs development and its application in reactive powder concrete

Abstract

Nanotechnology has been proved to be an important scientific field to produce advanced materials, which in turn, are objects of Chemical Engineering studies. The literature review indicates that nanomaterials possess singular properties, and their development and application can promote beneficial changes in cement-based composites, such as concrete. Carbon nanotubes and nano-silica are nanomaterials widely studied in cementitious composites, due to their capacity to improve performance. Considering these aspects and possible applications in special concretes, such as reactive powder concrete (RPC), this work presents the development of a hybrid material, composed of nanostructured silica (n-SiO2) supporting multi-walled carbon nanotubes (MWCNTs), to improve fracture toughness in RPC without fibers. MWCNTs were modulated and synthesized using the catalytic chemical vapor deposition method (CCVD), having methane as a carbon source and iron as a catalyst. Along with the study, the influences of the support and the method of catalyst incorporation on the characteristics of the MWCNTs were evaluated. To control the properties of different n-SiO2, these materials were produced by the sol-gel method. Five types of n-SiO2 were produced initially, and MWCNTs were synthesized on each one. Later, three methods of catalyst incorporation were evaluated. Finally, after the characterizations at each stage and based on the results, the hybrid material was produced with adequate MWCNTs characteristics to achieve toughness gains for the RPCs. Considering variations in quantity and using specific techniques, the appropriate proportion of the hybrid was previously determined by assessing the pozzolanic effect in solutions and cement pastes. Finally, the mechanical performance of the RPCs, with and without the use of the hybrid, was evaluated. Together with the microstructural evaluations, the results confirmed the initial hypothesis of the pozzolanic effect around the MWCNTs, improving the microstructure and reflecting on their mechanical behavior. During bending tests, it was verified that the incorporating of 2% bwoc of hybrid promoted increases in toughness in the order of 100%.