Advanced Cement Based Nanocomposites

Considerable research and development efforts have been directed towards high strength/high performance concrete with engineered properties, using three main concepts: a low water to binder ratio (w/b), and the partial replacement of cement by fine supplementary cementitious or pozzolanic materials and/or fibers. To better understand how material composition and microstructural modifications determine the concrete structural performance, and to develop new materials with specific properties, researchers at ACBM have taken a materials science approach with an application to nanotechnology to optimize the processing and micro/nanoscale structure of cement based materials. In particular, due to their exceptional mechanical properties, the reinforcing effect of highly dispersed multiwall carbon nanotubes (MWCNTs) and carbon nanofibers (CNFs) in cement paste matrix was investigated. The major challenge however, associated with the incorporation of MWCNTs and CNFs in cement based materials is poor dispersion. In this study, effective dispersion of different length MWCNTs in water was achieved by applying ultrasonic energy and with the use of a surfactant. The excellent reinforcing capabilities of the MWCNTs are demonstrated by the enhanced fracture resistance properties of the cementitious matrix. Additionally, nanoindentation results suggest that the use of MWCNTs can increase the amount of high stiffness C-S-H and decrease the porosity. Besides the benefits of the reinforcing effect, autogenous shrinkage test results indicate that MWCNTs can also have a beneficial effect on the early strain capacity of the cementitious matrix, improving this way the early age and long term durability of the cementitious nanocomposites.