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Effects of Carbon Nanofibers and Carboxyl Functionalized Multi-Walled Carbon Nanotubes on Mechanical Damping Behavior of Cement Paste.

Different ratios of carbon nanofibers (CNF) and carboxyl functionalized multi-walled carbon nanotubes (CMWCNT), dispersed by the polycarboxylate based superplasticizer, were added in this study to investigate mechanical damping behavior of cement paste. The additions of CNF and CMWCNT simultaneously improved loss tangent, storage modulus and loss modulus of cement paste to different extents at 0.2 Hz the frequency. The cement paste exhibited higher storage modulus and loss modulus with addition of CNF. The addition of CMWCNT provided higher loss tangent but lower modulus compared to the CNF modified cement paste. The damping mechanisms for cement incorporated with CNF and CMWCNT were explained by the effective "stick-slip" motion which was generated by the possible sliding among the nanofilaments at the interface between the fibers and cement particles. The enhanced stiffness was attributed to the optimized microstructure and bridge effect induced by the nanoscale nanofilaments. Both total porosity and mesoporosity decreased due to the nano-filler effect from the carbon nanofilaments. The SEM technique indicated that excessive addition of CNF/CMWCNT should be avoided to minimize possible fiber agglomeration in the cement matrix.