Influence of carbon nanofiber clustering on the chemo-mechanical behavior of cement pastes

The influence of carbon nanofiber (CNF) clustering on the chemo-mechanical behavior of cement pastes subjected to a decalcifying environment was studied. Portland cement pastes with and without CNFs were exposed to a concentrated solution of ammonium nitrate to accelerate decalcification. Microstructural changes and evolution of the porosity were examined as a function of exposure duration. Changes in the flexural response of the cement paste with CNFs were studied and reviewed in relation to CNF clustering and microstructural evolution. Results showed a strong coupling between decalcification, CNF clustering, microstructural evolution, and the flexural properties of the cement paste. After 7 days of decalcification by NH4NO3, the CNF clusters acted as weak zones that reduced the flexural strength retention of the cement paste. However, after 125 days of decalcification by NH4NO3, a dissolution-filling mechanism within the clusters created a better bond with the surrounding cement paste, slowing down the loss of flexural strength and providing added ductility to the cement paste.