Effect of Environmental Exposure on the Pore Structure and Transport Properties of Carbon Nanotube-Modified Mortars.

Τhe present study investigates the pore structure and transport properties of carbon nanotube-modified cementitious mortars after exposure to freeze-thaw cycles and immersion to sulfate ion solution (sulfate attack) and compares them to those of un-exposed mortars. The effect of parameters related to carbon nanotube content (within the range of 0.2-0.8 wt.%) and type of dispersant (superplasticizer/surfactant) are investigated. It is found that carbon nanotube inclusion results, overall, in a significant drop of the total porosity before exposure. Results demonstrate that environmental exposure leads to a reduction of the fraction of small diameter pores and a respective increase in capillary porosity for both dispersive agents compared to un-exposed specimens. Diffusion coefficients of nano-modified specimens are lower compared to those of un-modified mortars, both before exposure and after sulfate attack. In the case of freeze-thaw cycling, the diffusion coefficients were found to be higher in carbon nanotube-modified mortars when surfactants were used as dispersants, although with improved gas permeability values.