Properties of normal-strength concrete and mortar with multi-walled carbon nanotubes

This investigation studied the strength and performance of cementitious materials, such as concrete and mortar, with multi-walled carbon nanotubes (MWNTs). One hundred cylindrical specimens 10 cm in diameter and 20 cm in height were used to investigate strength variation and changes in the durability of concrete and mortar as a function of the weight percent (0∼1·5 wt%) of MWNTs and the effectiveness of a dispersion method that used a sodium naphthalene sulfonate formaldehyde solution. Industrial-grade MWNTs (purity: >90%, diameter: >50 nm) were used for the test. Ball milling with 1·5 wt% MWNT was processed for 7 h, followed by a dilution process with 0·25, 0·5, 0·75, 1·0, 1·25 and 1·5 wt% dispersive solutions. Ultrasonication treatments were then applied to each diluted solution for 20 min. Compressive strength, splitting tensile strength, permeability, electrical conductivity and the relative dynamic modulus of the concrete cylinders were tested under a 24 MPa mix design by increasing the wt% MWNT using standard ASTM guidelines. In parallel, MWNT mortar tests were performed for compressive strength, flexural bending and shrinkage with 50 prismatic specimens (4 × 4 × 16 cm in size).