Nanotube suspensions with concrete admixtures

For the cementitious nanocomposites which contain carbon nanotubes, a proper dispersion of the nanofiller is an important factor which determines the final properties of the composite. Large, singular concentration of the carbon nanofiller might negate all the additional properties that the carbon nanotubes provide, mainly electrical and thermal conductivity as well as material's strength. The carbon nanotubes are usually added in the form of water suspension; therefore, their uniform dispersion in the aqueous solution is the first and most important step in achieving a proper dispersion in the cementitious matrix. Typically used methods for achieving uniform dispersion of the nanotubes in water utilize the usage of ultrasonication and surfactants. The surfactants are usually specific chemical substances, however, commercially used concrete admixtures can also be used. The paper aims at assessing the usability of commercially available concrete admixtures along with sonication in making homogenous suspension of carbon nanotubes in water. The suspensions have been prepared with a fixed amount of nanotubes and water and examined via visual inspection. The results show that the ability to create a homogenous suspension of carbon nanotubes is largely connected with the basic chemical composition of the admixture. Depending on the chemical composition of the admixture, the suspensions showed different levels of flocculation from almost uniform dispersion up to large, easily observed flocs. This kind of behavior excludes those admixtures from usage in cementitious composites as it will not allow for uniform placement of carbon nanotubes in the cementitious matrix, therefore not creating homogenous properties within the composite.