Volume Stability of Calcium-Silicate-Hydrate/Polyaniline Nanocomposites in Aqueous Salt Solutions

The volume stability of phase pure calcium-silicate-hydrates. (C-S-H) and C-S-H/polyaniline nanocomposites prepared with two CaO-SiO2 molar ratio (C/S) variations (0.8 and 1.2) was assessed in MgSO4, MgCl2, LiCl, and NaCl aqueous solutions. The change in the crystalline structure of the samples with the time of immersion was also explored using X-ray diffraction, scanning electron microscopy, and thermal gravimetric analysis techniques. It was observed that the modification of the C-S-H samples with polyaniline significantly enhanced their volume stability and durability in all the salt solutions. The beneficial effect of the polyaniline modification was more pronounced in the C-S-H host with higher C/S (C/S = 1.2). The longitudinal expansion of the C-S-H/polyaniline nanocomposites with C/S = 1.2 in the salt solutions was about 30% of that of the phase pure C-S-H with a similar C/S ratio. In addition, the polyaniline modification of C-S-H samples reduced the rate of formation of gypsum, brucite, and other reaction products in the samples.