Evaluation of the Surface Performance of Mortar Matrix Subjected to Sodium Chloride Solution Modified with Hybrid Nanosilica Cement Paste

In order to prolong the service life of cement-based materials subjected to external chloride ion attacks, two kinds of methods, a surface treatment and chloride immobilization, were combined by fabricating a nanosilica-modified cement paste and coating it on mortar samples as a surface treatment material (HSM). The protective effect of the HSM was evaluated according to its surface hardness, and an RCM test was carried out, which indicated that the attached layer could both increase the surface hardness and decrease the chloride diffusion coefficient. Then, the chloride immobilization mechanisms were illustrated in terms of chloride blocking resistance, chemical binding and physical binding X-ray diffraction (XRD), and thermogravimetric/derivative thermogravimetric (TG/DTG) and thermodynamic modeling. The results showed that the hybrid nanomaterials that modified the cementitious surface treatment materials may effectively improve the chloride-resistant property of a matrix with content of no more than 1%. This research outcome could provide evidence that hybrid nanosilica can be applied in surface treatment technology.