Preparation and Hardening Performance of a Novel Surface Treatment Agent for Portland Cement–Based Materials

Surface treatment is essential for enhancing the mechanical performance of Portland cement–based materials. In this study, polymerized siloxane (PS) is proposed as a novel surface treatment agent. PS was synthesized from tetramethoxysilane through hydrolysis and condensation, yielding polymerized siloxanes with a final molecular weight ranging from 200 to 2,000  g/mol, as confirmed by various characterization methods. The PS was subsequently applied and solidified on the surfaces of cured Portland cement samples. Nanoindentation tests revealed significant increases in surface hardness, with cement and mortar showing improvements from 260 to 920 MPa and 352 to 751 MPa, respectively, following the PS treatment. The improvement in modulus indicates the formation of high-density calcium silicate hydrate (HD C-S-H) on the surfaces of the cement-based materials. With the treatment of PS, the surface of cement-based materials is covered with HD C-S-H generated by the reaction of PS and Ca(OH)2, resulting in a smooth surface without pores. AFM measurements revealed a substantial decrease in the surface roughness of the cement following PS application. Surface and cross-sectional morphologies observed via SEM and EDS confirmed the penetration depth of PS, evidenced by the distribution of Si and C elements. This study introduces PS as an effective surface treatment agent for achieving high-hardness surfaces on Portland cement–based materials.