Improvement of the durability of cement-based material through surface modification with nano-engineered releasing agents

Abstract

• Modified releasing agent with NS/NT to make nano-engineered releasing agent. • NS and NT increased the contact angle of releasing agent and help their adhesion on mold. • Reduction of the surface porosity (within 2 mm thick). • Nano-engineered releasing agent can achieve durable concrete surface. Aggressive substances can gain access to the inner structure of cement-based materials through the surface, resulting in deterioration of the structure. This work developed an effective way of improving the quality of cement-based materials surface by applying nanoSiO 2 -/nanoTiO 2 -engineered releasing agents (nSRa/nTRa) on the formwork surface. Continued with our previous work, the positive effects of nSRa/nTRa on cement hydration were used to improve the surface quality of the cement-based samples through its spraying on the mold surface. This work firstly characterized the adhesive properties of these agents on mold surface (contact angle and viscosity measurement), and then their effects on the surface microstructure and the durability of cement-based materials such as 1) sulfate resistance, 2) chloride resistance, and 3) freeze–thaw resistance were determined. Results showed that nanoparticle addition increased the contact angle of releasing agents and helped their adhesion to mold. Applying nSRa/nTRa on cement-based samples benefited the reduction of surface porosity (within 2 mm thick) by 14.2 %, 19.4 %, 8.6 %, and 18.9 % in the nS2Ra-, nS4Ra-, nT4Ra- and nT16Ra-engineered samples. After 120 days of sulfate attack, mortar samples cast in Ra-, nS4Ra-, and nT16Ra-coated molds showed reductions in compressive strength loss of 1.57 %, 0.73 %, and 0.23 %. Noticeable reductions in the chloride migration coefficient of 23.9 % and 26.6 % were found in the nS4Ra-/nT16Ra-modified mortar sample, while their relative dynamic modulus elasticity was 6.72 % and 12 % higher than Ra-sample after 200 freeze–thaw cycles. This work proved that nano-engineered releasing agents can effectively improve the durability of the concrete structure.