Isocyanate Microcapsules Recovering Automatically Impermeability of Cement Paste Through Self-Hydrophobic Broken Panels

Abstract

The current self-healing systems achieve impermeability recovery of matrix by the filling cracks. Few scholars have paid attention to the impermeability recovery through self-hydrophobic broken panels. In this paper, carbon nanotubes are used to improve the water resistance of isocyanate microcapsules, which possess a diameter of 237.6 ± 59.1 μm, distinct core-shell structure, and good dispersibility. The residual core fraction is 58.2% after 21 days in Ca(OH)2 aqueous solutions. The microcapsules maintain integrity without breakage when mixed with fresh cement paste and have good bonding compatibility with cement matrix. When microcapsules are embedded into cement paste, the cracks could break the microcapsules releasing isocyanate to wet the broken panels. The isocyanates react with the moisture with the formation of polyurea, changing the contact angle of broken panels from near 0° to 118.4 ± 0.1°. The hydrophobic panels could retard the water penetration and recover the impermeability of cement paste.

Keywords: Self-healing cement paste, IPDI microcapsules, Water resistance, Crack recovery, Self-hydrophobic mechanism