Accelerating autonomic healing of cementitious composites by using nano calcium carbonate coated polypropylene fibers

Abstract

Fibers can enhance self-healing of concrete by restricting crack propagation and supplying nucleation sites in cracks. To further improve the self-healing effect of fiber concrete, a new strategy of fiber modification for self-healing is proposed herein. In this study, polypropylene (PP) fibers were coated with nano calcium carbonate as nano seedings and ethyl cellulose film as a protective layer. The protective layer can inhibit the interactions of coated nano seedings with cement matrix before cracking. While after mortar mixing and cracking, the protective layer was gradually removed due to shear stress in mixing and friction during fiber pull-out in cracking processes, respectively. With the elimination of the protective layer, the remaining nano calcium carbonate coating at around 5.6 % of fiber mass could be exposed to cracks, thereby accelerating healing product generations by hydration and calcium carbonate precipitation, which was verified by scanning electron microscopic observations, Fourier-transform infrared spectroscopy and thermogravimetry analysis. Owing to the effects of modified fibers, closure of 300–500 μm wide cracks was enhanced and 100 % recovery of water tightness was subsequently achieved.