Carbon Nanotubes Strengthened Interphase in Textile Reinforced Mortar (TRM) Composites

Performance of inorganic matrix composite materials for structural purposes is strongly dependent on the matrix-to-fabric interphase bond strength. Consequently, owing to lack of congruence between the fabric and the matrix, design performance parameters are strongly penalised. Besides, yarn inner filaments (the core) easily slide over outer filaments (the sleeve) in the so-called telescopic failure. Broad experimental evidence supports the adoption of epoxy coatings to improve matrix-to-fabric strength and prevent telescopic failure, although the presence of the organic phase partially impairs the remarkable advantages associated to the inorganic matrix, such as thermal stability and water vapour permeability. Silica coatings appear as a promising alternative to traditional epoxy, by inducing localised pozzolanic reactivity, firmly linking synthetic fibres and hydraulic lime through the formation of highly cementing products at the interphase. In this work, the effect of a dispersion of multi-walled carbon nanotubes (MWCNT) in a silica nano-coating is assessed in uni-axial traction tests. The silica coating is prepared through sol-gel deposition in which carbon nanotubes are dispersed. The overall amount of carbon nanotubes in the silica sol is fixed at 0.5% wt. Silica-coated AR-glass and carbon fabric composite specimens, embedded in a commercially-available lime mortar matrix, are tested and compared. Carbon nanotubes provide a remarkable enhancement in both ultimate strength and elongation for AR-glass TRM, yielding an impressive two-fold increase in terms of strength. Differently, coated carbon fabrics composites show an increase up to 31% in terms of ductility, in view of an unexpected strength loss.