This paper investigates the effect of curing time and aggressive environmental exposure on the mechanical performance of impregnated Carbon Fabric Reinforced Cementitious Matrix (CFRCM) composite. Following the recently published IIC-ES AC434 guidelines, saltwater, distilled water, alkali and acid resistance are investigated together with freeze-thaw cycles. Mechanical characterization is based on tensile uni-axial tests under deformation control of rectangular-base prismatic specimens. 28- and 60-day curing times are considered for the control environment as well as for saltwater and alkali resistance. Deformation is monitored via digital acquisition. Besides uni-axial tests, experimental results comprise optical and scanning electron microscopy, crack pattern analysis and failure mechanism assessment. Focus is set on the determination of the design limits for the composite system at failure for the tested environments and curing times. In particular, a comparison is drawn with established design criteria already coded for FRP systems, which introduce the concept of safety (or partial) factors. Environmental conversion factors are also defined and calculated on a statistical basis in a twofold manner, as a mean to determine the design strain and strength limits of exposed specimens from the control (unexposed) data. It is found that they provide a convenient method for assessing the composite vulnerability to the aggressive environments at different curing times

In this paper, we investigate the effect of silica nano-coating for interphase bond enhancement on the mechanical performance of Textile Reinforced Mortar (TRM) composite materials aimed at structural rehabilitation and strengthening. Alkali-resistant glass (ARG) and carbon fabric reinforcements are preliminarily treated via sol-gel deposition of SiO 2 coating to promote bond formation capability with the mortar matrix. Optical and electron microscopy provide evidence of interphase bond enhancement. Mechanical performance is assessed both in traction, through uni-axial elongation of prismatic coupons, and in flexure, by three-point bending of laminated masonry bricks. Results are given in terms of mean strength curves, ultimate and design strength and strain values, cracked and uncracked moduli, mean crack spacing, mean crack width and energy dissipation. It is shown that mean absolute performance of silica coating offers a significant improvement over uncoated fabric, yet it is inferior to that of specimens which have been treated with a liquid partially-organic adhesion promoter (polymer coating). However, when design values are considered which incorporate the dispersion of experimental data, silica coating proves superior or at least equivalent to polymer coating, respectively for carbon and ARG fabric. These promising results describe the first application of silica nano-coating to fabric reinforced composite materials.

The mechanical performance of epoxy coated AR-glass fabric reinforced composite is investigated. A three-stage manufacturing process is considered, which involves fabric surface functionalization, liquid coating deposition and long-term setting and finally fabric embedment in the mortar matrix. Two epoxy coatings are considered, which differ only by the hardening agent. However, coating thickness is significantly diverse as a result of modified viscosity during liquid deposition. Performance is assessed in uni-axial tension as well as in threepoint bending and it is expressed in terms of strength curves, data dispersion, crack pattern and failure mechanism. Remarkably, despite being very similar, the analyzed coatings produce a significantly different performance, especially when data dispersion is incorporated and design limits are considered. Indeed, although both coatings are able to consistently deliver fabric rupture at failure, only the thinnest is associated with small data scattering and an almost plastic post-peak behavior in bending. The associated design elongation limit reaches the maximum allowed value according to the ICC guidelines. In fact, it appears that coating thickness plays a crucial role in determining mechanical performance and fabric flexibility. The proposed manufacturing process proves extremely effective at enhancing matrix-to-fabric adhesion and thereby prevent

No abstract

Motivated by the unexpected appearance of shear horizontal Rayleigh surface waves, we investigate the mechanics of antiplane wave reflection and propagation in couple stress (CS) elastic materials. Surface waves arise by mode conversion at a free surface, whereby bulk travelling waves trigger inhomogeneous modes. Indeed, Rayleigh waves are perturbations of the travelling mode and stem from its reflection at grazing incidence. As is well known, they correspond to the real zeros of the Rayleigh function. Interestingly, we show that the same generating mechanism sustains a new inhomogeneous wave, corresponding to a purely imaginary zero of the Rayleigh function. This wave emerges from ‘reflection’ of a bulk standing mode: This produces a new type of Rayleigh-like wave that travels away from , as opposed to along, the free surface, with a speed lower than that of bulk shear waves. Besides, a third complex zero of the Rayleigh function may exist, which represents waves attenuating/exploding both along and away from the surface. Since none of these zeros correspond to leaky waves, a new classification of the Rayleigh zeros is proposed. Furthermore, we extend to CS elasticity Mindlin’s boundary conditions, by which partial waves are identified, whose interference lends Rayleigh–Lamb guided waves. Finally, asymptotic analysis in the thin-plate limit provides equivalent one-dimensional models.