Sizings on alkali-resistant glass fibers:: Environmental effects on mechanical properties

The alkali-resistant glass fibers (ARG) are coated with special sizings to provide superior alkali resistance and are designed to reinforce cementitious and other alkali matrixes. The assessment of changes in the fiber surface nanomechanical properties is essential for understanding the fiber bulk mechanical fracture behavior. Here we present examples demonstrating sensitive surface stiffness and dissipated energy with regard to the depth profile at the nanoscale, using atomic force microscopy with nanoindentation. A nondimensional energy index is proposed to estimate inhomogeneous surface properties and account for the substrate effect. Additionally, the variations in surface chemistry were evaluated by Fourier transform infrared attenuated total reflection spectroscopy and thermal gravimetric analysis. Among three types of aqueous environments evaluated, an alkaline solution is the most aggressive to the fiber surface. Subsequently, we describe the effect of surface property variability on the fiber tensile performance using a modified bimodal Weibull statistical distribution analysis. A new effective surface thickness factor kappa(d) is given to reveal the influences of various surface treatments on the extrinsic failure. The sizing is shown to significantly affect both the population and size of flaws on the fiber surface by healing effects. Finally, we correlate the tensile strength and surface roughness with Griffith fracture predictions. The maximum height roughness of ARG fibers follows very closely the line predicted by the Griffith fracture criterion. It highlights the importance of the sizing to the environmental resistance of the alkali-resistant glass fibers.