Glass is a highly durable and infinitely recyclable material, yet in practice only a small portion of architectural glass products re-enters the value chain after its first use. An increasing rate of energy retrofits of the EU building stock will result in replacement of 85% of existing windows in near future; in the current linear glass supply chain, this will generate large amounts of glass waste. Despite high recycling rates of container glass in Europe, window glazing is very rarely recycled into new glazing, and reuse is almost entirely unexplored. For aged glazing to be reused in construction, better knowledge of its surface quality and structural performance is needed. The main objective of this paper is to explore the effects of ageing and exposure to indoor and outdoor environment on the strength of glass. A comparative investigation is undertaken to evaluate the strength and surface quality of the internally, externally and cavity-facing glass surfaces of insulating glass units (IGUs) after 30 years of use in a building envelope in the Netherlands. The glass panes are separated from the IGU assembly and cut into specimens for microscopy and coaxial double ring tests. The study shows that the visual quality is best preserved on the cavity-facing surface, consequently exhibiting the highest bending strength. The internally and externally facing surfaces, with visibly more extensive damage, exhibited similarly lower strengths at low probabilities of failure. When compared to the design strength of new annealed glass acc. to EN 16612, all the surfaces showed a reuse potential, with considerable bending strength.@en

Patterned acid-etched glasses are frequently used in horizontal glass surfaces that may be walked on, such as floors and staircase treads. These glasses provide useful antislip properties, but the foot traffic cause contact stresses and ageing mechanisms that are poorly understood and can affect the strength of the acid-etched glass. This study explores these strength-reducing effects by undertaking nondestructive and destructive evaluations of two acid-etched glasses with geometrically different surface patterns and comparing their mechanical performance to unetched float glass. In particular, residual surface stress, Hertzian fracture resistance, and fractographic characteristics are determined for each glass type. The surface tensile strength of the glasses is also evaluated by means of destructive flexural tests before and after artificial ageing. The flexural tests reveal that the ridge areas of the acid-etched surface patterns are more susceptible to the formation of digs and deeper surface flaws and are therefore weaker than both the valley areas of the acid-etched pattern and the surface of the unetched float glass. Correspondingly, the acid-etched glass with the highest proportion of ridges was more susceptible to ageing-induced flaws and had the lowest surface tensile strength. The contact (Hertzian) fracture resistance was also significantly affected by the presence of a surface pattern in the acid-etched glass; specifically, the lowest contact strengths were recorded for hard body contact on the ridges of the pattern. The fracture phenomena and new data presented in this paper provide useful insights on the long-term performance of etched patterned glass. The findings can provide the bases for real-world design decisions and for glass forensics.

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