A Novel Method for the Non-Destructive Assessment of Strength Degradation and Re-Use Potential of Weathered Float Glass From Facades

Abstract

Lack of knowledge about the properties of weathered (used) glass is currently a major barrier to glass reuse. This results in probably unnecessary recycling or down-cycling of architectural glass at the end of life. Avoiding this creates a significant opportunity to reduce resource depletion and decarbonize the built environment. This can be done by developing an optical non-destructive test method that estimates the strength of naturally weathered glass by characterizing surface flaws. This allows excessively damaged glass panels to be removed for surface repair or recycling. Specimens were made from 50+-year-old monolithic flat glass taken from a façade in the Hague, Netherlands, where it was exposed to salt in the air, water, cleaning, and abrasion from wind-driven dust and sand particles. The specimens were examined using a microscope and a handheld optical profilometer to determine surface flaw characteristics. The glass specimens were then tested using a ring-on-ring (coaxial double ring) setup. Similar tests were also conducted on new as-received float glass to provide a benchmark. Both the indoor-facing and outdoor-facing sides of the weathered glass and the air and tin side of the new glass were tested. A statistical analysis of the test results was made using conventional Weibull statistics. The results show that after 50+ years of natural aging the strength of the glass is significantly reduced and that the non-destructive scanning method trialed in this study can locate and determine in many cases the size of critical surface defects thereby allowing for direct safe re-use of 70+% of the glass. The handheld optical profilometer can identify severe damage on the glass, but further research and software development is needed to improve the accuracy and consistency of the scanning method and to automate this technique for routine/large-scale applications including as a prerequisite for surface repair.