Determination of Surface Flaw Parameters for Annealed and Fully Tempered Glass Exposed to NaCl

The use of glass in the exterior facades provides greater light transmission into the building and improved views for occupants. Coastal areas in particular leverage the transparency of glass to maximize views. However, the innate characteristic of glass, due to the presence of microscopic flaws attributed to the manufacturing process and handling and weathering of glass, is to lose strength over time, a phenomenon known as static fatigue of glass. The strength of glass reduces due to the presence of water vapor and tensile stress. In the coastal areas, glass is exposed to sodium chloride (NaCl) from the sea, in addition to water vapor and tensile stress. To date, the effect of NaCl on glass has not been documented. This research presents the results from a study to observe the effect of NaCl on the strength of glass. The study loaded 39 glass specimens to failure using a three-point bending test. The glass specimens were 457 mm (18 in) long, 203 mm (8 in) wide, and of different thicknesses and were categorized into three samples based on the type of glass (i.e., annealed vs fully tempered, and 4.77 mm (0.375 in) vs 6.35 mm (0.25 in) thickness). To understand the effect of NaCl on the strength of glass, 20 specimens were loaded to failure at the time of receiving the specimen from the manufacturer, while 19 specimens were soaked in a NaCl solution for a full year before loading to failure. Surface flaw parameters for both sample sets were determined by applying the maximum likelihood estimator to the glass failure prediction model. Results for surface flaw parameters are presented for NaCl-treated and untreated specimens and sample strength was compared at 0.008 and 0.001 probability of breakage. Results did not exhibit a consistent trend; two sample sets showed a decrease in strength at both probabilities of breakage, while another sample showed an increase in strength, but further testing is recommended.