Re-use of glass: Research and application at The Natural Pavilion

Float glass is a material which is used extensively for more than sixty years in the building industry, mainly as infill for windows or facade panels. Currently, most of the buildings undergo renovations and the existing glass elements are discarded because they do not meet the latest energy performance requirements. As a result, the glass waste increases and the need for new glass grows. However, neither glass production nor its recycling are sustainable processes, as both incorporate the use of gas furnaces, which produce high amounts of CO2 emissions. As engineer, I aim at minimizing the environmental footprint of our projects and by extension, that of the building materials used. When it comes to glass, I believe that its?re-use seems the only way to achieve that.

Re-use of glass at The Natural Pavilion

When the project of The Natural Pavilion came up, a pavilion constructed for the Floriade Expo 2022, which had high sustainability demands, the possibility of re-using glass for the transparent parts of its fa?ade was investigated. In general, the requirements that a fa?ade must fulfil are multiple, such as thermal performance, structural adequacy or fire safety. Thus, the challenges for incorporating old glass in new fa?ade elements are also multiple. However, in the sustainability-driven fa?ade design of the Natural Pavilion, an unconventional process was followed, in order to re-use the 55-year-old glass panels which were removed from an office building in The Hague. In particular, the fa?ade was designed in accordance to the dimensions of the existing glass elements instead of the other way around. In this way, 12.500 kg of glass was reused, saving up to 2 tons of CO2.

Investigation performance of old glass

The next challenge for ABT is to investigate the performance of old glass in-depth, in order to apply it also in permanent buildings with stricter design requirements. The greatest challenge in the reuse of glass is the estimation of its strength after several years of use. Unlike other materials, the strength of glass is not a material property but it is governed by its defects, which are induced by weathering, cleaning, maintenance etc. After several years of exposure to the natural environment, these defects grow and lead to a dynamic reduction of its strength. Therefore, in order to assess the residual strength of old glass, it is essential to quantify it in terms of defects.

Master thesis

Over the last couple of months, I carried out my master thesis at TU Delft and in collaboration with ABT, with the title “Methodology for the prediction of the strength of naturally aged glass based on surface flaw characterization”. The aim of my project was to develop the understanding on the performance of weathered, old glass, focusing on the link between its defects and its residual strength. Thus, I examined the 55-year-old glass, which was used in the Natural Pavilion along with new glass of similar characteristics, which I used as a reference. Throughout a series of non-destructive and destructive tests useful information emerged, regarding the type and amount of damage on the surface of weathered glass and its strength.

Results

The tests revealed that the surface of the old glass contained multiple defects whereas the new glass had occasionally few defects. This difference in terms of damage led to great difference in their strength, with the new glass being approximately two times stronger than the old glass. However, this strength decrease is strongly related to the conditions that the glass has been exposed to during its service life, such as weather phenomena and loading history. A valuable outcome of this research is the novel methodology that I proposed for the prediction of the residual strength of old glass, based on its surface defects. The methodology consists of two parts; a defect detection test with the Traceit, a mobile surface profilometer, and the calculation of the strength based on the theory of Linear Elastic Fracture Mechanics. This methodology led to very accurate prediction of the average strength of weathered glass and to conservative prediction of the design strength.

Next steps

Overall, this research provides important scientific information about the performance of weathered glass and most importantly, it brings us one step closer to the re-use of glass panels. Thus, having set the foundation for an in-depth research in this field, the next step is to test glass from different locations and work on the development of the methodology at a level which will allow its application in practice.

Read the complete thesis here.

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Text: Irene Sofokleous , intern and graduate student at ABT in 2022

Contact at ABT: ?Anna Eskes