Recycling of glass waste into foam glass boards: A comparison of cradle-to-gate life cycles of boards with different foaming agents

Glass residues are available worldwide and are disposed of in large amounts in landfills. However, glass waste presents great potential to be used as raw material to produce foam glass boards, a product used in industries such as the construction sector. Conventional foaming agents (e.g. carbon black, carbonates, and sulfates) used in the production of foam glass boards release greenhouse gases into the environment, such as carbon dioxide. Conversely, sodium hydroxide releases only steam during the foaming process. Consequently, an insightful study is necessary to analyze the advantages and disadvantages of sodium hydroxide in comparison to other common foaming agents. Accordingly, the objective of this research is to carry out a cradle-to-gate Life Cycle study with four foam glass boards produced by different foaming agents: sodium hydroxide, carbon black, silicon carbide and dolomite. Global warming potential (GWP), acidification and human toxicity by air were considered as impact categories for Life Cycle Impact Assessment (LCIA). The results from the four foam glass boards were compared to an expanded polystyrene (EPS) board. Results evidenced that the use of sodium hydroxide provides better environmental performance regarding GWP, releasing 0.46 kg CO₂ eq., while the use of carbon black has less acidification potential with 1.95. 10^-3 kg SO₂ eq. Human toxicity by air was the only impact category in which EPS has better performance (8.66. 10⁴ m³ air). LCIA results demonstrate that foam glass boards that stand out as safe (not emitting toxic gases in case of fire) are also interesting materials for the environment.