Construction and Building Materials
An experimental investigation was conducted to investigate the performance of geopolymers made with three different precursors consisting of fly ash, Ground Glass Fiber (GGF), and Glass-Powder (GLP) exposed to sodium sulfate solution. Precursors were activated using either sodium hydroxide solution or combinations of sodium hydroxide and sodium silicate solution with varying levels of sodium and silica content. Among the mixtures with each of the three precursors, mortar mixtures with the highest compressive strength were selected to test their resistance against exposure to a 5% sodium sulfate solution. Changes in the weight and compressive strength of the specimens were monitored up to 120 days of exposure. In addition, change in the microstructure of geopolymer samples and mineral phases was investigated using SEM-EDX and XRD analyses, respectively. Further, techniques such as mercury intrusion porosimetry (MIP) spectrometry and inductively coupled plasma mass spectrometry (ICP-MS) were used to study the pore structure and the leachability of elements from geopolymers, respectively. Results of this study revealed that the GGF and fly ash-based geopolymers performed significantly better in comparison to the GLP-based geopolymer, when exposed to the sodium sulfate solution. The durability of GGF and Fly ash based geopolymer samples could be related to their stable alumino-silicate gel that develops upon geopolymerisation as well as the low amount of calcium oxide in the geopolymer systems. On the other hand, the poor performance of the GLP-based geopolymer could be related to the less stable geopolymerisation products which result in increased porosity, and the high amount of available alkalis present in the raw GLP.
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