Corrosion mechanisms of steel reinforcement in fly ash/slag based powder form of geopolymer concrete

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To promote the use of geopolymer materials in structure applications, this study aimed to investigate on carbonation and chloride resistance of one-part fly ash/slag geopolymer concretes. Additionally, the possibility of using a sodium-based set retarder to address the issue of short setting time was included in the investigation. The key findings indicated that using the set retarder, with an amount of 2-6%, prolonged the setting time of one-part geopolymer binders and reduced the heat released by activation reactions. The results obtained also showed that carbonation alone might not lead to steel corrosion in one-part geopolymer concrete investigated because the pH in carbonated parts was always higher than 10. For assessing chloride resistance in an accelerated test in 16.5% NaCl solution, 40% fly ash/ 60% slag geopolymer concrete had a lower chloride resistance than OPC concretes, while chloride resistance of 60% fly ash/ 40% slag geopolymer concrete was worse. Due to the presence of both fly ash and slag in the precursor, chloride ions were physically and chemically bound in the one-part geopolymer concretes. Regarding RCPT, using 60 voltage, advocated in ASTM C1202, caused the issue of overheating, thus, RCPT performed at 30 voltage was highly suggested.
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