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    • Bond slip behaviour of deformed bar embedded in sustainable concrete at elevated temperature


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      Bond slip behaviour between deformed bar and concrete and its correlation with compressive strength, was investigated for post-fire exposure. For this, other than normal mix, six sustainable mixes were prepared adopting combined replacement approach by partially replacing natural sand by 30% and 50% withGranulated blast furnace slag (GBFS), and Ordinary Portland Cement (OPC) by 20%, 30% and 40% with Class F fly ash. Prepared specimens were later exposed to various temperatures for 4 h at 200°C, 400°C, 600°C and 800°C, followed by furnace cooling. Test results indicated that both the compressive and bond strength decreases usually at the rate of 9.2% /°C and 8.4%/°C. It was also observed that the relative bond deterioration compared to compression was higher for normal mix as compared to sustainable mixes. Even higher replacements of mineral admixtures (GBFS, FA) reduced the strength at ambient temperature, sustainable mixes exhibited higher residual bond or compressive strength than normal mix at elevated temperatures. The bond failure occurred with the splitting of concrete in the region bounded with a steel bar in both the normal and sustainable concrete up to 400°C, which turned into slipping type failure at 800°C. However, the critical temperature was 600C, where splitting with slipping was observed. Normalized bond strength (kT) of normal mix degraded sharply and exhibited lower value than the sustainable mixes at a temperature higher than 400°C. Comparison of residual bond strength and residual compressive strength with past research works and internationalcodes like ACI 216, CEB-FIP 90, and EN1992:1-2 for the fire exposure revealed that mineral additives might be an inventive approach to enhance the fire resistance even though sustainable mixes exhibited a debilitating strength at ambient temperature.

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