Dehydration and Rehydration of Blast Furnace Slag Cement

Influence of the Treatment Temperature on the Microstructure and Hydration Behavior of Thermoactivated Recycled Cement

“…in order to explore the rehydration ability of thermoactivated recycled cement (RC) [ 1 , 4 ]. Some authors simply concentrated on a single treatment temperature [ 5 , 6 ] and others approached only a few properties, namely the fresh behavior and the mechanical strength [ 4 , 7 , 8 , 9 , 10 , 11 , 12 , 13 ]. Other studies were dedicated to the incorporation of varying percentages of RC in mortars and concrete [ 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 ].…”

“…Two particularities of RC seem to be the high water demand [ 4 , 5 , 6 , 8 , 23 , 24 ] and reduced setting time [ 4 , 8 ]. However, the cause as well as the influence of the treatment temperature on these properties has yet to gather consensus.…”

“…A similar tendency was reported by Vysvaril et al [ 8 ], though higher w/b were obtained for the same array of temperatures (about 0.7–0.9 for 200–800 °C). Baldusco et al [ 5 ] ascribed the results to the high surface area of RC. Shui et al [ 4 ] and Xuan and Shui [ 13 ] mentioned that, besides the high surface area, the high water demand was also owed to the free CaO content of RC.…”

“…The rapid setting times of RC have been attributed to their fast rehydration, owed to their reactivity and surface area [ 4 , 5 , 6 ]. Moreover, the decrease of the setting time with the treatment temperature has been described by various authors [ 4 , 5 , 6 , 8 , 13 ], for treatment temperatures up to about 800 °C, though different results were reported. Diverging reasons for this have been presented, namely the increasing dehydration of RC [ 4 ] or growing CaO content [ 8 , 14 ].…”

“…The phase composition of the dehydrated cement with thermal treatment still has not been fully comprehended. Most studies have only been able to identify that after thermal treatment, C 2 S of varying reactivity are generated [ 5 , 8 , 9 , 10 ]. Through nuclear magnetic resonance spectroscopy ( 29 Si-NMR), Alonso and Fernandez [ 10 ] determined that the thermal treatment of the cement above 200 °C resulted in a new nesosilicate, which was less crystalline than the C 2 S of the original cement.…”