Mortars with thermo activated recycled cement: Fresh and mechanical characterisation

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

“…Compared with NT, the amount of carbonated phases tended to increase slightly in RC ( L dc , after taking into account the reduction of the hydration weight fraction in NT, Table 3 ), especially those treated above the dehydroxylation temperature. This indicates that some carbonation occurred after thermal treatment above 450 °C, as also suggested by Wang et al [ 9 ] and Carriço et al [ 22 ]. Overall, the CH content decreased and the estimated CaO content increased (Equation (4)) with the treatment temperature, as a result of CH dehydroxylation, as well as of CaCO 3 decarbonation, depending on the treatment temperature ( Table 3 ).…”

“…At 800 °C, a new different Q 0 resonance emerged at a δ( 29 Si) of −70.60 ppm ( Figure 7 f), which is consistent with the progressive formation of β-C 2 S [ 11 , 22 , 44 ] identified in the XRD analysis ( Figure 6 j). At 900 °C, this resonance shifts to a δ( 29 Si) of −70.81 ppm ( Figure 7 g), narrower and more intense than at 800 °C.…”

“…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 ]. Furthermore, results reported in the literature are contradictory, reflecting the lack of knowledge of these poorly explored new binders [ 1 ].…”

“…However, Serpell and Lopez [ 14 ] attributed this apparent rapid setting to a false set due to the quick hydration of CaO. Moreover, higher setting times in RC than in ordinary Portland cement (PC) were found by Bogas et al [ 15 ] and Carriço et al [ 22 ]. This less expected behavior was attributed to the agglomeration of RC particles and the higher pre-hydration propensity of RC, during cooling and storage.…”

“…Serpell and Zunino [ 11 ] reported that β-C 2 S and a more reactive C 2 S polymorph, α’ H -C 2 S, were identified above 740 °C, though, up to 800 °C, the predominant C 2 S polymorph was α’ H -C 2 S, and, at 900 °C, the main C 2 S polymorph was β-C 2 S. Shui et al [ 25 ] identified α-C 2 S, as well as β-C 2 S, above 800 °C. Through XRD analysis, Carriço et al [ 22 ] detected that, above 600 °C, a new C 2 S polymorph was created, with a similar structure to α’ L -C 2 S. Furthermore, the microstructure and hydration mechanism of RC has yet to be completely figured out, especially taking into account the influence of the treatment temperature. The initial hydration heat of RC was found to be significantly higher than that of ordinary PC [ 4 , 5 , 6 , 26 ], though the reasons for this phenomenon are yet to be entirely understood.…”