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Given the considerable share of cement industry on overall share of CO2 emissions, one of the most important current challenges is the adoption of strategies that reduce the use of cement without compromising the mechanical performance and durability of cementitious materials. Among these strategies, one of the commonly employed in some industrial segments is the reuse of pre-hydrated binder in production. The understanding of as pre-hydration changes the properties of cementitious pastes also has important scientific implication regarding the reaction kinetics of Portland cement, but mainly due to the impacts on the rheological properties of the paste, both after mixing and along hydration. It is known that pre-hydration alters the hydration kinetics of the cement, impacting its properties in the hardened state. In addition, pre-hydration modifies the physical properties of the cement, directly influencing the way as the particles agglomerates. However, much of the literature refers to the pre-hydration that occurs after bad storage, unlike this work that works with pre-hydration in suspension, more common in industrial applications. Thus, in this work the kinetics of reaction by isothermal calorimetry was evaluated while the rheological properties were evaluated by rotational and oscillatory rheometry. For the identification and quantification of the hydrates formed, the hydration was paralyzed and TG and XRD tests were performed. The results showed that the inclusion of the pre-hydrate alters the dissolution/precipitation kinetics of the anhydrous cement. Thus, the higher the pre-hydration content and the pre-hydration period, the shorter the induction time, anticipating the formation of the hydrates (silicates and aluminates), although the reaction rate in the acceleration period was not significantly affected. As for the physical properties of the particles, there were realized tests of particle size distribution, SSA (Specific Surface Area) and real density. The pre-hydration increases its SSA, which leads to an increase in the yield stress and viscosity of the pastes. Even if this increase of SSA is incorporated in certain models (YODEL and Interference) it is possible to predict these rheological properties. The increase in ASE is also responsible for the greater hardening and quickly setting time of the pre-hydrated suspensions. Correlating the chemical reaction with paste consolidation, it was demonstrated that the higher hardening of the pre-hydrated paste is related to the greater approximation between the particles, the initial ASE of the pastes and the reactivity of the pre-hydrate, optimizing then the formation of the microstructure by hydration.

Influência do ligante pré-hidratado nas propriedades de suspensões de cimento Portland.