Kinetics of lime/bentonite pozzolanic reactions at 20 and 50 °C: Batch tests and modeling

The effects of duration (1-100 days) and temperature (20 and 50 degrees C) were assessed from batch tests for Ca-bentonite mixed with 10 wt.% lime. The pozzolanic processes were monitored over time by Si-29 NMR (Cement Concr. Res. 42,2012), TGA-DTA, XRD and chemical analysis. Modeling considered kinetics and thermodynamics of mineralogical transformations and cation exchange. Kinetic laws were dependent on pH and temperature (Arrhenius energy). Lime hydration occurs within hours, modifying the bentonite exchangeable population and increasing the pH. These alkaline conditions initiate the pozzolanic reactions in a second stage. The rate-limiting step is the dissolution kinetics of the bentonite minerals, i.e. a relatively fast and total consumption of cristobalite in parallel to a long-term slower dissolution of montmorillonite. First C-S-H and then C-A-S-H are formed consequently. Temperature speeds up the pozzolanic reaction kinetics by a factor 5 from 20 to 50 degrees C, corresponding to an apparent activation energy of 40-50 kymol. (C) 2014 Elsevier Ltd. All rights reserved.