Calcium-carbonate powders were coprecipitated with Al 3+ and then decomposed in air and/or under a CO 2 flux between 590°C and 1150°C. The data were analysed using a consecutive-decomposition-dilatometer method and the kinetic results were discussed according to the microstructure analysis done by N 2 adsorption isotherms (78K), SEM and FT-IR measurements. Below 1000°C, CaCO 3 particle thermal-decomposition was pseudomorphic, resulting in the formation of a CaO grain porous network. When the CaO grains were formed, the Al 3+ diffused among them, producing AlO 4 groups that promoted the CaO grain coarsening and reduced O 2− surface sites available to CO 2 adsorbed molecules to form CO 3 2− . In pure CaO, CO 3 2− diffused through the grain boundary, enhancing Ca 2+ and O 2− mobility; AlO 4 groups reduced CO 3 2− penetration and CaO sintering rate. Above 1000°C, the sintering rate of the doped samples exceeded that of the undoped, likely because of Al 3+ diffusion in CaO and viscous flow.