Effect of accelerated carbonation curing on thermal evolution of hydrates in calcium sulfoaluminate cement

The present study investigated the effect of accelerated carbonation curing (ACC) at early age on the thermal evolution of hydrates in calcium sulfoaluminate (CSA) cement. CSA paste samples with a molar ratio of calcium sulfate to ye'elimite of 1 were cured under 10% atmospheric CO2 concentration until 28 days of curing. The CSA saFfigmples were subjected to 200, 400, 600, and 800 degrees C, thereafter the thermal evolution of the hydrates in the CSA samples was investigated. The main carbonation outcomes were aragonite and vaterite, and were recrystallized to calcite at exposed temperature between 400 and 600 degrees C, mitigating strength loss in the CSA cement. However, a significant strength loss was observed after exposure to 800 degrees C due to the decalcification of the calcium carbonates in the samples, showing a reduced strength of 65.7% and 53.0% compared to the carbonation-cured sample exposed to 600 degrees C and non carbonation-cured sample exposed to 800 degrees C. In addition, the both carbonation- and non carbonation-cured CSA samples showed similar 27Al and 29Si MAS NMR spectral shapes upon exposure to 800 degrees C, implying that the Si- and Al- environments became similar at high temperatures regardless of the ACC process.