Parametric Study towards Optimization of a Short Duration Carbonation Process of Recycled Cement Paste

The recycling process of concrete originates a byproduct, cement paste powder (CPP), which is a material composed mainly of hydrated cement. This cementitious material has demonstrated promising results when applied as a binder in new concrete batches, provided it has been subjected to a previous carbonation process. One of the obstacles to the industrial application of this strategy is the long duration of the typical carbonation process, which requires from 3 to 28 days. Recently, the authors have developed a short two-hour carbonation process and thoroughly analysed it over its entire extension. In this paper, a parametric analysis of the carbonation process is performed towards CO(2) uptake maximization, aiming to increase the feasibility of its short duration. CO(2) uptake is evaluated using the ignition by furnace method and thermogravimetric analysis. Among the parameters considered, the initial water content and the CPP thickness present the highest impact on CO(2) uptake. The investigation of different CO(2) concentrations inside the carbonation chamber showed that the maximum CO(2) uptake does not occur for the highest concentration value. Moreover, a minimum resident time for the forced carbonation of CPP in industrial contexts is presented, and is found to be highly dependent on the CO(2) concentration. The particle size and purity degree of CPP revealed a limited influence on the CO(2) uptake achieved. Additionally, this paper provides further insight into the mechanisms involved in the carbonation of mature cement paste while increasing the feasibility of our recently proposed short duration carbonation process.