An experimental approach based on the study of the pore solution of metakaolin-based geopolymer has been established in this study to investigate the phenomenon of carbonation in these materials. The results obtained showed a very fast decrease in the pH, compared to Portland cement, and an almost total carbonation of the pore solution in natural condition after only 14 days. In natural CO2 conditions, the formation of sodium carbonate did not lead to a decrease of pH below 10.5 at one year, thus limiting the risk of corrosion by depassivation of the reinforcement. Accelerated carbonation performed under 50% of CO2 highlighted the formation of large amounts of sodium bicarbonate responsible for a lower pH of the pore solution, and a potential risk of corrosion by carbonation. That result also demonstrated that the accelerated carbonation tests made for Portland cement are not representative of the natural reaction in geopolymer cases. (C) 2016 Elsevier Ltd. All rights reserved.