The present study investigated the evolution of a binder gel in carbonation-cured Portland cement in an acidic medium. Three types of Portland cement with varying chemical compositions were carbonation-cured and exposed to $H_2SO_4$ or HCl. An acid attack induced significant changes in the local Al environment in normally cured cement showing the formation of ettringite and Friedel’s salt, while the local environment of Al in carbonation-cured cement mainly consisted of a tetrahedral aluminate structure and showed much less structural alternation. A thermal analysis showed that the carbonation products of belite were more stable than those of alite, with less gypsum formation under $H_2SO_4$ in the cement with relatively more belite. Depolymerization of the carbonation product, Ca-modified silicate gel, was observed in the samples immersed in acid.