Two experimental methods to determine carbonation profiles in concrete

Carbonation is one of the major causes of deterioration in reinforced concrete because it leads to a pH reduction and mass increase partly due to the precipitation of calcite. Consequently, the steel reinforcing bars are not protected anymore by a passivation layer which forms at high pH-values and disappears when the pH decreases. The two experimental methods presented in this paper provide carbonation profiles that are related to the amount of chemically-fixed carbon dioxide at various depths in a concrete sample. The first method by gamma-ray measurement is nondestructive and is suited for samples submitted to laboratory tests, because the knowledge of the initial state is needed as a reference to obtain the difference between the virgin reference state and the carbonated one. This method is appropriate for monitoring the course of a carbonation-accelerated test. The second method is based on the thermogravimetric analysis and can be used on laboratory samples, as well as on core samples taken from concrete structures. The aim of this paper is to describe, validate, and compare these innovative methods by investigating various cementitious materials.