Two Experimental Methods to Determine Carbonation Profiles in Concrete

Carbon dioxide in the air can penetrate into concrete, dissolve in the interstitial solution, and react with the reinforcing steel in the reinforced concrete. This 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. This article reports on two experimental methods that provide carbonation profiles that are related to the amount of chemically-fixed carbon dioxide at various depths in a concrete sample. The first method, using 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. The second method, based on thermogravimetric analysis, can be used on laboratory samples, as well as on core samples taken from concrete structures. The authors describe, validate, and compare these innovative methods by investigating various cementitious materials. Gammadensimetry is nondestructive, which makes it possible to monitor the progression of the carbonation in the same sample subjected to either natural or accelerated carbonation. The authors conclude that gamma-ray measurement allows the determination of the kinetics of the carbonation phenomenon and the validation of the mathematical models.