Gérard Platret

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.

Comparaison et validité des méthodes de mesure de la carbonatation

ABSTRACT The modeling of concrete carbonation needs physical parameters well determined, especially those of the real carbonation front and the quantity of calcium carbonate formed after carbonation. This paper proposes a comparison between different carbonation measurement methods. Obtained results are slightly different from used method. Furthermore, the interest and the limit of each technique are showed.

Effect of gypsum content on sulfoaluminate mortars stability

ABSTRACT Calcium sulfoaluminate clinker is one of the most promising cements that would lower the greenhouse gas effect accompanying cement production. This article examines the effect of gypsum content on the dimensional stability of sulfoaluminate mortars. Mechanical properties as chemical evolution are studied. Our results show that the mortar with the greatest gypsum content expands without a decrease of its mechanical properties when it is cured in water. Two hypotheses about the mortars hydration are discussed to explain the differents macroscopic behaviours of the two mortars.

Comparaison de différentes méthodes de mesure du degré d'hydratation de pâtes de ciment Portland durcies

ABSTRACT This study, achieved as a part of the research project “Transfers in concrete and durability of structures”, deals with comparative measurements between two methods which evaluate the degree of hydration of different hardened Portland cement pastes: classical measurement of the chemically bound water, and image analysis on polished sections by scanning electron microscope in backscattered mode (SEM—BSE). The water/cement ratio ranging from 0.25 to 0.6 and time from 28 days to 2 years, are the two majors parameters of this study. The results indicate a good agreement between the two methods. Assumptions, advantages and limitation of each method are discussed, especially, when applied to other types of cements and to concrete.