EFFECTS OF SAMPLE PREPARATION AND INTERPRETATION OF THE THERMOGRAVIMETIRC CURVES ON THE CALCIUM HYDROXIDE CONTENT IN HYDRATED PASTES AND MORTARS

摘要

Calcium hydroxide (Ca(OH)2) is the one of the major constituents of hydrated portland cement paste. Itscontent can be used to trace the progress of cement hydration or serve as an indicator of the extent ofpozzolanic reaction. Thermogravimetric analysis (TGA) method is often used for determination of theCa(OH)2 content due to its being relatively easy and fast procedure. However, no universally agreed-uponmethod exists for preparation of the TGA specimens and for the interpretation of the resulting TGAcurves.This paper presents an investigation on the contents of Ca(OH)2 in samples subjected to differentpreparation techniques. The results show that a certain amount of calcium carbonate (CaCO3) wasproduced due to carbonation during the sample preparation process. The degree of carbonation wasdependent on the sample preparation, and carbonated Ca(OH)2 must be considered to determine theaccurate total Ca(OH)2 content.In addition, a modified interpretation of the TGA curve for Ca(OH)2 was suggested. In thisinterpretation, the mass losses caused by the other hydration products, except for the Ca(OH)2 and thecarbonated Ca(OH)2, were considered in order to determine the accurate content of Ca(OH)2. Thisinterpretation technique was verified by comparing the results with those obtained by differential scanningcalorimetry (DSC). Ultimately, the actual contents of Ca(OH)2 in pastes undergoing different samplepreparation techniques were determined using the modified interpretation of the TGA curve for theCa(OH)2. The results show that this interpretation yielded comparable contents of Ca(OH)2 in most ofsample preparation techniques used in this study.