Search

Diffuse Reflection Fourier Transform Infrared ( DR- FTIR) spectroscopy has previously proven to provide time-resolved insights into early cement hydration spanning ~30 s to ~36 h after completing the mixing. Here, a previously validated ex situ freeze-dry procedure to stop hydration at preset times is complemented by an in situ Attenuated Total Reflectance ( ATR) infrared spectroscopy method. The qualitative overall agreement between ex situ freeze-drying and in situ monitoring is demonstrated. Moreover, water conversion during hydration comes out clearly in the time-resolved ATR- FTIR spectra. This information is absent in DR- FTIR where buildups of crystal water and hydroxides are observed, while quenching of the hydration process requires removal of free water prior to acquiring the spectra. The ability of the IR technique to monitor the initial rate of hydration as a function of time is validated by comparing to calorimetry. The two approaches are understood to be complementary in that the former monitors alite grain surface hydration, while the latter reflects bulk hydration. IR is complementary to the calorimetry in cases of surface processes in conjunction with low enthalpy changes, that is, initial C-S-H formation and additive related surface chemistry. [ABSTRACT FROM AUTHOR]

Abstract: Isothermal calorimetry and diffuse reflectance infrared DR–FTIR spectroscopy are combined to correlate evolutions of spectroscopic signatures with rates of chemical reactions as reflected in the rate of heat emitted during the first 38h of cement hydration. Portland limestone cement mortar is employed and the analysis is repeated for two different mixing procedures. Intensive blender mixing with quartz sand is found to cause activation of the cement resulting in a faster hydration process. At early stages of hydration, two types of C–S–H are formed. The spectral intensity of the earlier C–S–H is found to saturate, while that of the later form continues to acquire intensity throughout the 38h of the experiment. Evidences are presented which support the interpretation that the two forms differ mainly in morphology and water content. Simultaneously with the saturation of the early C–S–H, a transient species is observed with DR–FTIR. This species correlates with the observed thermogram fine-structure. [ABSTRACT FROM AUTHOR]

Abstract: Diffuse Reflectance Infrared DR-FTIR spectroscopy is employed to monitor chemical transformations in pastes of Portland limestone cement. To obtain a sufficient time resolution a freeze-dry procedure is used to instantaneously ceasing the hydration process. Rapid re-crystallization of sulphates is observed during the first 15 s, and appears to be complete after ~30 min. After ~60 min, spectroscopic signatures of polymerizing silica start to emerge. A hump at 970–1100 cm−1 in conjunction with increasing intensity in the water bending mode region at 1500–1700 cm−1 is indicative of the formation of Calcium Silicate Hydrate, C-S-H. Simultaneously with the development of the C-S-H signatures, a dip feature develops at 800–970 cm−1, reflecting the dissolution of Alite, C3S. Setting times, 180 (initial) and 240 (final) minutes, are determined by the Vicat technique. Combining DR-FTIR, SEM and Vicat measurements it is concluded that the setting is caused by inter-particle coalescence of C-S-H. [Copyright &y& Elsevier]