Carbonation of Portland Cement Studied by Diffuse Reflection Fourier Transform Infrared Spectroscopy

Carbonation is a natural ageing process for cement. This study focuses on how the carbonation rate varies with selected hydration times and atmospheric conditions during the early stages of reacting dried cement paste. Diffuse reflection Fourier transform infrared spectroscopy is shown to be a suitable technique to monitor the formation of carbonates in cement. Combined with a previously developed freeze drying technique, carbonation can be studied at specific hydration stages. In ambient air both calcium hydroxide and calcium silicate hydrate (C–S–H) in cement are carbonated. Increased hydration time enhances the carbon dioxide uptake, which indicates that the calcium in the hydration products reacts more easily than the calcium in the clinker phase. In a humid CO2 atmosphere, the carbonation process is so pronounced that it decomposes C–S–H into calcium carbonate and silica. In a moist N2 atmosphere no carbonation occurs, but the sulfate chemistry of the cement seems to be affected due to the formation of ettringite

Monitoring Early Hydration of Cement by Ex Situ and In Situ ATR-FTIR – a Comparative Study

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

Insights into Early Hydration of Portland Limestone Cement from Infrared Spectroscopy and Isothermal Calorimetry

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 38 h 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 38 h 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

Early hydration and setting of Portland cement monitored by IR, SEM and Vicat techniques

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 similar to 30 min. After similar to 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

Crystal structure of radium sulfate: An X-ray powder diffraction and density functional theory study

Radium-barium sulfate (Ra0.76Ba0.24SO4) powder was examined using X-ray Diffraction (XRD) technique and its crystal structure was optimized using Density Functional Theory (DFT). XRD data show that radium and barium sulfate form a solid solution and that Ra0.76Ba0.24SO4 is orthorhombic and isostructural with pure RaSO4, barite (BaSO4), celestite (SrSO4) and anglesite (PbSO4), crystallizing in the space group Pmna (No. 62). The unit cell parameters of the Ra0.76Ba0.24SO4 crystal have been determined using Rietveld refinement and were extrapolated to unit cell parameters of the pure RaSO4 phase using Vegard's law: a=9.129(8), b=5.538(3), c=7.313(5) Å. DFT geometry optimization was used to derive atomic coordinates and interatomic distances in both Ra0.76Ba0.24SO4 and pure RaSO4. The experimental and DFT geometry optimization results obtained in this work are in good agreement with each other, and furthermore with literature data

Coordination of trivalent lanthanides with bismalonamide ligands:implications for liquid-liquid extraction

The complexation of the bismalonamide ligand 2,2'-(1,2-phenylenebis(methylene))bis(N,N,N',N'-tetraethylmalonamide) (L), bearing two C-alkylated N,N,N',N'-tetraethylmalonamide groups onto ortho-xylylene (C6H4(CH2)2) platform, with trivalent lanthanides was investigated both in solid- and solution states. The crystal structures [Nd2(NO3)6L2]·(CH3CN)3 (2), [Nd2(NO3)4L2]·[Nd(NO3)5]·(CH3CN)1.5 (3), Ce(NO3)3L2 (4) and [NdL2]·(ClO4)3·C2H5OH (5) were analyzed by single-crystal X-ray diffraction. The ortho-bismalonamide (L) is tetradentate in the structures 2, 3 and 5 and bidentate in 4 only. It was found that the structures 2 and 3 are composed of dimeric species. According to electrospray ionization - mass spectrometry the dimers are prevailing in acetonitrile solutions. The polydentate coordination of the ortho-bismalonamide (L) with trivalent lanthanides suggests that an entropy effect favors liquid-liquid extraction of the metal ions with this type of ligands

Coordination of trivalent lanthanides with bismalonamide ligands (dataset)

CCDC 1541623 CCDC 1541624 CCDC 1541625 CCDC 155541