The influences of cement hydration and temperature on the thixotropy of cement paste

The rheological properties of fresh cement paste are highly influenced by a large number of parameters, among which the most important factors are the applied shear stress, and the shear history, the age of the sample and the temperature. The effects of these parameters on the yield stress (designated as structural limit stress in this work), the viscosity and the structural recovery rate (i.e., the change in dynamic viscosity with time at rest) were studied. In parallel, the changes in ion composition of the carrier liquid, mineral phase content and granulometry were investigated. The results reveal that all investigated rheological parameters exhibit an approximated bi-linear trend with respect to the degree of hydration, with a period of quasi-constant properties until a degree of hydration of approximately 0.07, followed by a non-linear increase. This increase could be attributed to the formation of calcium hydroxide (CH) and calcium-silicate-hydrate (C-S-H) via calorimetry results. With regard to the effect of the shear history of the sample on the rheological properties, the structural limit stress showed a minor dependency on the shear history immediately after the end of shearing, which, however, vanished within the first minute at rest. The same is true for the structural recovery rate. The presented results give detailed insights into the influences of hydration and shear on the rheological properties—especially the thixotropy—of fresh cement pastes

Characterization data of reference cement CEM III/A 42.5N used for priority program DFG SPP 2005 “Opus Fluidum Futurum – Rheology of reactive, multiscale, multiphase construction materials”

Two types of cements were selected as the reference cement in the priority program 2005 of the German Research Foundation (DFG SPP 2005). A thorough characterization of CEM I 42.5 R has been made in a recent publication [1]. In this paper, the characterization data of the other reference cement CEM III/A 42.5 N are presented from the aspects of chemical and mineralogical compositions as well as physical and chemical properties. The characterization data of the slag, which is the second main constituent of this specific cement besides the clinker, are presented independently. For all data received, the mean values and the corresponding errors were calculated. The data shall be used for the ongoing research within the priority program. Also, researchers from outside this priority program can benefit from these data if the same materials are used

Evolution of the particle size distribution of tricalcium silicate during hydration by synchrotron X-ray nano-tomography

International audienceThe particle size distribution of tricalcium silicate (C 3 S) is essential for the modelling of early C 3 S hydration kinetics. In this study, this parameter is analysed during the main hydration period until the first 20 h by synchrotron near-field ptychographic (NF-PXCT) and holographic (HXCT) computed nano-tomography. Additionally, X-ray diffraction, 29 Si NMR, thermal analysis, scanning electron microscopy, and inductively coupled plasma-optical emission spectroscopy were used to investigate the system evolution. The time-dependent pore solution composition is also provided to gain further information. HXCT and NF-PXCT show comparable values regarding the evolution of the C 3 S particle size distribution during hydration, indicating that C 3 S particles smaller than 1.3 μm are completely dissolved after 20 h of hydration. The results can be reasonably reproduced by numerical models if for all particle sizes a constant reacted rim thickness for each degree of hydration is assumed. Data on the aqueous phase composition are also provided

Evolution of the particle size distribution of tricalcium silicate during hydration by synchrotron X-ray nano-tomography

The particle size distribution of tricalcium silicate (C3S) is essential for the modelling of early C3S hydration kinetics. In this study, this parameter is analysed during the main hydration period until the first 20 h by synchrotron near-field ptychographic (NF-PXCT) and holographic (HXCT) computed nano-tomography. Additionally, X-ray diffraction, 29Si NMR, thermal analysis, scanning electron microscopy, and inductively coupled plasma-optical emission spectroscopy were used to investigate the system evolution. The time-dependent pore solution composition is also provided to gain further information. HXCT and NF-PXCT show comparable values regarding the evolution of the C3S particle size distribution during hydration, indicating that C3S particles smaller than 1.3 μm are completely dissolved after 20 h of hydration. The results can be reasonably reproduced by numerical models if for all particle sizes a constant reacted rim thickness for each degree of hydration is assumed. Data on the aqueous phase composition are also provided

Rapid Poultry Spoilage Evaluation Using Portable Fiber-Optic Raman Spectrometer

The freshness changes in poultry fillets during storage were studied using a portable fiber-optic Raman spectrometer. Poultry fillets with the same storage life (9 days) and expiry date were purchased from a local store and stored at 4 °C. Their Raman spectra were measured on a daily basis up to day 21 using a QE Pro-Raman spectrometer with a laser excitation wavelength of 785 nm. The complex spectra were analyzed using Principal Components Analysis (PCA), which resulted in a separation of the samples into three quality classes according to their freshness: fresh, semi-fresh, and spoiled. These classes were based on and similar to the information inferred from the product label on the packages of poultry fillets. The PCA loadings revealed a decrease in the protein content of the poultry meat during spoilage, an increase in the formation of free amino acids, an increase in oxidation of amino acid residues, and an increase in microbial growth on the surface of the poultry fillets, as well as revealing information about hydrophobic interaction around the aliphatic residues. Similar groupings (fresh, semi-fresh, and spoiled) were also obtained from the results of an Agglomerative Hierarchical Cluster Analysis (AHCA) of the first five principal components. The results allow the conclusion that the portable fiber-optic Raman spectrometer can be used as a reliable and fast method for real-time freshness evaluation of poultry during storage