Heat evolution in hydrating expansive cement systems

Calorimetry was applied to follow the hydration of special cement mixtures exhibiting expansion or shrinkage compensation. The standard, common cements show generally less or more visible shrinkage on setting and hardening but mixed with and expansive agent, usually of aluminate and sulfate nature, they can exhibit the increase of volume. The calcium aluminate cement CAC 40 was ground together with special sulfate–lime sinter to produce an expansive additive to Portland cement (CEM I 42.5R). The expansive additive in the environment of hydrating cement transforms into ettringite at “right time” to give expansion before the final setting and hardening takes place. In the experiments the proportions of components of expansive mixture and basic cement were variable. The rate of hydration versus time for common cements is commonly known and reflects the moderate setting and early hardening during the first days after mixing with water (two peaks and the induction period between them). The aim of measurements presented in this study was to show the course of heat evolution curve and the heat evolved values, equivalent to the acceleration/retardation of hydration, in case of the paste with the expansive mixture, as well as the pastes produced from Portland cement and the components of expansive additives added in variable proportions. It was possible to see how the calorimetric curve and consequently the hydration process itself declines from the controlled setting/hardening. These measurements were supplied by the examples of phase composition studies by XRD.     

Calorimetry in the studies of cement hydration

Calorimetry was applied to an investigation of the early hydration of Portland cement (PC)–calcium aluminate cement (CAC) pastes. The heat evolution measurements were related to the strength tests on small cylindrical samples and standard mortar bars. Different heat-evolution profiles were observed, depending on the calcium aluminate cement/Portland cement ratio. The significant modification of Portland cement heat evolution profile within a few hours after mixing with water was observed generally in pastes containing up to 25% CAC. On the other hand the CAC hydration acceleration effect was also obtained with the 10% and 20% addition of Portland cement. As one could expect the compressive and flexural strength development was more or less changed—reduced in the presence of larger amount of the second component in the mixture, presumably because of the internal cracks generated by expansive calcium sulfoaluminate formation.     

Calorimetry in the studies of cement–Pb compounds interaction

The effect of PbO on cement hydration kinetics by calorimetric method was evaluated as a first step in this project. Substantial retardation of reaction with water at early stages with subsequent intensification of the process was found. As the next step, the model systems covering pure cement minerals and their mixtures of various composition as well as soluble Pb salts were taken into account to elucidate the mechanism of delayed, by quite good formation of products in the so-called post-induction period. The precipitation of sulphate, forming very thin impermeable layer seems to be responsible for this delaying effect in case of cement, however the other reactions of Pb compounds in alkaline environment of hydrating calcium silicate are not out of importance. In order to prove this, the studies of chemical composition in small areas were also carried out.     

Calorimetry of portland cement with silica fume and gypsum additions

The use of active mineral additions is an important alternative in concrete design. Such use is not always appropriate, however, because the heat released during hydration reactions may on occasion affect the quality of the resulting concrete and, ultimately, structural durability. The effect of adding up to 20% silica fume on two ordinary Portland cements with very different mineralogical compositions is analyzed in the present paper. Excess gypsum was added in amounts such that its percentage by mass of SO₃ came to 7.0%. The chief techniques used in this study were heat conduction calorimetry and the Frattini test, supplemented with the determination of setting times and X-ray diffraction. The results obtained showed that replacing up to 20% of Portland cement with silica fume affected the rheology of the cement paste, measured in terms of water demand for normal consistency and setting times; the magnitude and direction of these effects depended on the mineralogical composition of the clinker. Hydration reactions were also observed be stimulated by silica fume, both directly and indirectly – the latter as a result of the early and very substantial pozzolanic activity of the addition and the former because of its morphology (tiny spheres) and large BET specific surface. This translated into such a significant rise in the amounts of total heat of hydration released per gram of Portland cement at early ages, that silica fume may be regarded in some cases to cause a synergistic calorific effect with the concomitant risk of hairline cracking. The addition of excess gypsum, in turn, while prompting and attenuation of the calorimetric pattern of the resulting pastes in all cases, caused the Portland cement to generate greater heat of hydration per gram, particularly in the case of Portland cement with a high C₃A content.     

Calorimetry of Portland cement with metakaolins, quartz and gypsum additions

In this work two aluminic pozzolans (metakaolins) and a non-pozzolan were added to two Portland cements with very different mineral composition, to determine the effect on the rate of heat release and the mechanisms involved. The main analytical techniques deployed were: conduction calorimetry, pozzolanicity and XRD. The results showed that the two metakaolins induced stimulation of the hydration reactions due to the generation of pozzolanic activity at very early stage, because of their reactive alumina, Al₂O₃^r− contents, mainly. Such stimulation was found to be more specific than generic for more intense C₃A hydration than C₃S, at least at very early on into the reaction, and more so when 7.0% SO₃ was added, and for this reason, such stimulation is described as ‘indirect’ to differentiate it from the ‘direct’ variety. As a result of both stimulations, the heat of hydration released is easy to assimilate to a Synergistic Calorific Effect.     

Application of differential thermogravimetry to the hydration of expansive cement pastes

Differential thermogravimetric analysis was used to determine the hydration kinetics of expansive cement and its products at various ages of hydration. Analytical grade reagents, kaolin and Portland cement were used to prepare an expansive cement on the basis of calcium sulphoaluminate. Two mix compositions having the stoichiometric composition of trisulphate and monosulphate were synthesized from pure reagents. Three clinkers were also prepared from kaolin, gypsum and calcium carbonate with different compositions.The hydration of expansive cement prepared from the stoichiometric composition of trisulphate and Portland cement gives ettringite as the stable phase after seven days of hydration. The presence of more CaO than the stoichiometric composition of trisulphate favours the conversion of some ettringite to the monosulphate hydrate. The hydration of expansive cement prepared from the stoichiometric composition of monosulphate and Portland cement shows the presence of ettringite and the monosulphate phase. Ettringite is formed initially, and then transformed to the monosulphate form.     

Calorimetry studies of a chemical oscillatory system

The effect of putrescine (PUT) on KSCN-H₂O₂-CuSO₄-NaOH oscillating system was investigated by calorimetric method. The oscillating reaction was monitored in a closed reactor with stirring, and the result showed that the oscillating period was linearly related with putrescine concentration and the numbers of oscillation decreased with increase in putrescine concentration. When [PUT]=2.83·10⁻⁴ M, no oscillation was observed. A possible mechanism is proposed that putrescine is a scavenger of the active-oxygen species. The result of numerical simulation by a simplified mechanism consisting of 18 kinetic steps and 16 variables is consistent with the experimental findings.     

Calorimetry studies of explosion heat of non-ideal explosives

Heats of explosion of non-ideal RDX-based compositions in four various atmospheres (argon, nitrogen, air and argon/oxygen mixture) were measured. Charges of phlegmatized RDX containing 30% of two types of aluminium powders, coarse aluminium oxide, or fine lithium fluoride particles were fired in a calorimetric bomb of 5.6 dm³ in volume. The influence of inert and reactive additives and the atmosphere filling the bomb on the heat outcome was examined. To estimate the degree of afterburning of the detonation products and reactive particles, thermochemical calculations were also performed for the tested explosive compositions.     

Calorimetry and cryo-transmission electron microscopic studies of PEG2000-grafted liposomes

The phase behavior of poly(ethylene glycol) grafted liposomes (PEG-liposomes) was investigated by differential scanning calorimetry (DSC), dynamic light scattering (DLS) and cryo-transmission electron microscopy (cryo-TEM). PEG-liposomes were prepared from mixtures of dipalmitoyl phosphatidylcholine (DPPC) and distearoyl phosphatidylethanolamine with a covalently attached PEG molecular weight of 2000 (DSPE-PEG2000). From the results of DLS measurements, the coexistence of PEG-liposomes and small molecular assemblies were confirmed at mole fractions of DSPE-PEG2000 above about 0.1. Moreover, it was confirmed that small molecular assemblies were disk micelles by cryo-TEM. However, the phase transition enthalpies of PEG-liposomes were hardly changed according to the DSC measurement, though the mole fraction of the PEG lipid increased. From these results, it was suggested that the phase transition enthalpies hardly changed despite mixed micelles being formed because the bilayer structure of the disk micelle maintains high cooperativity between the DPPC molecules.     

Calorimetry studies for interaction in solid/liquid interface between the modified cellulose and divalent cation

Cellulose (Cel) was initially modified with thionyl chloride in order to increase its reactivity. In another step, chlorinated cellulose (CelCl) was reacted with ethylenediamine (CelEn) molecule. The last reaction step was reacting CelEn with ethylene sulfide molecule, yielding the solid named CelEnEs. The two last steps occur in free solvent conditions. Elemental analysis showed the incorporation of an enormous amount of chlorine in the CelCl structure, the nitrogen entrance from the ethylenediamine molecule, as well as the huge amount of sulfur that was added due to entry of the ethylene sulfide molecule. Infrared spectroscopy, thermogravimetry, and ¹³C NMR in the solid state demonstrated the effectiveness of the reaction, in which the last one has shown signals at 30 and 32 ppm for CelEnEs due to the change in the methylene group environment. Divalent metal uptake by chemically modified biopolymer gave the order Ni²⁺ > Co²⁺ > Cu²⁺ > Zn²⁺, reflecting the corresponding acidity of these cations in bonding to the sulfur and the basic nitrogen atoms available on the pendant chains. The equilibrium data were fitted to Langmuir model. The maximum monolayer adsorption capacity for the cations was found to be 5.561 ± 0.017, 4.694 ± 0.013, 1.944 ± 0.062, and 1.733 ± 0.020 mmol g^?1 for Ni²⁺, Co²⁺, Cu²⁺, and Zn²⁺, respectively. Through calorimetric titrations thermodynamic parameters could be obtained, and the results proved the favor of the interactions between cations and basic centers of modified cellulose. This new synthesized biopolymer can be used as a material for cation removal from aqueous solution.     

Rapid titrimetric methods for the determination of vanadium and molybdenum in mixtures

Summary A rapid and accurate method has been developed for the volumetric determination of molybdenum(VI) and vanadium(V) in mixtures, using cerium(IV) sulphate. In this procedure the sample solution is reduced in a mercury reductor (to give Mo^V and V^IV) and an aliquot of the reduced solution is titrated with Ce^IV solution using either ferroin, N-phenyl anthranilic acid, or barium diphenylamine sulphate as indicator. This titration gives the amount of molybdenum present, as V^IV does not interfere under the conditions applied. Another aliquot of the reduced solution is titrated with Ce^IV solution and rhodamine 6 G as indicator (observing the quenching of the fluorescence). This titration corresponds to the sum of molybdenum and vanadium. The vanadium content can be calculated by difference.

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Zusammenfassung Zur schnellen und genauen volumetrischen Bestimmung von Molybdän(VI) und Vanadium(V) in Mischungen wird Cer(IV)-sulfat als Reagens verwendet. Die Probelösung wird im Quecksilberreduktor reduziert (wobei Mo^V und V^IV gebildet werden) und ein aliquoter Teil der reduzierten Lösung wird mit Ce^IV-Lösung titriert, wobei Ferroin, N-Phenylanthranilsäure oder Bariumdiphenylaminsulfonat als Indicator dient. Aus dieser Titration erhält man den Molybdängehalt, da V^IV unter den angewendeten Bedingungen nicht stört. Ein weiterer Teil der reduzierten Lösung wird mit Ce^IV-Lösung gegen Rhodamin 6 G titriert (Endpunkt durch Fluorescenzlöschung), woraus man die Summe Mo + V erhält. Der Vanadiumgehalt ergibt sich aus der Differenz.

     

NMR methods for unravelling the spectra of complex mixtures

The main methods for the simplification of the NMR of complex mixtures by selective attenuation/suppression of the signals of certain components are presented. The application of relaxation, diffusion and PSR filters and other techniques to biological samples, pharmaceuticals, foods, living organisms and natural products are illustrated with examples.     

Reactivity of cement mixtures containing waste glass using thermal analysis

A laboratory study was undertaken to compare the performance of waste glass as a supplementary cementitious material (SCM) to traditional SCMs at the same particle size and level of replacement in both high and low alkali cement paste. The consumption of Ca(OH)₂ as measured by differential thermal analysis (DTA) is used as an indicator of reactivity. The DTA results of the pastes aged to 150 days are presented, and indicate that glass reactivity is similar to ground-granulated blast furnace slag (GGBFS) and lower than silica fume (SF) at comparable particle sizes. Alkali–silica reaction (ASR) is not present for particle sizes below 100 μm, but is induced by agglomeration of the glass particles and is observed by fluorescence in optical microscopy images. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) are used to compare the microstructural properties of the SCMs and measure the chemical composition of the reaction products. The alkalinity of the cement was found to influence the nature of composition as observed by thermal analysis, and the temperatures at which their reactions occurred.     

Dielectric studies of binary liquid-crystalline mixtures

Six binary liquid-crystalline mixtures have been studied by means of dielectric, microscopic and refractometric measurements. Induced smectic phases appear for four of them. The effective values of the components p_⊥ and p_∥ of the dipole moment per one molecule of the mixtures have been calculated from values of e_∥ and e_⊥. It has been established that the heterocomplexes formed in the mixtures are weak so that they do not cause any changes in the distribution of molecular charges. The observed deviations from linearity of the dielectric constants of the mixtures are caused either by dissociation of the cyanomesogen dimers or by a non-additive behaviour of the mixture density.     

Thermal studies of isoniazid and mixtures with rifampicin

Rifampicin–Isoniazid mixture is a frequently used product in the treatment of tuberculosis. Rifampicin exhibits polymorphism and exists in two polymorphic forms: the stable form I and the metastable form II. The aim of this work was to evaluate the thermal behavior of the binary mixtures of polymorphs I and II of rifampicin and isoniazid by using DSC. Mixtures of different forms (rifampicin form I and II) showed interaction with isoniazid indicating that the mixtures are less stable compared to the drug alone. Interaction was observed in case of both polymorphs of rifampicin.     

Ultrasonic and viscosimetric studies of samarium laurate in benzene-dimethylsulfoxide mixtures

Summary Ultrasonic and viscosity measurements of samarium laurate in benzene-DMSO mixtures of different compositions (7:3 and 1:1 V/V) have been used to determine the critical micelle concentration (CMC), soap-solvent interaction, and various acoustic parameters of the system. The values of critical micelle concentration increase with increasing amount ofDMSO in the solvent mixtures. The viscosity results have been explained on the basis of equations proposed byEinstein,Vand. Moulik, andJones-Dole. The values of CMC for samarium laurate obtained from the viscosity measurements are in agreement with the results obtained from ultrasonic measurements. The results show that the soap molecules do not aggregate appreciably below CMC; there is a marked change in the aggregation behaviour at CMC.

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Ultraschall- und Viskositätsmessungen an Samariumlaurat in Benzol-DMSO-Mischungen

Zusammenfassung Mit Hilfe von Ultraschall- und Viskositätsmessungen an Samariumlaurat in Benzol-DMSO — Mischungen verschiedener Zusammensetzung (7:3 und 1:1 v/v) wurden die kritische Micellenkonzentration (CMC), Seife-Lösungsmittel-Wechselwirkungen und verschiedene akustische Parameter des Systems bestimmt. Die Werte für die kritische Micellenkonzentration steigen mit wachsendem Anteil vonDMSO im Lösungsmittelgemisch. Die Érgebnisse der Viskositätsmessungen werden auf der Basis der Gleichungen vonEinstein,Vand,Moulik undJones-Dole erklärt. Die CMC-Werte für Samariumlaurat aus Viskositäts- und Ultraschallmessungen stimmen überein. Die Ergebnisse zeigen, daß die Seifenmoleküle bei Konzentrationen unter CMC nicht stark aggregieren; bei Erreichen des CMC-Werts tritt eine ausgeprägte Änderung im Aggregationsverhalten ein.

     

Calorimetry in the science of building materials

A new conceptual approach is proposed for evaluation of the most important properties of cement-containing composites on the basis of the rate and degree off completeness of hardening processes and study of the porous structure during material formation, within the limits of the system “composition-structure-process-property”.