Use of calorimetry and thermal analysis to assess the heat of supplementary cementitious materials during the hydration of composite cementitious binders

Journal of Thermal Analysis and Calorimetry - The present paper focuses on the suitability, variability and versatility of thermal analysis and calorimetry methods in the study of cement hydration...     

Thermomechanical treatment of two Ecuadorian zeolite-rich tuffs and their potential usage as supplementary cementitious materials

Two Ecuadorian zeolite-rich tuffs, coded as Zeo1 (Mordenite) and Zeo2 (Clinoptilolite–Heulandite–Mordenite), were treated and used as supplementary cementitious materials (SCM) so as to study the effect of the thermal and mechanical treatments on pozzolanic reaction in mortars. The treatment was carried out by means of thermomechanical process according to a central composite-blocked cube-star experimental design. In this experimental design as independent factors the milling time (48, 60, 90, 120 and 132 min) and the heating temperatures (559, 600, 700, 800 and 841 °C) were used but keeping a constant heating time (5 h), and zeolite-rich tuffs as experimental blocks. The proportion of SCM was kept constant i.e. 15 %. On the other hand, the compressive strength, fixed lime, normalized water in hydrates and mg Ca(OH)₂ per mg Cement at 7, 28 and 45 days, as well as hydration products related to dehydration degree of the zeolitic tuffs (DOD) were used as dependent factors. In addition, Quantitative and High-temperature chamber XRD, TG-DSC, particle size distribution and SEM-EDS were also carried out. The most significant factor was calcination leading to increase in the compressive strength compared to control, but just up to 800 °C because of recrystallization. As a conclusion, a meaningful loss of crystal structure of zeolites was not observed; but instead, the treatment could only lead to removing the water in cages and voids, thus improving the reaction with Ca(OH)₂, producing more hydrates. In addition, lime was not only fixed by pozzolanic reaction, but also by carbonation.     

Microcalorimetric studies of some cementitious materials

The Al doped tricalcium silicate hydration in the presence of active silica was studied by means of calorimetry, DTA, TG, XRD and conductometry of the hydrating suspension.

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Zusammenfassung Mittels Kalorimetrie, DTA, TG, Röntgendiffraktion und Konduktometrie der Hydratierungssuspension wurde in Gegenwart von aktivem Silizium-dioxid die Hydratation von mit Al versetztem Tricalciumsilikat untersucht.

     

Sample stacking in capillary zone electrophoresis: principles, advantages and limitations

The principles of stacking procedures are described and their properties are discussed, including the fundamentals of the behavior of zone boundaries and the consequences of the self-correcting properties of boundaries in moving boundary electrophoresis, isotachophoresis, and zone electrophoresis. Further, the diverse possibilities of stacking procedures and the unavoidable destacking are described, and several examples of practically applied stacking procedures are given, besides many references to applications. Some limitations in the use of stacking procedures are discussed. The paper is arranged in such a way that it can serve both as an introduction into the field and as a reference overview.     

Method development by an expert system advantages and limitations

Several approaches can be used for the prediction of the optimum eluent composition in RP-HPLC, but only a few are known that use the structure of the solute. The latest release of the computer program EluEx, version 3.0, was developed to help the chromatographer in practical work. The program is based on the prediction of the pK_a and log P (logarithm of 1-octanol-water partition coefficient) values of the solutes. The first eluent suggestion can be done without any preliminary practical work, based on the structural formulae of the solutes. In our experience, two or three experiments are usually sufficient to determine the optimized binary conditions. The surface heterogeneity and the diversity of RP columns, such as the effect of silanol interaction, can be handled by the program only to a limited extent. If the difference in hydrophobicity between two compounds is small, the elution order cannot be predicted properly in all instances. The same is true for some isomers, e.g., diastereomers. In this paper, the results of applying the program to some neutral, acidic and basic solutes are summarized.     

Pozzolanic reactivity of the supplementary cementitious material pitchstone fines by thermogravimetric analysis

Thermogravimetric (TG) analysis was applied to the characterisation of the pozzolanic reaction in mortars containing the supplementary cementitious materials (SCMs) pitchstone fines (PF) and fly ash (FA) as partial replacements for Portland cement (PC). TG analysis was used to determine the proportion of calcium hydroxide (CH) present from the hydration of the PC based on the dehydroxylation of the CH present in the blended PC-SCM mortars. The consumption of CH indicated that both SCMs underwent the pozzolanic reaction and that PF was found to compare favourably in its pozzolanic reactivity of FA, the industry and globally accepted standard artificial pozzolan.     

Crossed affino-immunoelectrophoresis or affino-blotting with lectins: advantages and limitations for glycoprotein studies

In contrast to the conventional combination of physical, chemical and enzymatic methods used for a structural analysis of glycans in glycoproteins, alternative methods involve affinity electrophoresis as a tool for the detection, characterization, and quantitation of glycoproteins and their carbohydrate moiety, owing to interactions with lectins. Two major approaches involve (i) crossed affino-immunoelectrophoresis and variations thereof, whereby lectin/glycoprotein interactions occur during the electrophoretic runs, or (ii) affino-blotting, where the glycoproteins are electrophoretically separated and then immobilized onto a solid support prior to their interaction with lectins. A critical comparison of these two series of techniques is the scope of the present paper. These techniques are of high interest by virtue of their ability at differentiating a classical glycan structure from unusual oligosaccharide side chains. The former structures will usually be qualitatively and quantitatively described with the easy and fast procedures as well as the simple equipment required for crossed affino-immunoelectrophoresis or affino-blotting, whereas the latter will be good candidates for further structural analyses.     

Gas chromatography-high-resolution time-of-flight mass spectrometry in pesticide residue analysis: advantages and limitations

In this study, 20 modern pesticides representing various chemical classes with a broad range of physico-chemical properties were selected for demonstration of applicability of exact mass orthogonal acceleration time-of-flight (TOF) mass spectrometer GCT (Micromass, UK) in GC analysis of their residues in purified peach extracts. The influence of experimental chromatographic conditions as well as various detector settings and data processing strategies on the performance characteristics of analytical procedure achieved during optimisation process were critically discussed. As documented in this study unbiased identification and reliable quantification of target analytes is possible due to: (i) application of narrow mass window (0.02-0.05 Da) for extracting analytical ions; (ii) availability of full spectral information even at very low levels of target analytes. With only a few exceptions, the limits of quantification for most of the pesticides involved in this study were fair below 0.01 mg/kg level, which represents the maximum EU residue limit set recently for pesticide residues in cereal-based foods and baby foods for infants and young children.     

Thermogravimetrical analysis for monitoring carbonation of cementitious materials

Cement paste carbonation, i.e., the reaction between CO₂ and the hydrated cement phases, mainly calcium hydroxide or portlandite, can lead to a pH decrease, which in turn can give rise to steel corrosion in reinforced concrete. At the same time, the carbonation reaction contributes to combine CO₂ and fix it as calcium carbonate. It is a crucial phenomenon from the point of view of structure durability and also for cement-based materials sustainability. Cement paste specimens with two w/c ratios and eight types of cements were submitted to different environmental conditions for 4?years and the evolution of calcium carbonate formed or carbon dioxide bound was followed by TG performed in inert atmosphere. The amounts of calcium hydroxide, evaporable and C?CS?CH gel water were also measured. The CO₂ bound follows the same trend in all samples and environments: at the beginning there is a sharp increase followed by a very slow stretch and reaching a maximum after less than 2?years in most cases. The calcium hydroxide amounts evolve very differently in each environment. While outside it is almost consumed after 1?year, inside there is a decrease in the first year, but an increase in the next 3?years. The behavior of the C?CS?CH water in both environments is similar to that of the portlandite inside. The evaporable water diminishes in all cases to 1?%. From the data obtained by TG, the quantification of the C?CS?CH gel as well as the calculation of the Ca/Si ratio and the hydration of the gel formed by different type of binders has been possible.     

Calorimetric studies of cementitious materials — chromium interaction

Cementitious systems based on portland cement are used for immobilization of toxic and hazardous wastes. The addition of waste material may impact the hydration reaction in cement matrix and consequently the setting and hardening process. The progress of reaction can be monitored by heat evolution measurements and the calorimetric results can indicate the declination from standard behaviour.In this study the microcalorimetry was used to evaluate the heat output during the hydration of cements in the presence of different chromium containing salts, viz. CrCl₃, Cr₂(SO₄)₃, Na₂CrO₄ and K₂CrO₄.     

Application and limitations of the flexural creep test for polymeric materials

Application and limitations of the flexural creep test are described. For this purpose six different thermoplastic materials are tested under low and moderate stress and temperature conditions. The log-log method and a nonlinear creep compliance is used to analyze and compare the data. In order to assess the applicability range of elementary small deflection theory in calculation of strain values, a large deflection analysis is performed. This analysis indicates the presence of an instability condition. Design curves are drawn to reveal the percentage difference between the deflection values obtained on the basis of small and large deflection theories.     

Aurivillius-type ceramics, a class of high temperature piezoelectric materials: Drawbacks, advantages and trends

The obtention of reliable and high performance piezoelectric ceramics for uses at high temperatures is still an open issue in the field of electroceramics. The materials used nowadays for such applications present limitations due to different causes: low piezoelectric coefficients, difficulties in processing that lead to the necessary use of single crystals, high cost of raw materials and more. In this sense, an increasing interest in materials with the so-called Aurivillius-type structure has occurred during recent years, due to their relatively high piezoelectric coefficients and high ferro–paraelectric phase transition temperature. However, some difficulties must be overcome, such as processing for obtaining highly dense ceramics and determining their real piezoelectric behaviour at high temperature. In this work, a review of the processing and properties of ceramics with this structure is shown. Effects of the use of precursors obtained by an alternative route mechanical activation on the microstructure are explained. A complete piezoelectric characterization at working temperatures (>300 °C), barely found in the literature, is also shown. The effects of trapped charges in the dielectric permittivity and in the piezoelectric radial resonance are also discussed.     

Liquid triarylamines: the scope and limitations of Piers-Rubinsztajn conditions for obtaining triarylamine-siloxane hybrid materials

New liquid triarylamine-siloxane hybrid materials are produced using the Piers-Rubinsztajn reaction. Under mild conditions, liquid analogues of conventional and commonly crystalline triarylamines are easily synthesized from readily available or accessible intermediates. Using a diverse selection of triarylamines, we explored the effects of siloxane group and substitution pattern on the physical properties of these materials, and we have demonstrated that relatively large molecular liquids with desirable electrochemical properties can be produced. The interactions between the strongly Lewis acidic catalyst used for this transformation, tris(pentafluorophenyl)borane (BCF), and the Lewis basic triarylamine substrates were studied. Through UV-vis-NIR and (19)F NMR spectroscopy, we have proposed that the catalyst undergoes a reversible redox reaction with the substrates to produce a charge transfer complex. The formation of this charge transfer complex is sensitive to the oxidation potential of the triarylamine and can greatly affect the kinetics of the Piers-Rubinsztajn reaction.     

Influence of Cu powders on the properties and characteristics of nano-MgO based aluminate cementitious materials

From the perspective of practical application, the development of desirable thermal and mechanical performance of solid sensible materials for thermal energy storage (TES) is highly needed. Here, we report the improved properties of nano-MgO optimized aluminate cementitious materials incorporated with Cu powders for TES. The composite TES materials were heated at 105, 350, and 900 °C, respectively. The results show that as the Cu powders content increases the thermal conductivity and volume heat capacity significantly increase, but there is a gradual decrease in compressive strength. Through the characterizations such as calorimetric test, XRD, FESEM, TG-DSC, and MIP, a significant feature of mass compensation also has been obtained, which might result from the oxidation reaction of the Cu powder at elevated temperatures.     

Structural heterogeneity in elastic and glassy polymeric materials revealed by positron annihilation and other supplementary techniques

Elastic and glassy polymers are normally considered as homogeneous disordered materials with unimodal (statistical) distribution of elementary free volumes. In this work, we discuss the results of our positron annihilation lifetime (PAL) measurements for a number of elastic and glassy polymers, where observations of the two long-lived ortho-positronium components in the PAL spectra and irregular (nonlinear) variations of annihilation characteristics in the vicinity of glass transition temperature reveal structural heterogeneity of these systems. The conclusion is confirmed by measurements of thermo-stimulated luminescence, thermo-mechanics and mobility of penetrants.     

Determination of the optimum parameters in the high resolution thermogravimetric analysis (HRTG) for cementitious materials

In this article, the methodology to implementation of high resolution thermogravimetric analysis (HRTG) for construction materials like Portland cement pastes is presented. The aim of this technique is to make easier the identification of the decomposition reactions that frequently are overlapping on conventional thermogravimetric analysis (TG) like is the case of some mineral phases in the cement pastes. The optimum parameters related to sample mass and purge flow gas were established. It is necessary carried out the analysis with high quantity of sample (60 mg in this case) and without purge gas in order to get better results and excellent reproducibility. The tests have average heating rate higher than 3 °C min⁻¹ in the temperature range studied (35–300 °C), showing that the HRTG is not time-expensive technique.     

One-dimensional (1D) nanostructured and nanocomposited LiFePO4: its perspective advantages for cathode materials of lithium ion batteries

Nanostructured materials have attracted recent research interest as battery materials due to their expected enhancement of properties. The characteristic nanoscale dimension and its structuring guarantees improved charge and mass transfer during charge/discharge processes. Among the potential cathode materials investigated as a substitute to LiCoO(2), one of the most promising materials is LiFePO(4) with olivine structure (LFP). In this perspective article, the current research and development in the synthesis and electrochemical studies of nanostructured LFP are reviewed with a special emphasis on one-dimensional (1D) nanostructures and nanocompositing with 1D conductive materials. In addition to various examples of 1D LFP with detailed synthetic methods, why 1D nanostructures could be meaningful is discussed in terms of a geometric point of view and the anisotropic lithiation/de-lithiation mechanism of LFP.