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]. Calorimetric studies of Portland cement [ 1 , 2 ] and calcium aluminate cement [ 3 , 4 ] pastes show that the FCC catalyst remarkably influences the hydration of various cements. It has been found that, in the compositions with Portland cement, the FCC
Introduction Calcium aluminate cements are hydraulic binders of special properties and applications. They are mainly applied in production of fire-resistant materials but this kind of cement is also useful in cases when
Introduction Calcium aluminate cement (CAC) is known as an indispensable material in the construction field for its resistance to chemical attack and high temperatures [ 1 ]. In the dry-mix mortar industry, such as self
Abstract
The use of by-product gypsum is an important alternative in concrete design. In present experiment, conduction calorimetry was applied to investigate the early hydration of calcium aluminate cement (CAC)/flue gas desulfurization (FGD) gypsum paste, supplemented with the determination of setting times and analysis of hydrates by X-ray diffraction (XRD). It was found that different profiles of heat evolution rate were presented depending on the CAC/FGD gypsum ratio. Two distinct exothermic peaks, associating with CAC hydration and ettringite formation respectively, appeared when the FGD gypsum content was less than 20%. Hydrate barrier mechanism was introduced to explain the difference in induction periods of the pastes with or without FGD gypsum. It is concluded that the blending of FGD gypsum accelerates the hydration of CAC for the quick formation of ettringite and generates greater hydration heat from per gram of pure CAC for the high exothermic effect of ettringite formation. The dissolution and diffusion of gypsum plays an important role of reacting controller during the hydrations of the pastes with FGD gypsum. The modified hydration process and mechanism in this case is well visualized by means of calorimetry.
Abstract
To use flue gas desulfurization (FGD) gypsum and limestone as supplement of cement, conduction calorimetry was applied to investigate the early hydration of ternary binder of calcium aluminate cement (CAC), Portland-limestone cement (PLC), and FGD gypsum, supplemented with the determination of setting times and X-ray diffraction (XRD) analysis. Different exothermal profiles were presented in two groups of pastes, in which one group (group A) sets the mass ratio of FGD gypsum/CAC at 0.25 and the other group (group B) sets the mass ratio of PLC/CAC at 0.25. Besides the two common exothermal peaks in cement hydration, a third exothermal peak appears in the pastes with 5–15% FGD gypsum after gypsum is depleted. It is found that not PLC but FGD gypsum plays the key role in such ternary binder where the reaction of ettringite formation dominates the hydration process. PLC accelerates the hydration of ternary binder, which mainly attributes to the nucleating effect of fine limestone particles and PC clinker. The modified hydration process and mechanism in this case is well visualized by the means of calorimetry and it helps us to optimize such design of ternary cementitious material.
Introduction Calcium aluminate cements (CACs) are quickly hardening hydraulic binders, which significantly differ in their chemical and phase compositions, properties and applications from often used Portland cements. They
Abstract
The most widely identified degradation process suffered by calcium aluminate cement (CAC) is the so-called conversion of hexagonal calcium aluminate hydrate to cubic form. This conversion is usually followed by an increase in porosity determined by the different densities of these hydrates and the subsequent loss of strength. Mixes of calcium aluminate cement (CAC) and silica fume (SF) or fly ash (FA) represent an interesting alternative for the stabilization of CAC hydrates, which might be attributed to a microstructure based mainly on aluminosilicates. This paper deals with the microstructure of cement pastes fabricated with mixtures CAC-SF and CAC-FA and its evolution over time. Thermal analysis (DTA/TG), X-ray diffraction (XRD) and mid-infrared spectroscopy (FTIR) have been used to assess the microstructure of these formulations.
Calorimetry in the studies of cement hydration
Setting and hardening of Portland cement–calcium aluminate cement mixtures
Abstract
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.
Abstract
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.
Abstract
The aim of this work is to compare the influence of addition of waste aluminosilicate catalyst on the initial periods of hydration of different cements, i.e. calcium aluminate cements of different composition and Portland cement, basing on the calorimetric studies. Cement pastes containing up to 25 mass% of additive were studied, where the water/(cement+additive) ratio was 0.5. An attempt was undertaken to explain the mechanism of action of introduced aluminosilicate in the system of hydrating cement, particularly in the case of calcium aluminate cement pastes. It was found that the presence of fine-grained additive caused in all studied cases the increase of the amount of released heat in the first period after the addition of water. In the case of aluminate cements with aluminosilicate addition, a significant reduction of induction time and faster precipitation of hydration products were observed compared to the reference sample (without additive). In the experimental conditions, the additive caused the acceleration of aluminate cements hydration, and the mechanism of its action is probably complex and can encompass: nucleative action of small grains and formation of new chemical compounds.
