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Abstract
Water, magnesium acetate, magnesium chloride, acetic acid and hydrochloric acid were used as hydrating agents for an industrially obtained MgO sample. The influence of these different hydrating agents on the pH of the hydrating solution, degree of hydration to Mg(OH)2, and product surface area was studied as a function of the temperature of hydration. When compared to the hydration in water, all hydrating agents improved the degree of hydration between 5 and 50% at all temperatures. MgCl2 and a mixture of HCl and Mg(CH3COO)2 seemed to be the most effective hydrating agents below 60C, while at temperatures above 60C Mg(CH3COO)2 formed the largest percentage Mg(OH)2. Mg(CH3COO)2 was the hydrating agent that showed the strongest temperature dependence. The mechanism of the hydration reaction seems to be dependent of the availability of Mg2+ ions and the increased formation of Mg(OH)2 as temperature increases.
The hydration of C3A with and without CaCO3 was studied. The techniques used were X-ray diffraction, thermogravimetry, differential thermogravimetry and calorimetry.
Abstract
The hydration of β-Ca2SiO4 stabilized by thermal treatment and barium addition was studied in CaCl2, Ca(NO3)2 and BaCl2 solutions. The heat evolution kinetics was followed by calorimetry. A considerable acceleration of the hydration process was found in the presence of electrolytes. The positive influence of barium ions was confirmed. The highest total heat output during the 3-day hydration was found for samples doped with 3 mole % BaO.
Abstract
This paper presents results of thermokinetic studies on the early stages of hydration of some slag minerals, slag alkaline binders of traditional and new-generation compounds. A possibility of adjustment and control of hardening processes through thermokinetic indices of hydration (intensity and completeness of heat evolution) for various compounds, types and quantities of the alkaline components and temperatures is proved.
1962 Geometry of structures consisting of water molecules in hydrated crystals J. Struct. Chem. 3 206 226 . J
The hydration processes of mixtures containing calcined gypsum, blastfurnace slag or fly ash, portland cement and/or hydrated lime, able to generate calcium trisulphoaluminate and silicate hydrates, have been studied by means of differential thermal analysis. Samples were aged at 55°,70° and 85°C for 16, 24 and 48 hours, followed by a further curing at room temperature and humidity up to 28 days.
Abstract
Thermogravimetry (TG) and derivative thermogravimetry (DTG) have been used by the authors as very effective tools to study hydration steps of cements used for solidification/stabilization of tanning wastes. The present paper presents a method which was applied to separate the peaks shown by DTG curves of type II Portland cement pastes, analyzed at different times during the first 4 weeks of setting. Through a specific software a more detailed study of the evolution of the cement hydration may be done, which allows the measurement of the amount of hydrated water present in tobermorite gel as well as in ettringite, which are the main phases formed from the original components of the cement. The number of moles of water present in the ettringite phase calculated by the method is in very good agreement with the values found in the literature, validating the method to calculate the same parameter in tobermorite gel. In the latter case the water content decreases significantly during the first day of hydration, then remains at a constant value over the rest of the analyzed period.
Abstract
The time required for maximum hydration of MgO obtained from the calcination of magnesite was determined. The MgO samples were hydrated for different time intervals in both water and magnesium acetate. A thermogravimetric analysis (TG) method was used to determine the degree of hydration to Mg(OH)2. Increasing the hydration time, the degree of hydration of MgO and surface area of the formed Mg(OH)2 increased. A leveling effect was observed on the percentage Mg(OH)2 obtained from hydration in magnesium acetate, and an optimum amount of 85% was obtained after 500 min. For the hydration in water, the leveling effect was only observed after 800 min giving a maximum of 65% Mg(OH)2.
Abstract
The calorimetric data of blended shrinkage-compensating binders with different compositions were measured at 25C at different water-binder ratios using an isothermal calorimeter. The hydration characteristics of shrinkage-compensating binders were evaluated and their influence on the expansive properties of blended shrinkage-compensating binders was determined. Composition and w/b ratio significantly affect the hydration rate and degree of shrinkage-compensating binders, as well as their expansive and mechanical properties. The total heat of hydration of binders decreases with w/c ratios. Its final hydration degree also decreases with w/c ratio. The ternary binders composed with Portland cement, mineral admixture and expansive agent show low hydration heat and rate of heat evolution, but their total heat of hydration increases continuously and surpasses that of binary binder in later period at low w/b ratio.
Abstract
Computer modelling of time dependences of radon release rate during hydration of 3CaO·SiO2 was carried out. It was demonstrated that the emanation thermal analysis (ETA) can be used for the characterisation of morphology changes during hydration of Portland cement clinker minerals. The presence of various additives and increased temperature affecting kinetics of hydration were simulated by the mathematical model of the radon release rate during hydration of 3CaO·SiO2. A good agreement between the mathematical model and ETA experimental results was found.
