Papers by Keyword: Portlandite

Abstract: In this work the peculiarities of phase formation of the cement stone at presence of nanostructured modifier of the silica composition were identified using the method of x-ray diffraction and raster electronic microscopy. Also the character of influence of modifier on the structure formation of the cement stone was defined. Polydisperse modifier with the presence of a highly active colloidal component, on the one hand, acts as a pozzolanic component, and on the other hand – as a submicron filler.

Abstract: We study the hydration and pozzolanic reactions of cement pastes made from Argentinian and Czech Portland cements as a function of age, using thermogravimetry. The measurements are done for 2, 7, 28, and 90 days cured samples in order to monitor the rate of hydration. The investigation is performed in the temperature range from 25 °C to 1000 °C with a heating rate 5 °C/min in an argon atmosphere. The mass change during the decomposition of calcium silicate hydrate gels, portlandite, and calcite are determined, and the changes in the portlandite amount are estimated in dependence on the time of hydration.

Abstract: The development of multi-scale modeling methods reveals to be of undeniable practical importance, especially to describe and predict the mechanical properties of structural materials. The present work aims to relate the atomic scale with the macro-scale performances. To this purpose a model of a crystalline structure based on the Atomic Finite Element Method (AFEM) is developed. The interatomic bonding forces of Van der Waals, the Coulomb electrostatic force and the covalent chemical bond are taken into account. It is then applied to Portlandite (CH) as well as to graphene (triple-layer graphene sheet, TLGSs). Elastic modulus of these structures based on AFEM is determined. Then, modeling of a single crystal can be traced back to the homogenized elastic properties of polycrystals. Elastic constants and elastic modulus by AFEM algorithm are in quite good agreement with literature experiment. These modeling method and algorithm provide some basic reference to other hexagonal structures.

Abstract: Limestone filler and aggregates are used widely in cement production and concrete mixing nowadays, which could be connected with thaumasite formation, and lead to a lack of durability further. This work deals with the sulfate minerals including of thaumasite, ettringite and gypsum in two types of cement pastes containing 35% w/w limestone powder immersed in MgSO₄ solution at 5°C±2°C for 15 weeks by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD). Two types of cements were used: (i) ordinary Portland cement (P·O), (ii) typeII Portland cement (P·II). Test results show that thaumasite is present in two types of cement pastes, amount of thaumasite as well as amount of portlandite reacted with external SO₄^2- in P·II cement paste are more than those in P·O cement paste. It indicates that P·II cement is more susceptible to thaumasite formation than P·O cement containing the same amount of limestone powder, and more gypsum formation could contribute to thaumasite formation possibly during the external MgSO₄ attack at low temperature.

Abstract: The objective of this study was to examine the influences of the type of cement and the CO₂ concentration on the carbonation progress of cement materials. Thermogravimetric analysis were used to follow mineralogical changes of standard CEM I and CEM II mortars which were submitted to an accelerated carbonation at 20% and 50% CO₂, 20°C and 65% relative humidity. The results indicated that the carbonation of portlandite is complete in the case of CEM II mortar while there is a persistence of residual portlandite in the case of CEM I mortar. In other words, the carbonation rate of CEM I mortar is slower than the one of CEM II mortar, which is not only because of its greater content of portlandite but also because of the coverage of portlandite crystals by newly formed calcite. These results allow us to conclude that the carbonation rate of cement mortars depends especially on the type of cement while the CO₂ concentration does not affect it at all.

Abstract: The main purpose of this work is to study the structure of Anadara granosa shell sample and its structural transformation upon heat treatments. The sample was ground and characterized as powder throughout this work. Structural identifications of all samples were characterized, and determined qualitatively by using X-ray diffraction, IR spectroscopy and thermogravimetry measurement (TGA). It was found that the specimen is made of aragonite, a common phase of CaCO3 mineral. The powder sample was annealed at specific temperatures over the range of 200°C - 900°C and the effects of heat treatment on the structure of Anadara granosa shell samples were studied. The results show that aragonite transforms to calcite at the temperatures between 200°C and 400°C and completely becomes calcite between 400-500°C. Then, the calcite transforms to calcium oxide at the temperatures between 500°C - 900°C. The exact structures and quantities of phase at different annealing temperatures were studied by Rietveld refinement. In our study, we also used IR spectroscopy and TGA to study the effect of water absorption of the samples on the phase transformation.

Abstract: The main purpose of this work is to study the structure of Anadara granosa shell sample and its structural transformation upon heat treatments. The sample was ground and characterized as powder throughout this work. Structural identifications of all samples were characterized, and determined qualitatively by using X-ray diffraction, IR spectroscopy and thermogravimetry measurement (TGA). It was found that the specimen is made of aragonite, a common phase of CaCO3 mineral. The powder sample was annealed at specific temperatures over the range of 200°C - 900°C and the effects of heat treatment on the structure of Anadara granosa shell samples were studied. The results show that aragonite transforms to calcite at the temperatures between 200°C and 400°C and completely becomes calcite between 400-500°C. Then, the calcite transforms to calcium oxide at the temperatures between 500°C - 900°C. The exact structures and quantities of phase at different annealing temperatures were studied by Rietveld refinement. In our study, we also used IR spectroscopy and TGA to study the effect of water absorption of the samples on the phase transformation.