Solid State Phenomena Vol. 321

Abstract: One of the main characteristics in the concreting of massive waterproof structures and dam bodies is the prediction of crack formation. This prediction is associated with an understanding of the mechanics of development of hydration temperatures that affect in particular the selected binder parts of concrete. A suitable combination of cement with mineral admixtures, as well as the use of so-called shrinkage-reducing admixtures, seems to be an effective tool for influencing the dynamics of development and maximum values of hydration temperatures. Appropriate selection of the formula itself can significantly extend the lifetime of the mentioned structures. The paper is focused on monitoring the influence of different types of mineral admixtures on the effect of volume changes of cement pastes. The association of these volume changes with the development of hydration temperatures of these pastes was also observed. In order to minimize both of these phenomena, the possibility of using a shrinkage-reducing admixture was verified.

Abstract: Hydration of cement systems modified by nano additives requires the understanding of its mechanisms. The present research is focused on the investigation of hydration processes in cement pastes modified by multi-walled carbon nanotubes (MWCNTs) suspension. The ultrasonication method was used for homogenization of MWCNTs in the volume of an aqueous suspension. The hydration of cement pastes was assessed by the calorimetry test. The prolongation of cement hydration in case of modification by MWCNT suspension was observed. The microstructure observation by scanning electron microscopy (SEM) was performed for identification of MWCNT's dispergation in hardened cement pastes and for the observation of cement hydration products. The compressive and flexural strength were tested to evaluate the effect of MWCNT on mechanical properties of hardened cement paste.

Abstract: The continuous tightening of emission limits for the production of harmful substances into the air and the rising price of emission allowances gradually force construction material producers to limit the use of binders with a high content of Portland clinker. In the production of concrete, this is achieved by using admixtures, which make it possible to reduce Portland cement doses. However, the single European market uses a method that maximises the use of blened cements, making it easier for cement plants to meet emission limits while not reducing cement production. The performed experiment focused on the possibility of using CEM II and CEM III cements and their comparison with CEM I cement not only in terms of the physical–mechanical parameters of concrete but also in terms of the stability of concrete mixtures made from these cements. The stability of concrete mixtures was monitored using the water separation value in the pressure method. In the experiment, the relationship between water separation and physical parameters of cement was explored.

Abstract: The paper is focused on one of the most important component of Portland clinker-on the tricalcium silicate. The study reported in this article is focuses on the changes in crystallite size of synthetic tricalcium silicate obtained using solid state reaction method. Crystallite size changes are monitored during the grinding in three types of laboratory mills in two different conditions. Changing in crystallite size at various grinding time up to 120 minutes are studied with the aid of X-ray diffraction and using the Scherrer equation. It has been found that the most efficient laboratory mill in terms of speed and fineness of the material was the planetary mill.

Abstract: The alkali–silica reaction (ASR) causes internal corrosion of concrete. The aim of this work is to verify the possibility of ultrasonic method in detection of concrete internal structure changes, which were initiated by the alkali-silica reaction. For this purpose, we prepared samples that contained aggregates of two types, namely one with 98% of SiO₂ content and one with a greywacke. The dependence of ultrasonic impulse propagation velocity on the changes in the structure of mortars containing aggregates from these rocks was researched. The results of this work are not unambiguous yet and therefore it is necessary to carry out more extensive investigation with using of other methods that will allow to examine changes in the internal structure of composites more detailed.

Abstract: This work deals with the basic research and development of new technologies of cement-based invert grouting, in the recipe of which the appropriately selected secondary raw materials will be used as much as possible. This new grout will be part of a new comprehensive system for the remediation of chemically exposed building structures, such as sewers, silage pits and wastewater treatment plants. The aim of this work is to monitor the influence of the method and the degree of homogenization of the developed recipes on selected physical-mechanical properties of the injection material. For the needs of this work, several basic recipes were proposed, as well as the methodology of production of test specimens, their storage and testing. At the same time, three homogenization methods were chosen, differing in the manner and degree of implementation. The basic characteristics of grouting materials, which were monitored in this work, include the viscosity and processability of fresh material. Due to the requirement for increased resistance of the new material, the compressive strength and absorbency of the hardened test specimens 40 × 40 × 160 mm were monitored depending on the maturation time. The research results so far show that thorough homogenization has a fundamental effect on achieving the required physical-mechanical properties. The final methodology of homogenization of dry components will be used in the pre-preparation of all materials of the new chemically resistant remediation system, including the sprayed mixture.

Abstract: In this study, the process of decomposition of CaCO₃ and crystallization of CaO has been analyzed. The aim of this work is to compare behavior and changes in microstructure between different limestone samples (as geological age and origin, total porosity, hardness category). Studied samples were analyzed in high temperature chamber during the firing process by XRD analysis. With the increasing temperature, the growth of crystallites was measured and computed. In multiple samples a different behavior in these properties was observed. Further analysis studied different temperatures of the end of decomposition of CaCO₃ and the beginning of formation of CaO in soft-porous and hard-recrystallized limestones.

Abstract: The paper presents the results of studies of the structure and properties of a fluorohydrite binder modified by a chrysotile nanotubes dispersion in a medium of calcium nitrate solution. It is shown that addition of this modifier into the anhydrite composition leads to a 106-fold decrease in electrical resistance. Microstructural analysis of the fluorohydrite composition showed changes in the morphology of new formations with the creation of crystalline hydrates of increased density. The presence of elongated nanocrystals on the surface of the hardened matrix was noted. In addition, IR spectrum absorption lines, prove the presence of calcium nitrate in the pore space of the composition, which contributes to a significant decrease in the electrical resistance of the developed composite.

Abstract: Research of alkali-activated materials and geopolymers suggests their increased ability to transfer the electric charge thus indicating their suitability for self-sensing and other multifunctional composites. In this paper, the electrical properties of metakaolin geopolymer are enhanced by the incorporated steel microfibres that also improve the mechanical and fractural properties of the composite. Selected electrical properties of metakaolin geopolymer mortars with steel microfibres (up to 30 % of metakaolin wt.) were assessed via impedance spectroscopy analysis and followed by testing their compressive and flexural strength. Mercury intrusion porosimetry and SEM imaging enabled to characterize the binder microstructure and quality of fibre-matrix bonding.