Solid State Phenomena Vol. 296

Abstract: Nowadays, the colouring is used in wide range of architectural concrete. Therefore, determination efficiency of pigments in case of particular combination of input materials is necessary. The research deals with influence of concentration of liquid inorganic pigments on the resulting colour of cement mortars. Two liquid pigments (yellow, red) were used for measurement purposes to verify their optimal ratio to achieve the best colouring of cement specimens. Pigments were mixed in the mortars of two types of cements used for architectural and decorative design. The colour change was determined using Konica Minolta spectrophotometer in colour space CIE Lab (1976). General definition of deviation in the colour space ΔELab was applied for calculating of colour deviation. From the results of the laboratory tests is obvious that significant change of the colour of cement specimens do not show between the concentration of 6% and 9% of the pigment per cement weight yet. Consequently, using of high ratio of pigment than 9% is not profitable neither for purchaser, nor builder. Future research will focus on trials with a more elaborate share of pigment and it will have importance for price optimization in the construction industry.

Abstract: Cement production belongs to the most important branch of industry. It is marked out by processing of great quantity of natural raw materials and of considerable energetic demand. Not only the intensification of the contemporary production processes is the permanent effort of the cement industry, but also the search for new energy less demanding methods. The paper is focused on one of the most important components of the intensification of cement production – on the preparation of raw meal. It mainly deals with the influence of granulometry and microhomogeneity of the input raw materials on the quality and economy of the process of production and on the final product. The study was carried out mainly by methods of optical microscopy and the determination of technological parameters of cements. It has been found that a change in granulometry of raw meal has a significant impact on the formation rate of the clinker phases. Subsequently, the grindability of the clinker and the strength of the cement are influenced, especially in the short-term hydration. Change of granulometry and homogeneity of raw meal can greatly optimize the quality and economy of the cement production process.

Abstract: This paper deals with hydrothermal stability of inorganic aluminosilicate polymers, which were prepared by mixing blast furnace slag, fly ash and cement kiln dust in ratio 4:2:1. Cement kiln dust was used as alkaline activator with 4M sodium hydroxide solution. Samples were cured under hydrothermal conditions up to 170 °C for 24h and changes in mechanical properties, phase composition and porosity were monitored. During the hydrothermal process, the formation of zeolite from cancrinite group was monitored. The effect of the change of composition on the thermal expansion/shrinkage was studied by thermal dilatometry. Autoclaved samples were subjected to significant irreversible shrinkage during heating to 900 °C.

Abstract: Significant reduction of carbon footprint of the construction industry is achieved through the use of composite Portland cements. However, substitution levels of additives in the composite cements are limited due to slow strength development arising from low reactivity of the pozzolana compared to clinker phases especially at the early age. The aim of the study was to evaluate effect of nanosilica on formation of strength properties and structure at the early age. The Portland composite cement containing clinker, granulated blast furnace slag, zeolite tuff as natural pozzolana and limestone with additives of nanosilica, Na₂SO₄ and polycarboxylate ether was investigated. The results obtained with the help of PSD, XRD, DTA, TG and SEM techniques showed that addition into the cement paste of the nanosilica particles with high surface reactivity improved the composite cement microstructure and leaching of calcium became significantly lower, because nanosilica particles react with calcium hydroxide with the formation of a denser C-S-H gel at the early age of hardening.

Abstract: Many years of experience in practice not only in the Czech Republic but also around the world have shown that crystallising waterproofing technology (mortars, coatings) improves the water and water-vapor impermeability of the treated structures and thus positively affects the durability of concrete. The sealing of pores, capillaries and cracks also prevents degradation due to physical and mechanical structural actions (e.g. the effects of ice and salts in pores, etc.). In the presented research, the influence of different crystallization admixture (CA) contents on the mechanical properties of polymer-cement mortar with 24% cement substitution by waste limestone was investigated. The crystallization admixture (CA) was added in different amounts at 0.8, 1.6 and 2.4% of the cement content in the mix. It was determined that the mechanical properties, namely the compressive and flexural strengths were not significantly influenced by the CA addition, with the highest difference recorded in the compressive strength (7%). The cohesion with the base concrete containing different amounts of limestone was sufficient, and the bond of the mortar to concrete was also closely examined using scanning electron microscopy (SEM). Through the SEM investigation it was determined that the presence of waste limestone of particle size below 250 μm did not affect the formation of crystals during the proper hydration process, in a climatic chamber at a high relative humidity (99%).

Abstract: Cement hydration is a chemical reaction that is associated with the development of hydration heat and changes in the volume of input components that transit from the solid and liquid phase to one homogeneous whole. In order to eliminate the volume changes already occurring during the hydration process, several principles can be applied, such as the use of active or inert admixtures as partial cement substitute or special shrinkage reducing additives. The experiment verifies the effect of anti-shrinkage additives on the course of hydration of cement pastes in terms of the development of hydration temperatures and elimination of volume changes of cement pastes. Volume changes will be monitored for the first 30 hours of cement mixing with water, i.e. in the time when the major changes occur due to this chemical reaction. Due to the expected hydration deceleration of the binder component by the effect of SRA, the impact of the use of these additives on the curing time of the composite and consequently on the mechanical parameters of the concrete will be verified.

Abstract: Of the existing modifications of dicalcium silicate (C₂S), the β-C₂S modification is the most important, because it is a regular constituent of Portland cement. β-C₂S is a metastable modification at all temperatures, yet it can be stabilised at ambient temperature by doping with different foreign ions into its crystalline lattice. If β-C₂S is produced in non-doped form, it is usually contaminated with variable amounts of γ-C₂S. This article deals with the preparation of β-C₂S without incorporating of different ions. The main aim of this article is to obtain β-C₂S in the purest form with the lowest amount of γ-C₂S. Stabilization of individual belite polymorphs affects many factors. For this article, one factor-cooling mode was chosen to stabilize β-C₂S.

Abstract: The paper deals with on comparison of selected properties of slag aggregate and natural aggregate in concrete. In mixtures was used as filler the slag aggregate from Koněv heap in Kladno and for comparison was used natural aggregate from Tovačov and Hrabůvka that is commonly used in concrete. The aim of this work was to verify whether this slag aggregate can be used in cement based mixtures. In the the experiment, the basic physical-mechanical parameters of both types of aggregates were determined, mixtures were proposed and then tested. Durability properties were also verified.

Abstract: This article deals with the preparation and laboratory milling of β-dicalcium silicate. Dicalcium silicate is the second most important calcium silicate of Portland clinker. β-C₂S is usually dominated in industrially produced clinker. Pure β-C₂S can be prepared in several ways. Traditional way is the solid phase synthesis of raw material mixture. The paper deals with the preparation of β-dicalcium silicate, which is based on the modified Wesselsky-Jensen method and with the influence of length and the technology of the milling process in 3 types of laboratory mills on the particle size, distribution and agglomeration of the synthetically prepared β-dicalcium silicate.