Karel Kulísek

The compressive strength of samples containing fly ash with high content of calcium sulfate and calcium oxide

Abstract Influence of composition of solid samples with fluidized bed combustion product, two types of cement binders and NaCl (as a chosen additive) on the compressive strength and the characteristics of microstructure of samples after 2 years of hardening were studied. NaCl causes marked increase of compressive strength after 28, 360 and 720 days of hardening. After 720 days of hardening the following detectable products of hydration are present in the samples: gypsum, portlandite, ettringite, hydroxylellestadite (Hexel — Ca 10 (SiO 4 ) 3 (SO 4 ) 3 (OH) 2 ). Relationships between characteristics of X-ray diffraction analysis and compressive strength of specimens after 720 days were found.

Influence of MSFC-type dispersant composition on the performance of soluble anhydrite binders

Abstract Synthetic soluble anhydrite binders, fluidized with melamine–sulfonate–formaldehyde condensates (MSFC), were investigated by rheological, calorimetric, mechanical and adsorption methods. The degree of sulfonation of the MSFC was found to be a key parameter in dictating its performance as a dispersant. A higher degree of sulfonation reduces the shear yield stress of the binder at early ages (20 min after mixing) but also reduces the subsequent rate of strength development.

Effect of Fluidized Bed Ash on the Thermodynamic Stability of Hydraulic Binders

Fluidized bed ash, which is the youngest industrial waste can be considered on the basis of research, a high-quality secondary raw material base which can be easily used in the production of Portland cements and, in general, other hydraulic binders. Regarding the direct effect of anhydrite on the course of hydrating mixed cement with the fluidized fly ash and the consequent behaviour of the originated cement stone, its reaction with clinker materials on the mentioned Aft (Al2O3–Fe2O3-–tri) phase is clear. The creation of AFt phases, if they originate additionally, due to their morphology, is accompanied by significant volume changes which may lead to deformation up to the destruction of the cement stone. Some foreign publications show the possibility of the transformation of this thermo-dynamically unstable mineral into the further mineral from the group AFt phase, which is thaumasite, Ca3Si (CO3)(SO4)(OH)6.12H2O.

The Use of FBC Fly Ash in the Preparation of Portland Cement Clinker

The present work focuses on the use of fluid fly ash for Portland clinker burning. Fluid ashes are carriers of all basic oxides represented in the cement raw meal. However, while the share of hydraulic oxides is in ashes sufficient, there is a significant deficiency in calcium oxide content. Preliminary studies have shown that the combination thereof with calcite as the second essential component of the fluid fly-ashes for the raw material based on Portland clinker burning application, it is necessary to solve a problematic issues. The first one concerns the potential leakage SOx resulting from decomposition of CaSO4 ash into the atmosphere. The second circumstance is the correction tracks raw meal in order to redistribute in the samples prepared under the initial studies, the obtained clinker minerals content in favor of calcium silicate, of them further in favor of alite. The last issue is the evaluation of the impact of fluid utilization of fly ash as a partial raw material bases for reducing CO2 emissions in the Portland clinker burning.

Belit Cement Based on Concrete Recyclate

Main phase of belite cement is β-C2S. This modification is distinguished by low hydration speed compared to alite, which is main mineral of commonly produced cement. It is possible to increase the low hydration speed by modification of raw mixture by potassic ions, which basically change the belite structure. It leads to the content increase of internal free energy and therefore its reactivity too. Positioning of potassic ions in produced clinker is solved by combined burning.

Thermodynamic Stability of Ettringite Formed by Hydration of Ye’elimite Clinker

In order to save limited natural resources by utilising industrial by-products, this paper focuses on an entirely new application of fluidized bed combustion fly ash (FBCFA) into Portland composite cements. It is not currently used because undesirable ettringite, 3CaO·Al2O3·3CaSO4·32H2O, is formed during the hydration of FBCFA. Although the stability of ettringite has been the subject of much research, the solution is not yet fully clear. Ettringite is generally considered to be stable up to a temperature of 110°C; however, some investigators claimed that ettringite may already decompose at even ambient temperatures. To prove these statements, ettringite was prepared by the hydration of ye’elimite, 3CaO·3Al2O3·CaSO4, and the system stored at laboratory temperature in two environments: in laboratory settings and in an environment of saturated water vapour. The mineralogical composition of ettringite was long term (up to 160 days of hydration) and was analysed by X-ray diffraction (XRD) and differential thermal analysis (DTA). The hydration of ye’elimite is a relatively complex process. Only approximately 30% of ettringite was formed under laboratory conditions that appeared to gradually convert into metaettringite. Within an environment of saturated water vapour, we observed the conversion of ettringite into monosulfate. Original ye’elimite was indicated as the dominant phase of both storages.

Synthesis of Ettringite

The exposure of cement to high concentration of sulphate anions for a prolonged time period can lead to the formation of secondary ettringite and thaumasite. The preparation of synthetic ettringite is described in this paper.

Synthesis of Pure Thaumasite

In this work, synthesis procedures to obtain thaumasite and different influences on its formation were revised. Theoretical background is compiled in this paper from published sources with focus on synthesis of pure thaumasite in laboratory environment.

Proposal and Testing Masonry Cement

This work deals with proposal and testing of cement mixtures normative called as Bricking cement. The norm demanded properties were tested on these cement mixtures depending on amount and type of used chemical admixtures. Technically it is possible to define this mixture binder as premix binder for ambulatory preparation of mortar and plaster admixtures.

The Use of Anthracite Fly Ash for the Production of Autoclaved Aerated Concrete

Burning high-quality anthracite coal produces ash with a high content of unburned residues, which in many cases permanently exceeds 20%. These ashes usually contain high levels of amorphous phase providing the pozzolanic activity, this making them particularly useful if potentially applied in the construction industry. Such potential of effective treatment necessitates reducing the content of unburned residues, the best level here being less than 4% w/w. This paper deals with the results of testing heat treatment of fly ashes particularly using the resources of eastern Slovakia. Tests have shown that tested process of heat treatment can safely reduce the content of unburned residues in fly ash whilst maintaining high levels of the glass phase. Raw materials thus modified meet the requirements for the use in cellular concrete production technology with beneficial use of exothermic reaction heat from fly ash treatment in pre-heating the autoclaves.