Marcela Fridrichová

Commercially Used Sulphate Binders Based on Anhydrite

The work was devoted to the analysis of a commercially manufactured binder imported from Germany which is supposed to represent a natural anhydrite according to the accompanying documentation, industrially modified by hydration process activating agents. A similar analysis of the anhydrite binder commercially manufactured in Germany was carried out at the very beginning of investigation into the given problem. In the introductory study of applied research engaged in the feasibility of preparation of self-levelling mixes based on anhydrite binder, a specimen binder made by a German producer declared as a purely anhydrite binder, was analysed. However, it was found out by the analyses performed that this binder is a premium quality -gypsum according to all manifestations by a modified liquefying and retarding agent, possibly by other compounds. Due to potential changes that may have occurred since the initial study in the composition of the so-called anhydrite binders, exploration of composition of the binders currently used in the Czech Republic for preparation of self-levelling mixtures was carried out in this part of the experimental work. The exploration detected that the composition of the binding phase is the matter of know-how for the majority of companies, and as a result, the only one sample of binder has been obtained so far from the company which reserved their anonymity for this work.

Method for the Accelerated Testing of the Durability of a Construction Binder using the Arrhenius Approach

Abstract The single most reliable indicator of a material’s durability is its performance in long-term tests, which cannot always be carried out due to a limited time budget. The second option is to perform some kind of accelerated durability tests. The aim of the work described in this article was to develop a method for the accelerated durability testing of binders. It was decided that the Arrhenius equation approach and the theory of chemical reaction kinetics would be applied in this case. The degradation process has been simplified to a single quantifiable parameter, which became compressive strength. A model hydraulic binder based on fluidised bed combustion ash (FBC ash) was chosen as the test subject for the development of the method. The model binder and its hydration products were tested by high-temperature X-ray diffraction analysis. The main hydration product of this binder was ettringite. Due to the thermodynamic instability of this mineral, it was possible to verify the proposed method via long term testing. In order to accelerate the chemical reactions in the binder, four combinations of two temperatures (65 and 85°C) and two different relative humidities (14 and 100%) were used. The upper temperature limit was chosen because of the results of the high-temperature x-ray testing of the ettringite’s decomposition. The calculation formulae for the accelerated durability tests were derived on the basis of data regarding the decrease in compressive strength under the conditions imposed by the four above-mentioned combinations. The mineralogical composition of the binder after degradation was also described. The final degradation product was gypsum under dry conditions and monosulphate under wet conditions. The validity of the method and formula was subsequently verified by means of long-term testing. A very good correspondence between the calculated and real values was achieved. The deviation of these values did not exceed 5 %. The designed and verified method does not also consider the influence of other effects, for instance, chemical corrosion or corrosion caused by frost-thaw cycles. However, this method could be a supplementary tool applicable to the study of degradation processes and the estimation of a binder´s durability as well.

Possibilities of Alpha Gypsum Preparation in Chloride Salt Solutions

The necessity of continuously saving of natural resources and the continuously increasing utilization of waste materials, which results in by product of the primary production, is in the interest of sustainable life on the Earth. These valuable secondary raw materials are stored as waste and urge for use as inexpensive and easily available material. The Institute of Building Materials and Elements Technology at the Brno University of Technology, solves in the long term the problem of alpha gypsum preparation by dehydrating the gypsum in the solution of chloride salts. The gypsum dehydrates to alpha-hemi-hydrate by this method under atmospheric pressure in liquid environment. The tests were brought as far as to the stage of laboratory production. The chloride ions are after dehydration washed out and afterwards the gypsum is dried.

Synthetic Preparation and Properties of Ettringite

This paper deals with the verification of the possibility of preparing synthetic ettringite in a way of direct addition of aluminum sulfate and calcium hydroxide as an alternative to the hydration of yeelimite. The stability of the resulting system was studied using the X-ray diffraction (XRD) and differential thermal analysis (DTA) in two different environments, namely in a laboratory environment and the environment of saturated water vapour. The evaluations of X-ray diffraction analysis and thermal analysis show that in the ettringite sample stored in the laboratory environment, evaporation of molecular water and subsequent transformation of ettringite into metaettringite or monosulfate can occur over time. Conversely, exposition of saturated water vapour environment can lead to saturation of the system by free calcium ions due to the slow dissociation of calcium carbonate, and thereby increase the amount of ettringite at the expense of gypsum and aluminum amorphous phase. To verify the above, it is recommended long-term monitoring of samples exposed in monitored environments.

Influence of Ambient Temperature on Course of Cement Stone Solidification

The aim of the work was to investigate the influence of extremely low and high temperature on the course of hydration of cement stone compared to the reference sample hydrated at normal conditions. The work was structured in such a way that Portland cement was first subjected to standard technological tests. Next, sets of test prisms using cement paste were prepared. This samples were immediately exposed to saturated water vapor in three temperature environments: 5 °C, 20 °C and 80 °C. The course of the hydration process during the first 28 days was monitored by the determination of the phase composition by XRD analysis and thermal analysis, and mediated by means of determination of tensile strength after bending and compressive strength. The low temperature did not have a negative effect on the final properties of the hardened cement stone. On the other hand, high temperature accelerated the initial phase of the hydration process, but negatively affected the resulting mechanical parameters

Study of Ettringite by Hydration of Yeelimite Clinker

This article describes the results of experimental works, dealing with long-term observing of ettringite stability (Ca6Al2(SO4)3(OH)12·26H2O). Thermodynamic stability of this mineral is important in terms of potential use of fluidized bed combustion (FBC) ash as an additive to Portland cement. Within the experimental work it was carried out observing of the ettringite formation by hydration of yeelimitu (Ca4Al6(SO4)·O12) in laboratory conditions. For the preparation of yeelimite it was proposed a three-component raw material mixture, consisting of a high percent limestone and gypsum and corundum. This mixture was subsequently placed in platinum crucibles and burnt in superkanthal kiln at 1200 °C. Formed clinker was mixed in chosen ratio with water and it was prepared a set of testing samples. These samples were exposed in the laboratory environment for up to 180 days. The hydration of the clinker was carried out using X-ray diffraction analysis (XRD) by determining the mineralogical composition.

Technological Properties Testing of Blended Portland Cements with Fluidized Filter Ash

The work aims to study the behaviour of blended cement with fluidized filter ash (FFA) considering to formation of the increased proportion of ettringite and its eventual transformation into thaumasite. In part of an experiment there were prepared three cements, two of them served as a reference one-component and the reference blended cement with limestone, a third one was tested blended cement with a FFA. All three cements were put to determination of basic technological properties and next they were observed during hydration process.

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.

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.

Study of Increasing of Belite Reactivity

Within the research at Institute of Technology of Building Materials and Components the questions of belite cement hydration speed improvement have been solved for a long time. In comparison with common Portland cements (alite type) these cements obtain almost identical final properties but the main shortage of them due to which they are not practically produced is their very low hydration process speed and thus insufficient initial strength for construction practice. A development of lower hydration heat is another difference of the belite cement from common Portland cements. In case of concreting of massive constructions as for example water dams this can be perceived as an important benefit, however in case of concreting during cold season of the year this appears as a definite negative. The belite cement also shows a lower inclination to concrete efflorescence and higher strength to aggressive environment due to lower CaO content. Both of the properties can be definitely understood as benefits compared to orthodox alite clinker. The raw material base of belite cements require less lime than production of common Portland cements and on that ground the implementation of its production would be a positive benefit for ecology in sense of CO2 emission reduction and also in improvement of economy of non-renewable raw material sources. The raw material is burnt to lower temperature than alite cement resulting in lower CO2 emission released in the atmosphere during the cement production. In addition at reduction of the temperature for more than 100 °C also heat consumption is reduced for 10 to 14 %, which has positive economical and ecological effects due to lower consumption of fuels. Within the research focussed on improvement of belite cement properties the study of hydration process course and technological properties of belite (C2S) prepared using low-energy burning modes was the aim of the research.