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Examination of microstructure of solidification product containing hazardous sludge
(Elsevier, 2016-08-03) Hodul, Jakub; Drochytka, Rostislav
The tests involved with the microstructure evaluation must be also added to the processes which significantly support the evaluation of long-term durability of solidification product (SP). Monitoring the microstructure by analyses such as scanning electron microscopy (SEM), X-ray powder diffraction (XRD) and differential thermal analysis (DTA) it can be assumed according to the new compounds being formed during the hydration whether the hydration products are modified. Moreover, it could also be determined how the pollutants contained in input hazardous waste (HW) are incorporated in solidification product (SP) matrix. Within this work four different types of sludges (S) containing dangerous substances, mainly heavy metals were selected as input hazardous waste (HW) for laboratory preparation of samples of the solidification products (SP) for the microstructure analyses. On the basis of the findings from microstructure analyses it can be assumed whether contaminants contained in input HW, sludges, is immobilized into the matrices of solidification products (SP) by incorporating into the hydration products of SP matrix.
Comparison of separate and co-grinding of the blended cements with the pozzolanic component
(Elsevier, 2016-08-03) Dvořák, Karel; Dolák, Dušan; Dočkal, Jakub
The main difference between separate and co-grinding of blended cement is the fact that co-grinding occurs interaction among the milled components. These interactions may speed up milling process, or on the contrary to slow it down. It depends on grindability of the components. Separate grinding and subsequent homogenization is more common. High speed disintegrator appears to be a promising technology for the homogenization of blended cements after separate milling process in traditional mills, which can be associated with final grinding. The aim of the work was to compare the effect of separate and co-grinding, and their combinations on the properties of the blended cement. At first the samples of pure glass, pure Portland cement and its mixture were pre-ground in the ball mill to the specific surface area of 400 m2/kg according to Blaine. The material was subsequently ground either in a ball mill or disintegrator by the various combinations of separate or co-grinding. All the samples were subjected to granulometric and morphological analysis and the analysis of the technological properties. In the case of the combination of cement and glass the co-grinding appeared to be more advantageous than the separate grinding with homogenization. The high speed disintegrator has produced sharp-edged grains with narrower particle size distribution curve than traditional ball mill. Technological properties of the cement have been also influenced by high speed disintegrator. Compressive strength in early age was higher than in the case of ball mill type cement, however, the final strength were essentially the same.
Method for the Accelerated Testing of the Durability of a Construction Binder using the Arrhenius Approach
(De Gruyter, 2016-05-02) Fridrichová, Marcela; Dvořák, Karel; Gazdič, Dominik
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.
Development of grout for additional seal embankment dams
(Elsevier, 2015-06-25) Michalčíková, Magdaléna; Černý, Vít; Drochytka, Rostislav
The technology of sealing sand and gravel by chemical injection has been known and used for a long time. Chemical grouting is however expensive and sometimes the use of cement does not lead to the desired effect. That is why we are trying to find new materials and methods of injection. Clay and cement are added to a mixture save chemical products. Clay-cement mixes are used not only because they are better quality, but also because these mixtures have a tendency to penetrate better into incoherent sediments that would need an additional sealant of a chemical injection. In order to reduce cost in future, ordinary clay is replaces in the mixture secondary raw materials can be a suitable substitute for ordinary clay to a certain extent. This is true above all for fly ash. This paper deals with the appropriateness of using fly ash (secondary raw material), cement and lime (binders) and liquefying additives and examining their properties in the mixture. The aim of the paper is to propose the optimal injection mixture for additional sealing of earth dams.
Using acoustic emission methods to monitor cement composites during setting and hardening
(MDPI AG, 2017-04-28) Topolář, Libor; Pazdera, Luboš; Kucharczyková, Barbara; Smutný, Jaroslav; Mikulášek, Karel
Cement-based composites belong among the basic building materials used in civil engineering. Their properties are given not only by their composition but also by their behaviour after mixing as well as by the methods of curing. Monitoring the processes and phenomena during the early stages of setting is vital for determining the resulting properties and durability. The acoustic emission method is a unique non-destructive method that can detect structural changes as a cement-based composite is setting. It can also detect the onset and growth of cracks during the service life of a cement-based composite since the moment it has been mixed. The paper discusses the use of the acoustic emission method with focus on the early stage of the lifespan of a cement-based composite including the measures necessary for its use and description of the parameters of acoustic emission signals.

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