Abstract: Paper is aimed at study of preparation possibilities of cementitious binders with waste diatomaceous earth. In the first step, the influence of ground diatomaceous earth on properties of cement mixture was studied. In the next step, diatomaceous earth was calcinated and, lastly, the influence of replacing FGD-gypsum with anhydrite II as a setting controller in the mixture containing calcined diatomaceous earth was monitored. Technological properties of the prepared mixtures were measured and compared with cement standard. For studying the influence of phase composition and microstructure of cements hardened by both untreated and calcinated diatomaceous earth, hardened cements were tested by DTA and their porosities were measured. The results show that it is possible to prepare binder containing calcinated diatomaceous earth which has slightly lower early strengths but higher long-term strengths and lower hydration heat development.
Abstract: One of the most important problem of concrete durability is increasing of waterproofing. Researches are devoted studying of cement mortars modified by carbon nanotubes, dispersed in plasticizers solutions. Were investigated physico-mechanical properties of cement paste, cement-sand mortar into which structure entered untreated carbon nanotubes (production of plant TM "Spetsmash" Kyiv, Ukraine) in various quantity. Were used as plasticizers in cement compositions additives substances of the various chemical nature – naphtaleneformaldehyde, melamineformaldehyde and polycarboxylate. Quantity of untreated nanotubes varied from 0,5%; 1,0% and to 1,5%. Concentration of additives was accepted taking into account recommendations of producers and made about 1% from the weight of cement. Were studied some technological processes of introduction untreated carbon nanotubes in cement system and is shown that the way of introduction of nanomodifiers has essential impact on strength characteristics of cementitious materials. Optimum decision introduction of untreated carbon nanotubes is using its in dispersion plasticizer of the working concentration prepared in an ultrasonic dispergator is established. Results of physico-mechanical tests of cement paste and cement-sand mortar showed positive influence at introduction of untreated carbon nanotubes as cement modifiers on strength characteristics of samples. Resalts is shown that the nanomodifier, used quantity about 1% in solution of lignosulfonate with polycarboxylate and melamineformaldehyde plasticizer has great impact on strength characteristics.
Abstract: Use of fluidized bed combustion fly ash as an admixture for manufacture of cement based composite materials is not quite common now, however, there are real ways of utilizing its potential. The most important negative feature of this fly ash is its variable chemical composition, which supports formation of new forms growing within the structure with negative impact of durability of the composite material. The morphology of this type of fly ash is also not very favorable as it has negative influence on consistency. Fluidized bed combustion fly ash considerably deteriorates consistency of cement mixture, which results in higher water-cement ratio and consequently worsening of physico-mechanical and durability parameters of the whole composite. Therefore the question arises how to eliminate this negative influence on consistency without the necessity of increasing water cement ratio.
Abstract: Paper describes a new way how to characterize early hydration and setting of Portland cement pastes with various dosages of setting accelerator CaCl2. The aim was not to characterize the role of well-known setting accelerator CaCl2 but to correlate rheology and calorimetry in view of early hydration of Portland cement. Characterization was based on measurements on rotational rheometer, isothermal calorimeter and semiadiabatic calorimeter. The courses of calorimetric exotherms in time were correlated to the development of the phase angle obtained by rheological oscillation tests. Heat flow peaks can be successfully correlated to rheological processes described by change of storage and elastic moduli up to the time that corresponds to the start of the setting which was found to be the limit for rheological tests. The start of the setting on calorimetric curve belongs to the onset point of the main silicate peak during acceleration period of hydration. The value of phase angle decreases as the setting cement paste changes from liquid to solid-like. Times of low values of phase angle ~ 2.5 (°) can be related to times of onset points of main peak for every dosage of setting accelerator.
Abstract: The article is focused on study of the effect of filtering diatomite as a partial replacement of cement in an amount of 5-30%. Diatomite is used in civil engineering especially for its high content of an amorphous SiO2, chemical resistance, high porosity, and good thermal insulating properties. Diatomite can be used as a pozzolanic material due to the high content of amorphous SiO2.Cement was replaced by filtering diatomite in amount of 5, 10, 15, 20, 25 and 30% by weight. Diatomite was characterized by chemical composition, granulometry and pozzolanic activity.The specimens were tested in bulk density, bending strength and compressive strength, hydration process was investigated using thermal analysis, and microstructure was observed by scanning electron microscopy. All results were compared to reference sample.
Abstract: 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.
Abstract: Good thermal insulation properties of the surface structures lead to reduction of heat losses in buildings. This reduces the energy required for heating which is positive fact from the view protection of the environment. The aim of the research intent, which is going at Faculty of Civil Engineering in Brno, is the development of high-quality, thermal insulating plasters using both conventional binders, and alternative binders, whose acquisition-production is in comparison with the technology production of cement less energy intensive. Due to the fact that increasing moisture leads to deterioration of the thermal insulating properties, further research works were devoted to the study of the influence of relative humidity and moisture content on the thermal insulation properties of lightweight plasters, including of the determination of capillary absorption coefficient.
This paper describes evaluation of the development of insulating plasters based on lightweight aggregates, using different ratio of cement and lime hydrate and other chemical additives. There are presented results of the study of basic physical and thermal insulating properties, including the study of sorption properties developed lightweight plaster mixtures.
Abstract: Alkali-activated slag has a higher resistance against exposure to high temperature compared to ordinary Portland cement concrete. Nevertheless, its mechanical properties are also deteriorated due to partial decomposition of the C-A-S-H matrix. This paper investigates the effect of various curing regimes applied to the samples which were exposed to temperature 200–1200 °C on the mechanical properties and microstructure of the alkali-activated slag/limestone blends. The amount of limestone was 15% from the mass of slag. On set of specimens was treated on air at laboratory conditions, the second set was immersed in water and the last was treated stored in humid chamber with 95% relative humidity for the period of 60 days. The results showed that water curing has a strong positive influence on the compressive as well as flexural strength of the specimens exposed to temperatures up to 600 °C. Specimens which were exposed to 800 and 1000 °C showed the best performance after treatment in humid chamber, and after exposure to 1200 °C the best compressive strength exhibited the air cured samples.
Abstract: Tobermorite is the main mineral which provides to aerated concrete mechanical properties. It is produces during hydrothermal conditions by reacting silicon and calcium oxides. Within this research was evaluated tobermorite formation using high temperature combustion fly ash and quartz sand, as the siliceous raw materials. As a binder was used lime. Emphasis was also placed on the molar ratio of C/S, which is crucial for the formation of tobermorite and was given 0.73 and 1.00. Hydrothermal synthesis was carried out in a laboratory autoclave at temperatures of 170 and 190 °C.