The paper demonstrates a spontaneous change in the micro-chemical composition of silica fume micropellets in a composite system of concretes with pozzolans admixtures. For 18 years, concrete was ...modified in laboratory conditions only with the use of drinking water. Using quantitative techniques of scanning electron microscopy (SEM) and microanalysis (EDX), the paper presents results of a hydration analysis of concrete prepared according to three different recipes from Portland cement mixed with silica fume and slag. Hydration and changes in the chemical composition of the silica fume micropellets were evaluated over a time-frame of 0, 5, 15, 18 years. The paper describes “spontaneous pure hydration”, during which compaction and change of the micro-chemical composition, density and chemical composition occur in two different morphology types of silica fume micropellets. The experiment confirmed the preventive effect of silica fume micropellets on the course of expansion reactions in concrete structures. Even after 18 years, no expansive alkaline silica gels were identified in the concrete. Silica fume has a positive effect on the speed of the expanding alkali-silica reaction, which, even at very low content (2 %), it slows down.
•Micro-chemical composition of silica fume micropellets in 18 years old concrete.•Preventive effect of silica fume on the course of expansion reactions in concrete structures.•Silica fume is a rapid absorber of alkali.
•Composition of CMSH-CASH in 15 years old SCC with slag.•Hydration of blast furnace slag particles analyzed by SEM and EDX.•Connection between the slag content and the hydration process.
The paper ...summarizes changes in slag microchemical composition and its hydration products in Portland cement self-compacting concrete after 15 years of exposure in water under laboratory conditions. Scanning electron microscopy (SEM) and X-ray microanalysis (EDX) techniques show the results of the degree of hydration of blast furnace slag particles. The experiment showed a connection between the slag content and the hydration process. It was verified that the average values of the base-forming oxides ratio (MgO + Al2O3)/CaO are inversely proportional to the slag content in the mixture. The results of these procedures provide valuable information not only in the long-term predictions of the effect of slag and other additives in cement concrete, but also in the evaluation of slag hydration in historical concrete structures.
Dating to the sixth millennium BC, the Halaf Period of northern Mesopotamia has long been considered a time of intense interaction and communication. This claim is based on the remarkable similarity ...that Halaf Period ceramic styles and especially painted pottery motifs show even over great distances. Analyzed for this paper are a series of potsherds from the contemporaneous levels of the site of Tell Kurdu located in the Amuq Valley of southern Turkey. A range of techniques including X-ray diffraction, wet chemical analysis, scanning electron microscopy and microanalysis, and petrography have been used in order to assess the source materials and to infer evidence for imports. Results show that although painted ceramic motifs at Tell Kurdu are Halaf-like in their general style, they are locally made. Moreover, at least one unpainted sherd may indicate that the sixth millennium inhabitants of Tell Kurdu must also have been involved in an inter-regional trade network. The latter conclusion mirrors similar results by other researchers who have consistently shown that ceramics were regularly traded across northern Mesopotamia in the sixth millennium BC.
New hydration products of ground granulated blast-furnace slag are formed during the hydration process of Portland slag cement concrete. Spatial distribution of microcracks in concrete is related ...also to newly formed slag hydrates. The chemical composition of hydration products is variable and unstable. The Si/Ca ratios rise in hydration products near the unhydrated slag core significantly. There is also a certain increase of Mg and Al content in the central parts of hydration rims. The scope of the paper is to find a relation between slag hydration products and the process of microcracking. The amount of microcracks was reduced in concretes with a lower content of vitreous fraction where the slag basicity was high. Neoformation of hydration products is accompanied by volume changes, which can lead to concrete microcracking.
The deterioration of concrete represents one of the most serious problems of civil engineering worldwide. Besides other processes, deterioration of concrete consists of sulfate attack and ...carbonation. Sulfate attack results in the formation of gypsum, ettringite and thaumasite in hardened concrete.
Products of sulfate attack may cause a loss of material strength and a risk of collapse of the concrete constructions. The authors focused especially on the microscopical research of sulfate attack. Concrete samples were taken from the Charles Bridge in Prague, Czech Republic. A succession of degrading mineral formation was suggested. Microscope methods represent a new approach to solving the deterioration problems. They enable evaluation of the state of concrete constructions and in cooperation with hydro-geochemistry, mathematics and statistics permit prediction of the durability of a structure. Considering the number of concrete constructions and their age, research of concrete deterioration has an increasing importance. The results obtained can also be useful for future construction, because they identify the risk factors associated with formation of minerals known to degrade structures.
The main goal was to determine the reaction potential of alkali-reactive aggregates containing unstable and metastable K-silicates together with quartz (predominant SiO2 polymorph) for alkali-silica ...reactions (ASR) in cement concrete pavements. Current methods used to determine the expansion potential of aggregates do not solve these problems. The study of mineral paragenesis of cataclased granite by the SEM/EDX method shows that the differences in the microstructural and microchemical composition of ASR products in the cement matrix reflect the mineral variability of the rocks. The final products (crystals alkali-calcium aqueous silicates (NK)CSH), formed from alkali-silica gel (ASG), not only have different K2O contents, but analysis of internal and external ASG led to the finding that the K2O content is highest in cataclased granites with polymineral paragenesis (K-feldspar, light mica, quartz). The monomineral cataclased granite aggregate (crushed quartz only), its outer edge and air-voids have a significantly lower K content. The highest K2O contents and at the same time lower CaO content were identified in ASGs appearing in paragenesis with light mica, and crushed feldspars. Based on the results presented in this work, it can be concluded that the presence of transformed feldspars and light mica significantly affect both the microchemical composition of ASR products and their crystalline product morphology.
•Mineral variability of the rocks: Alkaline silicates (light micas and feldspars) are sources of K+ and Na+ in ASG•The presence of alkaline silicates: Initiates the formation of transitional alkali calcium hydrosilicates to expandable ASG•(NK)CSH crystals: They have the highest K20 content and the lowest CaO content in paragenesis with light micas•Interaction of gel phases: There is limited miscibility of secondary sulphates and silicate hydrogels•Expanding knowledge of the relationship between ASG and CSH: Crystallization of sulphates (DEF) decreases the Ca content of gels
The publication is focused on late medieval pottery products with higher aesthetical effect. The key group is represented by stove tiles, where the unifying elements of relief decoration helped to ...define series of motifs for stoves with specific iconographic concept, which were found in various locations. The same approach can be also used with small ceramic sculptures, aquamaniles and relief-decorated floor tiles, even though the achieved information value in these cases is much lower. Micropetrographic, XRF and other analyses helped to identify the production centres and the distribution model of these ceramic groups. 3D documentation enabled a detailed comparison of differences between individual reliefs and specific traces of manufacturing procedures. Individual chapters contain active links to the source database of analysed items and to 3D models of selected specimens from reference collections.
The settlement in Hluboké Mašůvky is one of the most important sites of its kind in Moravia. This work presents the outcomes of the long-awaited assessment of rich archaeological evidence of the ...Moravian Painted Pottery Culture from post-war research.
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