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Frankovska J.,Slovak University of Technology in Bratislava | Andrejkovicova S.,Slovak Academy of Sciences | Janotka I.,Building Testing and Research Institute | Janotka I.,Slovak Academy of Sciences
Geosynthetics International

Sodium bentonite (Na-bentonite) is used as a sealing component in geosynthetic clay liners (GCL). Na-bentonite is very sensitive to chlorides, and flocculation occurs when it is exposed to saline environments. The purpose of this work is to investigate the properties of Na-bentonite and bentonite-palygorskite filler material for GCL in saline solutions in the range between 0.5% and 10% (0.09 and 1.8 M) NaCl concentration. The investigation has been carried out to evaluate and study the chemical and geotechnical properties of Na-bentonite and bentonite-palygorskite mixture. The observations suggest that the resistance of Na-bentonite to chlorides is increased by adding 40% palygorskite. The bentonite-palygorskite mixture is characterised by high liquid and plastic limits, and also by high water adsorption and free swell in water, crude oil and petrol. Hydraulic conductivity was determined for water and for 10% NaCl (1.80 M) solution. The results show that Na-bentonite palygorskite mixture serves as an effective absorber of both water and saline solutions up to a concentration of 10% (1.80 M) of NaCl without increasing the hydraulic conductivity. © 2010 Thomas Telford Ltd. Source

Osacky M.,Comenius University | Osacky M.,Building Testing and Research Institute | Sucha V.,Comenius University | Czimerova A.,Slovak Academy of Sciences | Madejova J.,Slovak Academy of Sciences
Applied Clay Science

The stability of seven dioctahedral smectites coming from bentonites of different origin was studied in the presence of iron to simulate the possible reactions between clay minerals and Fe canisters in a nuclear waste repository. The batch experiments were performed at 75°C for 35. days in a nitrogen atmosphere. The reaction products were examined by XRD, FTIR, HRTEM, BWA analysis and UV-Vis spectroscopy. Magnetite and 7-Å clay minerals (berthierine-like) were the main reaction products besides iron-smectite reaction. Bentonites reacted differently with iron. The quantitative XRD revealed that consumption of iron and formation of magnetite was significantly higher for Fe-rich smectites. Fe-rich smectites were the most affected by the reaction. This indicated that the octahedral iron ions may be largely responsible for smectite decomposition indicated by the decrease of the smectite content, partial dehydroxylation of its structure and alteration of octahedral and tetrahedral sheets. The layer charge and thickness of the smectites decreased during the reaction. Arrangement of the smectite layers was apparently changed, and rather large particles were split into thinner particles or even layers. © 2010 Elsevier B.V. Source

Krajci L.,Slovak Academy of Sciences | Moujmdar S.C.,University of New Brunswick | Kuliffayova M.,Slovak Academy of Sciences | Janotka I.,Building Testing and Research Institute
Journal of Thermal Analysis and Calorimetry

Two types of raw materials, original kaolin sand OKS I and OKS II were used for experiment. They were transformed (1 h at 650 °C with 10 °C/min temperature increase) to burnt kaolin sand (BKS I and BKS II) with pozzolanic properties. Contents of decisive mineral-metakaolinite-in BKSs are as follows: BKS I (fraction below 0.06 mm) 20%; BKS II (fraction below 0.06 mm) 36% and BKS II (fraction below 0.1 mm) 31% by mass. Mortars with blends of Portland cement (PC) and BKS were prepared announced as: MK I (0.06) with 5 and 10% cement substitution by metakaolinite; MK II (0.06) with 5 and 10% cement substitution by metakaolinite and MK II (0.1) with 5, 10, 15 and 20% cement substitution by metakaolinite. The reference mortar with 100% of PC was made for comparison. All mortars were adjusted on the constant workability 180 ± 5 mm flow. Besides significant increase in compressive strengths-the refinement of pore structure in mortars with BKS connected with decreases in permeability and Ca(OH)2 content were revealed. The above facts confirm pozzolanic reaction of BKS in contact with hydrated PC and indicate perceptiveness of BKS for the use in cement-based systems as a pozzolanic addition. © Akadémiai Kiadó, Budapest, Hungary 2010. Source

Sadovsky Z.,Slovak Academy of Sciences | Krivacek J.,Slovak Academy of Sciences | Ivanco V.,Technical University of Kosice | Duricova A.,Building Testing and Research Institute
Journal of Constructional Steel Research

Computational modelling of the buckling strength of cold-formed steel members as influenced by initial geometric imperfections is studied. The geometric imperfections are represented by the member eigenmode shapes. Along with the classical measure - the amplitude of imperfections, an energy measure defined by the square root of the elastic strain energy hypothetically required to distort the originally perfect structural element into the considered imperfect shape is used. Based on the measures, two approaches for the choice of the most unfavourable imperfections are suggested. Normalising imperfections by the amplitude, the energy measure is calculated as indicative parameter of imperfection significance. Vice versa, when adopting normalisation by the energy measure, the amplitude is used as a supporting parameter. The suggestions are illustrated on calculating the strength of an axially compressed steel lipped channel column with eigenmodes exhibiting local-distortional interactions. For eigenvalue and geometrically and materially non-linear strength calculations, the FEM codes MSC.NASTRAN and COSMOS/M are employed. © 2012 Elsevier Ltd. All rights reserved. Source

Krajci L.,Slovak Academy of Sciences | Kuliffayova M.,Slovak Academy of Sciences | Janotka I.,Slovak Academy of Sciences | Janotka I.,Building Testing and Research Institute
Procedia Engineering

The advancement of cement composites with different pozzolana types represents needful domain in civil engineering. Utility properties of such composites are closely approaching the level of standard quality. The raw materials - kaolin sand thermally transformed at 650 °C/hour and clayey diatomite calcined at 900 °C/hour were used in the experiment. Cement ternary composites containing 5 and 10 wt.% of metakaolinite as well as 5 and 10 wt.% of calcined clayey diatomite (in varied proportions) with water to solid ratio of 0.5 were manufactured for this study. The physical-mechanical and physical-chemical behaviour of relevant ternary systems after 28-days water curing are presented in this paper. Thermal analysis disclosed calciumsilicate hydrate (CSH) and calciumaluminate hydrate (CAH) formation, portlandite dehydroxylation and calcite decarbonation. Portlandite content reduction was found as a result of respective pozzolanic reaction unlike reference composite without pozzolana. This statement was confirmed by X-ray diffraction analysis. The favourable standard mechanical properties (compressive strength) in this study of composites were documented as well. Results exhibit the effective pozzolanic reaction susceptible the attainment of valuable utility properties of cement composites. © 2013 The Authors. Published by Elsevier Ltd. Source

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