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Abstract  

An optimization of mortar (as matrix), improved with bentonite clay, used for immobilization of radionuclides60Co,137Cs,85Sr and54Mn, is presented. A relatively simple mathematical model is given, which permits minimization of leach rate and permeability and maximization of compressive strength. An optimal solution, based on experimental data, is given. These results will be used for a future Yugoslav radioactive waste storing center.

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The research excavations in Brigetio at Komárom/Szőny–Vásártér between 1992–2014 unearthed a part of the civil town (municipium) with domestic buildings and workshops with several construction phases from the end of the 1st century AD to the second half of the 3rd century AD. Best preserved are the ruins from the Severan era which offer us an insight into the building techniques of the age: adobe walls with stone foundations, mortar floors, hypocaust heating systems, ceilings and vaulted ceilings, roofs covered with ceramic roof tiles, stair cases, door and window openings and wells.

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The boat imprint unearthed at the site of the Benedictine abbey from Bizere (Frumuşeni, Romania) is a unique discovery for two reasons: its preservation as a negative imprint, due to its reuse for preparing mortar, and its dating back to the 12th century, based on the context of its discovery. It has been identified as a logboat, due to the absence of any technical details specific for plank boats, and now stands as the only vessel of this type with known dating for the territory of Romania. The article also enquires into the wider historical context of the discovery, thus bringing forth the archival data available with regard to medieval inland navigation.

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Abstract  

Transport phenomena involved in the leaching of a radioactive material from a concrete composite matrix into surrounding water are investigated using three methods based on theoretical equations. These are: a diffusion equation derived for a plane source model, a rate equation for diffusion coupled with a first-order reaction and an empirical method employing a polynomial equation. The results are compared with respect to their applicability to the 137Cs leaching data. The results presented in this paper are part of those obtained in a 25-year mortar and concrete testing project which will influence the design of radioactive waste management for a future Serbian radioactive waste disposal center.

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Abstract

It is increasingly important that chemistry reaches people who have not studied directly this field of science but that, daily, have practices where chemistry is involved in various extents. This is what happens, for instance, in the activities related with the study and the preservation of cultural heritage. In this sense, the present work is a short review of the particular case of techniques based on the thermal analysis and calorimetry applied within the context of the characterization of art and archeological objects, exemplified by various case studies, as the characterization of mortars, preparatory grounds, ancient painting materials and drying oils.

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Summary  

Leach characteristics of 54Mn and 85Sr radionuclides from ordinary Portland cement have been studied using International Atomic Energy’s (IAEA) standard leach method. The retardation factors, K F, and coefficients of distribution, k d, have been determined using a simplified mathematical model for analyzing the migration of radionuclides. The lowest leaching values after 60 days were achieved in samples with 5% of vermiculite. Results presented in this paper are the examples of results obtained in a 10 year mortar and concrete testing project, which will influence the design of the engineered trench system for a future central Serbian radioactive waste storage center.

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Abstract  

Ceramic powder has been used as an artificial pozzolanic addition, in preparing pozzolanic mortars for the historic/traditional structures’ construction. In order to evaluate the pozzolanic activity of ceramic powder, several pastes were prepared, by mixing it with hydrated lime, in different ratios. The pastes were stored in standard conditions (RH=99±1%, T=25±1°C) and evaluated using thermal analysis (DTA/TG), X-ray diffraction (XRD), compressive strength tests and mercury intrusion porosimetry (MIP), in time. The obtained results revealed that the compounds formed were CSH and C4ACH11 (monocarboaluminate) after 270 days of curing. The calcium hydroxide consumption increases as the initial amount of the ceramic powder in the paste augments. The maximum strength development is obtained for ceramic powder/hydrated lime ratio 3:1.

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Abstract  

Thermal analysis was first used to investigate the pattern of dissociation of hydrated ordinary Portland cement. Portlandite (Ca(OH)2) decomposes at about 500C. This was confirmed by kinetic calculations. Thermal analysis was then performed to establish the effect of varying the cement content on the percent mass loss associated with the decomposition of Ca(OH)2 in cement mortar cured for 28 days. An increasing relation was obtained. Standard concrete cubes were then prepared with cement contents ranging from 200 to 450 kg m-3. The loss in mass on heating, up to 750C, of concrete samples cured for 28 days was then related to the cement content in concrete. The relation obtained was tested for concrete cubes of known cement content and found to be in better agreement than the results obtained by conventional chemical analysis. This method can be used for an approximate determination of the cement content in concrete.

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Abstract  

The so-called pozzolanic activity of waste catalysts from fluidised cracking was investigated. For this purpose a series of cement mixtures with this waste material were prepared and subsequently the pastes and mortars were produced. Waste aluminosilicate catalyst was used both in raw form and after grinding in a ball mill for 60 min. The hydrating mixtures were subjected to the calorimetric measurements in a non-isothermal/non-adiabatic calorimeter. After an appointed time of curing the hydrating materials were studied by thermal analysis methods (TG, DTG, DTA). The pozzolanic activity factors were determined, basing on the compressive strength data. The increased activity of cement — ground pozzolana systems has been thus proved. An accelerated Ca(OH)2 consumption as well as higher strength were found for materials containing ground waste catalyst, as compared to those, mixed with the raw one. Thus grinding was also proved to result in mechanical activation in the case of the waste catalyst from fluidised cracking.

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Calorimetry in the studies of cement hydration

Setting and hardening of Portland cement–calcium aluminate cement mixtures

Journal of Thermal Analysis and Calorimetry
Authors: Marek Gawlicki, Wiesława Nocuń-Wczelik, and Łukasz Bąk

Abstract  

Calorimetry was applied to an investigation of the early hydration of Portland cement (PC)–calcium aluminate cement (CAC) pastes. The heat evolution measurements were related to the strength tests on small cylindrical samples and standard mortar bars. Different heat-evolution profiles were observed, depending on the calcium aluminate cement/Portland cement ratio. The significant modification of Portland cement heat evolution profile within a few hours after mixing with water was observed generally in pastes containing up to 25% CAC. On the other hand the CAC hydration acceleration effect was also obtained with the 10% and 20% addition of Portland cement. As one could expect the compressive and flexural strength development was more or less changed—reduced in the presence of larger amount of the second component in the mixture, presumably because of the internal cracks generated by expansive calcium sulfoaluminate formation.

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