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Abstract  

The thaumasite form of sulphate attack (TSA) concerns cements and concretes containing limestone and is attributed to the formation of thaumasite. This work deals with the confirmation of thaumasite formation in cement mortars. Three types of cement were examined: Portland cement and Portland limestone cement containing 15 and 30% mass/mass limestone. The specimens were cured at 5C, for 12 months, in a 1.8% MgSO4 solution. The formation of thaumasite was checked and confirmed by XRD, TG and SEM. It was concluded that mortars containing limestone suffer from TSA at low temperature. The combination of XRD, TG and SEM leads to the positive identification of thaumasite and resolves the well known problem of thaumasite and ettringite confusion.

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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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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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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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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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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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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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Abstract  

To assess the safety of disposal of a radioactive waste-cement composite, the leaching of137Cs from a waste composite into a surrounding fluid has been studied. Leaching tests were carried out in accordance with a method recommended by IAEA.1 The leachability was measured as a function of bentonite clay to cement ratio. The fraction of137-Cs leached from a specimen of Portland cement is 0.03–0.13 at a leaching time of 400 d. Results presented in this paper are examples of data obtained in a 10 y mortar and concrete testing project, which will influence the design of the engineered trench system for a future Yugoslav radioactive waste storage center.2,3

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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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