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Slovakia denoted as kaolin sands [ 33 – 36 ]. The effect of cement substitution by burnt kaolin sand (with 36% of metakaolinite) on hydrated phases, pore structure development and mechanical properties in cement composites was evaluated and relevant

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Abstract  

Methods of thermal analysis are employed in a study of the high-temperature properties of three different types of glass fiber reinforced cement composites together with the measurements of their thermal and hygric parameters. First, basic TG and DTG measurements are carried out to get the first insight into the high-temperature behavior of the analyzed materials. Then, mercury porosimetry and scanning electron microscopy of specimens subjected to the temperatures of 600 and 800C are performed and compared to the reference specimens not exposed to any thermal load. Finally, measurements of thermal and hygric parameters of the studied materials are done and matched with the results of the material characterization experiments. Three main effects are found to influence the thermal and hygric properties of the analyzed materials. The first is the decomposition of the cement matrix, which is clearly a negative factor. The second is the positive effect of the presence of fibers that could partially keep the cement matrix together even after significant decomposition of cement hydration products. The third important factor affecting the thermal and hygric properties is the composition of the particular materials. The application of vermiculite aggregates instead of sand is found to be clearly positive because of its porous character leading to the bulk density decrease without worsening the other properties. Also, wollastonite aggregates are a better choice than sand because of its fibrous character that could partially magnify the effect of fiber reinforcement.

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Thermal conductivity, specific heat capacity, thermal diffusivity and linear thermal expansion coefficient of two types of carbon fiber reinforced cement composites are measured in the temperature range up to 800�C. Thermal conductivity and thermal diffusivity are also determined for the specimens exposed to thermal load up to 800�C before the measurement. Differential thermal analysis (DTA), mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD) are utilized for the assessment of thermal decomposition processes taking place in the high temperature range under consideration. The high temperature thermal properties of the studied materials are found to be positively affected by the application of the high alumina cement and in the case of the Portland cement based composite also by using the autoclaving procedure in the production process. Also, the randomly distributed carbon fibers that can reduce the damage of the pore structure by the thermal decomposition processes are identified as a positive factor in this respect. A comparison of thermal conductivity vs. temperature curves obtained for the specimens pre-heated to different temperatures is found to be a useful tool in the identification of major dynamic effects in the specimens due to the thermal decomposition reactions. The results are in a good agreement with the DTA, MIP, SEM and XRD analyses. The character of the thermal conductivity measurements that in fact includes the effects of convection and radiation into the thermal conductivity coefficient can be beneficial for a simple assessment of the influence of the fire on a dividing structure.

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Samples of the natural zeolites chabazite, clinoptilolite and a clinoptilolite-rich tuff, were loaded with the isotope 137Cs. Composites of these labeled materials were made with cement and blast furnace slag. Standard leaching experiments were carried out with synthetic sea, ground and "pond" waters, as well as distilled water. Rates of leaching were calculated and compared to similar systems.

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The uptake of137Cs and90Sr/90Y onto Syrian bentonite has been studed, using batch and column tracer techniques in order to investigate its utilization for aqueous radioactive effluent treatment. Parameters influencing the percent uptake considered and studied in this work are: nuclide concentration, pH of the aqueous phase, heat treatment and particle size. Leaching experiments using natural sea and ground waters were carried out on bentonite/cement composites. They demonstrated the effectiveness of calcination and cement containment.

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Composite absorbers of inorganic ion-exchangers and polyacrylonitrile binding matrix

V. Influence of ionising radiation on the leachability of137Cs from cemented composite NiFC-PAN absorber

Journal of Radioanalytical and Nuclear Chemistry
Authors: A. Motl, J. John, and F. Sebesta

Abstract  

Maximum attainable self-absorption dose for cemented composite ion-exchanger, consisting of nickel hexacyanoferrate and polyacrylonitrile binding matrix, loaded with137Cs up to repository acceptable level (1.1·1012 Bq·m–3) was calculated to be 105 Gy. The cemented absorber with sorbed caesium was irradiated by60Co source up to 1 MGy, and leach tests were performed to determine possible influence of self-irradiation on the caesium leachability. No radiation induced changes in caesium immobilisation in solidified ion-exchanger were observed.

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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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The effect of impregnation time on the physico-chemical and mechanical properties of polyester-cement mortar composite has been investigated. The samples were soaked in unsaturated polyester resin containing 40% styrene monomer at impregnation times ranging from 1–15 hours and then exposed to 50 kGy of γ-irradiation. The effects on polymer loading, compressive strength, apparent porosity, and water absorption in addition to IR spectra and TGA of the samples were studied. It was found that, the polymer loading and compressive strength increase with the increased of soaking time up to 4 hours and there is no significant improvement of the polymer loading and compressive strength increase with the increased of soaking time up to 4 hours and there is no significant improvement of the polymer loading and strength. Whereas, the apparent porosity and water absorption behave in an opposite direction. These are attributed to the presence of polymer in the pores of the samples. IR spectra showed that, new bands appeared as result of the reaction between polyester and set cement. TGA showed that, the polyester cement composite has higher thermal stability as a compared to irradiated polyester.

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hardened mortars are characterized with high early-strength, smooth surfaces and dense structure [ 7 , 9 ]. This research aims to study the phases, formed in different types of decorative cement composites. The accent of this study is on the phase

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Journal of Thermal Analysis and Calorimetry
Authors: Armando Lucas Cherem da Cunha, Mariana Santos Lemos, Sergio Meth, Jardel Pereira Gonçalves, and Jo Dweck

presents a typical result of curves TG and DTG of the cement composite with partial substitution using the ECAT fine fraction, using as basis the initial mass of the analyzed sample. The different losses of water mass are shown in the way that they were

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