75 research outputs found
Quantitative study of hydration of C3S and C2S by thermal analysis. Evolution and composition of C-S-H gels formed
No full textThis research is part of a European project (namely, CODICE project), main objective of which is modelling, at a multi-scale, the evolution of the mechanical performance of non-degraded and degraded cementitious matrices. For that, a series of experiments were planned with pure synthetic tri-calcium silicate (C3S) and bi-calcium silicate (C2S) (main components of the Portland cement clinker) to obtain different calcium–silicate–hydrate (C–S–H) gel structures during their hydration. The characterization of those C–S–H gels and matrices will provide experimental parameters for the validation of the multi-scale modelling scheme proposed. In this article, a quantitative method, based on thermal analyses, has been used for the determination of the chemical composition of the C–S–H gel together with the degree of hydration and quantitative evolution of all the components of the pastes. Besides, the microstructure and type of silicate tetrahedron and mean chain length (MCL) were studied by scanning electron microscopy (SEM) and 29Si magic-angle-spinning (MAS) NMR, respectively. The main results showed that the chemical compositions for the C–S–H gels have a CaO/SiO2 M ratio almost constant of 1.7 for both C3S and C2S compounds. Small differences were found in the gel water content: the H2O/SiO2 M ratio ranged from 2.9 ± 0.2 to 2.6 ± 0.2 for the C3S (decrease) and from 2.4 ± 0.2 to 3.2 ± 0.2 for the C2S (increase). The MCL values of the C–S–H gels, determined from 29Si MAS NMR, were 3.5 and 4 silicate tetrahedron, for the hydrated C3S and C2S, respectively, remaining almost constant at all hydration periods
Chikungunya Outbreak in Kedougou, Southeastern Senegal in 2009–2010
No full textBackground In Senegal, Chikungunya virus (CHIKV), which is an emerging mosquito-borne alphavirus, circulates in a sylvatic and urban/domestic cycle and has caused sporadic human cases and epidemics since 1960s. However, the real impact of the CHIKV sylvatic cycle in humans and mechanisms underlying its emergence still remains unknown. Methodology One thousand four hundred nine suspect cases of CHIKV infection, recruited from 5 health facilities located in Kedougou region, south-eastern Senegal, between May 2009 to March 2010, together with 866 serum samples collected from schoolchildren from 4 elementary schools in May and November 2009 from Kedougou were screened for anti-CHIKV immunoglobulin (Ig)M antibodies and, when appropriate, for viral nucleic acid by real-time polymerase chain reaction (rPCR) and virus isolation. In addition, mosquitoes collected in the same area from May 2009 to January 2010 were tested for CHIKV by rPCR and by virus isolation, and 116 monkeys sera collected from March 2010 to May 2010 were tested for anti-CHIKV IgM and neutralizing antibodies. Results The main clinical manifestations of the CHIKV suspect cases were headache, myalgia, and arthralgia. Evidence for CHIKV infection was observed in 1.4% (20 of 1409) of patients among suspect cases. No significant difference was observed among age or sex groups. In addition, 25 (2.9%) students had evidence of CHIKV infection in November 2009. Chikungunya virus was detected in 42 pools of mosquitoes, mainly from Aedes furcifer, and 83% of monkeys sampled were seropositive. Conclusions Our findings further documented that CHIKV is maintained in a sylvatic transmission cycle among monkeys and Aedes mosquitoes in Kedougou, and humans become infected by exposure to the virus in the forest.Additional co-authors: Kathryn A. Hanley, Anta T Dia, Denis Malvy, Scott C. Weaver, Amadou Alpha Sal
Differential scanning calorimetry evaluation of autoclaved cement based building materials made with construction and demolition waste
No full textThe effect of adding finely ground construction and demolition (C&D) waste fines, containing a significant amount of clay-brick, to mixtures of Portland cement and quartz sand autoclaved at 180°C was investigated by DSC. The incorporation of up to 41.25 mass% C&D waste fines enhanced the formation of aluminium-substituted tobermorite indicating that the mullite in the clay-brick fines is reactive under autoclaving conditions and supplied the aluminium required for the formation of this critical phase. C&D waste fine additions in excess of 41.25 mass% promoted the formation of aluminium-substituted C-S-H1 over aluminium-substituted tobermorite. © 2002 Elsevier Science B.V. All rights reserved
Synthesis and characterisation of cobaltite and ferrite spinels using thermogravimetric analysis and X-ray crystallography
No full textThe synthesis for a series of ferrite (M IIFe 2O 4) and cobaltite (M IICo 2O 4) spinels was investigated where M II is Mg, Co, Ni, Cu or Zn. The ferrites were prepared at a calcination temperature of 800 °C; the cobaltites at 500 °C. TG-MS indicated that reduction of CoIII to CoII occurs at ca. 800 °C, hence, the lower calcination temperature. For both the ferrites and the cobaltites, the evolution of water and CO 2 during the calcination suggests the presence of both species in the precipitates. The observed mass losses indicated that the precursor basic carbonate precipitates for the cobaltite synthesis were predominantly carbonate, while the precursor basic carbonate precipitates for ferrite synthesis were predominantly hydroxide in character. XRD data showed successful synthesis of the ferrites with minimal contamination from the parent oxides, while the cobaltites were observed to be predominantly of the spinel structure. © Akadémiai Kiadó, Budapest, Hungary 2011
Study of alkaline hydrothermal activation of belite cements by thermal analysis
No full textThe effect of alkaline hydrothermal activation of class-C fly ash belite cement was studied using thermal analysis (TG/DTG) by determining the increase in the combined water during a period of hydration of 180 days. The results were compared with those obtained for a belite cement hydrothermally activated in water. The two belite cements were fabricated via the hydrothermal-calcination route of class-C fly ash in 1 M NaOH solution (FABC-2-N) or demineralised water (FABC-2-W). From the results, the effect of the alkaline hydrothermal activation of belite cement (FABC-2-N) was clearly differentiated, mainly at early ages of hydration, for which the increase in the combined water was markedly higher than that of the belite cement that was hydrothermally activated in water. Important direct quantitative correlations were obtained among physicochemical parameters, such as the combined water, the BET surface area, the volume of nano-pores, and macro structural engineering properties such as the compressive mechanical strength
A TG analysis of the effect of calcination conditions on the properties of reactive magnesia
No full textThe reactivity of MgO obtained from calcination of magnesium carbonate at different temperatures has been investigated by means of hydration in a constant relative humidity environment at 40°C for periods up to 24 days. Natural magnesite and AR grade basic MgCO3 calcined in the range of 500-1000°C was characterised in terms of surface area, crystallite size, morphology, and hydration rate. It was found that the hydration rate is dependent on the surface area and crystallite size where temperature was the main variable affecting them. The most reactive MgO was produced at the lowest calcination temperature with the highest surface area and the smallest crystallite size. The basic MgO specimens showed higher degree of hydration compared to the natural MgO specimens due to the smaller surface area and larger crystallite size. The low MgO content of the starting natural magnesite is also attributable to the lower reactivity. This preliminary study serves as a mean to investigate potential utilisation of reactive MgO as a supplementary cementitious material in eco-friendly cements. © Springer-Verlag 2007
Combining multi-scale socio-ecological approaches to understand the susceptibility of subsistence farmers to elephant crop raiding on the edge of a protected area
No full textInternational audienc
FTIR study of the thermal degradation of poly(vinyl alcohol)
No full textThe degradation of poly(vinyl alcohol) was investigated using TG analysis and Fourier transform infrared spectroscopy to determine the effect of atmosphere on the process of degradation. In the spectra, four vibrational modes were identified that characterised the major steps of the degradation process. These were the O-H, C-H, C=O and C=C stretching modes. The mechanism observed for degradation in an inert atmosphere was in accordance with the accepted mechanism of elimination followed by pyrolisation. Evidence of conjugated polyenes, however, was not observed. For the air atmosphere, oxidation in both steps of the degradation process was observed
Low temperature DSC characterisation of water in opal
No full textA low temperature (-60 to +105 C) DSC characterisation of opal was carried out to determine the proportion of crystallisable water and to estimate the cavity size in which the crystallisable water is contained. Circa 10 % of the molecular water contained in the opals was found to be crystallisable suggesting that the remaining molecular water is present either trapped in silica cages or surface-adsorbed in micropores. For the opals derived from a sedimentary environment in Australia, the crystallisable water was found to melt in a manner consistent with the melting of bulk water, suggesting that the water is contained in cavities in the opal. The lack of depressed melting temperatures suggested little or no mesoporosity. A volcanic opal specimen of Mexican origin was found to contain both mesoporous and cavity water, while a Tintenbar opal, also of volcanic origin, was found to contain only mesoporous water due to the melting of the crystallisable water, with an estimated pore diameter size range 4-7 nm. The differences in mesoporosity observed between the volcanic and sedimentary opals are consistent with the demarcation in the physical properties observed between these types of opals in previous studies. © 2013 Akadémiai Kiadó, Budapest, Hungary
The effect of bottlenecks on a population of marked mixed VEEV clones during infection of <i>C. taeniopus</i> with two different starting titers.
No full text<p>The mean number of clones present at various time points and in various tissues (midgut, body, legs/wings, saliva) from <i>C. taeniopus</i> mosquitoes sampled following oral infection. (A) Mosquitoes infected with a high titer bloodmeal 5.7 log<sub>10</sub> pfu/ml (n = 4). (B) Mosquitoes exposed to a low titer bloodmeal 4.9 log<sub>10</sub> pfu/ml (n = 9).</p
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