Search

Cement and water within the concrete mass create a hydrated phase which acts as the glue for holding the sand and coarse aggregates in place to develop a strong construction material. The most important phase within the cement matrix is that of calcium silicate hydrate (CSH), which is largely responsible for the concrete strength. Decomposition of the CSH phase due to high temperatures will affect compressive strength of the concrete. Raman bands at 1083, 709 and 276 cm-1, which are representative of the CaCO3 and CSH presence in the concrete matrix phases can be used to assess changes in compressive strength as a result of thermal decomposition. The ratio between 1083/709 cm-1 bands was calculated and correlated to the compression strength of the concrete. The results show there is a rapid decline in strength around a critical peak ratio of 8.78 and a residual compressive strength of 0.62, closely following a polynomial curve. The tool developed here allows an indirect evaluation of the temperature the concrete has been exposed to by studying the band. A case study from a fire scene taken from a warehouse in Kingston (Jamaica) is also presented with the conclusion and results compared. The study showed that Raman spectroscopy has the potential to provide in-situ non-destructive testing of fire damaged concrete rapidly and accurately. [ABSTRACT FROM AUTHOR]

Ammonium nitrate fuel oil (ANFO) is one of the most favorite explosives used in terrorist attacks. This explosive is a complex mixture of 95-96% ammonium nitrate (AN) and 4-5% liquid hydrocarbons (fuel oil). In this study, we analyze a variety of ANFO explosive mixtures in order to classify their different sources of origin by observing the difference in fuel components. The study was performed by mixing ammonium nitrate with eight different diesel brands collected in Lincoln, UK in two seasons (winter and summer). The samples were extracted using appropriate solvent and extracts were subsequently analyzed in sextuplicate by gas chromatography-mass spectrometry (GC-MS) and Fourier transform infrared spectroscopy (FTIR). A classification model was performed using principal component analysis (PCA) and Lineal Discriminant Analysis (LDA). In this study, four fatty acid methyl ester (FAME) contents were observed by GC-MS in all summer samples but found lack in some winter sample resulting in seasonal variation effect. The classification of pre-blast ANFO samples was achieved using GC-MS and FTIR in a combination with PCA/LDA. The results significantly showed the variation of specific diesel components and providing different classification performance among ANFO samples with high classification performance. Therefore, this study can be beneficial in forensic investigation that the use of diesel components are able to classify among different ANFO samples. [ABSTRACT FROM AUTHOR]

The continuous emergence of NPS over the last years poses a series of novel challenges for forensic analysts. Most of those new compounds are synthesized with minimal chemical modifications to the structure of already known chemicals in order to avoid regulations. Some of these new compounds may undergo chemical changes during analysis leading to misidentification and detrimental legal consequences. GC-MS is one of the most widely used analytical techniques employed by forensic laboratories all over the world for drug analysis. Nevertheless, thermolabile NPS, such as 25I-NBOH can generate artefacts in the traditional GC-MS analysis. In this paper, we describe the fragmentation mechanism of the 25I-NBOH into a major peak corresponding to 2C-I and a minor one corresponding to the associated ortho-phenolic benzyl ether (o-PBE), which exact identity is directly linked with the solvent used for the analysis. Also, a series of method adjustments is displayed, encompassing variation on the injector temperature, split ratio and flow ratio, although with no success to prevent 25I-NBOH thermo degradation in the GC injector. Furthermore, differential scanning calorimetry and thermogravimetric analysis demonstrated that 25I-NBOH's thermal stability is due to a smaller temperature window between fusion and decomposition points. Finally, we perform derivatization experiments and demonstrate how to overcome 25I-NBOH degradation in the GC/MS analysis. [ABSTRACT FROM AUTHOR]