Characterization of supplementary cementitious materials by thermal analysis

Working Group 1 of RILEM TC 238-SCM ‘Hydration and microstructure of concrete with supplementary cementitious materials (SCMs)’ is defining best practices for the physical and chemical characterization of SCMs, and this paper focusses on their thermal analysis. Thermogravimetric analysis (TGA) can provide valuable data on the chemical and mineralogical composition of SCMs. Loss-on-ignition (LOI) testing is a commonly used, standardized, but less sophisticated version of TGA that measures mass at endpoints only, with heating generally in air. In this paper we describe the use of TGA and LOI to characterize Portland cement with limestone additions, coal combustion fly ashes, ground-granulated blast furnace slag, calcined clays, and natural pozzolans. This paper outlines the value and limitations of TGA and LOI (in the formats defined in different standards regimes) for material characterization, and describes testing methods and analysis. TGA testing parameters affect the mass loss recorded at temperatures relevant for LOI measurements (700–1000 °C) of slags and fly ashes, mainly associated with oxidation reactions taking place upon heating. TGA of clays and natural pozzolans is utilized to identify optimal calcination conditions leading to dehydroxylation and consequent structural amorphization, particularly for kaolinite. However, dehydroxylation and amorphization do not occur at similar temperatures for all clays, limiting the applicability of TGA for this purpose. Although TGA is widely utilized for characterization of SCMs, the testing parameters significantly affect the results obtained, and TGA results require careful interpretation. Therefore, standardization of TGA testing conditions, particularly for LOI determination of slags and fly ashes, is required

High performance illitic clay-based geopolymer : Influence of the mechanochemical activation duration on the strength development

Proceedings of the 3rd International Conference on Calcined Clays for Sustainable Concrete, New Delhi, INDE, 15-/10/2019 - 17/10/2019Demonstrate the feasibility of an illitic clay-based geopolymer is the purpose of this study. If the thermal activation of standard precursors such as kaolin is a well-known process, the reactivity of illitic precursors required the combination of thermal and mechanochemical activation. The structural changes of the precursor material submitted to various grinding durations were followed by X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) and the amorphous phase rate calculated from XRD analyses was correlated with this parameter as well as the compressive strength (Rc) of the manufactured geopolymers. Mechanical properties increased with the grinding time and the decrease of L/S ratio of the geopolymer paste. Illitic clay-based geopolymers may reach high performance as demonstrated with a Rc at 28 days reaching 102 MPa. Finally, the relations between the amorphisation rate and the compressive strength of the geopolymers have been highlighte

Reducing fluoroscopy time during cardioverter-defibrillator implantation, performed with considering of myocardium perfusion scintigraphy results in patients with coronary artery disease

Aim. Implantable cardioverter­defibrillator (ICD) implantation technique optimization in patients with coronary artery disease (CAD) in order to reduce fluoroscopy time and total radiation dose to staff.Material and methods. Patients with CAD and indications for the ICD implantation were examined. Patients were divided into two groups. In first group before ICD implantation, patients underwent cardiac 99mTc­methoxy­isobutyl­isonitrile scintigraphy for right ventricle wall perfusion disorders assessment. In this group defibrillating lead was implanted to the septal position, if the perfusion disorders were in the apical segments, and to the apical position, if perfusion disorders were in the septal segment. In second group lead was implanted using conventional approach. Fluoroscopy duration and radiation dose were compared.Results. There were 58 patients (male­52, female­6, age­64,5±8,5 years) enrolled. The first group consisted of 27 (46,5%) patients. For 13 (48,1%) patient ICD was implanted for primary, and 14 (51,9%) one for secondary sudden cardiac death (SCD) prevention. In 14 (51,9%) cases in this group defibrillating lead was implanted to the apical and in 13 (48,1%) — to the septal position. The 2­nd group consisted of 31 (53,5%) patients. For 13 (41,9%) patient ICD was implanted for primary, and 18 (58,1%) one for secondary SCD prevention. In 15 (48,3%) cases in this group defibrillating lead was implanted to the apical and in 16 (51,7%) — to the septal position. There were significant differences between groups in terms of fluoroscopy duration  — 85,5±28,1 and 131,6±53,5 sec (р=0,0001) and radiation dose — 0,14±0,07 and 0,21±0,08 (p=0,0004) mSv, respectively.Conclusion. Assessment of right ventricular perfusion before ICD implantation reduce fluoroscopy time and total radiation exposure to staff