Characterisation of mechanical and thermal properties in flax fabric reinforced geopolymer composites

This paper presents the mechanical and thermal properties of flax fabric reinforced fly ash based geopolymer composites. Geopolymer composites reinforced with 2.4, 3.0 and 4.1 wt% woven flax fabric in various layers were fabricated using a hand lay-up technique and tested for mechanical properties such as flexural strength, flexural modulus, compressive strength, hardness, and fracture toughness. All mechanical properties were improved by increasing the flax fibre contents, and showed superior mechanical properties over a pure geopolymer matrix. Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) studies were carried out to evaluate the composition and fracture surfaces of geopolymer and geopolymer/flax composites. The thermal behaviour of composites was studied by thermogravimetric analysis (TGA) and the results showed significant degradation of flax fibres at 300 °C

Συμβολή στη διερεύνηση των μηχανισμών γεωπολυμερισμού μεταλλουργικών αποβλήτων με έμφαση στις σκωρίες ηλεκτροκαμίνων

Development of new environmentally friendly technologies is required in order to improve the management of mining and metallurgical wastes and to moderate various environmental impacts, as well as, to minimise the disposal cost. Geopolymerisation is an emerging technology that may contribute to the utilisation of various wastes and the development of new materials withadvanced properties. Geopolymer synthesis using low calcium ferronickel slag is a novel researchtopic. Limited research has been carried out, specifically in Australia, France and Ukraine. Most of these efforts involve utilization of alumino-silicate materials, fly ash or high calcium slags (>40%) in order to develop new products and immobilize hazardous elements. The present PhD thesis aims to investigate the mechanisms of the reactions taking place when geopolymers are synthesised from mining and metallurgical wastes, with emphasis on ferronickel slag. The effect of various factors is examined when slag-based geopolymers are subjected to compressive strength testing, in order to optimise synthesis conditions. The factors examined include the use of alkaline activating solutionof various concentrations; the addition of kaolinite, metakaolinite, pozzolan, CaO, fly ash from Megalopolis or Ptolemais thermal power stations, red mud and silica sand; the water content, the pre-curing time, the heating temperature and the heating and aging period. Each of the above-mentioned factors plays a decisive role in the compressive strength of the final products. The excess of Al and Si provided from the raw materials does not fully react during geopolymerisation and, therefore, results in decreased compressive strength. The addition of an activating solution using the optimum concentrations (about 8 Μ ΚΟΗ or 6 Μ NaOH and 8 % w/w Na2SiO3) improves strength substantially. Optimum water content improves workability of the paste and prevents the development of pores and cracks. However, in order to develop new materials with desired mechanical properties for specific applications, appropriate pre-curing (2 days), heating (80 oC for 48 hours) and aging time (28 days) should be considered. Structural stability and durability of geopolymers, as well as dissolution of hazardous components were studied by immersing them in various corrosive and acidic solutions. Slag-based geopolymers show a better behaviour compared with slag-kaolinite geopolymers. The strength of geopolymers decreases substantially only when they are immersed in corrosive solutions, such as simulated acid rain, HCl 0.5 Ν or 0.05 Ν. Addition of heavy metals (Pb, Cu, Ni or Cr) as nitrate or sulfate salts in high percentages affects negatively the compressive strength. However, the application of TCLP test shows that Pb, Cu, Ni or Cr are stabilized effectively in slag-based geopolymers. In order to elucidate the microstructure of geopolymers mineralogical studies using XRD, optical microscopy with reflected light, SEM, FTIR and TG, were carried out. Despite the amorphous nature of geopolymers, these techniques when combined assist in the elucidation of several geopolymerisation mechanisms.Το πρόβληµα της διαχείρισης των µεταλλευτικών και µεταλλουργικών αποβλήτων ώστε να περιοριστούν οι διάφορες περιβαλλοντικές επιπτώσεις και να ελαχιστοποιηθεί το κόστος διάθεσης, οδηγεί στην αναζήτηση νέων φιλικών προς το περιβάλλον τεχνολογιών. Ο γεωπολυµερισµός αναδύεται ως µια πιθανή τεχνολογία που συµβάλλει στην αξιοποίηση µερικών αποβλήτων δηµιουργώντας νέα υλικά µε χαρακτηριστικές ιδιότητες και σηµαντικό εύρος εφαρµογών. Η σύνθεση γεωπολυµερών από σκωρίες σιδηρονικελίου µε χαµηλή περιεκτικότητα σε ασβέστιο, αποτελεί ένα πρωτότυπο ερευνητικό αντικείµενο. Αντίστοιχες προσπάθειες έχουν γίνει σε µερικά ερευνητικά ιδρύµατα του εξωτερικού, όπως της Αυστραλίας, Γαλλίας και Ουκρανίας. Οι περισσότερες έρευνες αφορούν στη χρήση αργιλο-πυριτικών υλικών, ιπτάµενης τέφρας ή σκωριών µε υψηλή περιεκτικότητα σε ασβέστιο (>40%) για την παραγωγή νέων προϊόντων και τη σταθεροποίηση επικίνδυνων συστατικών. Στόχος της παρούσας διδακτορικής διατριβής είναι να διερευνηθούν οιµηχανισµοί των γεωπολυµερικών αντιδράσεων που λαµβάνουν χώρα όταν χρησιµοποιούνται µεταλλευτικά και µεταλλουργικά απόβλητα και κυρίως σκωρία σιδηρονικελίου. Η επίδραση των διαφόρων παραγόντων ερευνάται µέσω δοκιµών αντοχής των γεωπολυµερών σε θλίψη, ώστε να βελτιστοποιηθεί η διαδικασία σύνθεσης. Οι παράγοντες που µελετήθηκαν είναι η χρήση αλκαλικού διαλύµατος ενεργοποίησης σε διάφορες συγκεντρώσεις, η προσθήκη καολινίτη, µετακαολινίτη,ποζολάνης, CaO, ιπτάµενης τέφρας Μεγαλόπολης/Πτολεµαΐδας, ερυθράς ιλύος και χαλαζιακής άµµου σε γεωπολυµερή σκωρίας, η περιεκτικότητα σε νερό, ο χρόνος ωρίµανσης, η θερµοκρασία θέρµανσης καθώς και η περίοδος θέρµανσης και γήρανσης. Κάθε ένας από τους παραπάνω παράγοντες παίζει καθοριστικό ρόλο στην αντοχή των τελικών προϊόντων. Η περίσσεια Al και Si που παρέχεται στο σύστηµα από τα προσθετικά υλικά δεν αντιδρά πλήρως µε αποτέλεσµα να µη συµµετέχει στις αντιδράσεις γεωπολυµερισµού µειώνοντας σηµαντικά την τελική αντοχή. Ηπροσθήκη διαλύµατος ενεργοποίησης στις κατάλληλες αναλογίες (περίπου 8 Μ ΚΟΗ ή 6 Μ NaOH και 8 % κ.β. Na2SiO3) ενισχύει την αντοχή των γεωπολυµερών. Το προστιθέµενο νερό βελτιώνει την πλαστικότητα του µίγµατος και περιορίζει την ανάπτυξη πόρων και ρωγµών. Ωστόσο, προκειµένου να αποκτήσουν τα γεωπολυµερή σκωρίας ικανοποιητικές αντοχές και να παραχθούν δευτερογένη προϊόντα µε επιθυµητές εφαρµογές, θα πρέπει να χρησιµοποιηθούν οι βέλτιστες συνθήκες ωρίµανσης (2 ηµέρες), θέρµανσης (48 ώρες στους 80 οC) και γήρανσης (28 ηµέρες). Η ανθεκτικότητα των γεωπολυµερών µελετήθηκε µέσω εµβάπτισής τους σε διαβρωτικά και όξινα περιβάλλοντα και προσδιορισµού των επικίνδυνων στοιχείων που διαλυτοποιούνται. Τα γεωπολυµερή σκωρίας εµφανίζουν γενικότερα καλύτερη συµπεριφορά από τα γεωπολυµερή σκωρίας-καολινίτη. Η αντοχή τους µειώνεται σηµαντικά µόνο όταν εµβαπτίζονται σε διαβρωτικά διαλύµατα όπως προσοµοιωµένης όξινης βροχής, HCl 0,5 Ν ή 0,05 Ν. Η προσθήκη βαρέων µετάλλων (Pb, Cu, Ni ή Cr) σε µορφή νιτρικών ή θειϊκών αλάτων επηρεάζει αρνητικά την τελική αντοχή των γεωπολυµερών όσο αυξάνεται το ποσοστό προσθήκης. Ωστόσο µέσω της δοκιµής τοξικότητας (TCLP) αποδεικνύεται ότι τα παραπάνω µέταλλα σταθεροποιούνται σε ικανοποιητικό βαθµό στα γεωπολυµερή σκωρίας. Για τη διερεύνηση της µορφολογίας των γεωπολυµερών χρησιµοποιήθηκαν οι µέθοδοι ορυκτολογικής ανάλυσης XRD, οπτική µικροσκοπία ανακλωµένου φωτός, SEM, FTIR και TG. Παρά τη χαρακτηριστική άµορφη φύση των γεωπολυµερών, οιτεχνικές αυτές συµβάλλουν σε κάποιο βαθµό, στην κατανόηση των πολύπλοκων µηχανισµών των αντιδράσεων που λαµβάνουν χώρα

Number words in ‘her’ language, dialogism and identity-work: the case of little Mariah

Based on an ethnographic study, we explore the potential of experimenting with multiple languages for number words as part of young children’s mathematical activity. Data from a preschool classroom activity on ‘number words in “other” languages’ exemplify a complex process of discursive identity-work and dialogism amongst children, parents, teacher, and researchers. The focus is on the case of little Mariah, a Pakistani immigrant girl in Greece, who experiences participation by sharing number knowledge in her mother tongue Urdu, and highlights how gendered, racial, or language-related discourses weave her learner identity in a multilingual preschool classroom. © 2016 Informa UK Limited, trading as Taylor & Francis Group

Investigation of the Retention Mechanism of Cephalosporins by Zwitterionic Hydrophilic Interaction Liquid Chromatography

The importance of cephalosporin antibiotics in medicine requires the development of high performance separation methods for their analysis. In this paper cefazolin, cefuroxime, cefoxitin, cefaclor and ceftriaxone were used as model compounds to investigate the retention mechanism under zwitterionic HILIC conditions. The analysis was performed using a ZIC®-HILIC analytical column (150.0 × 2.1 mm i.d., particle size 3.5 μm, 200 Å) with isocratic elution. The mobile phase was a mixture of acetonitrile and ammonium acetate or formate buffer. To get a better insight into the retention mechanism on ZIC®-HILIC columns the main factors influencing the retention and selectivity of the analytes have been thoroughly investigated. It is shown that the type of the salt and its concentration along with the volume fraction of water in the mobile phase and pH of the aqueous buffer greatly affect the retention of the tested cephalosporins due to their structures and physicochemical properties. The method was applied successfully to the analysis of injection dosage forms containing cefazolin, cefuroxime and cefoxitin. © 2016, Springer-Verlag Berlin Heidelberg

Adsorption of Scandium and Neodymium on Biochar Derived after Low-Temperature Pyrolysis of Sawdust

The objective of this study was to investigate the adsorption of two rare earth elements (REEs), namely scandium (Sc) and neodymium (Nd), on biochar produced after low temperature pyrolysis (350 °C) of wood sawdust. The biochar was characterized with the use of several analytical techniques, namely X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and thermogravimetric (TG) analysis, while the pH at point of zero charge (pHPZC) was also determined. The experimental conditions were: absorbent concentration 1–10 g·L−1, REE concentration in solution 20 mg·L−1, contact time for equilibrium 24 h, temperature 25 °C and stirring speed 350 rpm. The efficiency of biochar was compared to that of a commercial activated carbon. Geochemical modelling was carried out to determine speciation of Nd and Sc species in aqueous solutions using PHREEQC-3 equipped with the llnl database. The experimental results indicated the potential of low temperature produced biochar, even though inferior to that of activated carbon, to adsorb efficiently both REEs. The equilibrium adsorption data were very well fitted into the Freundlich isotherm model, while kinetic data suggested that the removal of both REEs follows the pseudo-second order kinetic reaction. Finally, the most probable adsorption mechanisms are discussed

Number words in ‘her’ language, dialogism and identity-work : the case of little Mariah

Based on an ethnographic study, we explore the potential of experimenting with multiple languages for number words as part of young children's mathematical activity. Data from a preschool classroom activity on number words in 'other' languages exemplify a complex process of discursive identity-work and dialogism amongst children, parents, teachers and researchers. The focus is on the case of little Mariah, a Pakistani immigrant girl in greece, who experiences participation by sharing number knowledge in her mother tongue Urdu, and highlights how gendered, racial or language-related discourses weave her learner identity in a multilingual preschool classroom

Number words in 'other' languages: The case of little Marram

International audienceThe present paper, based on a small scale critical eth-nographic study, explores the process of experimenting collaboratively with multiple language use for number words as part of young children's mathematical learning activity. Data from a teaching experiment called 'Number words in 'other' languages' is utilized to illustrate the creation of a culturally responsive context with children aged 4 to 6, their parents, the classroom teacher and the researchers. The focus is on the case of little Marram, a Pakistani girl who lives in Greece and who experiences participation by sharing number knowledge in her dominant home language, Urdu. It is highlighted how discourses on gender and language determine Marram's learner identity-work in the multilingual preschool classroom

Assessment of groundwater contamination risk in an agricultural area in north Italy

In the present study a specific approach is followed, considering the Pesticide DRASTIC and Susceptibility index (SI) methods and a GIS framework, to assess groundwater vulnerability in the agricultural area of Albenga, in north Italy. The results indicate “high” to “very high” vulnerability to groundwater contamination along the coastline and the middle part of the Albenga plain, for almost 49% and 56% of the total study area for Pesticide DRASTIC and SI methods, respectively. These sensitive regions depict characteristics such as shallow depth to groundwater, extensive deposits of alluvial silty clays, flat topography and intensive agricultural activities. The distribution of nitrates concentration in groundwater in the study area is slightly better correlated with the SI (0.728) compared to Pesticide DRASTIC (0.693), thus indicating that both methods are characterized by quite good accuracy. Sensitivity analysis was also performed to acknowledge statistical uncertainty in the estimation of each parameter used, assess its impact and thus identify the most critical parameters that require further investigation in the future. Depth to water is the parameter that exhibited the largest impact on the Pesticide DRASTIC vulnerability index followed by the impact of the vadose zone and topography. On the other hand, the SI method is more sensitive to the removal of the topography parameter followed by the aquifer media and the depth to water parameters