Thaumasite form of sulfate attack in limestone cement mortars: A study on long term efficiency of mineral admixtures

Concrete and mortar made from limestone cement may exhibit a lack of durability due to the formation of thaumasite. The addition of minerals that improve the concrete durability is expected to slow down the formation of thaumasite. in this work the effect of natural pozzolana, fly ash, ground granulated blast-furnace slag and metakaolin on the thaumasite formation in limestone cement mortar is examined. A limestone cement, containing 15% w/w limestone, was used. Mortar specimens were prepared by replacing a part of limestone cement with the above minerals. The specimens were immersed in a 1.8% MgSO4 solution and cured at 5 and 25 degrees C. The status of the samples after a storage period of 5 years was reported based on visual inspection, compressive strength, mass measurements, ultrasonic pulse velocity measurements and analytical techniques. It is concluded that the use of specific minerals, as partial replacement of cement, inhibits thaumasite formation in limestone cement mortar. (C) 2008 Elsevier Ltd. All rights reserved

THE HYDROMAGNESITE DEPOSITS OF THE ATLIN AREA, BRITISH COLUMBIA, CANADA, AND THEIR INDUSTRIAL POTENTIAL AS A FIRE RETARDANT

Η έρευνα αυτή έχει ως στόχο την μελέτη των αποθέσεων υδρομαγνησίτη της περιοχής Atlin της Βρετανικής Κολομβίας στον Καναδά και τη δυνατότητα αξιοποίησης τους στην διεθνή αγορά των επιβραδυντών καύσεως. Οι ορυκτοί επιβραδυντές καύσης, όπως τα Mg- και Ca/Mg-ανθρακικά πετρώματα, είναι φιλικοί προς το περιβάλλον, καθώς παράγουν μη-τοξικά και μη-διαβρωτικά αέρια και θεωρούνται ασφαλέστεροι. Στα πλαίσια αυτής της έρευνας, συλλέγησαν και αναλύθηκαν εβδομήντα αναγνωριστικά και δύο ολικά δείγματα από την εν λόγω περιοχή. Τα αποτελέσματα έδειξαν ότι τα ανωτέρω δείγματα αποτελούνται κυρίως από υδρομαγνησίτη, με μικρά ποσοστά πολύ λεπτόκοκκου, μαλακού και πεπλατυσμένου μαγνησίτη. Το γενικό συμπέρασμα είναι ότι η ορυκτολογική σύσταση των δειγμάτων, η συμπεριφορά τους κατά τη θερμική αποσύνθεση, καθώς και οι χημικές και φυσικές τους ιδιότητες, τα καθιστούν κατάλληλα για χρήση τους ως υλικά πυροπροστασίας. Επιπλέον, η ^κότητα των δειγμάτων είναι αρκετά υψηλή και συγκρίσιμη με άλλα εμπορεύσιμα υλικά που περιέχουν υδρομαγνησίτη. Τα αποθέματα υδρομαγνησίτη στην περιοχή Atlin είχαν υπερεκτιμηθεί στο παρελθόν στους 110.000 τόνους. Προτείνεται μια τεχνο-οικονομική εκτίμηση για να πραγματοποιηθεί ένας πιο ακριβής υπολογισμός των αποθεμάτων της περιοχήςThis research examines the potential of the hydromagnesite deposits at Atlin in British Columbia, Canada, for the mineral fire-retardant market. Mineral fire retardants, such as Mg- and Ca/Mg-carbonates, are environmentally friendly, producing non-toxic and non-corrosive gases during their thermal decomposition. During this research, 70 sediment samples and two bulk samples were collected from the study area and analysed. The results showed that the Atlin deposits are composed mostly of hydromagnesite with minor amounts of very fine-grained, soft and platy magnesite. The general conclusion is that the mineralogical composition of the samples, their behavior during thermal decomposition, and their chemical and physical properties, make them suitable for use as white fillers for flame-retardants. Additionally, the whiteness of the samples is sufficient and comparable to other commercial hydromagnesite-bearing rocks. The Atlin reserves of the hydromagnesite ore bodies were overestimated in past literature as 110,000 tons. A more precise calculation of the reserves during a technoeconomic assessment is required

THE HYDROMAGNESITE DEPOSITS OF THE ATLIN AREA, BRITISH COLUMBIA, CANADA, AND THEIR INDUSTRIAL POTENTIAL AS A FIRE RETARDANT

Η έρευνα αυτή έχει ως στόχο την μελέτη των αποθέσεων υδρομαγνησίτη της περιοχής Atlin της Βρετανικής Κολομβίας στον Καναδά και τη δυνατότητα αξιοποίησης τους στην διεθνή αγορά των επιβραδυντών καύσεως. Οι ορυκτοί επιβραδυντές καύσης, όπως τα Mg- και Ca/Mg-ανθρακικά πετρώματα, είναι φιλικοί προς το περιβάλλον, καθώς παράγουν μη-τοξικά και μη-διαβρωτικά αέρια και θεωρούνται ασφαλέστεροι. Στα πλαίσια αυτής της έρευνας, συλλέγησαν και αναλύθηκαν εβδομήντα αναγνωριστικά και δύο ολικά δείγματα από την εν λόγω περιοχή. Τα αποτελέσματα έδειξαν ότι τα ανωτέρω δείγματα αποτελούνται κυρίως από υδρομαγνησίτη, με μικρά ποσοστά πολύ λεπτόκοκκου, μαλακού και πεπλατυσμένου μαγνησίτη. Το γενικό συμπέρασμα είναι ότι η ορυκτολογική σύσταση των δειγμάτων, η συμπεριφορά τους κατά τη θερμική αποσύνθεση, καθώς και οι χημικές και φυσικές τους ιδιότητες, τα καθιστούν κατάλληλα για χρήση τους ως υλικά πυροπροστασίας. Επιπλέον, η ^κότητα των δειγμάτων είναι αρκετά υψηλή και συγκρίσιμη με άλλα εμπορεύσιμα υλικά που περιέχουν υδρομαγνησίτη. Τα αποθέματα υδρομαγνησίτη στην περιοχή Atlin είχαν υπερεκτιμηθεί στο παρελθόν στους 110.000 τόνους. Προτείνεται μια τεχνο-οικονομική εκτίμηση για να πραγματοποιηθεί ένας πιο ακριβής υπολογισμός των αποθεμάτων της περιοχήςThis research examines the potential of the hydromagnesite deposits at Atlin in British Columbia, Canada, for the mineral fire-retardant market. Mineral fire retardants, such as Mg- and Ca/Mg-carbonates, are environmentally friendly, producing non-toxic and non-corrosive gases during their thermal decomposition. During this research, 70 sediment samples and two bulk samples were collected from the study area and analysed. The results showed that the Atlin deposits are composed mostly of hydromagnesite with minor amounts of very fine-grained, soft and platy magnesite. The general conclusion is that the mineralogical composition of the samples, their behavior during thermal decomposition, and their chemical and physical properties, make them suitable for use as white fillers for flame-retardants. Additionally, the whiteness of the samples is sufficient and comparable to other commercial hydromagnesite-bearing rocks. The Atlin reserves of the hydromagnesite ore bodies were overestimated in past literature as 110,000 tons. A more precise calculation of the reserves during a technoeconomic assessment is required

Hippocampal - diencephalic - cingulate networks for memory and emotion: An anatomical guide

This review brings together current knowledge from tract tracing studies to update and reconsider those limbic connections initially highlighted by Papez for their presumed role in emotion. These connections link hippocampal and parahippocampal regions with the mammillary bodies, the anterior thalamic nuclei, and the cingulate gyrus, all structures now strongly implicated in memory functions. An additional goal of this review is to describe the routes taken by the various connections within this network. The original descriptions of these limbic connections saw their interconnecting pathways forming a serial circuit that began and finished in the hippocampal formation. It is now clear that with the exception of the mammillary bodies, these various sites are multiply interconnected with each other, including many reciprocal connections. In addition, these same connections are topographically organised, creating further subsystems. This complex pattern of connectivity helps explain the difficulty of interpreting the functional outcome of damage to any individual site within the network. For these same reasons, Papez’s initial concept of a loop beginning and ending in the hippocampal formation needs to be seen as a much more complex system of hippocampal–diencephalic–cingulate connections. The functions of these multiple interactions might be better viewed as principally providing efferent information from the posterior medial temporal lobe. Both a subcortical diencephalic route (via the fornix) and a cortical cingulate route (via retrosplenial cortex) can be distinguished. These routes provide indirect pathways for hippocampal interactions with prefrontal cortex, with the preponderance of both sets of connections arising from the more posterior hippocampal regions. These multi-stage connections complement the direct hippocampal projections to prefrontal cortex, which principally arise from the anterior hippocampus, thereby creating longitudinal functional differences along the anterior–posterior plane of the hippocampus

Assessing the chemical involvement of limestone powder in sodium carbonate activated slag

This study aims to investigate the effect of limestone powder (LP) on the reaction of sodium carbonate activated slag. The results show that the incorporated LP up to 30% improves the strength development, especially at advanced curing ages. A slightly accelerated reaction is observed for samples containing low amount of LP (≤5%), while mixture with 10% LP shows the optimized results with respect to the heat release and strength development. Chemical effect of incorporating LP is observed at high replacement levels (≥15%), indicated by the formation of a new phase, natron (Na2CO3·10H2O). Besides, relatively high contents of hydrotalcite-like phases are generated when increasing the dosage of limestone powder. The chemical changes, including the volume changes of generating natron and the transformation of natron to calcite, is potentially responsible for the enhanced mechanical properties