Acid Attack on Cement Mortars Modified with Rubber Aggregates and EVA Polymer Binder

The acid attack on cement mortars modified with rubber aggregates and EVA polymer binder was studied. Mortar specimens were prepared using a type CEM I 42.5 Portland cement and siliceous sand, as well as by substituting 25% of sand with shredded used automobile tires, and by adding EVA polymer in two percentages (5% and 10% of cement mass). Some specimens were only air cured, at laboratory conditions, and their compressive strength and water absorption were determined. The rest specimens were stored in acid solutions (HCl, H2SO4, HNO3) after 28 days of initial curing, and stored at laboratory temperature. Compressive strength tests, mass measurements and visual inspection took place for 28 days. Compressive strength and water absorption of the air-cured specimens were significantly decreased when rubber aggregates are used. The addition of EVA polymer further reduced water absorption, while had no important impact on strength. Compressive strength values were affected in a greater extent by hydrochloric acid solution, followed by sulfate and nitric acid solutions. The addition of EVA polymer decreased compressive strength loss for the specimens with rubber aggregates stored in hydrochloric and nitric acid solutions. The specimens without polymer binder showed similar mass loss, which was higher in sulfate acid solution followed by hydrochloric and nitric acid solutions. The use of EVA polymer delayed mass loss, while its content did not affect it significantly

Microstructural characterization of dental zinc phosphate cements using combined small angle neutron scattering and microfocus X-ray computed tomography.

Abstract Objective To characterize the microstructure of two zinc phosphate cement formulations in order to investigate the role of liquid/solid ratio and composition of powder component, on the developed porosity and, consequently, on compressive strength. Methods X-ray powder diffraction with the Rietveld method was used to study the phase composition of zinc oxide powder and cements. Powder component and cement microstructure were investigated with scanning electron microscopy. Small angle neutron scattering (SANS) and microfocus X-ray computed tomography (XmCT) were together employed to characterize porosity and microstructure of dental cements. Compressive strength tests were performed to evaluate their mechanical performance. Results The beneficial effects obtained by the addition of Al, Mg and B to modulate powder reactivity were mitigated by the crystallization of a Zn aluminate phase not involved in the cement setting reaction. Both cements showed spherical pores with a bimodal distribution at the micro/nano-scale. Pores, containing a low density gel-like phase, developed through segregation of liquid during setting. Increasing liquid/solid ratio from 0.378 to 0.571, increased both SANS and XmCT-derived specific surface area (by 56% and 22%, respectively), porosity (XmCT-derived porosity increased from 3.8% to 5.2%), the relative fraction of large pores ≥50 μm, decreased compressive strength from 50 ± 3 MPa to 39 ± 3 MPa, and favored microstructural and compositional inhomogeneities. Significance Explain aspects of powder design affecting the setting reaction and, in turn, cement performance, to help in optimizing cement formulation. The mechanism behind development of porosity and specific surface area explains mechanical performance, and processes such as erosion and fluoride release/uptake

Modular and generic IoT management on the cloud

Cloud computing and Internet of Things encompass various physical devices that generate and exchange data with services promoting the integration between the physical world and computer-based systems. This work presents a novel Future Internet cloud service for data collection from Internet of Things devices in an automatic, generalized and modular way. It includes a flexible API for managing devices, users and permissions by mapping data to users, publish and subscribe context data as well as storage capabilities and data processing in the form of NoSQL big data. The contributions of this work include the on the fly data collection from devices that is stored in cloud scalable databases, the vendor agnostic Internet of Things device connectivity (since it is designed to be flexible and to support device heterogeneity), and finally the modularity of the event based publish/subscribe service for context oriented data that could be easily utilized by third party services without worrying about how data are collected, stored and managed

Monitoring Durability of Limestone Cement Paste Stored at Conditions Promoting Thaumasite Formation

The durability of Portland-limestone cement with high limestone content was monitored at conditions promoting thaumasite formation. Pore structure and deterioration characteristics were assessed with X-ray micro-computed tomography and correlated with material‘s strength. Changes in crystalline and amorphous phases of the cement paste were investigated with X-ray powder diffraction and solid state nuclear magnetic resonance spectroscopy. Rapid deterioration was observed, evolving as a front causing concentric crack patterns followed by detachment of the part of specimen in contact with the corrosive solution. This ultimately led to loss of structural integrity after 4 months of exposure. During sulfate attack, thaumasite, ettringite and gypsum formed at the expense of portlandite, calcite and monocarboaluminate hydrate. Furthermore, polymerization of silicate chains in C-S-H and deterioration of C-S-H also occurre

Autonomous inspection and repair of aircraft composite structures

This paper deals with the development of an innovative approach for inspection and repair of damage in aeronautical composites that took place in the first two years of the H2020 CompInnova project which. The aim is a newly designed robotic platform for autonomous inspection using combined infrared thermography (IRT) and phased array (PA) non-destructive investigation for damage detection and characterization, while integrated with laser repair capabilities. This will affect the increasing societal need for safer aircraft in the lowest possible cost, while new and effective techniques of inspection are needed because of the rapidly expanding use of composites in the aerospace industry

Quantification of microstructural changes in limestone cement paste stored in sulfate environment at low temperature

Samples of cement paste based on mixed cement with limestone admixture were stored in a magnesium sulfate solution for 6 months at 5 ° C to monitor the development of sulfate corrosion and its effect on microstructure. The extent of corrosion was evaluated by several different techniques. The paste samples were scanned at monthly intervals by X-ray tomography for non-destructive quantification of the pore structure and extent of damage, along with a description of the phase changes in the microstructure using X-ray diffraction and infrared spectroscopy. Compressive strength testing confirmed the effect of corrosion on the mechanical resistance of the samples. The results show a rapid course of degradation propagating in an irregular band, caused primarily by the formation of expandable sulfur-based corrosion products, the consequent crack formation and loss of internal cohesion of the material. The occurrence of both ettringite and thaumasite and gypsum was confirmed in the damaged parts

Durability of limestone cement concrete in combined chloride and sulfate environment

The behavior of Portland limestone cements in the combined chloride and sulfate environment was studied. Portland limestone cements may contain limestone as a main constituent in percentages ranging between 6% and 35% (EN 197-1 (2000)). A problem associated with the use of limestone in cement and concrete is that it may exhibit a lack of durability due to the formation of thaumasite as a result of sulfate attack at low temperatures. Building constructions can be found in areas near the sea, where groundwater, contaminated with sea water, contains significant amounts of chloride and sulfate ions. Thus, it is of great interest to study the formation of thaumasite, the chloride diffusion, as well as the reinforcement corrosion in the combined chloride and sulfate environment. Concrete and mortar specimens were prepared using ordinary Portland cement and two Portland limestone cements. Additional specimens were made by partial substitution of the limestone cement with natural pozzolana, fly ash, ground granulated blastfurnace slag or metakaolin. The specimens were immersed in chloride and sulfate solutions and stored at 5oC. Concrete deterioration due to sulfate attack was evaluated using visual examination, as well as mass and compressive strength measurements. Thaumasite formation was identified using the XRD analytical technique. Chloride diffusion was studied through the chloride profiles that were experimentally obtained. Mortar reinforcement corrosion was investigated measuring corrosion potential, as well as using the linear polarization method, while mass loss of the steel rebars and specimens’ carbonation depth were also determined. Limestone cement concrete is more susceptible to thaumasite formation compared to that produced by ordinary cement. Both chloride diffusion and reinforcement corrosion are more intensive when limestone cements are used. The use of mineral admixtures in limestone cement concrete improved its durability against sulfate attack, while also lead to lower chloride diffusion. Chlorides intercept and delay the sulfate attack on concrete specimens made without mineral admixtures. On the contrary, chlorides amplify the deterioration caused by sulfates, when specimens contain mineral admixtures. Sulfates favor both chloride diffusion and reinforcement corrosion. Fly ash was proved as the most efficient mineral admixture, followed by metakaolin and blastfurnace slag. Natural pozzolana presented the most limited beneficial effect.Διερευνήθηκε η συμπεριφορά ασβεστολιθικών τσιμέντων σε συνδυασμένο περιβάλλον χλωριόντων και θειικών ιόντων. Τα ασβεστολιθικά τσιμέντα Portland μπορούν να περιέχουν τον ασβεστόλιθο ως κύριο συστατικό σε ποσοστά 6-35% (EN 197-1 (2000)). Το πρόβλημα, που σχετίζεται με τη χρήση τους, είναι η ενδεχόμενη σημαντική απώλεια ανθεκτικότητας του σκυροδέματος, λόγω της επίδρασης των θειικών ιόντων και του σχηματισμού του ταουμασίτη ως προϊόντος φθοράς σε χαμηλές θερμοκρασίες. Μεγάλο μέρος των δομικών έργων στη χώρα μας βρίσκεται σε περιοχές κοντά στη θάλασσα, όπου υπάρχουν υπόγεια ύδατα, που περιέχουν σημαντικά ποσοστά χλωριόντων και θειικών ιόντων, λόγω υφαλμύρωσης. Σκοπός της διατριβής είναι η μελέτη και η αντιμετώπιση του «προβλήματος του ταουμασίτη», της διάχυσης των χλωριόντων και της διάβρωσης του οπλισμού σε συνδυασμένο περιβάλλον των ανωτέρω ιόντων. Παρασκευάστηκαν δοκίμια σκυροδέματος και κονιάματος αμιγούς και δύο ασβεστολιθικών τσιμέντων Portland, καθώς και δοκίμια, όπου το ασβεστολιθικό τσιμέντο ενισχύθηκε με φυσική ποζολάνη, ιπτάμενη τέφρα, σκωρία υψικαμίνων και μετακαολίνη. Τα δοκίμια τοποθετήθηκαν σε διαλύματα χλωριόντων και θειικών ιόντων στους 5oC. Στα δοκίμια κονιάματος είχε πακτωθεί χαλύβδινος οπλισμός. Η προσβολή από τα θειικά ιόντα εκτιμήθηκε με οπτική επιθεώρηση και μετρήσεις μάζας και αντοχής σε θλίψη των δοκιμίων. Ο ταουμασίτης ταυτοποιήθηκε με την αναλυτική τεχνική XRD. Η διάχυση των χλωριόντων μετρήθηκε βάσει των προφίλ που προέκυψαν πειραματικά. Για τη διερεύνηση της διάβρωσης του οπλισμού έγιναν μετρήσεις δυναμικού διάβρωσης, γραμμικής πόλωσης, απώλειας μάζας των οπλισμών, καθώς και μέτρηση του βάθους ενανθράκωσης των δοκιμίων. Τα ασβεστολιθικά τσιμέντα οδήγησαν σε πιο ευάλωτο σκυρόδεμα κατά την προσβολή από τα θειικά ιόντα, σε μεγαλύτερη διάχυση χλωριόντων και σε εντονότερη διάβρωση του οπλισμού, σε σχέση με το αμιγές. Τα ποζολανικά υλικά βελτίωσαν, γενικά, τη συμπεριφορά του ασβεστολιθικού τσιμέντου. Τα χλωριόντα παρεμπόδισαν τη φθορά από τα θειικά ιόντα όταν δεν χρησιμοποιήθηκαν ποζολανικά υλικά στη σύνθεση του σκυροδέματος. Το αντίθετο συνέβη όταν αντικαταστάθηκε το ασβεστολιθικό τσιμέντο με τα συγκεκριμένα υλικά. Τα θειικά ιόντα οδήγησαν σε μεγαλύτερη διάχυση των χλωριόντων και σε εντονότερη διάβρωση του οπλισμού. Η ιπτάμενη τέφρα παρουσίασε τη μεγαλύτερη αποτελεσματικότητα ακολουθούμενη από το μετακαολίνη και τη σκωρία υψικαμίνων. Η φυσική ποζολάνη επέδειξε την πιο περιορισμένη ενισχυτική δράση

MAGINAV: Long-Term Accurate Navigation Algorithm Using Inertial and Magnetic Field Sensor Fusion

MAGINAV (MAGnetic Inertial NAVigation) algorithm provides accurate estimation of velocity, attitude and position in long-term. It is utilized in a specialized pedestrian navigation system that consists of a three-axis accelerometer, a three-axis gyroscope, and a three-axis magnetometer mounted on the shoe of a walking human. MAGINAV compensates for the attitude error, accumulated over time by using a second attitude estimation obtained by fusing the measurements of the accelerometer and the magnetometer Instead of employing a complex Attitude Heading Reference System (AHRS), MAGINAV utilizes the computationally efficient TRIAD algorithm, alongside two popular algorithms for zero-velocity detection and magnetic-disturbance detection respectively. The proposed algorithm undergoes testing in an outdoor environment using low-cost commercial inertial and magnetic field sensors. Remarkably, it achieves exceptional long-term accuracy, with a position error that is less than 0.25% of the total distance in a 20-minute walk spanning 1.3km

Durability of limestone cement concrete in combined chloride and sulfate environment

258 σ.Σκυρόδεμα, Ασβεστολιθικά τσιμέντα, Ανθεκτικότητα, Θειικά ιόντα, Χλωριόντα, Διάχυση χλωριόντων, Διάβρωση οπλισμούConcrete, Limestone cements, Durability, Sulfates, Chlorides, Chloride diffusion, Reinforcement corrosionΚωσταντίνος Χ. Σωτηριάδη