224 research outputs found

    Integrated sensor network for monitoring steel corrosion in concrete structures

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    [EN] Corrosion is one of the main triggering factors affecting the service life and durability of structures. Several methods are used for corrosion studies but electrochemical techniques are the most commonly applied. Corrosion processes monitoring and control by means of non-destructive techniques, such as the implementation of embedded sensors, has been the target of many works.  It is possible to obtain relevant information of structural corrosion processes in real time. This document describes a system including specific equipment and which allows obtaining relevant information about these corrosion processes. This system is formed by a sensor network. There are several types of electrodes, which are distributed throughout the structure under study and a specific equipment developed by the research group, which is used to determine pertinent parameters such as the corrosion potential (Ecorr) and the corrosion density (icorr) by applying sequences of potentiostatic pulses. The system allows to reliably determine the corrosion rate in different areas of the structure. The sensor, due to its configuration, provides information of a specific area of the structure, but on the other hand it is involved in the galvanic events that can occur along the structure by differential aeration, galvanic cells, etc. because the sensor is not isolated from the structure.  This system also procures information of buried and submerged elements. Besides, it is possible to obtain information related to temperature, concrete resistance. The system includes specific potentiometric sensors to monitor chloride access and carbonatation processes.The pre-doctoral scholarship was granted to Román Bataller Prats by the Research Staff Training Program, “Formación de Personal Investigador (FPI) 2012” from Universitat Politécnica de Valéncia and to José Enrique Ramón Zamora by the University Faculty Training Program FPU13/0091, “Formación del Profesorado Universitario (FPU) 2013” from the Spanish Ministry of Science and Innovation. ETSIE (UPV) by their support to the laboratory is also gratefully acknowledged.Ramón Zamora, JE.; Gandía Romero, JM.; Valcuende Payá, MO.; Bataller Prats, R. (2016). Integrated sensor network for monitoring steel corrosion in concrete structures. VITRUVIO - International Journal of Architectural Technology and Sustainability. 1(1):65-79. https://doi.org/10.4995/vitruvio-ijats.2016.5191SWORD65791

    Effect of synthesis parameters on the performance of alkali-activated non-conformant EN 450 pulverised fuel ash

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    The fly ash reported in this paper is coarser than conventional pulverised fuel ash (PFA), with loss on ignition (LOI) exceeding 10.8%. Consequently, it is precluded from being used as a supplementary cementitious material (SCM) according to EN 450 and disposed in landfills. Alkali-activation of such PFAs is considered here. Three concentrations of sodium hydroxide (NaOH) were separately blended with water glass at different ratios to modify the silica modulus. Heat of reaction, setting time, compressive strength and drying shrinkage were investigated as a function of activator composition. Specimens were either cured at room temperature or hydro-thermally treated at 75 °C for five hours. The results show that by optimizing the activator composition, a binder with a 28 day compressive strength of 25 MPa can be synthesised from such PFAs even at room temperature. Among the activator parameters, the alkali content was observed to be most influential

    The influence of rice husk ash addition on the properties of metakaolin-based geopolymers

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    This paper investigates the replacement of metakaolin (MK) with rice husk ash (RHA) in the production of alkali-activated binders or geopolymers. The influence of the RHA addition on compressive and flexural strength, as well as water absorption and apparent porosity were determined, in terms of the percentage of RHA in the mixture and molar ratios of the mixes. Fourier Transform Infrared (FTIR) spectroscopy and Energy Dispersive spectroscopy (EDS) were carried out to assess the changes in the microstructure of the geopolymer matrices with the RHA addition. Results have shown that RHA may be a supplementary precursor for geopolymers. The composition of the geopolymer matrices containing 0-40% RHA is very similar, which indicates that the additional Si provided by RHA is not incorporated to the geopolymer matrix. In addition, geopolymers with RHA content higher than 40% present a plastic behavior, characterized by extremely low strength and high deformation, which can be attributed to the formation of silica gel in formulations containing variable Si/Al ratio

    Influence of slag composition on the stability of steel in alkali-activated cementitious materials

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    Among the minor elements found in metallurgical slags, sulfur and manganese can potentially influence the corrosion process of steel embedded in alkali-activated slag cements, as both are redox-sensitive. Particularly, it is possible that these could significantly influence the corrosion process of the steel. Two types of alkali-activated slag mortars were prepared in this study: 100% blast furnace slag and a modified slag blend (90% blast furnace slag? 10% silicomanganese slag), both activated with sodium silicate. These mortars were designed with the aim of determining the influence of varying the redox potential on the stability of steel passivation under exposure to alkaline and alkaline chloride-rich solutions. Both types of mortars presented highly negative corrosion potentials and high current density values in the presence of chloride. The steel bars extracted from mortar samples after exposure do not show evident pits or corrosion product layers, indicating that the presence of sulfides reduces the redox potential of the pore solution of slag mortars, but enables the steel to remain in an apparently passive state. The presence of a high amount of MnO in the slag does not significantly affect the corrosion process of steel under the conditions tested. Mass transport through the mortar to the metal is impeded with increasing exposure time; this is associated with refinement of the pore network as the slag continued to react while the samples were immersed

    Depressurization and deformation characteristics of a bursting pipe : The effect of surrounding fluids

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    [No Abstract Available]Applied Science, Faculty ofMechanical Engineering, Department ofGraduat

    Properties and performance of SI-rich geopolymer binder systems

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    This paper examines specific roles of various constituent oxides on the hydrolysis and condensation reactions that underpin the properties and performance of high silica geopolymer binder systems. Geopolymer systems formulated to high Si/Al ratios provide an ideal system for this form of analysis given their potential for mainstream engineering applications. For this study, specific emphasis was placed on the roles of silica and alkali species present in the feedstock material and their impact on mechanical properties such as early strength development. It is observed, that high silica geopolymers with SiO2/Al2O3 > 15 can be synthesized as compared to conventional geopolymers which generally have SiO 2/Al2O3 = 2-4. Prior to curing, such high-Si mixtures display a more viscous consistency than conventional geopolymers and have a lower pH after setting. The relative high initial strength gains of the systems are complemented with good bonding characteristics. The overall performance trends of these silica-rich systems are explored and discussed in this Paper
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