Browsing by Keyword "Microwave"
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Item Application of microwave and induction heating on fibre-reinforced cementitious materials for the demolition of structures(Editorial Universitat Politecnica de Valencia, 2019) Treviño, Roque Borinaga; Orbe, Aimar; Canales, Javier; Cuadrado, Jesus; Norambuena-Contreras, Jose; Crespo, Iñigo; Banos, Beatriz Garcia; PROMETALNowadays, strengthening and refurbishing of existing structures on urban areas has gained interest in order to reduce costs by avoiding both the use of construction raw materials and the disposal of construction and demolition waste on landfill. Usually, existing structures need to be locally demolished in order to replace either the existing corroded reinforcement or strengthen the existing structure. Among all the existing demolition methods, microwave and induction heating have been proven as a good alternative to generate a local damage with little noise and dust production, which is a desirable feature when structures are in urban areas. However, there is a lack of information about the behaviour of both damaging methods when steel fibre-reinforced concretes are involved. This paper studies the influence of the steel fibre addition on the damaging capacity of both microwave and induction heating demolition methods. For that purpose, mortars containing two different steel fibres (steel fibres used for concrete reinforcement and brass covered steel needles used for mortar reinforcement) were added in three different proportions (0%, 0.5% and 1% by unit volume of mortar) and exposed to up to 10 min of either microwave heating (0.003-0.03 W/mm3, 2.45 GHz) or induction heating (0.016-0.023 W/mm3, 18 kHz). With the aim of evaluating the damage caused by the heating methods, test specimens were visually checked, and mechanical properties were determined via flexural and compressive strength tests. According to the results, mortars exposed to either microwave or induction heating suffered a sudden, violent disintegration without noticing any previous damage on the mortar specimens. Results proved that pressure increment on water-saturated pores caused the failure no matter the fibre type used as a reinforcement. However, for microwave heating, the reflection of microwaves on the fibres tended to concentrate the heating effect on the specimen surface, resulting in higher surface temperatures, but lower damaging potential of the demolition method. Furthermore, similar failure mechanism was observed on oven-dried mortars exposed to microwave heating. Nevertheless, oven dried mortars exposed to induction heating suffered a highly variable, silent and controlled damage, presenting a highly varying quantity of fracture planes that decreased its flexural and compressive strengths by up to 38% and 31%, respectively.Item A comparative study of the feasibility of cellular MAX phase preforms formation by microwave-assisted SHS and SPS techniques(2020-05) Dmitruk, Anna; Lagos, M.A.; Naplocha, Krzysztof; Egizabal, Pedro; EXTREMAT; Tecnalia Research & InnovationTwo methods were evaluated in terms of manufacturing of MAX phase preforms characterized with open porosity: microwaveassisted self-propagating high-temperature synthesis (SHS) and spark plasma sintering (SPS). The main purpose of fabrication of such open-porous preforms is that they can be successfully applied as a reinforcement in metal matrix composite (MMC) materials. In order to simulate the most similar conditions to microwave-assisted SHS, the sintering time of SPS was significantly reduced and the pressure was maintained at a minimum value. The chosen approach allows these two methods to be compared in terms of structure homogeneity, complete reactive charge conversion and energy effectivity. Study was performed in Ti-Al-C system, in which the samples were compacted from elemental powders of Ti, Al, C in molar ratio of 2:1:1. Manufactured materials after syntheses were subjected to SEM, XRD and STEM analyses in order to investigate their microstructures and chemical compositions. As was concluded, only microwave-assisted SHS synthesis allows the creation of MAX phases in the studied system. SPS technique led only to the formation of intermetallic secondary phases. The fabrication of MAX phases’ foams by microwave-assisted SHS presents some interesting advantages compared to conventional manufacturing methods. This work presents the characterization of foams obtained by microwave-assisted SHS comparing the results with materials produced by SPS. The analysis of SPS products for different sintering temperatures provided the better insight into the synthesis of MAX phases, supporting the established mechanism. Dissimilarities in the heating mechanisms that lead to the differing synthesis products were also discussed.