SEM analysis of bond epoxy based layer between hardened concrete and SFRC repairing

Thin bonded concrete overlay are commonly used nowadays in repairing concrete structures. Nevertheless, the performance of the structural system (repaired structure) depends on the sound bond behaviour between old and new concretes. Frequently, adhesives based on epoxy resins provide this liaison. In this work the behaviour of three different types of based epoxy adhesives was observed in the bonding of different strength concrete class. Samples for backscattered scanning electron microscopy (BSE) were prepared from extracted pieces - containing the bonding layer - of non reinforced concrete slabs overlaid with thin bonded steel fibre reinforced concrete (SFRC) layer. Different features of each bonding layer epoxy resin type which may explain differentiate mechanical pull-off results as well as failure modes were observed. Micrographs obtained with BSE give clearly bond layer arrangement and minimum and maximum thickness, typical air voids porosity, presence of hydrated cement paste embedded in epoxy layer, mineral admixtures contained in epoxy, and also relevant micro fissures existing in concrete substrate.Fundação para a Ciência e a Tecnologia (FCT) - PhD grant number SFRH/BD/11232/ 2002.Sika SA.Companhia Geral de Cal e Cimento SA (SECIL).Degussa Construction Chemicals Portugal SA.Pedreiras Bezerras.Bekaert NV

Core-shell nanocomposites prepared by hierarchical co-assembly: the role of the carbon shell in catalytic wet peroxide oxidation processes

The diffraction pattern of Fe3O4 (not shown) confirmed the presence of only one phase, corresponding to magnetite with a lattice parameter a = 8.357 Å and a crystallite size of 16.6 ± 0.2 nm. The diffraction pattern of MGNC (not shown) confirmed the presence of a graphitic phase, in addition to the metal phase, suggesting that Fe3O4 nanoparticles were successfully encapsulated within a graphitic structure during the synthesis of MGNC. The core-shell structure of MGNC is unequivocally demonstrated in the TEM micrograph shown in Fig. 1b. Characterization of the MGNC textural and surface chemical properties revealed: (i) stability up to 400 oC under oxidizing atmosphere; (ii) 27.3 wt.% of ashes (corresponding to the mass fraction of Fe3O4); (iii) a micro-mesoporous structure with a fairly well developed specific surface area (SBET = 330 m2 g-1); and (iv) neutral character (pHPZC = 7.1). In addition, the magnetic nature of MGNC (Fig. 2) is an additional advantage for possible implementation of in situ magnetic separation systems for catalyst recovery

Light absorption properties of southeastern Bering Sea waters: Analysis, parameterization and implications for remote sensing.

The absorption coefficients of phytoplankton (aPHY(λ)), non-algal particles (NAP) (aNAP(λ)) and colored dissolved organic matter (CDOM) (aCDOM(λ)) were investigated and parameterized in the southeastern Bering Sea during July 2008. The absorption coefficients were well structured with respect to hydrographic and biogeochemical characteristics of the shelf. The highest values of aPHY(443) were observed offshore and the lowest values of aPHY(443) were found in the coastal domain, a low productivity region associated with limited macronutrients. Values of aDG(λ) (aCDOM(λ) + aNAP(λ)) revealed an east–west gradient pattern with higher values in the coastal domain, and lower values in the outer domain. Lower chlorophyll specific aPHY(λ) (a*PHY(λ)) observed relative to middle and lower latitude waters indicated a change in pigment composition and/or package effect, which was consistent with phytoplankton community structure. aCDOM(λ) was the dominant light absorbing coefficient at all wavelengths examined except at 676 nm. Modeling of remote-sensing reflectance (Rrs(λ)) and the diffuse attenuation coefficient (Kd(λ)) from inherent optical properties revealed the strong influence of aCDOM(λ) on Rrs(λ) and Kd(λ). Good optical closure was achieved between modeled and radiometer measured Rrs(λ) and Kd(λ) with average percent difference of less than 25% and 19% respectively, except at red wavelengths. The aCDOM(λ) accounted for > 50% of Kd(λ) which was vertically variable. Chlorophyll-a calculated by the NASA standard chlorophyll-a algorithm (OC4.v6) was overestimated due to higher aCDOM(λ) and underestimated due to lower a*PHY(λ) at low and high concentrations of chlorophyll-a, respectively

The use of genetic algorithms for structural optimization of hybrid sandwich panels

This paper describes the procedures followed to develop an optimization method for the design of a sandwich panel to be used in flooring applications. This sandwich panel is composed of polyurethane foam core, fibre reinforced polymer bottom layer and webs, and a fibre reinforced mortar top layer. The possibility of adopting additional internal ribs to increase the flexural and shear stiffness was also considered. The panel was described using a standard stacking sequence, coded as a string, using continuous variables to describe the geometric, economic and environmental parameters, and discrete variables to describe the laminate stack architecture. The optimization procedure was based on a global approach strategy, divided into two steps: (i) firstly, the features of each individual panel solution were assessed by analytical procedures and a fitness was assigned using a ranking function; (ii) secondly, the multi-objective optimization problem was solved by using a genetic algorithm, which performs a random search from generation to generation and keeps the “best individuals”. Penalty criteria were also considered when any panel solution was not satisfying the restrictions and design requirements. Different solutions were obtained by imposing different restrictions to the design of the sandwich panel, namely considering: (i) the length; (ii) the width; and, (iii) the use of one or two types of fibres (carbon and glass). This paper discusses the results obtained, both regarding the performance of the optimization procedure developed and the optimal solutions obtained for each case studied.The study presented in this paper is a part of the research project “EasyFloor – Development of composite sandwich panels for rehabilitation of floor buildings”, with reference number 3480, supported by ANI, through FEDER. The last author acknowledge the grant SFRH/BSAB/114302/2016 provided by FCT.info:eu-repo/semantics/publishedVersio

Shear behaviour of polyurethane foam

Polymeric based foams are widely used as insulation or structural core materials. Typically, plastic foams such as polyurethane (PUR) are commercially available in a variety of densities and, consequently, with distinct mechanical properties to fulfil a wide range of uses and applications. Usually, in sandwich construction, PUR foams are used as core material enclosed by two external faces of higher stiffness and strength. Since the lightweight PUR foams are relatively inexpensive, they are prone to be used as core material in sandwich construction, but may limit the ultimate strength of the sandwich panels due to core shear failure. Thus, a detailed characterization of PUR mechanical properties, namely shear modulus and shear strength, is required to efficiently use these materials in structural applications. Thereby, the present study deals with the experimental characterisation of the shear behaviour of a specific PUR closed-cell foam, with density of 70 kg/m3, in particular, considering the implications of size effect on the obtained results and on the estimation of the material properties. The experimental procedure was based on the standards ISO 1922 and ASTM C273, as well as, other existing publications, considering that this PUR is intended to be used as structural core material in sandwich panels for flooring purposes. Instrumentation included a load cell, LVDTs and digital image correlation. The present work details the experimental program and analyses the main results obtained.The study presented in this paper is a part of the research project “EasyFloor – Development of composite sandwich panels for rehabilitation of floor buildings”, with reference number 3480, supported by ANI, through FEDER.info:eu-repo/semantics/publishedVersio

A hybrid cementitious based-G/CFRP sandwich panel: concept, design and initial outcomes

Nowadays, the advantages of using fibre-reinforced polymers (FRP) in Civil Engineering structures are very well-known. In comparison to other materials, the FRPs show high strength-to-weight and stiffness-to-weight ratios, as well as high corrosion resistance [1]. Moreover, they can be easily moulded into complex shapes during the manufacturing process. Due to the slenderness of the cross section components and systems [2], and their significant initial cost [3], the FRPs are typically used along with other materials in composite structural elements. In the recent years, the FRPs have been increasingly used in composite sandwich panels designed for the building and housing industry [4]. However, in terms of flooring solutions, the sandwich panels still reveal some limitations for the most typical values of spans and loads in buildings [5]. In order to overcome the aforementioned drawbacks, the EasyFloor project was launched to develop enhanced composite sandwich panels for rehabilitation of floors in buildings. One of the important innovations included in the project relies on the use of both glass and carbon fibre roving (G/CFRP). This hybrid solution aims at improving significantly both the strength and stiffness. Furthermore, the top face of the panel is made of steel fibre reinforced self-compacting micro concrete (SFRSCMC), instead of the usual FRP compressive face, aiming to overcome face wrinkling issues. Additionally, this solution can provide higher ductility, fire endurance and impact resistance [6]. Furthermore, polycianurate (PIR) closed-cell foam is used as core material of the panel. Proper adhesion between G/CFRP and SFRSCMC is developed in order to obtain the full bending capacity of the composite solution. Finally, the FRP component is produced by pultrusion, taking all the advantages of this manufacturing process. The final proposal for the hybrid sandwich panel was obtained through the use of genetic algorithms in the design, which consisted in optimizing the geometric and the mechanical properties of the panel, taking into account the following features: (i) structural and energy efficiency; (ii) durability, versatility of use, ease of handling, quick assembly and production; (iii) low maintenance needs and aesthetics. The present work describes the design solution that resulted from the optimization procedure and subsequently presents initial experimental results regarding the mechanical characterization of the different materials, as well as the FRP/SFRSCMC interface. The experimental program comprised: (i) tensile and flexural tests on both the bottom and external ribs of the C/GFRP laminate skins; (ii) tensile, compressive and direct shear tests on both foam core materials (PIR); (iii) compressive and flexural tests on the SFRSCMC top face, and; (iv) pull-off tests for the characterization of the connection between the SFRSCMC and FRP using different types of adhesives.This work is part of the research project “EasyFloor – Development of composite sandwich panels for rehabilitation of floor buildings”, involving the company ALTO – Perfis Pultrudidos, Lda., CERis/Instituto Superior Técnico and ISISE/University of Minho, supported by FEDER funds through the Operational Program for Operational Program for Competitiveness and Internationalization (POCI) and the Portuguese National Innovation Agency (ANI) - project no. 3480 (POCI-01-0247-FEDER-003480). The authors would like to thanks the following companies for suppling the adhesives: KERAKOLL, MAPEI and SIKADUR.info:eu-repo/semantics/publishedVersio

From program strategic planning to program initiation: lessons learned from a collaborative university-industry R&D case study

This paper aims to contribute to knowledge by presenting the lessons learned resultant from a large case study composed by three collaborative University-Industry RD funded programs between the University of Minho (UMinho) and Bosch Car Multimedia Portugal (Bosch). The three programs selected amount to a total investment of above €109 million, over the period between 2013 and 2021, involving more than one thousand University researchers and Industry collaborators. The lessons learned are limited to the time span from Program Strategic Planning, where new project ideas/innovation opportunities are identified and developed for the preparation of the 'Funding Application', to Program Initiation, where the program effectively initiates after the negotiation of the 'Funding Contract'. The collection, analysis and implementation of lessons learned allowed the development of a structured process to guide University-Industry partners on the path to transform some newly identified project ideas into the initiation of a large RD funded program. The proposed process is currently adopted by the governance structure of Bosch and UMinho partnership and other UMinho partnerships with Industry.This work has been supported by FCT – Fundação para a Ciência e Tecnologia within the Project Scope: UID/CEC/00319/2019, by the Research Grant: SFRH/BPD/111033/2015, and by the Portugal Incentive System for Research and Technological Development. Project in co-promotion nº 039334/2018