Indirect tensile behaviour of fibre reinforced alkali-activated composites

There are currently still some sustainability-related issues that need to be tackled within the construction sector. Namely, cement production is accountable for nearby 5% of the worldwide total CO2-eq release. Therefore, environmentally viable and economically sustainable solutions need to be pursued in order to mitigate the use of Portland cement. The incorporation of industrial waste in concrete compositions, such as fly ash (from coal combustion in power stations) is a feasible alternative. The properties of these residues may be enhanced through alkaline activation, which is able to yield aluminosilicate-based materials with excellent physico-chemical properties. Nonetheless, these materials exhibit a brittle behaviour. Therefore, the present work addresses the study of alkali-activated composites reinforced with sisal fibres. For that purpose, alkali-activated Class F fly ash was mixed with natural fibres and the composite mechanical behaviour was assessed through both indirect tensile and compressive tests. Four different fibre contents, in wt % of fly ash (0, 0.2, 0.6 and 1%), two fibre lengths (13 and 50 mm) and four curing periods (14, 28, 56 and 112 days) were considered. Results confirm that the post-cracking response of these composites was improved with the inclusion of sisal fibres. In general, higher residual tensile strengths and dissipated energy were observed for the lengthier fibres, i.e., 50 mm.info:eu-repo/semantics/publishedVersio

Rate effect in inclined fibre pull-out for smooth and hooked-end fibres: a numerical study

Based on a numerical model to simulate the static behaviour of a smooth fibre extracted from a cementitious matrix, a rate dependent friction law, widely used in earthquake engineering for steady-state slip phenomena, is proposed to capture the rate effect observed in dynamic pull-out tests for both smooth and hooked-end fibres. After calibrating the friction coefficients with the experimental results of smooth fibres, the model is subsequently applied to predict the pullout behaviour of both smooth and hooked-end fibres at different inclination angles (0∘, 30∘ and 60∘) loaded at three different velocities (0.01, 0.1 and 1 mm/s). The global tendency of all the pull-out curves was captured, fibre’s cross sectional deformations were also reproduced remarkably well. Moreover, the developed model helps to cast light on the different mechanisms related to the pull-out process.Ministerio de Ciencia, Innovación y Universidades, Spain, through the projects BIA2015-68678-C2-1-R and RTC-2017-6736-3, is acknowledged. Elisa Poveda appreciates the funding from the International Campus of Excellence CYTEMA, as well as, the University of Castilla-La Mancha, throughout Ayudas para estancias en universidades en el extranjero en 2019 en el ámbito del plan propio de investigación susceptibles de co-financiación por el Fondo FEDER, Programa 010100021 to fund her stay in the University of Minho during 2018 and 2019, respectively. Manuel Tarifa acknowledges the financial support from the Department of Applied Mechanics and Project Engineering, UCLM (2018), and from the Programa propio de I+D+i de la Universidad Politécnica de Madrid para realizar estancias de investigación internacional igual o superior a un mes (2019), with the same purpose. The last two authors acknowledge the support provided by the project ICoSyTec (POCI-01-0145-FEDER-027990) financed by FCT and co-funded by FEDER through the Operational Competitiveness and Internationalization Programme (POCI). The authors thank BEKAERT for the supply of fibre

Betão de alta resistência reforçado com fibras exposto a elevadas temperaturas

Atualmente, a utilização de betões de elevada resistência tem vindo a aumentar, nomeadamente, em aplicações com requisitos especiais, tais como arranha-céus, torres eólicas, centrais nucleares, etc. No entanto, com o aumento significativo da resistência, este tipo de material desenvolve um comportamento significativamente mais frágil. Adicionalmente, quando expostos a elevadas temperaturas, como no caso de incêndio, dependendo da temperatura e tempo de exposição poder-se-á verificar uma diminuição significativa da resistência à compressão, fissuração bem como uma rotura explosiva. Neste trabalho apresentam-se e discutem-se os resultados do estudo da influência da temperatura no comportamento mecânico de microbetão de alta resistência reforçado com fibras de aço. Diversos provetes de betão de elevada resistência foram expostos a distintas temperaturas durante um período superior a uma hora, designadamente, 400, 500, 600 e 700 ºC. O comportamento mecânico, após exposição às diferentes temperaturas, foi avaliado através de ensaios de compressão, flexão e tração uniaxial e posteriormente comparado com o betão de referência (exposto à temperatura ambiente). Na generalidade, as propriedades mecânicas do betão de alta resistência diminuíram com o aumento da temperatura. Verificou-se um decréscimo mais acentuado da resistência à compressão, tração uniaxial e tração em flexão para temperaturas superiores a 400ºC.PTDC/ECM-EST/2635/2014, SFRH/BSAB/114302/2016.info:eu-repo/semantics/publishedVersio

Bond-Slip Mechanisms of Hooked-End Steel Fibers in Self-Compacting Concrete

Abstract. The experimental results of hooked-end steel fibers pullout tests on a self-compacting concrete medium are presented and discussed in this work. The influence of fiber embedment length on the fiber pullout behavior is studied. The role of the end hook of the fiber on the overall pullout behavior is also investigated by carrying out tests with fibers without its end hook, in order to separate the contribution of the frictional bond component from those derived from the mechanisms provided by the end hook of the fiber. Finally, the experimental bond-slip relationships are modeled by an analytical model

Earth-based render of tabique walls – an experimental work contribution

A research work focused on studying earth render for tabique application purposes is presented. Initially, a brief description of the tabique building technique is provided. The relevance of the application of this traditional building technique is also highlighted. Different compositions of earth render are experimentally analysed and the respective performance is evaluated. Flexural and compressive strengths, workability, drying shrinkage cracking and water resistance are the material properties assessed. A simple earth render is selected as being adequate for tabique building applications and it is applied on the manufacturing of a tabique wall sample. This wall sample is monitored in terms of thermal insulation ability and its thermal transmission coefficient is estimated. Taking into account that there is still a lack of published technical information related to this topic, this paper may contribute to solve this limitation and to give some guidance in future repairing processes of tabique construction. The technological benefit of adding lime or cement with earth is researched. Real tabique timber structure samples are applied in order to validate the obtained experimental results.info:eu-repo/semantics/publishedVersio

Power electronics converters for an electric vehicle fast charging station with energy storage system and renewable energy sources

Fast Charging Stations (FCS) are a key element for the wide spreading of Electric Vehicles (EVs), by reducing the charging time to a range between 20 to 40 minutes. However, the integration of FCS causes some adverse impacts on the Power Grid (PG), namely the huge increase in the peak demand during short periods of time. This paper addresses the design of power electronics converters for an EV DC FCS with local storage capability and easy interface of renewables. In the proposed architecture, the energy storage capability is used to smooth the peak power demand and contributes to stabilize the PG. When integrated in a smart grid, the proposed architecture may even return some of the stored energy back to the PG. The accomplishment of the aforementioned objectives requires a set of different power electronics converters, described and discussed along the paper. In order to demonstrate the potentialities of the proposed EV DC FCS architecture, four different case studies were analysed.This work has been supported by FCT – Fundação para a Ciência e Tecnologia within the Project Scope: UID/CEC/00319/2019. This work is financed by the ERDF – COMPETE 2020 Programme, and FCT within project SAICTPAC/0004/2015-POCI-01-0145-FEDER-016434 and FCT within project PTDC/EEI-EEE/28813/2017. Mr. Luis A. M. Barros is supported by the doctoral scholarship PD/BD/143006/2018 granted by the Portuguese FCT agency. Mr. Tiago Sousa is supported by the doctoral scholarship SFRH/BD/134353/2017 granted by the Portuguese FCT agency

Photocatalysis of functionalised 3D printed cementitious materials

The main objective of this study was to evaluate the photocatalytic behaviour of 3D printed cementitious mortars that were functionalised with TiO2 nanoparticles. This study is one of the few available regarding functionalisation of 3D concrete printing (3DCP) with photocatalytic properties. Despite the fact 3DCP research is swiftly growing, it is still necessary further investigation to fully understand these materials’ physicochemical and mechanical properties, which will influence the functionalised properties of the composite. Due to the freeform nature of the 3DCP there are no moulds, therefore the functionalisation through coating can be performed in a much earlier stage than in conventional moulded concrete. The developed smart 3D printed concrete could promote the photodegradation of pollutants for self-cleaning and air purification. In particular, this study investigated the effect of two parameters on photocatalytic behaviour: light power intensity and the coating rate of nano-TiO2 particles. Surface coating was adopted as the functionalisation method, and the Rhodamine B dye degradation efficiency was used as an indicator to evaluate the photocatalytic behaviour. Additionally, the surface roughness and microstructure of the 3D printed cementitious mortar specimens were assessed to distinguish between the reference and TiO2 coated series. Scanning electron microscopy (SEM), X-ray Energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD) crystallography were carried out as three techniques to evaluate the morphology, composition, and microstructure of the specimens, respectively. The results indicated successful activation of catalyst particles under illumination, where higher light power intensity increased the degradation efficiency. Furthermore, dye degradation efficiency increased with increasing coating rates of nano-TiO2 particles on the surface of the specimens. The roughness of the 3D printed specimens’ surface was sufficient for settling the nano-TiO2 particles. Finally, microscopy results confirmed the presence and suitable distribution of the nano-TiO2 particles on the surface of the coated specimens.Support SECIL, SIKA, ELKEM and UNIBETAO, which graciously provided the required materials for printing the cementitious specimensThis work was partly financed by Fundaç˜ao para a Ciˆencia e a Tecnologia (FCT)/MCTES through national funds (PIDDAC) under the R&D Unit Institute for Sustainability and Innovation in Structural Engineering (ISISE), under reference UIDB/04029/2020. The authors acknowledge the support of DST group construction company for funding the project Chair dst/IB-S: Smart Systems for Construction. The first two authors would like to acknowledge the PhD grants SFRH/BD/143636/2019 and SFRH/BD/137421/2018 provided by the Portuguese Foundation for Science and Technology (FCT). Additionally, the authors would like to acknowledge FCT for the financing this research work by the project NanoAir PTDC/FIS-MAC/6606/2020 and the Strategic Funding UIDB/04650/ 2020–2023

Effect of the displacement rate and inclination angle in steel fiber pullout tests

This paper summarizes the results obtained in an experimental campaign on the effect of the displacement pullout rate and the inclination angle of the steel fiber pullout tests. For that purpose, specimens were obtained from a self-compacting concrete with a compressive strength of 86 MPa. In the experimental program, hooked-end steel fibers of 0.75 mm diameter and 60 mm length were used. Tests were executed with both hooked-end fibers, and smooth fibers obtained from the former by cutting the hooked end. For both type of fibers, their embedment length into concrete was 20 mm, and the influence of fiber inclination angle toward the load direction was investigated by adopting values of 0∘, 30∘ and 60∘. The tests were performed at displacement rates of 0.01, 0.1 and 1 mm/s. The results have shown that the peak pullout load increased with the inclination angle, in particular for the smooth series. Furthermore, higher displacement rates led to a higher energy absorption capacity for the pullout of the smooth fibers, while the energy absorption remained almost stable for hooked-end fibers.project BIA2015-68678-C2-1-R. M. Tarifa appreciates the financial support from the Department of Applied Mechanics and Project Engineering, UCLM (2018), and from the Programa propio de I+D+i de la Universidad Politécnica de Madrid para realizar estancias de investigación internacional igual o superior a un mes (2019), to do two stays at the University of Minho, Guimarães, Portugal. E. Poveda acknowledges the funding from the International Campus of Excellence CYTEMA and the University of Castilla-La Mancha, throughout Ayudas para estancias en universidades y centros de investigación en el extranjero en 2019 en el ámbito del plan propio de investigación susceptibles de cofinanciación por el Fondo Europeo de Desarrollo Regional (FEDER), Programa 010100021 to fund her stays in the University of Minho during 2018 and 2019, respectively. The authors thank the support of the Department of Civil Engineering and the Laboratory of the Structural Division (LEST), University of Minh

Application of nano-TiO2 and micro-PTFE on recycled asphalt mixtures for superhydrophobic functionalization

The main objective of this research is to improve the efficiency and durability of the superhydrophobic capability on asphalt mixtures. In general, the benefits of this capability on materials are several, for example, water-resistance, anti-icing, antibacterial, contaminant-free, self cleaning, anticorrosive, among others [1]. Through this type of functionalization, road engineering researchers seek to improve water repelling and resistance, and prevent ice formation on pavements [2–4]. Additionaly, it generates the self-cleaning ability, relevant to remove remove dust from the surface. All these aspects are mostly related to the mitigation of friction decrease caused by water, ice, or even dust over the surface of the pavements. The superhydrophobic capability is achieved when the Water Contact Angle (WCA) between a water droplet and the material surface is higher than 150° [1]. In this research, three asphalt mixtures, type AC 10, were functionalized: R (reference), without any recycled material; F, with 30% reclaimed asphalt pavement (RAP); and A, with 30% steel slags (SS). The functionalization process consisted of two successive spraying coatings: i) spraying of a diluted resin epoxy and ii) spraying of a solution composed of nano-TiO2 and micro-PTFE (under ethyl alcohol medium with a concentration of 4 g/L of each solute). The epoxy resin was diluted using butyl acetate with a proportion of 1:1 in mass. The cut asphalt mixture samples (25 x 25 x 15 mm3 ) were sprayed with 0.25, 0.50, 1, and 2 g of the diluted resin, resulting in a covering ratio of 0.1, 0.2, 0.4, and 0.8 mg/cm2 , and with 8 mL/cm2 of the particles’ solution both at room temperature. The wettability of the mixtures without any treatment, with only resin spraying coating and with both spraying coatings (resin and particles) was assessed by the Water Contact Angle (WCA). The results showed that F and R present similar initial WCA, 108° and 115° respectively, while mixture A presented a much higher WCA (131°). The spraying of the resin decreases the WCA, the higher resin content lead to lower WCA. The superhydrophobic capability was achieved for R and F samples with 0.25 and 0.50 g of resin spraying with particles. The mixture A achieved the superhydrophobicity only with 0.25 g of resin spraying with particle

MDL28170, a Calpain Inhibitor, Affects Trypanosoma cruzi Metacyclogenesis, Ultrastructure and Attachment to Rhodnius prolixus Midgut

BACKGROUND: Trypanosoma cruzi is the etiological agent of Chagas' disease. During the parasite life cycle, many molecules are involved in the differentiation process and infectivity. Peptidases are relevant for crucial steps of T. cruzi life cycle; as such, it is conceivable that they may participate in the metacyclogenesis and interaction with the invertebrate host. METHODOLOGY/PRINCIPAL FINDINGS: In this paper, we have investigated the effect of the calpain inhibitor MDL28170 on the attachment of T. cruzi epimastigotes to the luminal midgut surface of Rhodnius prolixus, as well as on the metacyclogenesis process and ultrastructure. MDL28170 treatment was capable of significantly reducing the number of bound epimastigotes to the luminal surface midgut of the insect. Once the cross-reactivity of the anti-Dm-calpain was assessed, it was possible to block calpain molecules by the antibody, leading to a significant reduction in the capacity of adhesion to the insect guts by T. cruzi. However, the antibodies were unable to interfere in metacyclogenesis, which was impaired by the calpain inhibitor presenting a significant reduction in the number of metacyclic trypomastigotes. The calpain inhibitor also promoted a direct effect against bloodstream trypomastigotes. Ultrastructural analysis of epimastigotes treated with the calpain inhibitor revealed disorganization in the reservosomes, Golgi and plasma membrane disruption. CONCLUSIONS/SIGNIFICANCE: The presence of calpain and calpain-like molecules in a wide range of organisms suggests that these proteins could be necessary for basic cellular functions. Herein, we demonstrated the effects of MDL28170 in crucial steps of the T. cruzi life cycle, such as attachment to the insect midgut and metacyclogenesis, as well as in parasite viability and morphology. Together with our previous findings, these results help to shed some light on the functions of T. cruzi calpains. Considering the potential roles of these molecules on the interaction with both invertebrate and vertebrate hosts, it is interesting to improve knowledge on these molecules in T. cruzi