bluuebunny/crossref_metadata_2025 huggingface dataset:
Flipped Classroom: Do Students Perceive Readiness for Advanced Discussion?
Authors: Hoover Carrie Ann , Dinndorf-Hogenson Georgia Ann , Peterson Jennifer Lee , Tollefson Bethany Renae , Berndt Jodi Lisbeth , Laudenbach Nikki
Published: March 2018

Background:

Use of the flipped classroom model is recognized as a popular method of instruction. Effective preclass preparation methods can create more time for instructors to reinforce application, evaluation, and analysis of information using active learning strategies.

Method:

This quasi-experimental study used a convenience sample of 42 third-year baccalaureate nursing students. Students were randomized into two groups and received either a narrated video (vodcast) or guided readings for the preclass preparation. A quiz was administered to assess preparation prior to class, and students completed a survey following the classroom activities.

Results:

Students preferred media preparation to guided readings. This preference translated to higher quiz scores. Positive correlations were noted between quiz scores and students' understanding and increased confidence.

Conclusion:

Students' preference for the vodcast translated to the perception of an increase in confidence and understanding of the material. [
J Nurs Educ.
2018;57(3):163–165.]
Mobile Devices: A Distraction, or a Useful Tool to Engage Nursing Students?
Authors: Gallegos Cara , Nakashima Hannah
Published: March 2018

Background:

Engaging nursing students in theoretical courses, such as research, can be challenging. Innovative instructional strategies are essential to engage nursing students in theoretical nursing courses.

Method:

This article describes an educational innovation using technology as a tool in an undergraduate nursing research class. All students in the course received iPads for the semester. Lecture material was presented in class using Nearpod, an interactive presentation embedded with slides, multimedia components, and learning activities.

Result:

Students reported that using the mobile technology helped them minimize off-task activities, interact more with each other and the instructor, solve problems in the class, and develop skills and confidence related to their career.

Conclusion:

Allowing device use in the classroom, such as iPads and interactive mobile applications, can be a useful learning tool. Intentional use of technology and pedagogy can increase engagement and interaction with students. [
J Nurs Educ.
2018;57(3):170–173.]
Static and cyclic performance of cementitious composites reinforced with glass-fibres
Authors: Arabi N.
Published: March 2018

This paper concerns an experimental study of the influence of short glass-fibres randomly oriented of a reinforced cement-based composite on the mechanical behaviour. The matrix material parameters used are: cement/sand ratio and water/cement ratio fixed at 0.5; the glass-fibre content (0%, 0.5%, 1.0%, 1.5%, 2% and 2.5%) and fibre lengths (3, 6 and 12 mm). Composites mechanical characterisation under static behaviour at flexural and compression tests, shows that the reinforcement effect is beneficial only in flexural case. A synergy (matrix-reinforcement) was observed when fibre length of 12 mm is used with application rate of 2% in flexural. The fatigue behaviour determined by Wöhler plots (stress-number of cycles to rupture), derived from experimental results; showed a large results dispersion which is attributed to many causes initiating this damage. The cyclic tests illustrate brittle character of these materials; even with low-amplitude cycles of loading no adaptation of these materials can be reported.
Combined effect of nano-SiO2 and nano-Fe2O3 on compressive strength, flexural strength, porosity and electrical resistivity in cement mortars
Authors: Sanjuán M. A. , Argiz C. , Gálvez J. C. , Reyes E.
Published: March 2018

The compressive strength, flexural strength, porosity and electrical resistivity properties of cement mortars with nano-Fe2O3 and nano-SiO2 are studied. Amorphous silica is the main component of pozzolanic materials due to its reaction with calcium hydroxide formed from calcium silicate (C3S and C2S) hydration. The pozzolanic reaction rate is not only proportional to the amount of amorphous silica but also to the surface area available for reaction. Subsequently, fine nano-Fe2O3 and nano-SiO2 particles in mortars are expected to improve mortar performance. The experimental results showed that the compressive strength of mortars with nano-Fe2O3 and nano-SiO2 particles were lower than those obtained with the reference mortar at seven and 28 days. It was shown that the nano-particles were not able to enhance mechanical strength on every occasion. The continuous microstructural progress monitored by mercury intrusion porosimetry (MIP) measurements, pore-size distribution (PSD), total porosity and critical pore diameter also confirmed such results.
Using Google to Search Language Patterns in Web-Corpus: EFL Writing Pedagogy
Authors: Kvashnina Olga S. , Sumtsova Olga V.
Published: March 2018

The use of the Web as a corpus of language data and Google as a concordancer has been considered as one of the promising directions in the development of the EFL pedagogy. It has been stated by several researchers that the use of the popular search engine Google to hunt and define authentic language patterns is mostly advantageous for teaching EFL writing as well as mastering learning autonomy of the EFL students. The present article focuses on the advantages and opportunities of Google as a search engine in the Web-corpus for EFL writing pedagogy in technical universities. The authors compare the results of the current investigation with the outcomes of their previous study aimed at examining the potential of traditional linguistic corpora for EFL classroom. Although there is a strong need for further in-depth study of the considered issue, the comparative results obtained at this stage reveal high potential and remarkable advantage of the global web as a corpus, and Google as a search and access tool to authentic language patterns.
Design and Development of SECI and Moodle Online Learning Systems to Enhance Thinking and Innovation Skills for Higher Education Learners
Authors: Chootongchai Suparoek , Songkram Noawanit
Published: March 2018

This study aimed to design and develop an online learning system to enhance thinking and innovation skills for higher education learners. The objectives were to (1) design a system diagram, system architecture and functional structure for online learning framed by the SECI process (Socialization, Externalization, Combination and Internalization) and Moodle, (2) develop an online learning management system (LMS) with a new plug-in using Moodle, and (3) evaluate system suitability for the development of students’ thinking and innovation skills. The research methodology was developed using a literature review to identify core components, focus group interviews to verify the process, software development by Moodle LMS, and assessments to measure learning outcome. Research instruments consisted of interview questions, Moodle LMS, and a self-assessment questionnaire. Assessment data was evaluated through pre-test and post-test analysis. Results revealed a statistically significant difference between pre- and post-test scores in both thinking and innovation skills, with the post-test score higher than pre-test score at a 0.01 level of significance. Findings revealed that online learning systems had a positive influence on students’ thinking and innovation skills.
Construction of Multimedia Teaching Resource Management Evaluation Model in the Big Data Environment
Authors: Bian Wei
Published: March 2018

In view of the deficiencies in the studies of the multi-media teaching resource management method and resource management evaluation model, a multi-media teaching resource management evaluation model in the big data environment is proposed in this paper based on the existing work. The teaching resource management evaluation method of the proposed model is further studied based on the elaboration of the component elements of the model. Guided by the multimedia teaching resource management evaluation model, the construction method for the multimedia teaching resource management evaluation model is studied in the open big data environment. And the multimedia remote teaching data of 360 encyclopedia and news web pages are used as the basis for experimental verification. The results show that the proposed model and method can effectively evaluate the multimedia teaching resource management.
The Construction of Piano Teaching Innovation Model Based on Full-depth Learning
Authors: Wei An Shi
Published: March 2018

This paper presents a new method of building piano teaching innovation model based on full depth learning. The model includes the following main steps: (1) The normal behavior samples of piano teaching are obtained by the method of spectral clustering based on dynamic time homing (DTW), and the hidden Markov model; (2) to further train the hidden Markov model parameters in a large sample by means of iterative learning; (3) to use the maximum a posteriori (MAP) adaptive method to estimate the Hidden Markov Model (HMM) of the piano teaching behavior in a supervised manner; (4) The behavioral hidden Markov topology model is established for model estimation. The main features of this method are: it can automatically select the kinds and samples of the normal behavior patterns of piano teaching to establish an innovative model of piano teaching; the problem of under-learning of Hidden Markov Model (HMM) can be avoided in the case of fewer samples. The experimental results show that this model is more reliable than other methods.
Impact of Computer Remote Education on CLL Learning and Solutions
Authors: Liu Xuezhou
Published: March 2018

This paper aims at some impacts of computer remote education on the Chinese Language and Literature (CLL) learning of Chinese overseas students with a learning software enabled with remote education as a study case, to conduct a survey and analysis on how this type of learning software serves the students when they study and what is the best commercial learning software in the market by questionnaire survey, statistical analysis and summary methods. On this basis, it is concluded that the CLL learning software plays an important role in improving the learning efficiency and level of Chinese overseas students. But beyond that, the existing learning software in the market still have many limitations. In the end, to make such learning software play a better role in overseas students’ learning process, this paper proposes strategies for upgrading software in question by virtue of operating and popularizing more mature English learning software with remote education function, which provides a valuable reference for future improvement and promotion of similar software
Investigating Relationship Between Discourse Behavioral Patterns and Academic Achievements of Students in SPOC Discussion Forum
Authors: Liu Zhi , Zhang Wenjing , Cheng Hercy N. H. , Sun Jianwen , Liu Sannyuya
Published: March 2018

As an overt expression of internal mental processes, discourses have become one main data source for the research of interactive learning. To deeply explore behavioral regularities among interactions, this article firstly adopts the content analysis method to summarize students' engagement patterns within a course forum in a small private online course (SPOC) system. Secondly, through sentiment word matching and sentiment density calculation, the authors characterize the evolution trends of collective positive and negative sentiments, and compare sentiment strengths of different achieving students. The analytical result shows that there is a significant correlation between most engagement patterns and academic achievements, and high-achieving group seems more active than low-achieving group in terms of interactive, register, question, viewpoint and thematic postings. Besides, both of high and middle-achieving students are superior to low-achieving students on positive sentiment. But, there is no significant difference among high-, middle- and low-achieving students on negative sentiments.
An Analysis of the Structure and Evolution of the Distance Education Research Area Community in Terms of Coauthorships
Authors: Gomes Rodrigo Richard , Barbosa Marcelo Werneck
Published: March 2018

This article aims at characterizing the research community of Distance Education (DE) with respect to coauthorship, a special kind of collaboration among researchers, according to publications of 11 relevant DE journals. This article identified who the central researchers are, the topological properties of the coauthorship networks analyzed, the coauthorship patterns of each journal and the evolution of the DE community in the last 30 years. In order to achieve these goals, Social Network Analysis (SNA) was used, deriving centrality metrics, which depict the importance of researchers in the networks. This study found out that researchers who publish more papers are not necessarily the ones considered more central according to SNA. Besides, promising researchers, those linked to central researchers and are considered more likely to coauthor papers in the near future. Different coauthorship patterns among journals are described. Finally, a steep increase in the number of publications and coauthorships in the last decades was observed.
Digital Participatory Platforms for Co-Production in Urban Development
Authors: Falco Enzo , Kleinhans Reinout
Published: March 2018

A renewed interest has appeared in citizen co-production of public services due to financial pressure on governments. While social media are considered an important facilitator, many digital participatory platforms (DPPs) have been developed to facilitate co-production between citizens and governments in the context of urban development. Previous studies have delivered a fragmented overview of DPPs in a few socio-spatial contexts and failed to take stock of the rise of DPPs. This article aims to provide a more comprehensive picture of the availability and functionalities of DPPs. Through a systematic review, 113 active DPPs have been identified, analysed, and classified within a citizen-government relationship typology. Almost a quarter of these DPPs demonstrate a realistic potential for online and offline co-production between governments and citizens. The article critically analyses the characteristics of these DPPs and explores their real-world applications in urban development. The article concludes with directions for further research.
Game Creation in Youth Media and Information Literacy Education
Authors: Costa Conceição , Tyner Kathleen , Henriques Sara , Sousa Carla
Published: March 2018

This article presents the preliminary findings of GamiLearning (2015-2018), a research project that aims to promote critical and participative dimensions of Media and Information Literacy (MIL) in children through the creation of digital games. The project presents an innovative approach by arguing that MIL can be promoted through the process of creation and development of videogames. Students ages 9 to 14 years old from Portugal and Austin, Texas (USA) participated in the study. which included an intervention at school, was based on a constructivist/project-based approach. Fieldwork was conducted at four schools and a MIL questionnaire was used, based in a theoretical framework, and were administered before and after the project's intervention. Results from the four schools indicate statistically significant differences between pre and post questionnaires, considering MIL skills in general, and in several groups of skills, namely Operational Skills, Editorial Skills, Digital Identity Management Skills, Critical Media Literacy, Learning and Social Interaction.
Toward a Propensity-Oriented Player Typology in Educational Mobile Games
Authors: Gholizadeh Mehran , Taghiyareh Fattaneh , Alvandkoohi Saeed
Published: March 2018

The pivotal role of identifying types of players is inevitable in the game contexts, and educational games are not an exception. This article aims to present a model of player-game interaction in the mobile game-based learning setting regarding the behavioral propensity. This model comprises five different features inherited from the player typology literature including precision, perfection, punctuality, presence, and pace. To this end, we analyzed the activities of players in a mobile educational game and then tried to classify players based on their preferences in how to deal with the game. Furthermore, as a step toward determining the association of features with each other, multiple linear regression analysis was conducted. The outcome of the investigations resulted in a model representing player interaction with the game in a way that it could be used to classify different types of players in educational mobile games.
A Randomized Framework for Estimating Image Saliency Through Sparse Signal Reconstruction
Authors: Fu Kui , Li Jia
Published: March 2018

This article proposes a randomized framework that estimates image saliency through sparse signal reconstruction. The authors simulate the measuring process of ground-truth saliency and assume that an image is free-viewed by several subjects. In the free-viewing process, each subject attends to a limited number of regions randomly selected, and a mental map of the image is reconstructed by using the subject-specific prior knowledge. By assuming that a region is difficult to be reconstructed will become conspicuous, the authors represent the prior knowledge of a subject by a dictionary of sparse bases pre-trained on random images and estimate the conspicuity score of a region according to the activation costs of sparse bases as well as the sparse reconstruction error. Finally, the saliency map of an image is generated by summing up all conspicuity maps obtained. Experimental results show proposed approach achieves impressive performance in comparisons with 16 state-of-the-art approaches.
The Research on Shape Context Based on Gait Sequence Image
Authors: Wang Rong , Liu Yongkang , Hu Mengnan
Published: March 2018

A gait feature extraction method based on resampling shape context is proposed in this article. First, the moving target detection is carried out to obtain the target area of the human body. Second, the gait cycle is measured, and the contour points and the lower limb joints are selected as sampling points. Then, the different sampling points is placed in the polar coordinates of the origin, the number of sampling points in different cells is counted as the shape context; Finally, the feature vectors are constructed according to the shape context, and the minimum distance is used for classification and recognition. Simulation experiments based on resampling shape context are tested in CASIA gait Database A and Database B. The experimental results show that the method proposed in this article has a lower computational complexity and higher recognition rate when compared with the original shape context method, which can be used for gait recognition.
Visual Analytics of Long-Term Care Resource Utilization in Taiwan
Authors: Chu Kuo-Chung , Lu Hsin-Ke , Jiang Peng-Hua
Published: March 2018

This article describes how the phenomenon of an aging population in Taiwan has become increasingly evident in recent years as the elderly population dependency ratio has gradually risen. Therefore, a study on long-term care (LTC) resources has been a key issue that had needed discussion. Currently, Taiwan's government has enacted legislation and policies related to LTC, but most of them involved institutional care. The traditional idea of most elderly is aging in place, so this study has become very necessary. The study analyzed the Open Government Data of LTC to discuss the home care service resource utilization with regard to LTC.
A Hybrid Meta-Heuristic Approach for QoS-Aware Cloud Service Composition
Authors: Bhushan S. Bharath , Reddy Pradeep C. H.
Published: March 2018

Cloud is evolving as an outstanding platform to deliver cloud services on a pay-as-you-go basis. The selection and composition of cloud services based on QoS criteria is formulated as NP hard optimization problem. Traditionally, many optimization techniques are applied to solve it, but it suffers from slow convergence speed, large number of calculations, and falling into local optimum. This article proposes a hybrid particle swarm optimization (HPSO) technique that combines particle swarm optimization (PSO) and fruit fly (FOA) to perform the evolutionary search process. The following determines a pareto optimal service set which is non-dominated solution set as input to the proposed HPSO. In the proposed HPSO, the parameters such as position and velocity are redefined, and while updating, the smell operator of fruit fly is used to overcome the prematurity of PSO. The FOA enhances the convergence speed with good fitness value. The experimental results show that the proposed HPSO outperforms the simple particle swarm optimization in terms of fitness value, execution time, and error rate.
Recent Insights into CD4+ Th Cell Differentiation in Malaria
Authors: Soon Megan S. F. , Haque Ashraful
Published: March 2018

CD4+ Th cell differentiation is crucial for protecting against blood-stage Plasmodium parasites, the causative agents of malaria. It has been known for decades that more than one type of Th cell develops during this infection, with early models proposing a biphasic Th1/Th2 model of differentiation. Over the past decade, a large body of research, in particular, reports over the past 2–3 y, have revealed substantial complexity in the Th differentiation program during Plasmodium infection. In this article, we review how several studies employing mouse models of malaria, and recent human studies, have redefined the process of Th differentiation, with a particular focus on Th1 and T follicular helper (Tfh) cells. We review the molecular mechanisms that have been reported to modulate Th1/Tfh differentiation, and propose a model of Th1/Tfh differentiation that accommodates observations from all recent murine and human studies.
Decision to Return to Sport After Anterior Cruciate Ligament Reconstruction, Part I: A Qualitative Investigation of Psychosocial Factors
Authors: Burland Julie P. , Toonstra Jenny , Werner Jennifer L. , Mattacola Carl G. , Howell Dana M. , Howard Jennifer S.
Published: March 2018

Context: 

Return-to-sport criteria after anterior cruciate ligament (ACL) injury are often based on “satisfactory” functional and patient-reported outcomes. However, an individual's decision to return to sport is likely multifactorial; psychological and physical readiness to return may not be synonymous.

Objective: 

To determine the psychosocial factors that influence the decision to return to sport in athletes 1 year post–ACL reconstruction (ACLR).

Design: 

Qualitative study.

Setting: 

Academic medical center.

Patients or Other Participants: 

Twelve participants (6 males, 6 females) were purposefully chosen from a large cohort. Participants were a minimum of 1-year postsurgery and had been active in competitive athletics preinjury.

Data Collection and Analysis: 

Data were collected via semistructured interviews. Qualitative analysis using a descriptive phenomenologic process, horizontalization, was used to derive categories and themes that represented the data. The dynamic-biopsychosocial model was used as a theoretical framework to guide this study.

Results: 

Six predominant themes emerged that described the participants' experiences after ACLR: (1) hesitation and lack of confidence led to self-limiting tendencies, (2) awareness was heightened after ACLR, (3) expectations and assumptions about the recovery process influenced the decision to return to sport after ACLR, (4) coming to terms with ACL injury led to a reprioritization, (5) athletic participation helped reinforce intrinsic personal characteristics, and (6) having a strong support system both in and out of rehabilitation was a key factor in building a patient's confidence. We placed themes into components of the dynamic-biopsychosocial model to better understand how they influenced the return to sport.

Conclusions: 

After ACLR, the decision to return to sport was largely influenced by psychosocial factors. Factors including hesitancy, lack of confidence, and fear of reinjury are directly related to knee function and have the potential to be addressed in the rehabilitation setting. Other factors, such as changes in priorities or expectations, may be independent of physical function but remain relevant to the patient-clinician relationship and should be considered during postoperative rehabilitation.
Dyslexic learners’ experiences with their peers and teachers in special and mainstream primary schools in North-West Province
Authors: Leseyane Monicca , Mandende Peter , Makgato Mary , Cekiso Madoda
Published: March 2018

Background: Inclusive education requires that the framework within which education is delivered should be broad enough to accommodate equally the needs and circumstances of every learner in the society. This includes learners with disabilities like dyslexia who have been excluded from the formal education system. This article reports the findings of a qualitative study that explored and described the dyslexic learners’ experiences with their peers and teachers in special and public schools in North-West Province of South Africa.Methods: The study adopted a qualitative methodology and used a phenomenology research design. The sample was purposively selected and comprised nine dyslexic learners. All the learners were in public schools previously and were later moved to a special school after being diagnosed as dyslexic. The participants were aged 9–12 years. The researchers conducted one-on-one interviews with the participants and content-analysed the data.Findings: The findings revealed that in public schools the dyslexic learners were exposed to ill-treatment by other learners who despised, ridiculed, bullied and undermined them. The findings further revealed that teachers in public schools were not patient with dyslexic learners, did not give them extra attention and that some teachers used negative comments that embarrassed them.Conclusion: The article spells out the barriers experienced by dyslexic learners in public schools and also recommends training of teachers so that they know how to deal with dyslexic learners, thereby eliminating the barriers. The study further recommended awareness campaigns among the student body about dyslexia.
Coolant Hose (Supplement to SAE J20 for Government Use Replacing Part of MS52130)
Authors:   Non-Hydraulic Hose Committee
Published: March 2018

This SAE Standard provides ordering information for any SAE 20R1 through SAE 20R4 hose type (such as EC, HT, LT, or combination thereof.) It is a supplement for Government use but may be used by others.
Clamping Force Test Procedure
Authors:   Non-Hydraulic Hose Committee
Published: March 2018

This SAE Recommended Practice is a test procedure to obtain force data for self-compensating type clamps (SAE Type E, CTB, and CTW).
Exploring the Impact of Telecollaboration in Initial Teacher Education: The EVALUATE project
Authors: O'Dowd Robert
Published: March 2018

This article provides an introduction to the EVALUATE project (Evaluating and Upscaling Telecollaborative Teacher Education). This project aims to gauge the impact of telecollaborative learning on student-teachers involved in Initial Teacher Education in various European countries and regions.  The project is funded by the Erasmus+ KA3 programme (EACEA/34/2015) and is a European Policy Experiment (EPE). 
Estudo de viabilidade técnica para substituição parcial de cimento por lignina no concreto auto-adensável (CAA)
Authors: Calado Carlos Fernando de Araújo , Camões de Azevedo Aires Fernando Fernandes Leite , De Santana Silva Fabrízio Elias , Dalpane Gabriella Ferreira , Dantas Bruna Ferraz Carvalho
Published: March 2018

A lignina, produto final do metabolismo da planta, é uma macromolécula aromática, de constituição e estrutura molecular irregulares, cuja base estrutural é o fenilpropano, tendo como composição elementar carbono, hidrogênio e oxigênio. Dependendo do tamanho, a molécula da lignina apresenta comportamento solúvel ou polimérico coloidal. Obtém-se em maior escala a partir dos resíduos gerados na produção de celulose, papel e etanol celulósico. Apenas a indústria brasileira de celulose e papel produziu em 2013 resíduos com potencial de extração de aproximadamente sete mil toneladas de lignina. Alguns estudos têm procurado adicionar as cinzas resultantes da queima da lignina ao concreto, como adição ou substituição parcial do cimento, obtendo melhores desempenhos de resistência e durabilidade. Mas, essa queima representa mais uma etapa industrial de intervenção no resíduo, exigindo gasto de energia e custos de produção. Dessa forma, a pesquisa aqui desenvolvida procurou inicialmente obter respostas quanto à possibilidade de aplicação direta da lignina ao concreto, eliminando-se a etapa de obtenção de suas cinzas e reduzindo os custos financeiros e ambientais. O concreto auto-adensável (CAA) caracteriza-se pela fluidez e capacidade de adensamento sem necessidade de vibração mecânica, permitindo emprego de adições finas em substituição ao cimento. Torna-se então relevante aplicar diretamente lignina ao CAA, pois representa ganho duplo com a redução de gasto de energia e de poluentes gerados na fabricação do cimento e na obtenção da cinza da lignina. Na pesquisa em desenvolvimento estão sendo aplicados, nas argamassas dos concretos, ensaios de espalhamento na fase fresca e de resistência à compressão com 24 horas ou 03 dias, 07, 28 e 90 dias e durabilidade: coeficiente de absorção de água por capilaridade, ascensão capilar e índice de vazios, aos 90 e 180 dias, na fase endurecida. Corpos de prova cilíndricos de diâmetro 5 e altura 10 cm, três para cada ensaio aplicado em nove diferentes composições, C1 a C9, variando percentual de lignina, relação (a/l), tipo de cimento e combinações de aditivos superplastificante e plastificante. A lignina foi obtida após processo Kraft de produção de celulose de eucalipto. Com os resultados dos ensaios que já estão sendo obtidos, verifica-se ser possível contribuir com informações técnico-científicas para esclarecer da viabilidade de substituição parcial de cimento por lignina, sem necessidade de sua queima e transformação em cinzas, com efetivo ganho ambiental e indicativo de desempenho que aponte o melhor percentual de substituição a ser adotado em compatibilidade com demais constituintes das composições estudadas.DOI: http://dx.doi.org/10.4995/HAC2018.2018.5093
Estratégias de mitigação da retração em betões autocompactáveis
Authors: Oliveira Miguel José , Bettencourt Ribeiro António , Garrido Branco Fernando
Published: March 2018

Grande parte dos avanços verificados nos últimos anos na tecnologia do betão prendem-se com o uso de betões com muito baixas relações água/ligante. Nestes betões a retração total e, em particular, a retração autogénea tornaram-se fatores dominantes. A retração autogénea é já considerada como o “Tendão de Aquiles” dos betões de alta resistência/alto desempenho. Os betões autocompactáveis (BAC), devido à utilização de menores dosagens de agregado grosso e de maiores dosagens de pó também são incluídos no mesmo grupo. O BAC apresenta-se atualmente como um material que demonstrou ter um elevado potencial, nas áreas da produtividade, condições de trabalho e até mesmo em matérias resultantes das suas características intrínsecas. Nomeadamente, apresenta propriedades especiais, que justificam a sua preferência em muitas aplicações. No entanto, são conhecidos vários casos de comportamento inadequado, devido principalmente ao comportamento deficiente deste material durante o processo de hidratação e secagem. A retração tem uma importância significativa na conceção, dimensionamento, processo construtivo e comportamento em serviço das estruturas de betão. No entanto, não estão ainda completamente esclarecidos os mecanismos básicos a ela inerentes e a forma como interagem entre si. Os modelos de previsão existentes e exigências normativas específicas não consideram de forma adequada a influência dos fatores existentes. Além disso, a possibilidade de utilização de novos materiais limita fortemente a aplicação do conhecimento existente. Nesse sentido, e de modo contribuir para a resolução de uma das principais desvantagens do material betão autocompactável – a sua elevada retração, foi realizada uma extensa campanha de ensaios em provetes, tendo em vista a avaliação da respetiva retração. Entre outros materiais ou técnicas, foi dada especial importância à utilização de adjuvantes redutores de retração e adições expansivas. Com base nos resultados obtidos nos ensaios realizados, foi possível avaliar a eficiência da utilização dos materiais testados e estabelecer algumas limitações de utilização. Obtiveram-se melhoramentos significativos nas propriedades estudadas, que permitiram formular uma hierarquização das estratégias de mitigação da retração estudadas. Apresentam-se soluções técnicas satisfatórias, em termos de melhoramento de comportamento e viabilidade económica, recorrendo apenas a materiais disponíveis no mercado português. DOI: http://dx.doi.org/10.4995/HAC2018.2018.5191
Comportamento mecânico de betão auto-compactável produzido com agregados reciclados provenientes da indústria de pré-fabricação
Authors: Da Silva Pedro Raposeiro , Santos Sara Almeida , De Brito Jorge
Published: March 2018

Actualmente, devido à crise económica e às exigências de desenvolvimento sustentável, a tecnologia do betão requer uma nova abordagem, baseada essencialmente em três vectores: métodos de produção e colocação com menor consumo de energia, aumento da durabilidade das estruturas e maior taxa de reciclagem de materiais, nomeadamente através da sua reintrodução (reutilização) no processo de construção. O uso de betão autocompactável (BAC) e a incorporação de agregados reciclados na produção de argamassas e de betão são soluções com grande potencial, particularmente para a indústria de pré-fabricação, na qual os requisitos do produto final são maiores. Por esta razão, os resíduos desta indústria são também aqueles com maior potencial para serem utilizados como agregados reciclados (AR) de alta qualidade na produção de novos elementos de betão. Seguindo esta linha de raciocínio, este artigo pretende avaliar a viabilidade de reintrodução de agregados reciclados de betão na indústria de pré-fabricação. Desse modo, foram avaliadas as propriedades mecânicas do BAC com incorporação de AR (grossos e finos - AGG e AFR) a partir de elementos pré-fabricados triturados. A intenção foi avaliar a capacidade de produção de BAC com um desempenho mínimo pré-estabelecido em termos de resistência mecânica, incorporando diferentes percentagens de AR (AFR / AGR% 25/25%, 50/50%, 0/100% 0%) produzidos a partir de betão pré-fabricado com desempenho alvo semelhante. Esta avaliação foi feita para duas classes de resistência (45 MPa e 65 MPa), com a intenção de obter como resultado final betão com agregados reciclados cujas características fossem compatíveis com as de um BAC com agregados naturais, em termos de trabalhabilidade e resistência mecânica. Também se pretendeu avaliar a influência da incorporação de agregados finos e grossos nas propriedades mecânicas do betão. O principal objectivo desta investigação foi proporcionar à indústria de pré-fabricação uma forma inovadora de eliminação e recuperação de resíduos auto-gerados, minimizando o consumo de recursos naturais e, consequentemente, reduzindo significativamente seu impacto ambiental. Além dos aspectos ambientais, há também aspectos económicos associados, já que este procedimento reduz os custos de compra e transporte dos materiais.Os resultados permitiram estabelecer conclusões sobre os BAC produzidos com agregados finos e grossos reciclados da indústria de pré-fabricação, com base nas suas propriedades mecânicas. As propriedades estudadas são fortemente afectadas pelo tipo e quantidade de agregados reciclados. É enfatizado o potencial demonstrado, principalmente no estado endurecido, pelo uso conjunto de agregados finos e grossos reciclados.DOI: http://dx.doi.org/10.4995/HAC2018.2018.ID.5299
Critérios para definição da composição de betões leves autocompactáveis com agregados de argila expandida
Authors: Nepomuceno Miguel C. S. , Pereira-de-Oliveira Luiz A. , Pereira Sandrine F.
Published: March 2018

Este artigo descreve um estudo experimental que teve como objetivo a definição de parâmetros para a composição de betões leves autocompactáveis (LWSCC), incorporando agregados grossos de argila expandida e agregados finos de areia natural rolada. Assumiu-se como referência a metodologia proposta por Nepomuceno et al. para os betões autocompactáveis de densidade normal (SCC) e investigaram-se as alterações necessárias para obter os LWSCC. A campanha experimental incluiu a caracterização dos materiais constituintes, com especial ênfase na absorção dos agregados leves. Avaliou-se a curva granulométrica de referência para os agregados grossos leves e as propriedades do escoamento das argamassas adequadas à produção dos LWSCC. Investigou-se a relação entre os parâmetros da mistura e a resistência à compressão do betão, a massa volúmica seca e a trabalhabilidade (ensaio de espalhamento, ensaio de fluidez no funil-V e a capacidade de passagem na caixa-L). Foi ainda avaliada qualitativamente a segregação estática através da imagem da secção longitudinal de cilindros moldados. O estudo permitiu concluir que a absorção dos agregados leves constitui um aspeto relevante. Constatou-se que a curva de referência dos agregados grossos e as propriedades reológicas das argamassas propostas por Nepomuceno et al. para os SCC são adequadas à obtenção de LWSCC. No estado fresco, todos os betões cumpriram os critérios de autocompactabilidade e a análise qualitativa das secções longitudinais de cilindros revelou misturas homogéneas, sem segregação. Concluiu-se que a resistência à compressão dos LWSCC depende não só da razão água/cimento mas também do volume de agregados grossos leves na mistura. Por outro lado, o volume de agregados leves afeta a massa volúmica seca, pelo que a composição terá de resultar do equilíbrio entre a resistência à compressão e a massa volúmica pretendidas. Foram obtidas as correlações necessárias para a definição da composição de betões leves autocompactáveis com agregados de argila expandida. DOI: http://dx.doi.org/10.4995/HAC2018.2018.5352
Control de fisuración en vigas de hormigón armado reforzado con diferentes fibras
Authors: Plizzari Giovanni , Fasciolo Michele , Conforti Antonio , ZERBINO RAUL LUIS
Published: March 2018

La incorporación de fibras al hormigón controla la propagación de fisuras dando lugar a incrementos en la resistencia residual y tenacidad del material. Cuando se incorporan en elementos estructurales de hormigón armado las fibras contribuyen a la resistencia al corte y favorecen el control en el ancho de fisuras con sus consecuentes ventajas en lo concerniente a la vida en servicio y la durabilidad del material. Este trabajo presenta los resultados de un estudio de la influencia del tipo y contenido de fibra sobre el control de fisuración en flexión en vigas de hormigón armado. Se estudió la distribución y propagación de fisuras en ensayos de flexión con cargas en cuatro puntos realizados sobre vigas de hormigón armado con una sección rectangular con 150 mm de arista y una luz entre apoyos de 840 mm. Se compara la respuesta de hormigones que incorporan diferentes contenidos de fibras de acero, macrofibras poliméricas y macrofibras de vidrio. Como referencia se realizaron ensayos de flexión en tres puntos sobre prismas entallados de 150 x 150 x 600 mm según norma EN14651 para la caracterización del hormigón con fibras y ensayos de compresión sobre cilindros. Los resultados obtenidos ponen en evidencia la contribución del tipo y contenido de fibras sobre el control de fisuras en flexión.DOI: http://dx.doi.org/10.4995/HAC2018.2018.5502
Protocolo de valorización de residuos en la fabricación de materiales de base cemento: sedimentos dragados como componente de hormigón autocompactante
Authors: Castillo Talavera Angel , Rozas Francisco , Martínez Sierra Isabel , Castellote Armero Marta
Published: March 2018

A pesar del gran esfuerzo de investigación que se ha llevado a cabo sobre el tema de la valorización de residuos en materiales de construcción, no se han encontrado protocolos para evaluar de forma sistemática la viabilidad de un residuo para formar parte de una matriz de base cemento.  Acometer esta parte es el objetivo de esta investigación, que presenta unas reglas generales para analizar la viabilidad del uso de residuos en la fabricación de hormigón. El procedimiento se ilustra con un ejemplo, obteniendo hormigón autocompactante (SCC) que incorpora un sedimento dragado de un puerto español.  La razón para elegir sedimento dragado como residuo se debe a que las contribuciones en este tema se han centrado fundamentalmente en la reutilización de residuos industriales y de demolición, no siendo tan frecuente encontrar trabajos en los que se incorporen sedimentos dragados en la fabricación de hormigón, a pesar de la gran cantidad de sedimentos que se dragan cada año en el mundo. Se ha elegido SCC como ejemplo por las características del propio residuo, considerando además las características de este material como tecnología intrínsecamente amigable desde un punto de vista medioambiental: fluye bajo su propio peso, eliminando la necesidad de vibrado, lo que implica un considerable ahorro energético, de horas hombre y de tiempo de construcción.  Adicionalmente, contribuye a un entorno laboral más saludable al eliminar el impacto del ruido y la vibración, que a su vez repercuten en un bienestar social al acortar y hacer menos molestos los periodos de obras.DOI: http://dx.doi.org/10.4995/HAC2018.2018.5637
Influencia de la naturaleza y granulometría de los áridos en el comportamiento reológico de morteros de cementos activados alcalinamente
Authors: Alonso Maria del Mar , Gismera-Diez Sara , Puertas Francisca
Published: March 2018

Actualmente, la búsqueda de materiales cementantes eco-eficientes y sostenibles es un reto obligado, con el fin de adaptar el sector de la construcción hacia un tipo de economía circular y sostenible. Estos materiales, además,  deben cumplir una serie de requisitos de prestaciones mecánicas, durables y de trabajabilidad que los haga competitivos. Dentro de estos materiales eco-eficientes, destacan los sistemas de cementos activados alcalinamente (Alkali-Activated Materials, AAMs), con muy buenas prestaciones mecánicas y durabilidad, pero cuya reología y trabajabilidad no están suficientemente estudiados. En trabajos previos se ha determinado que el comportamiento reológico de pastas y morteros de escorias y cenizas activadas alcalinamente (AAS y AAFA) depende de la naturaleza y la concentración del activador alcalino. Asimismo se corroboró que la trabajabilidad de los morteros AAS y AAFA es más sensible a los cambios en la relación líquido/sólido que los morteros de OPC. Sin embargo hay parámetros cuya influencia sobre la reología de estos morteros de AAMs están por determinar, como son la granulometría y naturaleza del árido en el sistema. Se han preparado morteros con una relación árido/ligante 2:1 variando el diámetro máximo del árido (0.5, 1 y 2 mm) y la naturaleza del mismo (silíceo, calizo y remplazamiento parcial por árido reciclado). Los morteros de AAS se activaron con una disolución de silicato sódico hidratado (waterglass) (módulo SiO2/Na2O de 1.5 y 4% de Na2O sobre peso de escoria), mientras que los de cenizas volantes se activaron con una disolución de NaOH 10M. Se elaboraron igualmente morteros de OPC con el fin de comparar con un sistema tradicional. La trabajabilidad de los morteros se evaluó a partir de la prueba de fluidez y se han realizado ensayos de Stress Growth Test y determinación de parámetros reológicos por el ensayo del Flow curve test. Los resultados han mostrado, en primer lugar, que la fluidez de los morteros de AAMs presenta mayor variación con el tamaño de árido, frente a los morteros de OPC. De igual manera, la naturaleza del árido afecta a la demanda de líquido y a la fluidez de dichos morteros. Además, la disminución del tamaño máximo de los áridos, produce en todos los casos un aumento en el valor del esfuerzo umbral de cizalla estático y dinámico, así como de la viscosidad plástica. Por último, se ha constatado que los morteros de OPC, AAS y AAFA se ajustan al modelo reológico de Bingham, independientemente de la naturaleza y diámetro máximo de partícula del árido.DOI: http://dx.doi.org/10.4995/HAC2018.2018.6002
Características mecánico-resistentes de hormigones fabricados con residuos siderúrgicos como conglomerantes y reducción de cemento
Authors: Rubio Cintas Mª Dolores , Parrón Rubio Mª Eugenia , Pérez García Francisca , Contreras de Villar Francisco , Pelufo Carbonell Mª José
Published: March 2018

Uno de los principales problemas de la siderurgia en lo referente a la fabricación de acero, son los productos secundarios que se producen, provocando en los últimos años nuevos tipos de residuos industriales que en función de la sostenibilidad del medio ambiente, son reutilizados o bien tratados. Este trabajo propone el análisis del comportamiento resistente de residuos en probetas de hormigón, como son polvos de humo provocados por hornos de arco eléctrico, cuando se produce la fusión de los materiales. Mediante la reducción de cemento y sustitución por este material, pueden tener una segunda vida en el mercado evitando que sean depositados en el vertedero. DOI: http://dx.doi.org/10.4995/HAC2018.2018.6127
Reforço ao corte de vigas em betão armado recorrendo a painéis em micro betão auto compactável reforçado com fibras metálicas de pneus reciclados
Authors: Lourenço Lúcio , Zamanzadeh Ziaadin , Barros Joaquim , Gonçalves Delfina , Costa Inês
Published: March 2018

No passado recente, o grupo de investigação "Structural Composites" da Universidade do Minho e a empresa CiviTest – Pesquisa de Novos Materiais para a Engenharia Civil, Lda. têm realizado vários estudos experimentais e numéricos avançados, em parceria, que permitiram a aquisição de conhecimento e o desenvolvimento de materiais de matriz cimentícia reforçados com fibras recicladas, BRFR (Betão Reforçado com Fibras Recicladas), nomeadamente as provenientes da indústria da reciclagem de pneus. A investigação desenvolvida tem evidenciado que as fibras recicladas possuem elevadas potencialidades como reforço efetivo do betão, nomeadamente no reforço ao corte. No presente trabalho pretende-se apresentar os resultados relativos à avaliação da eficácia do reforço ao corte de vigas em betão por intermédio da aplicação de painéis em microbetão auto-compactável reforçado com fibras de aço de pneu reciclado nas faces de vigas de betão armado existentes. Para tal foram efetuados ensaios comparativos de resistência ao corte entre vigas em betão armado de referência (viga I com 1.25 x 0.15 x 0.30 m3; alma com 0.09 m) e vigas similares reforçadas na alma com painéis em microbetão auto-compactável reforçado com fibras recicladas de 2 cm de espessura usando dois sistemas de fixação às respetivas vigas em betão armado. Os resultados e conclusões obtidos são apresentados na presente publicação. A eficiência da aplicação dos referidos painéis em vigas demonstrou que é possível obter aumentos de capacidade de carga da ordem dos 250 % em vigas não fendilhadas e em vigas previamente fendilhadas. DOI: http://dx.doi.org/10.4995/HAC2018.2018.6143