Concreto autoadensável com baixo consumo de cimento: impacto da redução do consumo de cimento na resistência à compressão

A consolidação do concreto como segundo material mais consumido no mundo tem instigado a busca de soluçõespara reduzir o consumo de clínquer e as emissões de CO2. Visando o fornecimento de uma contribuiçãopara a sustentabilidade ambiental e da indústria de cimento, esta pesquisa busca analisar a viabilidadeeconômica do concreto autoadensável (CAA) com baixo consumo de cimento. Por intermédio da aplicaçãodo método de dosagem de Gomes (2002) para o CAA, foi realizado um estudo da otimização do esqueletogranular e da composição da pasta, sendo aferido reduções de até 25% do consumo de cimento em relação aoCAA de referência. No que tange aos índices de consumo relativo de cimento e de custo unitário por MPadesenvolvido em 1 m³ de concreto, foi verificado que os CAAs com baixo consumo de cimento apresentaramreduções de até 34,75% e 16,83%, respectivamente, ao ser comparado com o CAA de referência. A maiorefetividade na redução do índice de consumo relativo a resistência mecânica à compressão do que no consumode cimento por m³ de concreto observado, se deve a constatação de maiores patamares de resistência mecânicaà compressão para a composição com menor volume de pasta e de maior proximidade ao índice ótimode vazios encontrado na etapa do empacotamento de agregados. Tal resultado, demonstra indícios de quemesmo nas circunstâncias de dosagens com volume de pasta inferiores, a resistência mecânica à compressãopode ser aumentada, comprovando desta maneira a superioridade técnica e financeira do CAA com baixoconsumo de cimento em relação as dosagens convencionais de CAA, além dos ganhos em sustentabilidadeobtidos pela redução do consumo de clínquer e das emissões de CO2 inerentes a menor quantidade de massade cimento por m³ de concreto.Palavras-chave: Concreto autoadensável, consumo de cimento, emissões de CO2, resistência à compressã

Manufacturing strategy incorporated in aggregate production planning through a multi-objective linear programming model

Aggregate Planning activity is a relevant stage of the production planning process and has been regularly discussed in the literature for almost 50 years. It seeks to suggest a production strategy in order to meet demand, given capacity constraints. This paper presents a model based on multi criteria decision analysis to overcome the problem of aggregate planning. This decision model takes into account performance objectives obtained in the manufacturing strategy planning process. To do so, the decision maker chooses the most appropriate combination of resources to meet foreseen demand, in accordance with trade-offs amongst the performance objectives. Therefore the resulting aggregate plan refl ects the competitive factors of the business. That is, the proposed decision model allows the implementation of the manufacturing strategy by the production function

Analysis of the bond stress when using GFRP bars

For most of the structural solutions, the construction industry in Brazil is based on the use of conventional reinforced concrete elements composed of concrete and steel bars. However, problems related to this traditional structural system, such as the corrosion of metallic bars exposed to aggressiveness environments, motivate the study of new materials to be used as a replacement of conventional bars. In this context, FRP (Fiber Reinforced Polymers) bars can be viable due to their good mechanical properties and resistance to aggressive environmental agents. Thus, the main objective of this paper was the evaluation of the bond stress of GFRP bars using pullout tests. Thus, twenty specimens were analyzed with two concrete compressive strengths of 30 MPa and 60 MPa and two different GFRP bar diameters of 9.5 and 16.0 mm. According to the test results, it was verified a high variability of the adhesion between the GFRP bar and the concrete. Concerning the statistical analysis of pullout tests performed and considering the methodology proposed to analyze the quality control, the variation coefficient varied from 13.71% to 20.17%, classifying the pullout tests performed as medium or poor. These results demonstrate that the response of the GFRP bars obtained in the pullout tests was not reliable, demonstrating the need for new research to obtain adhesion coefficients and anchoring lengths for use in structural designs with such materials

Variability of the bond and mechanical properties of self-compacting concrete

This main objective of this research is to evaluate the variability of the mechanical properties (compressive strength, modulus of elasticity and tensile strength) and bond strength of the self-compacting concrete (SCC), with 50 MPa compressive strength at 28 days, varying the maximum aggregate size and the SCC fluidity. The tests were made in 15 x 30 cm concrete cylinders and in beams standardized by Rilem-Ceb-Fib (1973). In agreement with the obtained results, can be concluded that the variability of the self-compacting concrete is small for the modulus of elasticity and for the compressive strength, but the tensile strength presented a significant variability due to the failure mode. About the bond strength, the variability was small showing that the self-compacting concrete is reliable and possesses great potential for use in the civil construction.Peer ReviewedPostprint (published version

Numerical approach of the steel-concrete bond behavior using pull-out models

This paper deals with the analysis of monotonic loading behavior in pull-out tests. The main objective is toobtain a reliable numerical model to represent the steel-concrete bond behavior using previously obtainedexperimental results. The tests were performed in RILEM pull-out specimen using 10 mm steel bar andconcrete with compressive strength of 30 MPa. The numerical study used Ansys® software, based on FEM(Finite Elements Method). The numerical simulation adopted non-linear constitutive relationships to representthe behavior of both concrete and steel. A contact surface composed of special finite elements modeled theinterface between the concrete and the steel bar, allowing a steel–concrete slip. The numerical analysisperformed with variation of the main parameters of the software permitted determining the best ones, andchoosing them to obtain a good representation of the bond phenomena. The numerical results had a goodagreement with the experimental results. Both linear and non-linear approaches represented the pre-peakbehavior, however only the non-linear model gave the best approach for the pull-out force. In addition, thenumerical results had shown the simplified model can be used to represent the steel-concrete bond behaviorreducing the processing time for current structures analysis.Keywords: bond strength, pull-out tests, numerical approach, contact surface, finite element method

Fatigue design in reinforced concrete bridges according to Brazilian code

There has been an increase in the flow of freight vehicles commuting on Brazilian highways. Then, special attention to the structural performance of bridges regarding the fatigue in beams is needed. Brazil has neither normative metrology to study real data flow of vehicles, nor specific fatigue load train models and coefficients to the analysis and design of road bridges. The same load train that is used for general dimensioning, TB 450, is used for the fatigue verification. Hence, this work aims to verify if the current TB 450 is representative of the freight heavy vehicles with 2 to 9 axles concerning the effects of fatigue in the longitudinal reinforcement of beams of theoretical reinforced concrete bridges with two, three, and five beams. This verification is performed analyzing the stress variations found in the longitudinal reinforcement of vehicles with 2 to 9 axles and the TB 450. Based on the results, the longitudinal steel reinforcement was more susceptible to fatigue\u27s effects. Freight vehicles with 5, 6, 8 and 9 axles presented the most significant stress, therefore, they tend to cause more deleterious effects. Hence, the adoption of a Brazilian normative fatigue specific load train and coefficients is necessary to analyze pre-existing road bridges and design new ones most accurately

Tumor cardíaco - cuidados de enfermagem no pós-operatório ao paciente com mixoma: revisão de literatura / Cardiac tumor - nursing care in the postoperative period for patients with myxoma: literature review

Introdução: O mixoma é um tumor cardíaco primário e que, devido a sua rara ocorrência, costuma ser de difícil diagnóstico. Geralmente não é cogitado como uma das suspeitas iniciais e tem sintomatologia inespecífica semelhante a outras doenças cardiovasculares. O mixoma pode ser resolvido cirurgicamente, num procedimento que necessitará de assistência da equipe multiprofissional, mas que paralelamente costuma vir acompanhado de muita insegurança e até mesmo medo, da parte do paciente. Objetivo: Avaliar os cuidados de enfermagem pós-operatórios ao paciente com mixoma. Métodos: Trata-se de uma revisão de literatura na Biblioteca Virtual de Saúde (BVS) e base de dados Medical Literature Analysis and Retrieval System Online (MEDLINE), em março de 2021, sendo utilizados os descritores: Mixoma; Cuidados Pós-Operatórios; Enfermagem e Neoplasias Cardíacas. Os critérios de inclusão foram: Artigos publicados nos últimos 10 anos (2011-2021), com texto disponível na íntegra e nos idiomas português, inglês e francês. Resultados: Dos 1.174 artigos resultantes da consulta às bases de dados, 8 obedeciam a todos os critérios para serem avaliados no estudo. Verificou-se que a literatura consultada aponta para a relevância de, através de uma visão holística, identificar as necessidades do paciente para que seja possível construir um melhor plano de assistência. No pós-operatório imediato, os enfermeiros deverão planejar os cuidados que objetivam a manutenção e oferta adequada da ventilação, oxigenação e estabilidade hemodinâmica, assim como controlar a dor, favorecer a cicatrização da ferida cirúrgica e auxiliar na recuperação funcional. Conclusão: A assistência de enfermagem no pós-operatório do paciente com mixoma é fundamental. O conhecimento das possíveis alterações fisiológicas provocadas pelo procedimento cirúrgico favorece a melhor interpretação da evolução clínica. A enfermagem é reconhecida pela sua presença constante a beira leito e, por isso mesmo, é a primeira a perceber as alterações no quadro clínico, devendo estar sempre pronta para lidar com o paciente

Clinical and echocardiographic parameters associated with low chronotropic index in non-elderly patients

FUNDAMENTO: Apesar das inúmeras evidências de aumento da morbimortalidade, a incompetência cronotrópica (IC) ainda não é um diagnóstico rotineiro e bem definido nos protocolos de avaliação cardiológica e sua importância clínica ainda é subestimada. OBJETIVO: Avaliar os parâmetros clínicos e ecocardiográficos associados à IC em pacientes não idosos submetidos à ecocardiografia sob estresse físico (EEF). MÉTODOS: Foram avaliados 1.798 pacientes com idade média de 48,4 ± 7,5 anos submetidos à EEF entre Janeiro/2000 e Agosto/2009. Pacientes com índice cronotrópico menor que 0,8 foram considerados incompetentes cronotrópicos e comparados aos competentes quanto às características clínicas e ecocardiográficas. RESULTADOS: A duração do esforço físico foi em média de 9,3 ± 2,4 minutos. Duzentos e setenta (15%) pacientes eram incompetentes cronotrópicos. O índice cronotrópico de tal grupo foi de 0,7 ± 0,1 vs. 1,0 ± 0,1 para os competentes. A análise de regressão logística multivariada identificou os seguintes parâmetros como independentemente associados à IC: dispneia no exame [odds ratio (OR) = 4,27; p < 0,0001], dor torácica prévia na história clínica (OR = 1,51; p = 0,0111), maiores valores de índice de massa do ventrículo esquerdo nos incompetentes (IMVE) (OR = 1,16; p = 0,0001), equivalentes metabólicos (METs) (OR = 0,70; p = 0,0001), infradesnivelamento do segmento ST (OR = 0,58; p = 0,0003) e elevação da pressão arterial sistólica (ΔPAS) (OR = 0,87; p = 0,0011). Isquemia miocárdica não se associou à IC. CONCLUSÃO: A IC está associada a parâmetros funcionais, tais como: dispneia ao esforço, história de dor torácica e menores valores de METS. Está também associada ao parâmetro estrutural índice de massa do ventrículo esquerdo. Além disso, incompetência cronotrópica não parece aumentar a chance de isquemia miocárdica em pacientes não idosos. _________________________________________________________________________________________ ABSTRACT: BACKGROUND: Despite abundant evidence of increased morbidity and mortality, chronotropic incompetence (CI) is not a routine diagnosis well defined in protocols of cardiac evaluation and its clinical importance is still underestimated. OBJECTIVE: To evaluate the clinical and echocardiographic parameters associated with HF in non-elderly patients submitted to stress echocardiography (SE). METHODS: One thousand seven hundred ninety-eight patients with a mean age of 48.4 ± 7.5 years, who underwent SE between January/2000 and August/2009 were evaluated. Patients with chronotropic index smaller than 0.8 were considered chronotropic incompetent as compared to competent patients as to clinical and echocardiographic characteristics. RESULTS: The duration of the exercise was 9.3 ± 2.4 minutes on average. Two hundred and seventy (15%) patients were chronotropic incompetent. The chronotropic index of this group was 0.7 ± 0.1 vs. 1.0 ± 0.1 for competent patients. Multivariate logistic regression analysis identified the following parameters as independently associated with HF: dyspnea on examination [odds ratio (OR) = 4.27, p <0.0001], previous chest pain on medical history (OR = 1.51; p = 0.0111), higher left ventricular mass rate in incompetent patients (LVMI) (OR = 1.16, p = 0.0001), metabolic equivalents (METs) (OR = 0.70, p = 0 , 0001), ST segment depression (OR = 0.58, p = 0.0003) and high systolic blood pressure (ΔSBP) (OR = 0.87, p = 0.0011). Myocardial ischemia was not associated with HF. CONCLUSION: HF is associated with functional parameters, such as dyspnea on exertion, history of chest pain and lower METS. It is also associated with structural benchmark index of left ventricular mass. In addition, chronotropic incompetence does not appear to increase the chance of myocardial ischemia in non-elderly patients

Integrating the pastoral component in agricultural systems

This paper aims to discuss the impact of the introduction of pastures and grazing animals in agricultural systems. For the purposes of this manuscript, we focus on within-farm integrated crop-livestock systems (ICLS), typical of Southern Brazil. These ICLS are designed to create and enhance the synergisms and emergent properties have arisen from agricultural areas where livestock activities are integrated with crops. We show that the introduction of the crop component will affect less the preceding condition than the introduction of the livestock component. While the introduction of crops in pastoral systems represents increasing diversity of the plant component, the introduction of animals would represent the entry of new flows and interactions within the system. Thus, given the new complexity levels achieved from the introduction of grazing, the probability of arising emergent properties is theoretically much higher. However, grazing management is vital in determining the success or failure of such initiative. The grazing intensity practiced during the pasture phase would affect the canopy structure and the forage availability to animals. In adequate and moderate grazing intensities, it is possible to affirm that livestock combined with crops (ICLS) has a potential positive impact. As important as the improvements that grazing animals can generate to the soil-plant components, the economic resilience remarkably increases when pasture rotations are introduced compared with purely agriculture systems, particularly in climate-risk situations. Thus, the integration of the pastoral component can enhance the sustainable intensification of food production, but it modifies simple, pure agricultural systems into more complex and knowledge-demanding production systems