Wellington Mazer

Ultra-High-Performance Concrete (UHPC) is known for its exceptional properties. The objective of this research was to analyze the influence of steel fiber content and paste volume on the properties of UHPC and to evaluate its performance in the fresh and hardened state. Tests were carried out with different steel fiber contents (0% to 5%) and paste volumes (20%, 40%, 60% and 80% excess paste), considering spreadability, workability and compressive strength. In the fresh state, it was observed that the addition of fibers reduced the spreadability, with a decrease between 6% and 21%. On the other hand, increasing the amount of excess paste improved the flowability and workability of the mixes. In the cured state, there was no statistically significant difference between the mixes with different paste contents. However, it was found that increasing the fiber content reduced the compressive strength of UHPC. Increasing the amount of excess paste did not have a significant effect on strength, but did improve the flowability and consistency of the mix when fresh. The research showed that the fiber content affects the workability and strength of the UHPC, while the paste volume favors the flowability without compromising the compressive strength in the hardened state.

O uso do grafeno em argamassas cimentícias e no concreto armado, tem se tornado frequente, devido aos ganhos nas propriedades físicas. Não se limitando às propriedades físicas, o grafeno, por melhorar a capacidade piezoelétrica do concreto, o que permite que seja utilizado em aplicações de blindagem eletromagnética, pode ser utilizado para melhorar os ciclos de congelamento e descongelamento do concreto, através do refinamento dos poros da argamassa cimentícia, tornando-o adequado para a execução de pisos de câmaras frias, mais resistentes, e diversas outras possíveis aplicações. A adversidade do uso do grafeno em argamassas cimentícias e no concreto armado, se encontra na dispersão do grafeno, pois suas propriedades são perdidas em caso de aglomeração. Neste contexto, esta pesquisa apresenta um processo de dispersão do grafeno em solução aquosa, contendo superplastificantes para evitar a aglutinação. Foram testados os teores de grafeno testados, de 2,5, 5,0, 7,5 e 10,0 gramas, com resultados positivos, para a dispersão e não aglutinação do grafeno na solução.

Este artigo investiga o comportamento residual de vigotes de concreto armado submetidos a incêndio, considerando pré-carregamentos proporcionais ao Estado Limite de Serviço (ELS). Utilizou-se um simulador de flashover do CBMPR para reproduzir incêndio compartimentado, monitorado por termopares tipo K, seguido de ensaios de flexão. Foram avaliados também cinco grupos: controle para ELU/ELS e vigotes sem pré-carregamento, com 50%, 100% e 125% do ELS, testados em temperatura ambiente e após incêndio. A exposição térmica atingiu picos superiores a 500 °C por 25 minutos. Os resultados indicaram reduções de resistência de 32% no grupo referência aquecido e perdas progressivas nos elementos fissurados: 35% (50% ELS + fogo), 56% (100% ELS + fogo) e até 86%–90% no nível de 125% ELS, com menor ductilidade. ANOVA e teste de Tukey confirmaram claras diferenças significativas. Conclui-se que fissuração prévia potencializa a degradação térmica, impondo a necessidade de considerar histórico de carregamento e inspeções pós-incêndio em critérios de projeto e reabilitação.

In civil construction, the materials used must maintain a sustainable approach, contributing to the lifespan of structures. The durability of cementitious materials considers chloride ion diffusion as an important factor, since corrosion caused by chloride ions compromises the lifespan of structures. In this research, the prediction of chloride ion attack depth was performed using Brownian motion modeling. The use of only the Stokes-Einstein equation was considered to obtain the diffusion coefficient. Parameters such as the diffusion coefficient and surface chloride ion concentration were predicted. The spray zone was considered in determining these parameters. In the simulation to determine depth, surface concentration, chloride ion concentration, and diffusion coefficient, the time period considered was 10 years. As predicted in several studies, chloride ion diffusion decreases with depth, as does chloride ion concentration. The importance of this research for 10-year predictions relates the behavior of chloride ion attack over time to the prediction of structural service life.

Reinforced concrete has enabled the development of large-scale infrastructure for commercial, industrial, and residential purposes. In recent years, there has been an increase in structural pathologies associated with exposure to electromagnetic fields, particularly due to the intensive use of power transformers and other electronic devices. However, current technical standards do not yet provide specific protocols for measuring, preventing, and mitigating, through preventive maintenance, these effects. This study aims to analyze and compare, through case studies, the damage caused by electromagnetic fields in reinforced concrete structures, considering magnetic field intensity. Measurements were taken on two transformers and a residential distribution panel, assessing the relationship between field intensity, distance, and power. For the transformer located on a university campus, an inverse relationship between magnetic field intensity and distance from the source was observed. The findings indicate that even structures housing smaller equipment are susceptible to the harmful effects of prolonged exposure to electromagnetic fields.

The determination of the optimum amount of constituents, for UHPC production still needs studies, because in many cases this definition is empirical. This work aims to present a methodology for determining the amount of silica fume and to establish a water/binder ratio based on laboratory tests. To define the quantity of constituents necessary for the formation of the paste, the wet packaging method was used and the concentration of solids, the volume of voids and the excess of water were determined. The results indicated that the adopted methodology is adequate, leading to commonly used values.

Chloride ion transport helps predict the durability of reinforced concrete structures. For this purpose, predicting chloride ion penetration, diffusion and tortuosity for porous structural materials improves the definition of structural service life. This work proposes the definition of models to determine the diffusion coefficient of chloride ions through the application of fractals, more precisely using Brownian motion. In the research, the Stokes-Einstein diffusion equation and the equations to determine the diffusion coefficient, Langevin and Einstein relations were used as reference. These equations were combined and resulted in new diffusion equations. Thus, two paths emerged for carrying out Brownian motion in research: one considering two types of correction in the displacement when using the Langevin equations and the Einstein relation to follow the Brownian motion and another where the correction occurs in the combination of the Stokes-Einstein, Langevin and Einstein equations to determine the diffusion and subsequently implement the Brownian motion. These combinations prevent the numerical value of tortuosity from being greater than that found with the reference equation and slow diffusion. With this, modeling of the prediction of chloride ion penetration, prediction of diffusion for a future time, and definition of tortuosity for porous structural materials can be performed in new ways.

Polymer residues can be reused in civil construction by partially replacing mineral aggregates in concrete, thereby reducing the extraction of natural resources. This study aimed to evaluate the use of powdered poly (ethylene terephthalate) (PET) and polyethylene (PE) residues, accumulated in shaving-mill filters during the extrusion of multilayer films used in food packaging, in the production of sealing masonry blocks. The PET/PE residues were characterized by Fourier Transform Infrared Spectroscopy (FTIR), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). Cylindrical specimens were produced in which part of the sand, by volume, was replaced with 10, 20, 30, 40 and 50% polymer residue. The cylindrical specimens were evaluated for specific mass, water absorption and axial and diametral compressive strengths. The 10% content provided the highest compressive strength. This formulation was selected for the manufacture of concrete blocks, which were evaluated and compared with the specifications of ABNT NBR 6136:2014. The concrete blocks showed potential for applications without structural function and were classified as Class C. The results, in line with previous investigations on the incorporation of plastic waste in concrete, underscore the promising application potential of this strategy.

Imaging Analysis Techniques (IATs) have become instrumental in civil engineering materials research, providing critical insights into the microstructural characteristics of mixtures and enabling associations between these features, numerical parameters, and laboratory-derived mechanical performance data. However, using IATs specifically for Concrete Paving Blocks (CPBs), particularly when modified with crumb rubber (CR), remains underexplored. In this study, two numerical parameters derived from IATs – interlocking parameter (PINT) and interlocking rate (IR) – were investigated for their correlations with the estimated compressive strength (fpk,est) of CPBs after a 28-day curing period. CPBs were prepared with CR at 5%, 10%, 15%, and 20% by mass, with a reference concrete mixture designed per American standards for no-slump concrete and a target fpk,est of 50 MPa. PINT and IR were calculated using custom Python-based software developed by the authors. Consistent with prior findings, increasing CR content resulted in a decrease in fpk,est, a trend that was well-represented by linear and power regression models. Both IR and PINT showed potential for explaining the reductions in fpk,est, with IR demonstrating stronger predictive capabilities. Consequently, IR proves to be a promising parameter for describing the microstructural characteristics of CPBs, whether containing CR or not, due to its consistently good correlations with both fpk,est, and CR content.