Silica fume (SF) is the most commonly mineral admixture used for the production of high-strength concrete (HSC) due to its chemical characteristics of pozzolanic reactivity and physical filling effect. The objective of the present work is to compare the SF content by the chemical analysis of the pozzolanic reaction and the physical behavior by particle packing techniques. The first step of the study was to analyze the SF content to consume the calcium hydroxide (CH) produced during the hydration of Portland cement (PC), based on stoichiometric calculations. Then, the SF content for maximum packing density was obtained using analytical particle packing models and experimental tests. The compressive strength of the pastes was also measured. The results showed that the theoretical SF content for consuming CH is 15.6%, replacing PC. According to the packing density analytical models, the ideal SF content is 15% of the total fine materials. However, the experimental results indicated the use of a smaller SF content (10%). This difference between theoretical and experimental results is probably due to the high specific surface of the SF, which results in important surface forces between the grains, particle agglomeration and difficulty in SF densification with water.

Cement is considered the basic component with the highest environmental impact in construction, in terms of CO₂ emissions. As for the aggregates, the process of comminution of rocks, in addition to artificial sand, generates stone powder that ends up being stored outdoors, generating environmental damages. Thus, the replacement of cement by stone powder appears as an attractive alternative towards the sustainable concretes. In this context, the objective of this paper is to determine the maximum packing density in Portland cement, silica fume and stone dust pastes, to determine the optimal cement substitution content for the stone powder. In addition, it is intended to verify the influence of excess water on the consistency of the mixtures produced. The substitution was done in contents equal to 0%, 7%, 14% and 21% by volume and, for each content, the packing density was determined analytically by CPM model and combinations were reproduced experimentally. Excess water was checked by the mini Kantro cone test. The results showed that the higher cement substitution content of the stone powder obtained the higher packing density, experimental and analytical, and the higher workability, allowing economic and environmental advantages. Analyzing each material, the stone powder resulted in the highest packing density and silica fume is the lowest one. Therefore, finer particles resulted in lower packaging densities, due to the greater specific surface area, which demands more water. The agglomeration resulted in more empty gaps between the grains. In addition, mixtures flowability increased with the increase of the stone powder content. As the excess water is responsible for mixture lubrication, a higher packing density for a given volume of water improves the flowability.

The aim of this study is to explore more sustainable approaches by replacing Portland cement (OPC) with recycled mixed powder (RMP) derived from construction and demolition waste (CDW), with a focus on reducing carbon emissions. The CDW was subjected to grinding and sieving until a fraction <0.15 mm was obtained. The particles were then thermally activated at 800°C in a muffle for 0.5, 1, 2, and 3 hours. The OPC replacement levels by RMP were defined based on the particle packing method, ranging from 0 to 65%. The study was carried out on pastes with a water/fines ratio ranging from 0.07 to 0.14 and superplasticizer admixture (SP), evaluating the compressive strength at 28, 63, and 91 days. The mechanical and environmental performance of Portland cement pastes composed with RMP showed compressive strength higher than the reference, reaching 37 MPa for a 45% replacement content at 28 days, reducing the CO₂ emissions per m³ of paste by up to 53%. This study suggested that the treatment and packaging RMP particles may potentially increase the mechanical and environmental performance, making it an alternative to promote the circular economy and low-carbon cement.

RCC using hematite as an aggregate has interesting characteristics for use in massive structures or structures for radiation shielding. In Brazil, there is a considerable amount of hematite ore tailings without practical use, which makes this material an environmental problem and a matter of public safety. Thus, the search for alternatives to use these tailings is a priority environmental concern. An RCC containment dam with hematite aggregate was constructed to protect the basin of the Barao de Cocais River, including the city of Barao de Cocais in the State of Minas Gerais in Brazil, from a possible rupture of the Sul Superior tailings dam in the Congo Soco iron mine. Approximately 150,000 m³ of RCC was deposited in three months. In this article, the results of the technological control tests during the construction of the containment are presented and compared with the results of the cores extracted after the construction, showing their coherence and strength performance compared with RCC using conventional aggregate. Also, studies related to the performance of radiation shielding of this RCC are presented. An attenuation of 10% of 1.6 MeV gamma radiation in relation to conventional concrete was observed.

Most of the dams registered on the National Information System on Dam Safety (SNISB of Brazil) do not have enough information to assess whether they fit into the National Dam Safety Policy (PNSB), or to assess their safety conditions. According to the National Agency of Waters (ANA, 2021b), there are currently 122 dams with some important structural problems indicated by their inspectors in 23 states. Therefore, this article proposes a methodology for identifying faults in dam safety activities. The method applies to all types of existing dams. The proposed methodology comprises ten stages that, according to the progress of the steps, are defined by three levels of completeness of the information. Tables were developed with the objective of being a verification guide for these ten stages. This research applied the proposed methodology to two dams in Paraná, Brazil. The first is the Iraí dam, located in the metropolitan region of Curitiba, and the second is the Jordan River Derivation dam, located in Reserva do Iguaçu. The example of the Iraí dam could complete all stages of the proposed methodology. For the Jordan River Derivation dam, stages 1 to 5 of the proposed methodology were carried out. The application of the proposed methodology intends to become a useful tool, especially for inspectors, aiming at a more effective registration process, accelerating the completion of the SNISB.

O concreto é um dos materiais mais utilizados na construção civil devido à sua versatilidade e desempenho estrutural. No entanto, sua produção é uma das principais fontes de emissão de gases de efeito estufa, em grande parte devido ao elevado consumo de cimento Portland. Frente a essa problemática, a substituição parcial do cimento por resíduos industriais, como a escória de alto forno, apresenta-se como uma solução promissora para o desenvolvimento de misturas mais sustentáveis e eficientes, sem comprometer a eficácia do material. Este trabalho tem como objetivo avaliar concretos sustentáveis produzidos com a substituição de 20% do cimento Portland por escória de alto forno proveniente de aciaria na cidade de Açailândia – MA. Foram analisadas as propriedades físicas e mecânicas de concretos utilizando seixo rolado e brita granítica como agregados graúdos, tanto sem adições quanto com a substituição parcial de 20% do cimento. Os ensaios realizados incluíram o teste de abatimento (slump test) no estado fresco e ensaios de compressão uniaxial no estado endurecido, além da análise microestrutura por ensaio de ultrassom. O concreto de referência com seixo rolado apresentou resistência média de 33,07 MPa aos 28 dias, enquanto o concreto com substituição parcial por escória alcançou 21,67 MPa. Para o concreto com brita granítica, a resistência média foi de 25,67 MPa, reduzindo-se para 12,23 MPa com a substituição de parte do cimento por escória. Os resultados evidenciam os desafios e potencialidades da aplicação de escória de alto forno em concretos, destacando a importância de estratégias para otimizar suas propriedades mecânicas e fomentar práticas mais sustentáveis na construção civil.