Marçal Rosas Florentino Lima Filho

Coral reefs are very important ecosystems for the planet, offering ecological and socio-economic benefits. However, they are under threat due to anthropogenic factors and environmental changes. This study assesses the feasibility of weathered Portland cement concrete as a material for marine artificial reefs by comparing its physicochemical and mechanical properties with those of natural coral skeletons from the coast of Paraíba, Brazil. Analyses included microstructural and physical characterization, compressive strength and ultrasonic pulse velocity tests, as well as pH monitoring. The results indicated that weathered concrete exhibits mineralogical similarity to corals, with the presence of carbonate phases and portlandite absent due to advanced carbonation. The compressive strength of the concrete (27.6 MPa) was significantly higher than that of the coral samples (1–6 MPa), while the porosity of the corals (34–41%) exceeded that of the concrete (14%). The alkaline nature of the concrete (pH 9.7) remained stable. Although differences in physical and mechanical properties are evident, the values are within the ranges reported for cementitious materials in marine applications. Mineralogical similarities between coral skeletons and concrete support its potential as a functional analog in artificial reefs, while adjustments in geometry and porosity are suggested to enhance ecological compatibility.

This study aims to deepen the understanding of the formation of tricalcium silicate (alite) polymorphs in synthetic clinker, produced under controlled conditions that simulate industrial scenarios, with the goal of contributing to more sustainable practices in Portland cement production. The innovation of this research lies in the combined evaluation of the effects of crystallinity and particle size of silica—in the forms of crystalline quartz and amorphous silica gel, across different granulometric ranges—on the nucleation and stabilization of the M1 and M3 monoclinic polymorphs of alite. Using advanced characterization techniques such as laser granulometry, X-ray fluorescence, X-ray diffraction, and optical microscopy, it was demonstrated that increasing the silica particle size, regardless of crystallinity, reduces the alite content and promotes an increase in the content of free lime and belite. Furthermore, the silica particle size directly influences the size of alite crystals, while the interaction between crystallinity and particle size has a significant impact on the stabilization of alite polymorphs. These findings are essential for optimizing the clinker manufacturing process, potentially reducing energy consumption and promoting the production of more reactive forms of cement, thereby contributing to sustainability in the cement industry.

The rational use of materials in construction, particularly cementitious materials, is crucial for environmental preservation. One way to optimize this consumption, especially in mortar production, is to study the packing of fine aggregates and their interactions with the cementitious phase. Several factors influence the rheology of such composites, including void ratio and packing density. This study investigates the role of particle size distribution in packing density by applying classical models and a modified approach. Twenty granular sets were analyzed using these theoretical models, considering different numbers of grain size distribution classes. In this work, packing densities were determined using the CPM (Compressible Packing Model) and a proposed alternative method, while natural sand was used to experimentally validate the theoretical results, reproducing nine of the twenty developed sets. From the analyzed grain size distributions, theoretical models were found to fit natural four-class sands, but their accuracy declined when the number of classes exceeded five classes. The results indicated that increasing the number of grain classes enhances packing density up to 7,5% in natural sands, with this effect being more pronounced in sets derived from theoretical models, ranging up to 13%. The correlation between packing density and the uniformity coefficient followed a sigmoidal fit, suggesting that less uniform sands have higher void ratios. Experimental validation of the theoretical results revealed that the packing density values obtained using the CPM model were 11% to 16% lower than the experimental values. The proposed modified model yielded better results, demonstrating less sensitivity to increases in the fineness modulus.

Anais do Congresso Internacional de Engenharia Mecânica e Industrial (2764-4294) - Avaliação Da Ventilação Natural Para Salas De Aula De Um Edifício Universitário

Solar energy presents the greatest potential by which to produce heat energy with reduced carbon emissions for power generation. To increase its harvesting and conversion, it is necessary to understand fundamental concepts and develop new materials. Although many processes can obtain selective absorbing surfaces (SAS) for application in solar energy exploitation, including electroplating methods, those processes have not sufficiently investigated the substrate’s treatment impact. The present work investigates 304 stainless steel (SS304) substrates treatment influence on the film’s (coatings) optical properties of SAS based on CrO₃ electroplating. For this purpose, three main steps featured in the methodology: substrates treatment, coatings deposition, and physical-chemical characterization. The former was performed by detergent cleaning (DC), acid treatment (AT), and electropolishing (EP). Then, coatings were electroplated towards chromium deposition on the substrates with different deposition times. Finally, films were characterized by Profilometry, UV-Vis-NIR, and IR regions Spectroscopy and Scanning Electron Microscopy (SEM). The results indicated that, in terms of surface treatments on the substrate, the electropolished (EP) substrates presented average roughness values of 35 nm, reflectivity of 5.09%, and clear morphological difference (SEM) when compared to other treatments in this study (DC and AT). A SAS was successfully obtained, and the electropolished substrates (EP) presented coatings with better optical performance than other samples (DC and AT), with absorptivity values around 98% and emissivity of approximately 7%. A relationship between substrate treatment, its roughness, and the impacts on the optical selectivity of SASs was observed. Therefore, electropolishing is presented as a promising treatment for the SASs substrates.

A análise de obras civis para detecção de patologias e anomalias tem empregado cada vez mais a metodologia da termografia infravermelha (IRT), permitindo ao olho humano a “leitura” da temperatura dos objetos. Dada importância de se realizar a identificação de tubulações embutidas em alvenaria, quando não mais se possui os projetos hidráulicos e sanitários, o objetivo do presente trabalho foi de aplicar a metodologia ITR para: identificar infiltrações não perceptíveis e investigar o seu uso para detecção de tubulações de água fria e quente embutidas. Com relação a identificação de infiltrações, os resultados confirmaram a adequação da metodologia para tal finalidade, inclusive para detecção de infiltrações não perceptíveis. No entanto, para identificação de tubulações hidráulicas embutidas nas paredes a metodologia apresentou a limitação ao ser executada em parede de revestimento cerâmico, que impede a captação da temperatura da parede. Na investigação em paredes de revestimento simples a IRT não se mostrou eficiente para identificação de tubulações de água fria, contudo, sinalizou potencialidade da termografia para detecção de tubulações de água quente, uma vez que ocorre elevado gradiente de temperatura entre a tubulação e a parede.

The Alkali-Aggregate Reaction (AAR) phenomenon in concrete structures is perceived via expansion and cracking, swelling of gel like material, causing damage and disruption in structural elements. Despite extensive standardization, AAR cases are still persistently occurring worldwide. The literature on susceptibility of concrete to AAR reported examples of false negative and positive results. Hence, long-term prediction is a problem still posing great challenge to engineers. The severity of AAR on the structural integrity can be mostly elucidated by the assessment of the historic of elastic properties. There is consensus that AAR causes decrease in the load capacity concrete, reflected by reduction of elasticity modulus due damage progresses. Non-destructive techniques are often used as first approach, as they can provide relatively fast assessment in situ as well as in large structural elements. Its data interpretation carries certain degree of complexity due intrinsic characteristic of many of these methods. This is the case of Ultrasonic Pulse Velocity (UPV), which have been considered to present several limitations for such purpose. This paper deals the potential use of the Longitudinal Resonance Frequency (LRF) method as tool to evaluate the elastic historic of AAR prone elements. The LRF possesses higher energy than UPV. Also, using modulation of frequency in input signal combined the test geometry, the LRF allow application to larger samples as well as to extract complementary information alongside the dynamic elastic modulus. This way, the LRF was applied to study concrete beams tested under controlled conditions for about 1.5 year. The independent variables to the tests are: time, frequency, aggregate type, cement content, alkali content and water to cement ratio. The dependent variables are: damping, loss factor and elasticity modulus. The analysis associate damage with vibration damping, confirming reduction of elasticity through damage with experimental validation and prediction of AAR under rheological model.

Simulação e avaliação dos parâmetros dinâmicos da luz natural para salas de aula da Universidade Federal da Paraíba – UFPB / João Pessoa / Simulation and evaluation of dynamic parameters of natural light for classrooms of the Federal University of Paraíba - UFPB/João Pessoa