EM - Escola de Minas
URI permanente desta comunidadehttp://www.hml.repositorio.ufop.br/handle/123456789/6
Notícias
A Escola de Minas de Ouro Preto foi fundada pelo cientista Claude Henri Gorceix e inaugurada em 12 de outubro de 1876.
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7 resultados
Resultados da Pesquisa
Item Sensitivity analysis of coating mortars according to their specific heat, specific gravity, thermal conductivity, and thickness in contribution to the global thermal performance of buildings.(2022) Mendes, Vítor Freitas; Fardin, Welington; Barreto, Rodrigo Rony; Caetano, Lucas Fonseca; Mendes, Júlia CastroAlthough coating (plastering) mortars are an important element of masonry systems, their impact on the building's overall thermal performance is still unclear. In this sense, the present work performed a sensitivity analysis on the influence of the thermophysical properties of coating mortars on the internal temperature and thermal load of two buildings. The authors aimed to fill the gap between the mortars' properties, their manufacturing specifications, and the actual effect of their application on the building's total energy perfor- mance. The methodology included energy simulations on EnergyPlus considering all Brazilian bioclimatic zones. We varied the mortars' specific heat, specific gravity, thermal conductivity, and thickness from 25% to 200% from baseline values. We also analysed the results through Decision Tree technique (XGBoost). The thermal conductivity (proportional to the specific gravity) was the less significant property, whereas the thickness and the specific heat were the most influential ones. The differences between the best and worst mortars reached 356 ◦C and 224 kWh/year for the house, and 736 ◦C and 45 kWh/year for the commercial building. The results showed that the optimal combination of the tested properties is a function of the bioclimatic characteristics of the region, the building layout, and the existence and schedule of the HVAC system. The simulations also evidenced that the strategy of solely decreasing the thermal conductivity without considerations for the thermal capacity, which is often used in the manufacturing of conventional insulating mortars, is ineffective. Therefore, assertively adjusting the mortars' thermophysical properties can be a promising complementary strategy for improving the thermal performance of buildings.Item Compressive strength of reduced concrete specimens considering dimensional distortion of coarse aggregates.(2020) Azevedo, Carlos Felipe de; Carvalho, José Maria Franco de; Mendes, Júlia Castro; Castro, Arthur Silva Santana; Barreto, Rodrigo Rony; Peixoto, Ricardo André FiorottiThe present study investigates the mechanical behavior of small cylindrical specimens (£50 100 mm) in relation to the minimum standard size (£100 200 mm) recommended by ASTM and Brazilian codes. Statistical and dimensional analyses were performed for three different classes of compressive strength (20, 30, and 40 MPa), and four grades of coarse aggregates (Dmax 9.5, 12.5, 19, and 25 mm). To this purpose, the Student’s t-Test for two means and equations from the Similitude Theory were applied. The following evaluations were performed: a) influence of the dimensional distortion of aggregates on the compressive strength of small concrete specimens; b) analyses through hypothesis testing between strength means; c) the use of prediction coefficients with statistical reliability for correcting the dimensional distortion of aggregates; and d) influence of the wall effect for different specimen sizes and concrete mixes. The results showed that the reduced and the standard specimens have similar compressive strengths, despite the reduced ones having presented higher variability of results. Also, innovative quantitative results from Wall Effect analysis show agreement with the strength results and illustrate the phenomena from a new perspective.Item Coating mortars based on mining and industrial residues.(2020) Mendes, Júlia Castro; Barreto, Rodrigo Rony; Vilaça, Vanessa de Freitas; Lopes, Amanda Vitor; Souza, Henor Artur de; Peixoto, Ricardo André FiorottiThe present work assesses the feasibility of using mining and industrial residues as aggregates of coating mortars in terms of building thermal performance. For this purpose, we investigated four types of aggregates (river sand—REF, iron ore tailings—IOT, friable quartzite—QTZ, and steelmaking slag—SLG). Initially, the specifc gravity (density) and thermal conductivity of the residue-based mortars were experimentally obtained. Subsequently, a sensitivity analysis was performed through energy simulations of two existing dwellings. Mortars with SLG and IOT presented the best performance due to their low thermal conductivity and, more importantly, their high density. Mortars with SLG presented 64% of thermal performance classifcations as “superior” and “intermediate”, versus an average of 53% for the other aggregates. They were followed by those with IOT, REF and lastly those with QTZ. Therefore, these mortars are cost-efective and sustainable solutions to passively improve the thermal performance of buildings, as well as to mitigate the impacts of the disposal of these residues.Item Correlation between ultrasonic pulse velocity and thermal conductivity of cement-based composites.(2020) Mendes, Júlia Castro; Barreto, Rodrigo Rony; Costa, Laís Cristina Barbosa; Silva, Guilherme Jorge Brigolini; Peixoto, Ricardo André FiorottiThe thermal conductivity of construction materials is among the main factors influencing the thermal performance of buildings. This property is, thus, extensively demanded for design purposes. The thermal conductivity is especially related to the pore system and the composition of cement-based composites, the same factors that affect their Ultrasonic Pulse Velocity (UPV). In this sense, the present work evaluates the correlation between thermal conductivity and UPV. To this purpose, mortar specimens were investigated, with varying mix proportions, fine aggregate types, and dosages of air-entraining admixture. A satisfactory determination coefficient (R2 > 0.9) was obtained between thermal conductivity and UPV of the mortars when they were grouped under similar components and pore structure. It was observed that the pore system of the mortars tested is more influential to the UPV than their overall porosity. In this sense, a better correlation was found between UPV and thermal conductivity than between thermal conductivity and specific gravity. Additionally, the fine aggregate type presents a significant impact—not only due to its chemical and mineralogical properties but also as a result of the morphology that each aggregate generates within the matrix. In conclusion, this technique potentially presents high applicability to the thermal characterisation of cement-based composites.Item Factors affecting the specific heat of conventional and residue-based mortars.(2020) Mendes, Júlia Castro; Barreto, Rodrigo Rony; Castro, Arthur Silva Santana; Silva, Guilherme Jorge Brigolini; Peixoto, Ricardo André FiorottiThe present work investigates the specific heat of cement-based composites and the factors influencing it. To this purpose, coating mortars with Portland cement and hydrated lime were investigated, along with four types of aggregates: river sand, friable quartzite (QTZ), steelmaking slag (SLG), and iron ore tailings (IOT). Initially, the aggregates were characterised chemically and physically. Subsequently, the mortars were evaluated according to their physical and thermal properties. Adiabatic calorimetry was used to measure the specific heat of the samples in two conditions: oven-dried and saturated. The advantages and limitations of the method were discussed. Results showed that the microstructure of the mortars was more significant to the resulting specific heat than their chemical composition or density. Mortars with high specific heat and density, such as those with IOT and SLG, have great potential as sensible heat storage. Therefore, for application purposes, the specific heat should preferably be obtained through techniques that maintain the structure of the composite mostly intact, such as adiabatic calorimetry.Item Macroporous mortars for laying and coating.(2019) Mendes, Júlia Castro; Pinto, Paloma Bárbara; Silva, Henrique Emanuel Américo da; Barreto, Rodrigo Rony; Moro, Taís Kuster; Peixoto, Ricardo André FiorottiThe envelope of a building is responsible for its physical protection against external agents, including humidity and temperature. Thus, the present work seeks to evaluate the effect of air entraining admixtures (AEA) in mortars for laying and coating to improve their physical and thermal performances. The AEA generates macropores, interrupting the system of canaliculi that allows the capillary absorption of water. The AEA used is based on biodegradable surfactant molecules of Linear Alkyl Benzene Sodium Sulfonate. Results compare physical tests (water absorption, capillary coefficient, specific gravity, and mechanical strength), and thermal evaluation (thermal conductivity and specific heat) from two mortars mixtures with varying levels of AEA. Scanning electron microscopy (SEM) of the pore system were also analysed. All mixtures studied presented higher workability and cohesion, reduced thermal conductivity, decreased specific heat, and a reduction in the effects of water absorption, capillary elevation and specific gravity (density). In this sense, the durability of mortars to humidity effect is potentially improved, along with several other properties. Therefore, this work seeks to contribute to the quality of built environments, as well as to promote the technological development of cement-based composites.Item On the relationship between morphology and thermal conductivity of cement-based composites.(2019) Mendes, Júlia Castro; Barreto, Rodrigo Rony; Paula, Ana Carolina Barbieri de; Elói, Fernanda Pereira da Fonseca; Silva, Guilherme Jorge Brigolini; Peixoto, Ricardo André FiorottiThe present work discloses the factors related to the morphology of the matrix that affect the thermal conductivity of cement-based composites. For this purpose, we investigated three mortar mixes with cement and hydrated lime (1:3, 1:1:6 and 1:2:9); and three types of aggregates (river sand, iron ore tailings, friable quartzite). We studied how the chemical composition and particle characteristics of the aggregates affect the overall properties of the mortars. In this sense, physical and chemical characterisation of the aggregates were performed; along with the physical, thermal and morphological evaluation of the resulting mortars. It is concluded that the morphology of the matrix is more relevant to the thermal conductivity of mortars than the chemical composition of its components. Also, the pore system generated by the aggregates in the mortar is more correlated to its thermal conductivity than its total porosity and specific gravity.