Explosive Spalling Behavior of Single-Sided Heated Concrete According to Compressive Strength and Heating Rate

In this study, the effects of heating rate and compressive strength on the spalling behavior of single-sided heated ring-restrained concrete with compressive strengths of 60 and 100 MPa were investigated. The vapor pressure and restrained stress inside the concrete were evaluated under fast- and slow-heating conditions. Regardless of the heating rate, the concrete vapor pressure and restrained stress increased as the temperature increased, and it was confirmed that spalling occurred in the 100-MPa concrete. Specifically, it was found that moisture migration and restrained stress inside the concrete varied depending on the heating rate. Under fast heating, moisture clogging and restrained stress occurred across the concrete surface, causing continuous surface spalling for the 100-MPa concrete. Under slow heating, moisture clogging occurred, and restrained stress continuously increased in the deep area of the concrete cross-section owing to the small internal temperature difference, resulting in explosive spalling for the 100-MPa concrete with a dense internal structure. Additionally, while the tensile strength of concrete is reduced by heating, stress in the heated surface direction is generated by restrained stress. The combination of stress in the heated concrete surface and the internal vapor pressure generates spalling. The experimental results confirm that heating rate has a significant influence on moisture migration and restrained stress occurrence inside concrete, which are important factors that determine the type of spalling.

Investigation on the performance of fiber reinforced concrete subjected to standard fire exposure

Purpose Aim of this research work is to examine the stress–strain behavior and modulus of elasticity of fiber-reinforced concrete (FRC) exposed to elevated temperature. The purpose of this paper is to study the effect of standard fire exposure on the mechanical and microstructure characteristics of concrete specimens with different strength grade. Design/methodology/approach An electrical bogie hearth furnace was developed to simulate the ISO 834 standard fire curve. Specimens were exposed to high temperatures of 821°C, 925°C and 986°C for the duration of 30, 60 and 90 min, respectively, as per standard fire curve. Peak stress, peak strain, modulus of elasticity and damage level of heated concrete specimens were evaluated by experimental investigation. SEM-based microstructure investigation has been carried out to analyze the microstructure characteristics of heated concrete specimens. Findings The results revealed that carbon fiber reinforced concrete was found to be better than the FRC made with other fibers on improving the modulus of elasticity of concrete. An empirical relationship has been established to predict the modulus of elasticity of temperature exposed specimens with different type of fiber and grade of concrete. In comparison with low melting point fibers, high melting point fibers exhibited higher modulus of elasticity under all tested conditions. Surface damage and porosity level of concrete with carbon and basalt fibers were found to be lower than other FRC. Originality/value Empirical relationship was developed to determine the modulus of elasticity of concrete exposed to elevate temperature, and this will be useful for concrete design applications. This research work may be useful for finding the residual compressive strength of concrete exposed to elevate temperature. So that it will be helpful to identify the suitable repair/retrofitting technique for reinforced concrete elements.

Feasibility Study of Digital Image Correlation in Determining Strains in Concrete Exposed to Fire

Concrete is prone to spalling when exposed to fire. During fire tests, the strains of concrete elements are hard to identify, both from the fire-exposed face and the non-exposed face. This paper presents a field experiment which employed the original CivEng digital image correlation (DIC) method developed at the Cracow University of Technology to measure the strain fields of elements exposed to heating by a pin-point gas burner. The paper presents experimental proof that it is possible to analyze the deformation of both unheated and fire-exposed sides of heated concrete by the DIC method. The strain fields, crack patterns and modes of crack development are presented. The study shows the encouraging results of employing the DIC method to test concrete behavior under fire attack.

Strength and microstructure characteristics of concrete with different grade exposed to standard fire

Purpose The purpose of this study is to investigate the effect of standard fire on the strength and microstructure properties of concrete with different strength grades. Design/methodology/approach Different strength grades of concrete used for the investigation are M20, M30, M40 and M50. An electrical bogie hearth furnace was developed to simulate the International Standards Organization 834 standard fire curve.Concrete samples were subjected to high temperatures of 925, 1,029, 1,090 and 1,133°C for the duration of 1, 2, 3 and 4 h, respectively, as per standard fire curve. Compressive strength, tensile strength, thermal crack pattern and spalling of heated concrete specimens were evaluated by experimental investigation. Scanning electron microscopy and thermo-gravimetric analysis were performed to investigate the microstructure properties of heated concrete specimens. Findings Test results indicated reduction in the strength and changes in the microstructure properties of concrete exposed to elevated temperature. The degree of weight and the strength loss were found to be higher for concrete with higher grades. An empirical relation is proposed to determine the residual strength of concrete with different strength grade using regression analysis. Social implications Results of this research will be useful for the design engineers to understand the behavior of concrete exposed to elevated temperature as per standard fire. Originality/value When concrete is exposed to elevated temperature, its internal microstructure changes, thereby strength and durability of concrete deteriorates. The performance of concrete with different strength grade exposed to standard fire is well understood. This research’s findings will be useful for the designers to understand more about fire resistance of concrete. A simple relationship is proposed to determine the residual strength of concrete exposed to various durations of heating.

EVALUATION OF BEHAVIOR IN PIGLETS USING DIGITAL IMAGE PROCESSING

EVALUATION OF BEHAVIOR IN PIGLETS USING DIGITAL IMAGE PROCESSING FLAVIO ALVES DAMASCENO1, CLÁUDIO MAGELA SOARES2, CARLOS EDUARDO ALVES OLIVEIRA3, LEIDIMAR FREIRE BRANDÃO DAMASCENO4 e PATRICIA FERREIRA PONCIANO FERRAZ5 1 Departamento de Engenharia, Universidade Federal de Lavras – Av. Dr. Sylvio Menicucci, 1001, Kennedy, 37200-000, Lavras, Minas Gerais, Brasil. E-mail: [email protected] 2 Campus Anápolis de Ciências Exatas e Tecnológicas Henrique Santillo, Universidade Estadual de Goiás – BR 153, nº 3105, 75132-000, Anápolis, Goiás, Brasil. E-mail: [email protected] 3 Departamento de Engenharia, Universidade Federal de Lavras – Av. Dr. Sylvio Menicucci, 1001, Kennedy, 37200-000, Lavras, Minas Gerais, Brasil. E-mail: [email protected] 4 Departamento de Engenharia Civil, Universidade Federal de Ouro Preto – Rua Prof. Paulo Magalhães Gomes, 122, Bauxita, 35400-000, Ouro Preto, Minas Gerais, Brasil. E-mail: [email protected] 5 Departamento de Engenharia, Universidade Federal de Lavras – Av. Dr. Sylvio Menicucci, 1001, Kennedy, 37200-000, Lavras, Minas Gerais, Brasil. E-mail: [email protected] ABSTRACT: World production of pork has increased in recent years, and currently Brazil is the fourth largest producer. One of the major challenges in animal production systems is providing adequate thermal comfort. In the pork industry, the lactation area presents a peculiar environmental requirement: the lactating sows need to be cooled while the piglets need to be heated, requiring two distinct microenvironments. Thus the objective of this study was to evaluate the behavior of piglets using digital image analysis techniques, detecting the presence and calculating the time of the animals inside the shelter equipped with different types of heating system. The study was conducted during the summer of 2015, in a swine maternity, where four different heating systems were used: a) shelter equipped with 250 W infrared light (SALI); b) shelter equipped with heated concrete floor heating by means of solar water heater constructed with alternative materials (SASA); c) shelter equipped with heated concrete floor heating by conventional solar water heater (SASC) and d) retractor shelter equipped with thermal concrete floor heating by means of electric resistance (SAEL). During the study, the environmental variables were monitored inside the shelter. A sequence of images of the piglets was used to evaluate the behavior of the animals. The algorithm developed was able to detect the presence of the piglets, and thus reduce the time for manual analysis of video monitoring. Keywords: Thermal comfort, swine, segmentation AVALIAÇÃO DE COMPORTAMENTO DE LEITÕES UTILIZANDO PROCESSAMENTO DIGITAL DE IMAGENS RESUMO: A produção mundial de carne suína vem crescendo nos últimos anos, sendo que atualmente o Brasil é o quarto maior produtor. Um dos grandes desafios na produção é o conforto térmico dos animais. Na suinocultura, a maternidade é onde encontra-se o maior problema, pois a porca necessita ser resfriada e o leitão aquecido, necessitando de dois microambientes diferentes. Objetivou-se com o presente trabalho, avaliar o comportamento de leitões por meio da análise de imagem, detectando a presença e calculando o tempo de permanência dos animais dentro do abrigo escamoteador equipado com diferentes tipos de sistema de aquecimento. Todo o estudo foi conduzido durante o período de verão de 2015, numa maternidade de suínos, onde instalou-se quatro diferentes sistemas de aquecimento: a) abrigo escamoteador equipado com lâmpada infravermelho de 250 W (SALI); b) abrigo escamoteador equipado com piso térmico de concreto aquecido por meio de tubos de água quente construído com materiais alternativos (SASA); c) abrigo escamoteador equipado com piso térmico de concreto aquecido por meio de tubos de água quente convencional (SASC) e d) abrigo escamoteador equipado com piso térmico de concreto aquecido por meio de resistência elétrica (SAEL). Durante o estudo, foram monitoradas as variáveis ambientais no interno ao abrigo escamoteador. Para avaliar o comportamento dos animais foram utilizadas a técnicas de processamento de uma sequência de imagens dos leitões. O método de avaliação por imagens digitais mostrou-se viável na avaliação do comportamento dos leitões, diminuindo o tempo de análise manual da monitoração por vídeo. Palavras-chaves: conforto animal, suíno, segmentação de imagem