• Proceedings of the Korean Institute of Building Construction Conference
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• 한국건축시공학회 2021년도 봄 학술논문 발표대회
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• pp.133-134
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• 2021

In this study, the effects of aggregates on the properties of concrete as a study to determine the mechanical properties of high-temperature damaged concrete were examined. The samples to be reviewed are cement paste, mortar, and concrete, and the strength characteristics were reviewed after heating the compression strength and tensile strength properties. The increase in magnetic shrinkage at around 100℃ showed a significant drop in strength in mortar, which does not contain aggregates or has a small diameter, and after 300℃, concrete showed a sharp drop in strength due to the hydration and aggregation of cement.

• International Journal of Concrete Structures and Materials
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• 제10권sup3호
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• pp.19-31
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• 2016

The objective of this paper is to investigate the effect of thickness and moisture on temperature distributions of reinforced concrete walls under fire conditions. Toward this goal, the first three wall specimens having different thicknesses are heated for 2 h according to ISO standard heating curve and the temperature distribution through the wall thickness is measured. Since the thermal behavior of the tested walls is influenced by thickness, as well as moisture content, three additional walls are prepared and preheated to reduce moisture content and then tested under fire exposure. The experimental results clearly show the temperatures measured close to the fire exposed surface of the thickest wall with 250 mm thickness is the highest in the temperatures measured at the same location of the thinner wall with 150 mm thickness because of the moisture clog that is formed inside the wall with 250 mm of thickness. This prevents heat being transferred to the opposite side of the heated surface. This is also confirmed by the thermal behavior of the preheated walls, showing that the temperature is well distributed in the preheated walls as compared to that in non-preheated walls. Finite element models including moisture clog zone are generated to simulate fire tests with consideration of moisture clog effect. The temperature distributions of the models predicted from the transient heat analyses are compared with experimental results and show good agreements. In addition, parametric studies are performed with various moisture contents in order to investigate effect of moisture contents on the thermal behaviors of the concrete walls.

• Computers and Concrete
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• 제22권1호
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• pp.93-100
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• 2018

It is seldom possible that geotechnical materials like rocks and concretes found without joints, cracks, or discontinuities. Thereby, the impact of micro-cracks on the mechanical properties of them is to be considered. In the present study, the effect of micro-crack on the failure mechanism of rock specimens under uniaxial compression was investigated experimentally. For this purpose, thermal stress was used to induce micro-cracks in the specimens. Several cylindrical and disk shape specimens were drilled from granite collected from Zanjan granite mine, Iran. Some of the prepared specimens were kept in room temperature and the others were heated by a laboratory furnace to different temperature levels (200, 400, 600, 800 and 1000 degree Celsius). During the experimental tests, Acoustic Emission (AE) sensors were used to monitor specimen failure at the different loading sequences. Also, Scanning Electron Microscope (SEM) was used to distinguish the induced micro-crack by heating in the specimens. The fractographic analysis revealed that the thin sections heated to $800^{\circ}C$ and $1000^{\circ}C$ contain some induced micro-fractures, but in the thin sections heated to $200^{\circ}C$, $400^{\circ}C$ and $600^{\circ}C$ have not been observed any micro-fracture. In the next, a comprehensive experimental investigation was made to evaluate mechanical properties of heated and unheated specimens. Results of experimental tests showed that induced micro-cracks significantly influence on the failure mode of specimens. The specimens kept at room temperature failed in the splitting mode, while the failure mode of specimens heated to $800^{\circ}C$ are shearing and the specimens heated to $1000^{\circ}C$ failed in the spalling mode. On the basis of AE monitoring, it is found that with increasing of the micro-crack density, the ratio of the number of shear cracks to the number of tensile cracks increases, under loading sequences.

• Proceedings of the Korean Institute of Building Construction Conference
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• 한국건축시공학회 2013년도 추계 학술논문 발표대회
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• pp.58-59
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• 2013

In this study, the standard specimen heated to curing experiments and simulation experiments the absence of porosity distribution and the effect on the compressive strength has been investigated.

• Computers and Concrete
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• 제26권2호
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• pp.115-125
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• 2020

To reduce the damage of concrete in fire, a new type of lightweight cinder aggregate concrete was developed due to the excellent fire resistance of cinder. To further enhance its fire resistance, Polypropylene (PP) Fibers which can enhance the fire resistance of concrete were also used in this type of concrete. However, the bond behavior of this new type of concrete after fire exposure is still unknown. To investigate its bond behavior, 185 specimens were heated up to 22, 200, 400, 600 or 800℃ for 2 h duration respectively, which is followed by subsequent compressive and tensile tests at room temperature. The concrete-rebar bond strength of C30 PP fiber-reinforced cinder concrete was subsequently investigated through pull-out tests after fire exposure. The microstructures of the PP fiber-reinforced cinder concrete and the status of the PP fibre at different temperature were inspected using an advanced scanning electron microscopy, aiming to understand the mechanism of the bonding deterioration under high temperature. The effects of rebar diameter and bond length on the bond strength of PP fiber-reinforced cinder concrete were investigated based on the test results. The bond-slip relation of PP fiber-reinforced cinder concrete after exposure at different temperature was derived based on the test results.

• Computers and Concrete
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• 제21권1호
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• pp.87-94
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• 2018

This paper presents the results of an experimental study to investigate the influences of high temperatures on the mechanical properties of concrete containing recycled fine aggregate. A total of 150 concrete prisms ($100{\times}100{\times}300mm$) and 150 concrete cubes ($100{\times}100{\times}100mm$) are cast and heated under five different temperatures ($20^{\circ}C$, $200^{\circ}C$, $400^{\circ}C$, $600^{\circ}C$, $800^{\circ}C$) for test. The results show that the mass loss, compressive strength, elastic modulus, splitting tensile strength of concrete specimens containing recycled fine aggregate decline significantly as the temperature rise. At the same temperature, the compressive strength, splitting tensile strength, elastic modulus of concrete specimens containing recycled coarse aggregate and recycled fine aggregate (RHC) is lower than that of concrete specimens containing natural coarse aggregate and recycled fine aggregate (RFC). The shape of stress-strain curves of concrete specimens at different temperatures is different, and the shape of that become flatter as the temperature rises. Normal concrete has better energy absorption capacity than concrete containing recycled fine aggregate.

• Proceedings of the Korean Institute of Building Construction Conference
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• 한국건축시공학회 2017년도 춘계 학술논문 발표대회
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• pp.246-247
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• 2017

In this study, it reviewed the effect of moisture migration in concrete with heating rate on concrete spalling. Concrete specimens with compressive strength 30MPa and 110MPa are used and its size is □100×100×h200mm. And, two kinds of heating rate are set such as IS0 834 and 1℃/min. As a result, in the concrete specimen exposed to ISO 834 standard heating condition, moisture could migrate through pore network and surface concrete pieces fall out by generating moisture clog near the surface in 110MPa concrete specimen. Meanwhile, In the case of concrete specimens exposed to 1℃/min. heating condition, it is appeared that moisture could not migrate because temperature is distributed uniformly. Therefore, surface spalling is not occurred with low heating rate. However, in the case of 110MPa concrete specimen is exploded even though it heated by low heating rate.

• Journal of the Korea Safety Management & Science
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• 제9권4호
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• pp.83-90
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• 2007

This study is to find out if it can be recycled for making better concrete. Therefore, waste paper as of newspaper and newspaper are added into concrete to see if waste paper-mixing concrete can have any particular characteristic. The test result of paper concrete was compared and analyzed through four kinds of tests such as compressive strength as of a fundamental one of concrete resistant capacity against heat. $200^{\circ}C,\;400^{\circ}C\;and\;600^{\circ}C$ heated concrete were compressively tested in order to find out concrete strength resistant to high temperature. heat capacity was also tested, based on the expectancy of its low conductivity. finally flexural strength test using four reinforced concrete beams with size of $20cm{\times}30cm{\times}160cm$ was made. And concrete property exposed to the temperature showed that there are almost not effect for the strength up to $400^{\circ}C$, but it was decreased down to 50% of the original condition. volume of paper mixed with concrete without relation to paper kinds of new and waste one.

• Proceedings of the Korea Concrete Institute Conference
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• 한국콘크리트학회 2005년도 추계 학술발표회 제17권2호
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• pp.49-52
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• 2005

The purpose of this study is to investigate the relation between color change and residual compressive strength in concrete exposed to high temperature. In order to study the color image analysis, the specimens have been tested with variables of concrete strengths (20Mpa, 40Mpa, 60Mpa) in transient heating conditions($800^{\circ}C$ heating and 4 hour preservation). The results show that the residual strength of specimens are coincident with the full development of the pink/red color and the method may be used to define the distance from a heated surface where strength degradation has occurred.

• Proceedings of the Korea Concrete Institute Conference
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• 한국콘크리트학회 2006년도 춘계학술발표회 논문집(I)
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• pp.74-77
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• 2006

The purpose of this study is to investigate the relation between color change and residual compressive strength in concrete exposed to high temperature. In order to study the color image analysis, the specimens have been tested with variables of concrete strengths(20Mpa, 40Mpa, 60Mpa) in transient heating conditions($800^{\circ}C$ heating and 2 hour preservation). The results show that the residual strength of specimens are coincident with the full development of the pink/red color and the method may be used to define the distance from a heated surface where strength degradation has occurred.