• Journal of The Korean Society of Agricultural Engineers
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• v.53 no.5
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• pp.25-33
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• 2011

In this paper, the effects of aggregate and curing temperature on strength development characteristics of UP (Unsaturated Polyester)-MMA (Methyl Methacrylate) based polymer mortar under sub-zero temperature are experimentally investigated to provide a criterion for repair and production of precast products. The result showed that the setting time of the binder was 4 minutes at $20^{\circ}C$ whereas 35 minutes at $-20^{\circ}C$. The result also revealed that the compressive, flexural, and splitting tensile strengths of UP-MMA based polymer mortar significantly decreased as the aggregate and curing temperatures decreased. However, sufficient strengths which can be implemented in actual practices -36.6 MPa of compressive strength, 6.11 MPa of flexural strength, and 5.81 MPa of splitting tensile strength - were obtained even though both aggregate and curing temperatures were $-20^{\circ}C$. Strength development of polymer mortar is largely affected by curing temperature rather than aggregate temperature. It was found that the effects of aggregate temperature on strength development become smaller as the curing temperature becomes lower. Also, toughness, a ratio of compressive strength to flexural strength, increased from 3.5 to 5.9 as both aggregate and curing temperatures decreased from $20^{\circ}C$ to $-20^{\circ}C$.

• Journal of The Korean Society of Agricultural Engineers
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• v.46 no.4
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• pp.49-55
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• 2004

Properties of concrete using low heat portland cement is different from using ordinary portland cement and temperature of aggregate can be expected to have an important influence on its properties. In this study, experiment by setting up 5 levels (40, 30, 20, 4, $-2^{\circ}C$) by temperature of aggregate for evaluation properties of concrete using low heat portland cement was conducted. The experiments include slump test, air content test, change of slump, change of air content and compressive strength of concrete test. As the result of experiments, slump and air content was decreased by increasing temperature of aggregate. But it was not exceeding it's limit. Change of slump and air content was rapidly decrease by decreasing temperature of aggregate. At early age, compressive strength was influenced by the temperature of aggregate.

• Structural Engineering and Mechanics
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• v.65 no.3
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• pp.343-348
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• 2018

This paper reports mechanical behavior of recycled fine aggregate concretes after high temperatures. It is found that compressive strength of recycled fine aggregate concretes decline significantly as the temperature rises. The elastic modulus of recycled fine aggregate concretes decreases with the increase in temperature, and the decrease is much quicker than the decrease in compressive strength. The split tensile strength of recycled fine aggregate concrete decrease as the temperature rises. Through the regression analysis, the relationship of the mechanical behavior with temperature are proposed, including the compressive behavior, elastic modulus and split tensile strength, which are fitting the test data.

• Computers and Concrete
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• v.21 no.1
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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.

• Computers and Concrete
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• v.23 no.3
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• pp.155-160
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• 2019

The use of recycled aggregate concrete for the purpose of environmental and resource conservation has gained increasing interest in construction engineering. Nevertheless, few studies have reported on the bonding performance of the bars in recycled aggregate concrete after exposed to high temperatures. In this paper, 72 pull-out specimens and 36 cubic specimens with different recycled coarse aggregate content (i.e., 0%, 50%,100%) were cast to evaluate the bond behavior between recycled aggregate concrete and steel bar after various temperatures ($20^{\circ}C$, $200^{\circ}C$, $400^{\circ}C$, $600^{\circ}C$). The results show that the recycled aggregate concrete pull-out specimens exhibited similar bond stress-slip curves at both ambient and high temperature. The bond strength declined gradually with the increase of the temperature. On the basis of a regression analysis of the experimental data, a revised bond strength mode and peak slip ratios relationship model were proposed to predict the post-heating bond-slip behavior between recycled aggregate concrete and steel bar.

• Journal of the Korea Concrete Institute
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• v.26 no.3
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• pp.247-254
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• 2014

Strain properties of concrete member which acts as an important factor in the stability of the concrete structure in the event of fire, significantly affected the characteristics of the coarse aggregate, which accounts for most of the volume. For this reason, there are many studies on concrete using artificial lightweight aggregate which has smaller thermal expansion deformation than granite coarse aggregate. But the research is mostly limited on concrete using clay-based lightweight aggregate. Therefore, in this study, the high temperature compressive strength and elastic modulus, thermal strain and total strain, high temperature creep strain of concrete was evaluated. As a result, remaining rate of high-temperature strength of concrete using lightweight aggregate is higher than concrete with general aggregate and it is determined to be advantageous in terms of structural safety and ensuring high-temperature strength from the result of the total strain by loading and strain of thermal expansion. In addition, in the case of high-temperature creep, concrete shrinkage is increased by rising loading and temperature regardless of the type of aggregate, and concrete using lightweight aggregate shows bigger shrinkage than concrete with a granite-based aggregate. From this result, it is determined to require additional consideration on a high temperature creep strain in case of maintaining high temperature like as duration of a fire although concrete using light weight aggregate is an advantage in reducing the thermal expansion strain of the fire.

• Computers and Concrete
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• v.19 no.6
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• pp.609-615
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• 2017

In this paper, the effects of elevated temperatures on the strength and compressive stress-strain curve (SSC) of recycled coarse aggregate concrete with different replacement percentages are presented. 90 recycled coarse aggregate concrete prisms are heated up to 20, 200, 400, 600, $800^{\circ}C$. The results show that the compressive strength, split tensile strength, elastic modulus of recycled aggregate concrete specimens decline significantly as the temperature rise. While the peak strain increase of recycled aggregate concrete specimens as the temperature rise. Compared to the experimental curves, the proposed stress-strain relations for recycled aggregate concrete after exposure elevated temperatures can be used in practical engineering applications.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2015.05a
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• pp.67-68
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• 2015

Recently, usage of ultra-high strengh concrete(UHSC) have been increased. Concrete has been recognized as a material which is resistant to high temperatures, but chemicophysical property of concrete is changed by the high temperature. So, mechanical properties of concrete may be reduced. Therefore, this study evaluated effect of the coarse Aggregate volume by high temperature mechanical properties of UHSC. Residual mechanical properties are evaluated under fine aggregate ratio 40,60% and 500℃ temperature on UHSC of W/B 15, 20%. As result, residual mechanical properties of UHSC are high by lower coarse aggregate volume.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2010.05a
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• pp.91-94
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• 2010

The purpose of this study is to produce artificial lightweight aggregate. The properties of aggregate are deducted by analysing the plasticity of aggregate according to the addictive contents of $CaCO_3$ and $Al_2O_3$ on constant plastic temperature($1150^{\circ}C{\sim}1160^{\circ}C$) and the specific gravity, the percentage of water absorbtion. The density on the temperature of $1150^{\circ}C{\sim}1160^{\circ}C$ which results from that the plastic temperature of pottery stone is decreased by increasing the addictive contents of $CaCO_3$ and $Al_2O_3$ manufacturing artificial light weight aggregate using pottery stone is included in the arrange of light weight aggregate density. And the percentage of water absorbtion is 4.2~14% which is similar to or lower than existing artificial light weight aggregate. The unit volume weight is in inverse proportion to density and to increase addictive contents of flux.

• Journal of Korean Society of Water and Wastewater
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• v.27 no.6
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• pp.743-750
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• 2013

In this study, the carbonized aggregate of light weight and high mechanical strength using sewage sludge was evaluated with changing carbonation variables of temperature, detention time and feed condition. Porosity and mechanical strength was simultaneously increased according to increase of carbonization temperature unexpectedly. Carbonization detention time above 1 hour nearly affect on the porosity, but mainly on mechanical strength of the carbonized aggregate in case of clay addition. On $900^{\circ}C$, porosity and mechanical strength was increased rapidly, but above $1000^{\circ}C$, porosity began to decrease. Clay addition was very effective on increase of mechanical strength following much loss in porosity. The carbonized aggregate manufactured at $900^{\circ}C$ adding 30 % clay in sewage sludge was higher a little in porosity and 3 times in mechanical strength than those at $700^{\circ}C$ not adding clay. Consequently, in manufacturing the carbonized aggregate having simultaneously high porosity and mechanical strength, it is desirable to have operational condition of $900{\sim}1000^{\circ}C$ temperature and 1 hour time, and clay addition within 30 % for further higher mechanical strength.