• Steel and Composite Structures
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• 제41권5호
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• pp.731-746
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• 2021

The purpose of this paper is to investigate the axial bearing capacity and residual properties of steel reinforced recycled aggregate concrete (SRC) column after elevated temperature. A total of 48 SRC columns were designed for the static loading test after elevated temperature. The variables include replacement ratios, designed temperature, target duration, thicknesses of cover concrete, steel ratios and stirrup spacing. From this test, the mass loss ratio and stress load-deformation curve were obtained, and the influence of various parameters on residual bearing capacity were analyzed. ABAQUS was used to calculate the temperature field of specimens, and then got temperature damage distribution on the cross-section concrete. It was shown that increasing of the elevated temperatures leaded to the change of concrete color from smoky-gray to grayish brown and results in reducing the bearing capacity of SRC columns. The axial damage and mechanism of SRC columns were similar to those of reinforced natural aggregate concrete columns at the same temperatures. Finally, the calculation method of axial compressive residual bearing capacity of SRC columns recycled concrete columns after high temperature was reported based on the test results and finite element analysis.

• 콘크리트학회논문집
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• 제23권6호
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• pp.749-756
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• 2011

FRP 보강근의 화재 노출시 내구성능에 대한 연구들은 고온 노출이 인장성능에 미치는 영향에 대한 분석이 대부분을 차지한다. 그러나, 신설 구조물에 삽입된 FRP 보강근은 먼저 콘크리트 내에서 습윤환경 및 알칼리에 의한 성능저하가 발생하며, 이와 같은 FRP 보강 콘크리트 구조물에 화재가 발생하면, 보강근은 고온에 노출된다. 그러므로 화재에 의해 손상 받은 FRP 보강근의 평가시에는 콘크리트 환경과 고온에 의한 영향을 동시에 고려하여야 한다. 이 연구에서는 장기간동안 용액에 노출된 FRP 보강근에 $60^{\circ}C$, $100^{\circ}C$, $150^{\circ}C$ 및 $300^{\circ}C$의 온도를 가하고, 계면전단강도를 측정, 비교 하였다. 실험 결과에 따르면, 환경과 고온의 복합영향이 FRP 보강근의 역학적 특성에 미치는 영향이 환경만의 영향 또는 고온만의 영향 보다 큰 것으로 나타났다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 봄 학술발표회 논문집
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• pp.237-242
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• 2001

The objective of this study is to investigate growth of grass planted with planting concrete using recycled aggregste. Planting concrete blocks are constructed on the roof of existing building. Temperature variation according to planting concrete method are also investigate. According to test results, it shows that grass grows very well under planting concrete method. When planting concrete method is applied, it brings about temperature reducing effects about 1~$2^{\circ}C$ at inner part of the buildings at cooling required period compared to that with existing roof, and at heating required period temperature insulating effects about 2~$4^{\circ}C$.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 가을 학술발표회 논문집
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• pp.1199-1202
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• 2001

The objective of this study is to examine the effect of frost damage immediately after placement on compressive strength of concrete. Obviously frost damage produced under low curing temperature at early ages causes the loss of compressive strength of concrete. In order to find the degrees of the loss of compressive strength, compressive strength tests was peformed at 7 and 28-day ages on concrete specimen with various curing temperature history. The results from the tests showed that the loss of compressive strength relative to concrete cured under isothermal temperature at $20^{\circ}C$ was generally from 20 to 50% for 7-day ages and below 20% for 28 day ages. Considering the serious loss of compressive strength over 50% for some cases, careful attention may be needed to placing of concrete under low atmospheric temperature.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1995년도 봄 학술발표회 논문집
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• pp.263-267
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• 1995

The usual methods for the temperature control of mass-concrete structures include the use of low-heat cement, pre-cooling, post-cooling, or sheet curing. In order to control the heat of hydration during the construction of mass-concrete structures, the combination of the above methods is commonly employed. For the construction of mass-concrete structures such as massive pier or anchor, it is necessary to control the curing temperature with pipe cooling. In this study, the method of analysis on the effect of pipe of was proposed to prevent the thermal cracking due to heat of hydration In addition the effect of covering the concrete surface with blanket insulation was investigated. The results of the present study may be useful for the prediction of curing temperature of mass-concrete structures and the reasonable construction management.

• Computers and Concrete
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• 제13권1호
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• pp.97-115
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• 2014

Silica fume is a by-product of induction arc furnaces and has long been used as a mineral admixture to produce high-strength, high-performance concrete. Due to the pozzolanic reaction between calcium hydroxide and silica fume, compared with that of Portland cement, the hydration of concrete containing silica fume is much more complex. In this paper, by considering the production of calcium hydroxide in cement hydration and its consumption in the pozzolanic reaction, a numerical model is proposed to simulate the hydration of concrete containing silica fume. The heat evolution rate of silica fume concrete is determined from the contribution of cement hydration and the pozzolanic reaction. Furthermore, the temperature distribution and temperature history in hardening blended concrete are evaluated based on the degree of hydration of the cement and the mineral admixtures. The proposed model is verified through experimental data on concrete with different water-to-cement ratios and mineral admixture substitution ratios.

• Computers and Concrete
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• 제7권1호
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• pp.63-81
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• 2010

We present the shape determination method of 3-D reinforcement corrosion based on observed temperature on concrete surface. The non-destructive testing for reinforcement corrosion in concrete using a heat image on concrete surface have been proposed by Oshita. The position of the reinforcement of corrosion or the cavity can be found using that method. However, the size of those defects can not be precisely measured based on the heat image. We therefore proposed the numerical determination system of the shape for the reinforcement corrosion using the observed temperature on the concrete surface. The adjoint variable method is introduced to formulate the shape determination problem, and the finite element method is employed to simulate the heat transfer problem. Some numerical experiments and the examination for the number of the observation points are shown in this paper.

• Computers and Concrete
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• 제23권3호
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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.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2008년도 추계 학술논문 발표대회
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• pp.31-36
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• 2008

This study aims to examine the effects of thickness of the concrete members and curing temperature on the properties of low heat concrete through heat of hydration analysis. Type of the members that was analyzed in the experiment is ternary mixture of ordinary portland cement, blast-furnace slag incorporating ratio(20%) and fly ash incorporating ratio(30%), which formed a mat foundation. Thicknesses of the concrete members were 1, 2 and 3(m) and three levels of curing temperatures were 10, 20 and 30(℃). They were applied to analyze the effects on the temperature and thermal cracking index. As a result, for temperature history, temperature difference between the central area and the surface tended to decrease as the thickness of the concrete members get thinner. For the temperature cracking index, on the other hand, the risk of cracking tended to decrease as the curing temperature gets higher and as the thickness gets thinner.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2000년도 가을 학술발표회논문집(I)
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• pp.31-45
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• 2000

Because of the high unit cement content in the concrete mix, major concrete temperature rises are observed in the initial stages of hardening in structural members with large cross-sections made of high-strength concrete. While this temperature rise in the initial stages of hardening contributes to the initial development of the concrete strength, it also causes thermal cracking and obstructs medium to long-term increases of the concrete strength. In the study reports below, investigations were made on the effects of the concrete temperature rise in the initial stages of hardening on the medium to long-term development of the strength of structural concrete between the ages of 28 and 91 days. In the study, comparisons were made, for example, between the compressive strength of a control specimen subjected to standard curing at 28 days and the compressive strength of core specimens taken from structural members, and observations were made on the methods of evaluating the concrete strength in structure, defined here as the compressive strength of core specimens at 91 days. The results obtained indicate that, when the maximum temperature of the concrete is the structure does not exceed $60^{\circ}C$, the concrete strength in structure at the age of long-term will generally be greater than the compressive strength of the standard-curing specimens at 28 days, allowing one to evaluate the strength of the structural concrete in terms of the compressive strength of the 28-days standard-curing specimens. When, on the other hand, the maximum temperature of the concrete in the structure exceeds $60^{\circ}C$, the strength in concrete structure may be smaller than the compressive strength of the 28-days standard-curing specimens, creating risks in the evaluation of the concrete strength in structure by latter.