• Computers and Concrete
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• 제31권2호
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• pp.111-121
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• 2023

The influence of material composition such as aggregate types, addition of supplementary cementitious materials as well as exposed temperature levels have significant impacts on concrete residual mechanical strength properties when exposed to elevated temperature. This study is based on data obtained from literature for fly ash blended concrete produced with natural and recycled concrete aggregates to efficiently develop prediction models for estimating its residual compressive strength after exposure to high temperatures. To achieve this, an extensive database that contains different mix proportions of fly ash blended concrete was gathered from published articles. The specific design variables considered were percentage replacement level of Recycled Concrete Aggregate (RCA) in the mix, fly ash content (FA), Water to Binder Ratio (W/B), and exposed Temperature level. Thereafter, a simplified mathematical equation for the prediction of concrete's residual compressive strength using Gene Expression Programming (GEP) was developed. The relative importance of each variable on the model outputs was also determined through global sensitivity analysis. The GEP model performance was validated using different statistical fitness formulas including R², MSE, RMSE, RAE, and MAE in which high R² values above 0.9 are obtained in both the training and validation phase. The low measured errors (e.g., mean square error and mean absolute error are in the range of 0.0160 - 0.0327 and 0.0912 - 0.1281 MPa, respectively) in the developed model also indicate high efficiency and accuracy of the model in predicting the residual compressive strength of fly ash blended concrete exposed to elevated temperatures.

• Geomechanics and Engineering
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• 제34권2호
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• pp.173-186
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• 2023

In order to prevent environmental pollution, initiatives to increase the sustainability of resources are supported by society. However, the performance of recycled materials does not generally match that of natural materials. This study looks into the use of geogrid to improve various types of recycled aggregates. For this purpose, five different recycled aggregates were created by recycling wastes from the construction industry. Besides, direct shear tests (DS tests) were carried out on these recycled aggregates to determine their shear strengths. Following that, a triaxial geogrid was placed in the recycled aggregates to provide reinforcement, and the DS tests were conducted on the reinforced recycled aggregates. The results of the tests were also compared to those of tests performed on natural aggregates (NA). In conclusion, it was found that the recycled aggregates have lower shear strengths than the NA. Nonetheless, when reinforced with geogrid, the shear strength of the recycled concrete aggregates (RCA) and construction and demolition wastes (CDW) exceeded that of the NA. Furthermore, the geogrid reinforcement increased the shear strength of the recycled crushed bricks (CB), though not to the level of the NA.

• 한국지반공학회논문집
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• 제40권1호
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• pp.29-37
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• 2024

본 연구에서는 이산화탄소 처리를 통한 순환골재의 지반공학적 성능 개량을 평가하기 위하여 5kg급 프로토타입 반응조를 제작하였다. 제작된 반응조를 이용하여 이산화탄소 처리한 순환골재와 미처리 순환골재의 골재 파쇄값과 노상토지지력비를 측정하였다. 이산화탄소 처리를 통해 골재 파쇄값은 35.6%에서 33.2%로 2.4% 감소하고 노상토지 지력비는 97.5%에서 102.4%로 4.9% 증가하는 것이 관찰되었다. 탄산화 반응을 통해 생성된 탄산칼슘 염으로 인해 순환골재의 세립분 생성이 감소하고 지지력이 증가함을 알 수 있었다. 또한 교반을 함께할 경우 추가적인 역학적 개량 효과를 통해 골재 파쇄값이 30.3%로 감소하고 노상토지지력비는 137.7%로 증가하였다. 본 연구에서 기술된 이산화탄소 처리 기술의 현장 적용 시 건설 산업의 탄소배출을 효과적으로 줄일 수 있을 것으로 보인다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 춘계 학술발표회 제20권1호
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• pp.1093-1096
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• 2008

본 연구에서는 철근의 배근방향(수직, 수평) 및 위치(상단근, 하단근)를 주요 실험변수로 하여 이형철근과 순환굵은골재와의 부착거동을 평가하기 위한 실험을 실시하였다. 본 연구를 통하여 얻어진 실험결과를 종합해 보면, 수평 시험체의 상부철근 시험체의 경우 하부철근 시험체 보다 부착강도가 저하되는 것으로 나타났으며, 밑면으로부터 225mm 위치에 배근된 수평 상단철근 시험체는 CEB-FIP 규준식을 만족하지 못하는 것으로 나타났다. 이는 굵은골재의 편중현상 및 콘크리트의 블리딩 등의 영향으로 인하여 상부철근의 하부에 다수의 공극이 발생되어 부착면적이 작아진 것에 기인하는 것으로 판단된다. 본 시험체에서는 콘크리트와 이형철근의 기계적 맞물림에 의한 지압력이 충분히 발현되지 않은 것으로 관측되었다.

• Earthquakes and Structures
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• 제23권5호
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• pp.445-462
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• 2022

To investigate and evaluate the seismic damage behaviors of steel reinforced recycled concrete (SRRC) filled circular steel tube composite columns, in this study, the cyclic loading tests of 11 composite columns was carried out by using the load-displacement joint control method. The seismic damage process, hysteretic curves and performance indexes of composite columns were observed and obtained. The effects of replacement rates of recycled coarse aggregate (RCA), diameter thickness ratio, axial compression ratio, profile steel ratio and section form of profile steel on the seismic damage behaviors of composite columns were also analyzed in detail. The results show that the failure model of columns is a typical bending failure under the combined action of horizontal loads and vertical loads, and the columns have good energy dissipation capacity and ductility. In addition, the replacement rates of RCA have a certain adverse effect on the seismic bearing capacity, energy consumption and ductility of columns. The seismic damage characteristics of composite columns are revealed according to the failure modes and hysteretic curves. A modified Park-Ang seismic damage model based on the maximum displacement and cumulative energy consumption was proposed, which can consider the adverse effect of RAC on the seismic damage of columns. On this basis, the performance levels of composite columns are divided into five categories, The interlayer displacement angle and damage index are used as the damage quantitative indicators of composite columns, and the displacement angle limits of composite columns at different performance levels under 80% assurance rate are calculated as 1/105, 1/85, 1/65, 1/28, and 1/25 respectively. On this basis, the damage index limits corresponding to each performance level are calculated as 0.045, 0.1, 0.48, 0.8, and 1.0 respectively. Finally, the corresponding relations among the performance levels, damage degrees, interlayer displacement angles and damage indexes of composite columns are established. The conclusions can provide reference for the seismic design of SRRC filled circular steel tube composite columns, it fills the vacancy in the research on seismic damage of steel reinforced recycled concrete (SRRC) filled circular steel tube composite columns.

• 콘크리트학회논문집
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• 제27권3호
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• pp.215-227
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• 2015

본 연구에서는 순환골재를 사용한 강섬유보강 콘크리트보의 전단거동을 알아보기 위하여 순환골재 치환율은 30 %로 고정하고, 전단경간비(a/d = 2, 3, 4), 인장철근비(${\rho}=0.8$, 1.27 %) 및 강섬유 혼입율($V_f=0$, 0.5, 0.75, 1%)을 변수로 한 총 24개의 강섬유보강 콘크리트보를 만들어 실험하였다. 또한 순환골재를 사용한 강섬유보강 콘크리트보의 전단강도를 여러 연구자들의 제안식과 비교 분석하였다. 즉, 순환골재를 사용한 강섬유보강 콘크리트보의 전단거동에 따른 전단내력을 분석하고, 강섬유보강 전단강도 제안식과 실험값을 비교하여 순환골재를 사용한 강섬유보강 콘크리트보의 사용가능성을 평가하고자 하였다. 대부분의 실험값이 제안식에 의한 이론값보다 높게 나타나 순환골재를 사용한 강섬유보강 콘크리트보를 구조부재로 사용하여도 무방하다고 판단된다.

• Earthquakes and Structures
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• 제14권1호
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• pp.73-84
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• 2018

Low cyclic loading tests are conducted on the steel reinforced recycled concrete (SRRC) column-steel (S) beam composite frame joints. This research aims to evaluate the earthquake damage performance of composite frame joints by performing cyclic loading tests on eight specimens. The experimental failure process and failure modes, load-displacement hysteresis curves, characteristic loads and displacements, and ductility of the composite frame joints are presented and analyzed, which shows that the composite frame joints demonstrate good seismic performance. On the basis of this finding, seismic damage performance is examined by using the maximum displacement, energy absorbed in the hysteresis loops and Park-Ang model. However, the result of this analysis is inconsistent with the test failure process. Therefore, this paper proposes a modified Park-Ang seismic damage model that is based on maximum deformation and cumulative energy dissipation, and corrected by combination coefficient ${\alpha}$. Meanwhile, the effects of recycled coarse aggregate (RCA) replacement percentage and axial compression ratio on the seismic damage performance are analyzed comprehensively. Moreover, lateral displacement angle is used as the quantification index of the seismic performance level of joints. Considering the experimental study, the seismic performance level of composite frame joints is divided into five classes of normal use, temporary use, repair after use, life safety and collapse prevention. On this basis, the corresponding relationships among seismic damage degrees, seismic performance level and quantitative index are also established in this paper. The conclusions can provide a reference for the seismic performance design of composite frame joints.