• 대한토목학회논문집
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• 제34권3호
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• pp.763-771
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• 2014

최근 국내에서는 원유 정제과정에서 많은 양의 부생황이 발생하고 있다. 유황콘크리트는 시멘트 풀을 유황개질 바인더로 대체한 콘크리트로서 시멘트 제조시에 대량으로 발생되는 $CO_2$의 저감 및 원유 정제산업에서 부생되는 황을 활용할 수 있는 이점이 있다. 또한 유황콘크리트는 반복해서 재활용할 수 있는 친환경적이고 지속가능한 재료이다. 이 연구에서는 개질유황 바인더를 사용한 유황콘크리트의 물리적 특성을 실험을 통하여 검토하였다. 실험 결과, 유황콘크리트는 대체적으로 50~80MPa 이상의 고강도 특성을 보였다. 단위질량, 탄성계수 및 인장강도는 포틀랜드 시멘트 콘크리트(PCC)와 유사하였다. 순환굵은골재를 유황콘크리트에 적용하는 경우 순환골재의 단점을 보완하는 동시에 고강도콘크리트 제조가 가능하다. 유황콘크리트의 열팽창계수는 PCC보다 다소 큰 값으로 나타내고 있으나, 채움재를 혼입하여 일반 콘크리트 수준의 열팽창계수를 보이는 것으로 나타났다.

• 구강회복응용과학지
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• 제23권4호
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• pp.313-326
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• 2007

With rising prevalency of mouth breathing children caused by developing civilization and increasing pollution, there are many maxillary transverse discrepancy patients with undergrowth of maxilla. For improving this, maxillary mid-palatal suture splitting was often performed. The purpose of this study was to analyse the stress distribution on the craniofacial suture and cranium after rapid maxillary expansion by finite element model. The boy(13Y6M) was chosen for taking computed-tomography for finite element model. Three-dimensional model of maxilla, first premolar, first molar, buccal and lingual part of rapid maxillary expansion were constructed. 1. The alveolar bone adjacent to the first molar and the first premolar that was affected directly by rapid maxillary expansion was displaced laterally approximately 4.04mm at maximum. The force decreased toward anterior region and frontal alveolar bone displaced laterally about 3.18mm. 2. A forward maximum displacement was exhibited at zygomatic process middle region. 3. At maximum, maxillary median part experienced 0.973mm downward repositioning and 0.65mm upward repositioning at lateral alveolar bone. 4. Von mises stress was observed the largest stress distribution around teeth and zygomatic buttress. 5. The largest tensile force was observed around alveolar bone of teeth, while compression force was observed at zygomatic buttress.

• Smart Structures and Systems
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• 제17권4호
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• pp.593-610
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• 2016

In this study, an innovative and smart glass fiber-reinforced polymer (GFRP) hybrid bar was developed for stronger durability of concrete structures. As comparing with the conventional GFRP bar, the smart GFRP Hybrid bar can promise to enhance the modulus of elasticity so that it makes the cracking reduced than the case when the conventional GFRP bar is used. Besides, the GFRP Hybrid bar can effectively resist the corrosion of conventional steel bar by the GFRP outer surface on the steel bar. In order to verify the bond performance of the GFRP hybrid bar for structural reinforcement, uniaxial pull-out test was conducted. The variables were the bar diameter and the number of strands and pitch of the fiber ribs. Tensile tests showed a excellent increase in the modulus of elasticity, 152.1 GPa, as compared to that of the pure GFRP bar (50 GPa). The stress-strain curve was bi-linear, so that the ductile performance could be obtained. For the bond test, the entire GFRP hybrid bar test specimens failed in concrete splitting due to higher shear strength resulting in concrete crushing as a function of bar deformation. Investigation revealed that an increase in the number of strands of fiber ribs enhanced the bond strength, and the pitch guaranteed the bond strength of 19.1 mm diameter hybrid bar with 15.9 mm diameter of core section of deformed steel the ACI 440 1R-15 equation is regarded as more suitable for predicting the bond strength of GFRP hybrid bars, whereas the CSA S806-12 prediction is considered too conservative and is largely influenced by the bar diameter. For further study, various geometrical and material properties such as concrete cover, cross-sectional ratio, and surface treatment should be considered.

• 한국구조물진단유지관리공학회 논문집
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• 제16권3호
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• pp.99-108
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• 2012

본 연구에서는 철근콘크리트 슬래브의 내부식성과 경량화를 도모하기 위하여 GFRP bar를 휨보강근으로 사용하는 경량골재콘크리트 슬래브를 고려하고 이 구조물에 대하여 기초적인 거동을 조사하였다. 경량콘크리트의 압축강도 및 인장강도 그리고 콘크리트 파괴에너지 측정, 일련의 슬래브 휨실험, 비선형유한요소해석을 통한 수치해석, 휨실험과 수치해석의 결과비교 등이 행하여졌다. 그 결과, GFRP bar를 휨보강근으로 사용한 경량콘크리트 슬래브는 기준시험체로 사용된 동일 규격의 철근콘크리트 슬래브에 비하여 무게를 28%정도 감소시킬 수 있었지만 파괴하중은 36%정도 감소되었다. 이는 GFRP bar의 낮은 축강성과 경량콘크리트의 낮은 부착강도 때문인 것으로 판단된다. 그리고 경량콘크리트의 부착력 감소 특성을 고려하기 위하여 GFRP bar와 콘크리트 경계면 사이에 계면요소를 사용한 수치해석 결과는 계면요소의 사용이 실험결과에 더 근접해갈 수 있는 방법임을 보여주었다.

• 한국지반공학회논문집
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• 제29권12호
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• pp.95-104
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• 2013

최근 시멘트혼합토(CSG)가 많은 설계 시공에 적용되어지고 있다. CSG재료는 경화 초기엔 흙과 같은 역학적 특성을 보이지만 시간이 경과함에 따라 점차 콘크리트 재료적 특성을 발현하게 된다. 경화된 시멘트혼합토는 작은 변형률에서 최대강도가 발현되고 이 후 급격한 취성파괴에 도달하는 탄성적인 성질을 띠게 된다. 본 연구에서는 이러한 CSG재료의 취성거동특성을 완화하고 상대적으로 취약한 인장성능을 개선하고자 PVA 섬유보강재를 적용하였다. 섬유보강 CSG재료는 재하시 하상시료와 섬유사이의 결합력으로 섬유에 인장력이 발생하여 혼합시료의 인장강도 증가와 급작스런 취성파괴발생을 방지할 수 있다. 실험결과 섬유보강만으로도 CSG재료의 응력-변형특성을 취성파괴에서 연성파괴로 유도할 수 있으며, 섬유보강에 의한 잔류강도 증가효과를 확인 할 수 있었다.

• 한국건설순환자원학회논문집
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• 제7권3호
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• pp.202-209
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• 2019

이 연구의 목적은 저량의 기포가 혼입된 바텀애시 골재 기반 경량 콘크리트(Lightweight concrete made using bottom ash aggregates and foam, LWC-BF)의 압축강도 발현 및 역학적 특성에 대한 재현성 평가이다. 이를 위해 Ji et al.에 의해 수행되었던 동일한 배합표를 기준으로 총 6 배합을 수행하였다. 배합에서의 주요변수는 기포 혼입율과 물-결합재 비로서 각각 0~25% 및 25~30%로 변화하였다. 굳지 않은 콘크리트에서 초기 슬럼프, 슬러리 밀도와 굳은 콘크리트에서 재령별 압축강도, 쪼갬인장강도 및 파괴계수는 재현성 평가대상 이전 실험결과와 대체적으로 비슷하였다. 따라서, LWC-BF의 압축강도 및 역학적 특성은 기포 혼입에 의한 배합관리가 어려움에도 불구하고 그 재현성이 비교적 우수하였다.

• Advances in concrete construction
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• 제8권3호
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• pp.239-246
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• 2019

Substitution of natural fine aggregates with industrial by-products like precious slag balls (PS Balls) offers various advantages like technical, economic and environmental which are very important in the present era of sustainability in construction industry. PS balls are manufactured by subjecting steel slag to slag atomizing Technology (SAT) which imparts them the desirable characteristics of fine aggregates. The main objective of this research paper is to assess the feasibility of producing good quality concrete by using PS balls, to identify the potential benefits by their incorporation and to provide solution for increasing their utilization in concrete applications. The study investigates the effect of PS balls as partial replacement of fine aggregates in various percentages (20%, 40%, 60%, 80% and 100%) on mechanical properties of concrete such as compressive strength, splitting tensile strength, and flexural strength. The optimum mix was found to be at 40% replacement of PS balls with maximum strength of 62.89 MPa at 28 days curing. Permeability of concrete was performed and it resulted in a more durable concrete with replacement of PS balls at 40% and 100% as fine aggregates. These two specific values were considered as optimum replacement is 40% and also the maximum possible replacement is 100%. Scanning electron microscope (SEM) analysis was done and it was found that the PS balls in concrete were unaffected and with optimum percentage of PS balls as fine aggregates in concrete resulted in good strength and less cracks. Hence, it is possible to produce good workable concrete with low water to cement ratio and higher strength concrete by incorporating PS balls.

• Advances in concrete construction
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• 제11권4호
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• pp.335-345
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• 2021

It is known from the literature that there are relatively few studies on the engineering properties of ultra-high performance concrete (UHPC) in early age. In fact, in order to ensure the safety of UHPC during construction and sufficient durability and long-term performance, it is necessary to explore the early behavior of UHPC. The test parameters (test control factors) investigated included the percentage of cement replaced by silica fume (SF), the percentage of cement replaced by ultra-fine silica powder (SFP), the amount of steel fiber (volume percent), and the amount of polypropylene fiber (volume percentage). The engineering properties of UHPC in the fresh mixing stage and at the age of 7 days were investigated. These properties include freshly mixed properties (slump, slump flow, and unit weight) and hardened mechanical properties (compressive strength, elastic modulus, flexural strength, and splitting tensile strength). Moreover, the effects of the experimental factors on the performance of the tested UHPC were evaluated by range analysis and variance analysis. The experiment results showed that the compressive strength of the C8 mix at the age of 7 days was highest of 111.5 MPa, and the compressive strength of the C1 mix at the age of 28 days was the highest of 128.1 MPa. In addition, the 28-day compressive strength in each experimental group increased by 13%-34% compared to the 7-day compressive strength. In terms of hardened mechanical properties, the performance of each experimental group was superior to that of the control group (without fiber and without additional binder materials), with considerable improvement, and the experimental group did not produce explosive or brittle damage after the test. Further, the flexural test process found that all test specimens exhibited deflection-hardening behavior, resulting in continued to increase carrying capacity after the first crack.

• 한국구조물진단유지관리공학회 논문집
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• 제23권1호
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• pp.113-121
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• 2019

본 연구에서는 시멘트 복합재료와 직접 혼합 가능한 자기치유 마이크로 캡슐을 제조하였으며, 자기치유 마이크로 캡슐이 혼합된 시멘트 복합재료의 품질 및 균열 치유 성능 특성을 평가하였다. 종래의 경우 자기치유 캡슐 제조와 균열 치유 특성 평가에만 치중되어 평가되어 왔다. 따라서 자기치유 마이크로 캡슐은 시멘트 복합재료와 혼합시 시멘트 복합재료의 품질에 미치는 영향이 있기 때문에 이에 대한 검토를 수행하였다. 자기치유 마이크로 캡슐을 혼합한 시멘트 복합재료의 테이블 플로우 및 공기량 평가 결과 혼합율에 관계없이 테이블 플로우 및 공기량은 큰 영향이 없는 것으로 나타났다. 압축강도 및 쪼갬인장강도는 캡슐 혼합율이 증가할수록 강도가 감소하는 경향이 나타났다. Water Flow에 따른 균열 치유 특성 평가 결과 초기 투수량이 감소하는 결과가 나타났으며, 시간 경과에 따라 반응 생성물 발생하여 균열이 치유되는 것을 확인 할 수 있었다.

• Computers and Concrete
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• 제27권4호
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• pp.333-341
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• 2021

Steel slag, an industrial reject from the steel rolling process, has been identified as one of the suitable, environmentally friendly materials for concrete production. Given that the coarse aggregate portion represents about 70% of concrete constituents, other economic approaches have been found in the use of alternative materials such as steel slag in concrete. Unfortunately, a standard framework for its application is still lacking. Therefore, this study proposed functional model equations for the determination of strength properties (compression and splitting tensile) of steel slag aggregate concrete (SSAC), using gene expression programming (GEP). The study, in the experimental phase, utilized steel slag as a partial replacement of crushed rock, in steps 20%, 40%, 60%, 80%, and 100%, respectively. The predictor variables included in the analysis were cement, sand, granite, steel slag, water/cement ratio, and curing regime (age). For the model development, 60-75% of the dataset was used as the training set, while the remaining data was used for testing the model. Empirical results illustrate that steel aggregate could be used up to 100% replacement of conventional aggregate, while also yielding comparable results as the latter. The GEP-based functional relations were tested statistically. The minimum absolute percentage error (MAPE), and root mean square error (RMSE) for compressive strength are 6.9 and 1.4, and 12.52 and 0.91 for the train and test datasets, respectively. With the consistency of both the training and testing datasets, the model has shown a strong capacity to predict the strength properties of SSAC. The results showed that the proposed model equations are reliably suitable for estimating SSAC strength properties. The GEP-based formula is relatively simple and useful for pre-design applications.