• 콘크리트학회논문집
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• 제28권2호
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• pp.177-185
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• 2016

이 논문에서는 강섬유 보강 초고성능 콘크리트(UHPC)의 부재의 휨거동을 특성을 파악하고자 하였다. 하이브리드 강섬유보강 초고성능 콘크리트의 압축강도는 150 MPa이다. 부피비 1.5%의 하이브리드 강섬유 보강 초고성능 콘크리트의 휨거동 특성 실험을 수행하였다. 강섬유보강 콘크리트의 압축 및 인장거동 재료 특성은 구조거동 예측을 위해 매우 중요하다. 강섬유 보강 초고성능 콘크리트의 하중-균열개구변위 측정결과를 이용하여 인장거동 특성을 파악하였다. 실험결과는 하이브리드 강섬유 보강 UHPC는 균열제어에 유리한 것을 나타낸다. 또한, 강섬유 보강 UHPC 보의 연성지수는 1.6~3.0을 나타내어 연성거동에 효과적임을 나타낸다. 모멘트-곡률 관계 측정결과와 해석결과를 비교하였다. 휨철근을 배근하지 않은 UHPC 보에 대한 휨강도 예측결과는 측정 휨강도를 다소 과다평가하고 있다. 전반적으로 본 연구에서 제시한 강섬유 보강 초고성능 콘크리트 재료 및 휨 거동 모델링 제안기법에 의해 압축강도 150 MPa 급의 강섬유 보강 콘크리트 보의 합리적인 휨성능 예측이 가능하다.

• 대한토목학회논문집
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• 제31권5A호
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• pp.379-387
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• 2011

초고성능콘크리트(UHPC)의 개발은 재료 역학적 특성면에서 기존의 일반 및 고성능 콘크리트에 비해 월등한 역학적 성능을 발휘하는 것으로 인식되고 있으나, 이에 관한 시공성 및 구조적 안전성에 대해서는 향후 많은 수정 및 보완 작업을 필요로 함이 예상되어진다. 이 연구에서는 UHPC를 적용한 프리캐스트 접합부의 전단 거동 특성의 분석을 위해 접합부 사이에 전단키를 설치한 경우의 접합 방식 및 횡구속 응력에 따른 전단 거동 특성 실험을 수행하였다. 실험 결과 에폭시 접합을 이용한 UHPC 접합의 경우가 현장 타설을 모사한 일체 타설의 경우보다 파괴 하중 및 전단 저항 응력면에서 우수함을 보였고, 횡구속 응력의 증가에 의해 전단 응력은 증가되지만, 횡구속 응력과 전단 응력 사이의 상호 효과에 따른 최적 임계 횡구속 응력이 존재하고 있음을 제시할 수 있었다.

• Structural Engineering and Mechanics
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• 제81권2호
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• pp.163-178
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• 2022

This paper aimed to study the local bond-slip behavior between ultra-high-performance concrete (UHPC) and a reinforcing bar after exposure to high temperatures. A series of pull-out tests were carried out on cubic specimens of size 150×150×150 mm with deformed steel bar embedded for a fixed length of three times the diameter of the tested deformed bar. The experimental results of the bond stress-slip relationship were compared with the Euro-International Concrete Committee (CEB-Comite Euro-International du Beton)-International Federation for Prestressing (FIP-Federation Internationale de la Precontrainte) Model Code and with prediction models found in the literature. In addition, based on the test results, an empirical model of the bond stress-slip relationship was proposed. The evaluation and comparison results showed that the modified CEB-FIP Model code 2010 proposed by Aslani and Samali for the local bond stress-slip relationship for UHPC after exposure to high temperatures was more conservative. In contrast, for both room temperature and after exposure to high temperatures, the modified CEB-FIP Model Code 2010 local bond stress-slip model for UHPC proposed in this study was able to predict the test results with reasonable accuracy.

• Advances in concrete construction
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• 제5권5호
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• pp.481-492
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• 2017

The aim of this paper is to investigate the effect of quartz powder (Qp), quartz sand (Qs), and different water curing temperature on mechanical properties including 7, 14, 28-day compressive strength and 28-day splitting tensile strength of Ultra High Performance Concrete and also finding the correlation between these variables on mechanical properties of UHPC. The response surface methodology was monitored to show the influences of variables and their interactions on mechanical properties of UHPC, then, mathematical models in terms of coded variables were established by ANOVA. The offered models are valid for the variables between: quartz powder 0 to 20% of cement substitution by cement weight, quartz sand 0 to 50% of aggregate substitution by crushed limestone weight, and water curing temperature 25 to $95^{\circ}C$.

• 한국건설순환자원학회논문집
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• 제11권3호
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• pp.210-217
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• 2023

Various performances of ultra-high performance concrete (UHPC) applied with microplastics and expanded polystyrene (EPS) beads were evaluated. CompressIve and flexural strength, performance after ignition, flow-down in fresh state, and effective bond strength were evaluated. Designed weight of the cement panel with these mixtures was calculated based on the flexural strength. As a result of the experiments, it was confirmed that the EPS could reduce the density of UHPC with largest range. By maximum addition of EPS beeds, the density of UHPC decreased to 1300 kg/m³, and the compressive and flexural strengths for this mixtures were in ranges of 20-30 MPa and 15-20 MPa, respectively. On the other hand, lightest cement panel could be designed with UHPC having a density ranges about 2.0 g/cm³.

• 콘크리트학회논문집
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• 제28권2호
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• pp.223-234
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• 2016

이 연구에서는 노치 도입 인장시편을 사용하여 직접인장강도 실험을 통해 UHPC의 파괴거동을 살펴보고, 강섬유 혼입률에 따른 UHPC의 초기균열강도와 인장강도를 제안하였다. 실험결과 UHPC와 초기균열강도와 인장강도, 그리고 파괴에너지 등은 강섬유 혼입률이 증가할수록 증가하는 것으로 나타났다. 균열선단에서의 응집응력은 Barenblatt의 가정을 사용하여 결정되었으며, 이를 토대로 변형경화 현상이 발생하는 강섬유 혼입률이 1% 이상인 UHPC의 최대응집응력을 예측할 수 있는 간편식을 제안하였다. 인장강도는 강섬유 혼입률과 압축강도의 함수로 제안되었으며, 파괴에너지는 인장강도의 함수로 제안되었다. 제안된 간편식들은 실험값과 비교적 잘 일치하였으며, 향후 압축강도가 140~170 MPa이고, 강섬유 혼입률이 2% 이하인 UHPC에 적용가능 할 것으로 판단된다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 춘계 학술발표회 논문집(II)
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• pp.61-64
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• 2006

Comparing with traditional high performance concrete, ultra high performance concrete (UHPC) has the property of high-tenacity. However, drying shrinkage and autogenous shrinkage can be arisen as the major defect to UHPC. In this study, therefore, it was tested to reduce drying shrinkage and autogeneous shrinkage by adding expanding admixture (EA) and shrinkage reducing agent (SRA). As a result, for a case drying shrinkage, the shrinkage was decreased by 94% when EA was exchanged, and it was decreased by 64% when SRA was added. For the case of autogenous shrinkage, the mortar was expanded at early age and the shrinkage was decreased by 87% when EA was exchanged, and the shrinkage was decreased by 70% when SRA was added.

• Structural Engineering and Mechanics
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• 제49권6호
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• pp.763-773
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• 2014

The recently developed Ultra High Performance Concrete (UHPC) displays outstanding compressive strength and ductility but is also subjected to very large autogenous shrinkage. In addition, the use of forms and reinforcement to confine this autogenous shrinkage increases the risk of shrinkage cracking. Accordingly, this study adopts a combination of shrinkage reducing admixture and expansive admixture as a solution to reduce the shrinkage of UHPC and estimates its appropriateness by evaluating the compressive and flexural strengths as well as the autogenous shrinkage according to the age. Moreover, the coefficient of thermal expansion known to experience sudden variations at early age is measured in order to evaluate exactly the autogenous shrinkage and the thermal expansion is compensated considering these measurements. The experimental results show that the compressive and flexural strengths decreased slightly at early age when mixing 7.5% of expansive admixture and 1% of shrinkage reducing admixture but that this decrease becomes insignificant after 7 days. The use of expansive admixture tended to premature the setting of UHPC and the start of sudden increase of autogenous shrinkage. Finally, the combined use of shrinkage reducing admixture and expansive admixture appeared to reduce effectively the autogenous shrinkage by about 47% at 15 days.

• 한국구조물진단유지관리공학회 논문집
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• 제19권4호
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• pp.49-56
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• 2015

초고성능 콘크리트는 높은 강도와 유동성을 갖는 우수한 재료 특성을 나타내는 콘크리트이다. 그러나 고연성 시멘트 복합체에 비하여 낮은 연성을 나타낸다. 이 연구에서는 강섬유와 마이크로섬유의 조합이 초고성능 콘크리트의 인장거동에 미치는 영향을 조사하였다. 이를 위하여 강섬유와 폴리에틸렌, 폴리비닐알코올, 현무암섬유 조합에 따라 4가지 초고성능 콘크리트 배합을 결정하였고, 인장거동을 평가하기 위하여 직접인장 실험을 수행하였다. 또한 마이크로섬유가 제조과정에서 의도하지 않은 과도한 기포를 생성하는지를 확인하기 위하여 밀도실험을 수행하였다. 실험결과 인장강도가 높은 폴리에틸렌섬유는 초고성능 콘크리트의 인장거동을 향상시키는데 효과적임을 확인하였고, 현무암섬유는 초고성능 콘크리트의 균열강도 및 인장강도를 증가시키는데 효과적임을 확인하였다. 또한 마이크로섬유가 의도하지 않은 기포를 생성하지 않는다는 것도 확인하였다.

• Steel and Composite Structures
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• 제50권3호
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• pp.319-336
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• 2024

Ultra-high-performance concrete (UHPC) has attracted increasing attention in prefabricated steel-concrete composite beams as achieving the onsite construction time savings and structural performance improvement. The inferior replacement and removal efficiency of conventional prefabricated steel-UHPC composite beams (PSUCBs) has thwarted its sustainable applications because of the widely used welded-connectors. Single embedded nut bolted shear connectors (SENBs) have recently introduced as an attempt to enhance demountability of PSUCBs. An in-depth exploration of the mechanical behavior of SENBs in UHPC is necessary to evidence feasibilities of corresponding PSUCBs. However, existing research has been limited to SENB arrangement impacts and lacked considerations on SENB geometric configuration counterparts. To this end, this paper performed twenty push-out tests and theoretical analyses on the shear performance and design recommendation of SENBs. Key test parameters comprised the diameter and grade of SENBs, degree and sequence of pretension, concrete casting method and connector type. Test results indicated that both diameters and grades of bolts exerted remarkable impacts on the SENB shear performance with respect to the shear and frictional responses. Also, there was limited influence of the bolt preload degrees on the shear capacity and ductility of SENBs, but non-negligible contributions to their corresponding frictional resistance and initial shear stiffness. Moreover, inverse pretension sequences or monolithic cast slabs presented slight improvements in the ultimate shear and slip capacity. Finally, design-oriented models with higher accuracy were introduced for predictions of the ultimate shear resistance and load-slip relationship of SENBs in PSUCBs.