• Advances in concrete construction
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• 제10권2호
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• pp.127-140
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• 2020

This study explores the feasibility of granite waste aggregate (GWA) as a partial replacement of natural fine aggregate (NFA) in binary blend self-compacting concrete (SCC) prepared with fly ash. Total of nine SCC mixtures were prepared wherein one was Ordinary Portland cement (OPC) based control SCC mixture and remaining were fly ash based binary blend SCC mixtures which included the various percentages of GWA. Fresh properties tests such as slump flow, T₅₀₀, V-funnel, J-ring, L-box, U-box, segregation resistance, bleeding, fresh density, and loss of slump flow (with time) were conducted. Compressive strength and percentage of permeable voids were evaluated in the hardened state. All the SCC mixtures exhibited sufficient flowability, passing ability, and resistance to segregation. Besides, all the binary blend SCC mixtures exhibited lower fresh density and bleeding, and better residual slump (up to 50% of GWA) compared to the OPC based control SCC mixture. Binary blend SCC mixture incorporating up to 40% GWA provided higher compressive strength than binary blend control SCC mixture. The findings of this study encourage the utilization of GWA in the development of binary blend SCC mixtures with satisfactory workability characteristics as a replacement of NFA.

• 콘크리트학회논문집
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• 제26권1호
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• pp.23-34
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• 2014

초고성능 콘크리트(UHPC)를 현장에서 타설 하기 위해서는 타설 장비, 배근 상태, 타설 환경 등 현장 조건을 고려한 유동성 조절이 필요하다. 구성 재료와 배합비가 최적화된 UHPC 제품에서 유동성 조절을 위해 현실적으로 변경 가능한 방법은 물-결합재 비(W/B) 또는 고성능 감수제 혼입률(SP/C)을 조절하는 것이며, 경제적 이유로 강섬유 혼입률도 변경 할 수 있다. 일반 콘크리트와는 달리 UHPC는 아주 작은 재료와 배합비 변화에도 굳기 전 또는 굳은 성능에 많은 차이를 나타낸다. 따라서 이 연구에서는 이러한 요인들이 UHPC의 슬럼프 플로와 공기량에 미치는 영향, 그리고 인장 및 압축 성능에 미치는 영향을 알아보았으며, 슬럼프 플로와 공기량과의 선형적인 상관관계를 이용하여 이러한 성능들을 예측할 수 있는 식을 유도 하였다. UHPC의 특성 중 하나인 자기 충전성을 만족하는 조건에서 압축강도에 관한 최적 W/B와 SP/C는 각각 16.8%와 3%로 결정 되었으며, 이러한 조건에서 측정된 공기량은 3.2~4.2%로 이 범위에서의 공기량은 압축강도에 영향을 미치지 못하는 것으로 나타났다. 휨 인장강도에 있어 W/B와 SP/C는 무시할 만큼 작은 영향을 미쳤으며, 상온 양생한 UHPC의 경우 섬유 혼입률이 휨 인장성능을 지배 하는 것으로 평가 되었다. 다만, 체적비로 1%의 강섬유가 혼입된 시편의 경우 섬유가 혼입되지 않은 시편과 달리 균열 후 연성적인 거동은 보였으나, 강도 증진에는 효과가 없는 것으로 나타났다. 반면, 체적비 2%의 강섬유가 혼입된 시편은 강도와 연성을 크게 증가시켰다.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2011년도 추계 학술논문 발표대회
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• pp.53-54
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• 2011

The facilities producing the nuclear energy chosen for resolving the recent global energy problem have been increasingly constructed, and hence more frequent durability tests on radiation shielding concrete are required due to NPP(Nuclear Power Plant) life extension and increase of radioactive waste repositories. Bulk dry density is one of the critical factors ensuring the durability and performance of the radiation shielding concrete because the design of the radiation shielding reinforced concrete structures for NPPs is based on the bulk dry density of the concrete. Bulk density of unconsolidated shielding concrete can be calculated utilizing a test assuring to satisfy the bulk dry density, or existing credible data set. This study evaluated correlation between bulk density and bulk dry density of the concrete used for Korean NPPs (y=1.0913X-0.2458) and developed a correlation expression considering standard deviation of bulk dry density (y=1.0913X-0.3358).

• Advances in concrete construction
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• 제5권1호
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• pp.31-48
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• 2017

Supplementary cementitious materials (SCM) have turned out to be a vital portion of extraordinary strength and performance concrete. Metakaolin (MK) is one of SCM material is acquired by calcinations of kaolinite. Universally utilised as pozzolanic material in concrete to enhance mechanical and durability properties. This study investigates the fresh and hardened properties of conventional concrete (CC) and self compacting concrete (SCC) by partially replacing cement with MK in diverse percentages. In CC and SCC, partial replacement of cement with MK varies from 5-20%. Fresh concrete properties of CC are conducted by slump test and compaction factor tests and for SCC, slump flow, T500, J-Ring, L-Box, V-Funnel and U-Box tests. Hardened concrete characteristics are investigated by compressive, split tensile and flexural strengths at age of 7, 28 and 90 days of curing under water. Carbonation depth, water absorption and density of MK based CC and SCC was also computed. Fresh concrete test results indicated that increase in MK replacement increases workability of concrete in a constant w/b ratio. Also, outcomes reveal that concrete integrating MK had greater compressive, flexural and split tensile strengths. Optimum replacement level of MK for cement was 10%, which increased mechanical properties and robustness properties of concrete.

• International Journal of Concrete Structures and Materials
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• 제8권1호
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• pp.15-26
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• 2014

In order to study the capacities of a new occurrence of Brazilian clay samples as partial replacements of cement, a bentonite sample was selected for utilization in the natural and modified forms for present study. The natural bentonite (BBT) was modified by anchorament of 3-aminopropyltrietoxisilane ($BBT_{APS}$) and 3,2-aminoethylaminopropyltrimetoxisilane (BBTAEAPS) in the surface of component minerals of bentonite sample. The original and organo-bentonite samples were characterized by elemental analysis, scanning electron microscopic and textural analyses. The values of micropore area were varying from $7.2m^2g^{-1}$ for the BBT to $12.3m^2g^{-1}$ for the $BBT_{AEAPS}$. The bentonite samples were characterized by the main variable proportion of bentonite in the natural and intercalated forms (2, 5, 10, 15, 20, 25, 30, and 35 % by weight of cement) in the replacement mode whiles the amount of cementations material. The workability, density of fresh concrete, and absorption of water decreased as the substitution of ordinary Portland cement by perceptual of natural and modified bentonite increased. The results reveal that workability decreased with decrease of the amount of natural bentonite in the concrete, same behavior is observed for bentonite functionalized, varying from 49 to 28 mm. The energetic influence of the interaction of calcium nitrate in the structure of blends was determined through the calorimetric titration procedure.

• Steel and Composite Structures
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• 제39권3호
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• pp.307-318
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• 2021

Utilizing fibers is an effective way to avoid the brittle behavior of the conventional concrete and can enhance its ductility. In particular, propylene fibers can improve concrete properties, including energy absorption, physical and mechanical properties, controlling shrinkage cracks. The increase of fiber density leads to an increase of the overlapping surface of the fiber of concrete and, in turn, a decrease of cracks developed in the concrete. However, the workability of fiber reinforced concrete tends to be lower than the conventional concrete owing mainly to the hairline thickness and excessive concentration of fibers. The low slump of concrete impedes the construction of reinforced concrete members. In this research, we study if the utilization of magnetic water can alleviate the workability issue of young fiber reinforced concrete. To this end, the compressive and flexural strength of four types of concrete (conventional concrete, fiber reinforced concrete, magnetic concrete, magnetic fiber-reinforced concrete) is studied and compared at three different ages of 7, 14, and 28 days. In order to study the influence of the fiber density and length, a study on specimens with three different fiber density (1, 2, 5 kg of fiber in each cubic meter of concrete) and fiber length (6, 12, 18 mm) is undertaken. The result shows the magnetic fiber concrete can result in an increase of the flexural and compressive strength of concrete at higher ages.

• Computers and Concrete
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• 제19권5호
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• pp.555-566
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• 2017

Recently some efforts have been performed to combine the advantages of light-weight and self-compacting concrete in one package called Light-Weight Self-Compacting Concrete (LWSCC). Accurate prediction of hardened properties from fresh state characteristics is vital in design of concrete structures. Considering the lack of references in mixture design of LWSCC, investigating the proper mixture components and their effects on mechanical properties of LWSCC can lead to a reliable basis for its application in construction industry. This study utilizes wide range of existing data of LWSCC mixtures to study the individual and combined effects of the components on the compressive strength. From sensitivity of compressive strength to the proportions and interaction of the components, two equations are proposed to estimate the LWSCC compressive strength. Predicted values of the equations are in good agreement with the experimental data. Application of lightweight aggregate to reduce the density of LWSCC may bring some mixing problems like segregation. Reaching a higher strength by lowered density is a challenging problem that is investigated as well. The results show that, the compressive strength can be improved by increasing the of mixture density of LWSCC, especially in the range of density under $2000Kg/m^3$.

• Computers and Concrete
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• 제26권6호
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• pp.577-585
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• 2020

By the increasing amount of waste materials, it eventually dumped into the environment and covering a larger area of the landfill which cause several environmental pollution problems. The utilization of Palm Kernal Shell Ash (PKSA) in concrete might bring a great benefit in addressing both environmental and economic issues. This article investigates the effect of PKSA as a partial cement replacement of High Strength Concrete (HSC). Several concrete mixtures were prepared with different PKSA of 0%, 10%, 20%, and 30% replaced by the cement mass. This procedure was replicated twice for the two different target mean strengths of 40 MPa and 50 MPa. The mixtures were prepared to test different fresh and hardened properties of HSC including slump test, the compressive strength of 3, 7, 14, 28, and 90 days, flexural strength of 28-days, drying shrinkage, density measurement, and sorptivity. It was observed 10% PKSA replacement as optimum percentage which reduced the drying shrinkage, sorptivity, and density and improved the late-age compressive strength of concrete.

• 한국구조물진단유지관리공학회 논문집
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• 제17권5호
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• pp.67-76
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• 2013

본 연구에서는 전기방식 종류에 따른 문헌 고찰 및 굳지 않은/굳은 상태의 콘크리트에 대해 전기방식 적용 시 방식 효과와 관련하여 연구를 실시하였다. 굳은 콘크리트의 경우 우선적으로 철근의 부동태피막 파괴를 유도하기 위하여 NaCl을 혼입한 후, 2주일동안 250, 500, $750mA/m^2$의 방식전류를 통전하였다. 그 후 부동태피막 복원화와 염소 이온 추출에 대해서 정량화를 실시하였다. 동시에, 굳지 않는 상태의 콘크리트에 대해서는 굳은 상태와 동일한 양의 방식전류를 타설 직후부터 동일한 기간동안 통전하여 전기방식을 실시하였다. 후광산란(Backscattered electron; BSE) 이미지를 이용하여 철근-콘크리트 계면을 관찰하였으며, 염소이온 확산에 대해서 염소이온 이동 속도와 철근 부식 저항성에 대한 콘크리트의 성질 변화에 대해 측정하였다. 결과적으로 보면, 전기 방식은 부동태피막 복원화에 매우 효육적이며, 콘크리트 내의 염소이온 중 63-73% 정도가 추출되는 것으로 확인 되었다. 굳지 않는 상태의 콘크리트에 전기방식을 적용할 경우, 철근 표면에서 $Ca(OH)_2$ 층이 조밀하게 되어 철근 부식 저항성이 향상되었다. 다만, 방식 전류에 따라 콘크리트 표면 염화물량이 증가하는 경향이 나타나는 것을 확인 할 수 있다.

• Computers and Concrete
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• 제8권6호
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• pp.677-692
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• 2011

Particle packing on meso-level has a significant influence on workability of fresh concrete and also on the mechanical and durability properties of the matured material. It was demonstrated earlier that shape exerts but a marginal influence on the elastic properties of concrete provided being packed to the same density, which is not necessarily the case with different types of aggregate. Hence, elastic properties of concrete can be treated as approximately structure-insensitive parameters. However, fracture behaviour can be expected structure-sensitive. This is supported by the present study based on discrete element method (DEM) simulated three-phase concrete, namely aggregate, matrix and interfacial transition zones (ITZs). Fracture properties are assessed with the aid of a finite element method (FEM) based on the damage materials model. Effects on tensile strength due to grain shape and packing density are investigated. Shape differences are shown to have only modest influence. Significant effects are exerted by packing density and physical-mechanical properties of the phases, whereby the ITZ takes up a major position.