• Computers and Concrete
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• 제25권5호
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• pp.401-409
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• 2020

Artificial neural networks are used as a useful tool in distinct fields of civil engineering these days. In order to control long-term quality of Self-Compacting Semi-Lightweight Concrete (SCSLC), the 90 days compressive strength is considered as a key issue in this paper. In fact, combined artificial neural networks are used to predict the compressive strength of SCSLC at 28 and 90 days. These networks are able to re-establish non-linear and complex relationships straightforwardly. In this study, two types of neural networks, including Radial Basis and Multilayer Perceptron, were used. Four groups of concrete mix designs also were made with two water to cement ratios (W/C) of 0.35 and 0.4, as well as 10% of cement weight was replaced with silica fume in half of the mixes, and different amounts of superplasticizer were used. With the help of rheology test and compressive strength results at 7 and 14 days as inputs, the neural networks were used to estimate the 28 and 90 days compressive strengths of above-mentioned mixes. It was necessary to add the 14 days compressive strength in the input layer to gain acceptable results for 90 days compressive strength. Then proper neural networks were prepared for each mix, following which four existing networks were combined, and the combinatorial neural network model properly predicted the compressive strength of different mix designs.

• Computers and Concrete
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• 제22권2호
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• pp.183-196
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• 2018

The rheological behaviour of high strength self compacting concrete (HS-SCC) studied through an experimental investigation is presented in this paper. The effect of variation in supplementary cementitious materials (SCM) $vis-{\grave{a}}-vis$ four different types of processed crushed sand as fine aggregates is studied. Apart from the ordinary Portland cement (OPC), the SCMs such as fly ash (FA), ground granulated blast furnace slag (GGBS) ultrafine slag (UFS) and micro-silica (MS) are used in different percentages keeping the mix -paste volume and flow of concrete, constant. The combinations of rheology, strength and durability are equally important for selection of mixes in respect of high-rise building constructions. These combinations are referred to as the rheo-strength and rheo-durability which is scientifically linked to performance based rating. The findings show that the fineness of the sands and types of SCM affects the rheo-strength and rheo-durability performance of HS-SCC. The high amount of fines often seen in fine aggregates contributes to the higher yield stress. Further, the mixes with processed sand is found to offer better rheology as compared to that of mixes made using unwashed crushed sand, washed plaster sand, washed fine natural sand. The micro silica and ultra-fine slag conjunction with washed crushed sand can be a good solution for high rise construction in terms of rheo-strength and rheo-durability performance.

• Steel and Composite Structures
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• 제18권3호
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• pp.623-639
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• 2015

Self-compacting Concrete (SCC) Filled Square steel Tubes (SCFST) was used to strengthen square RC columns. To establish the efficiency of this strengthening method, 17 columns were tested under axial compression loading including 3 RC columns without any strengthening (WRC), 1 RC column strengthened with concrete jacket (CRC), 13 RC columns strengthened with self-compacting concrete filled square steel tubes (SRC). The experimental results showed that the use of SCFST is interesting since the ductility and the bearing capacity of the RC columns are greatly improved. The improvement ratio is significantly affected by the nominal wall thickness of steel tubes (t), the strength grade of strengthening concrete (C), and the length-to-width ratio (L / B) of the specimens. In order to quantitatively analyze the effect of these test parameters on axial loading behavior of the SRC columns, three performance indices, enhancement ratio (ER), ductility index (DI), and confinement ratio (CR), were used. The strength of the SRC columns obtained from the experiments was then employed to verify the proposed mode referring to the relevant codes. It was found that codes DBJ13-51 could relatively predict the strength of the SRC columns accurately, and codes AIJ and BS5400 were relatively conservative.

• Structural Monitoring and Maintenance
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• 제6권1호
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• pp.47-66
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• 2019

One method of retrofitting concrete structures is to use fiber reinforced polymers (FRP). In this research, the shear, torsional and flexural strengthening of self-compacting reinforced concrete (RC) girders are fulfilled with glass fiber reinforced polymer (GFRP) and carbon fiber reinforced polymer (CFRP) materials. At first, for verification, the experimental results were compared with numerical modeling results obtained from ABAQUS software version 6.10. Then the reinforcing sheets were attached to concrete girders in one and two layers. Studying numerical results obtained from ABAQUS software showed that the girders stiffness decreased with the propagations of cracks in them, and then the extra stresses were tolerated by adhesive layers and GFRP and CFRP sheets, which resulted in increasing the bearing capacity of the studied girders. In fact, shear, torsion and bending strengths of the girders increased by reinforcing girders with adding GFRP and CFRP sheets. The samples including two layers of CFRP had the maximum efficiencies that were 90, 76 and 60 percent of improvement in shear, torsion and bending strengths, respectively. It is worth noting that the bearing capacity of concrete girders with adding one layer of CFRP was slightly higher than the ones having two layers of GFRP in all circumstances; therefore, despite the lower initial cost of GFRP, using CFRP can be more economical in some conditions.

• 콘크리트학회논문집
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• 제26권3호
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• pp.277-285
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• 2014

이 연구는 현장에서 사용하는 재료의 품질 및 계량오차, 현장조건 등에 따라 병용계 자기충전 콘크리트의 유동특성에 영향을 미치는 변동요인의 범위를 실험적으로 규명하기 위한 것이다. 병용계 자기충전 콘크리트의 재료는 벨라이트 시멘트와 석회석 미분말을 사용한 벨라이트계 및 슬래그 시멘트와 석회석 미분말을 사용한 슬래그계가 선정되었으며, 선행연구에서 제시된 최적배합 조건을 대상으로 하였다. 변동요인으로 (1) 콘크리트의 온도 3종류, (2) 잔골재의 표면수율 5종류, (3) 잔골재의 조립률 5종류, (4) 고성능AE감수제의 사용량 5종류, (5) 석회석 미분말의 분말도 3종류 등을 대상으로 민감도 시험을 실시하였다. 민감도 시험의 항목은 슬럼프 플로우, 500 mm 플로우 도달시간, V-깔대기 유하시간, U-box 충전성 높이를 대상으로 하였다. 실험 결과, (1) 콘크리트 온도는 $10{\sim}20^{\circ}C$ 범위, (2) 잔골재의 표면수율은 ${\pm}0.6%$ 범위, (3) 잔골재의 조립률 $2.6{\pm}0.2$ 범위, (4) 고성능AE감수제의 사용량은 ${\pm}0.2%$ 범위, (5) 석회석 미분말의 분말도는 $6000cm^2/g$ 범위에서 현장품질을 관리해야 한다. 벨라이트계 및 슬래그계에 따른 차이는 크지 않았지만, 석회석 미분말 및 $C_2S$ 함량이 높은 벨라이트계가 안정적인 경향을 나타내었다. 따라서 이러한 결과를 현장 시공현장에서 병용계 자기충전 콘크리트의 관리방안으로 제안하고자 한다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 춘계 학술발표회 제20권1호
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• pp.977-980
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• 2008

최근 터널 라이닝콘크리트의 고질적인 문제점 중에서 유동성 부족 및 충전 불량을 해결하기 위해 자기충전 콘크리트를 적용하고자 하는 연구가 활발하게 진행되고 있다. 본 연구에서는 최근 다년간에 걸친 연구 결과인 개발한 자기충전 라이닝콘크리트(이하 SCLC로 약함)를 타설 전.후의 유동 특성 및 역학적 특성을 검토하여 현장적용 타당성을 검증하고자 하였다. Packing Factor 배합법에 의해 개발된 SCLC를 현장여건과 골재특성에 따라 현장배합으로 변경하여 타설하였으며 타설 전 SCLC의 Slump flow, 공기량 등을 통하여 유동성능과 내구성능을 검토하였다. 또한, 시간경과에 따른 Slump flow loss를 측정하여 현장타설 가능성을 평가하고자 하였다. 나아가 국내 터널 라이닝에 적용된 첫 번째 타설임을 감안하여 차후 자기충전 라이닝콘크리트를 현장 적용할 때 주의해야할 사항 등과 시공방법을 제시하고자 하였다.

• Advances in concrete construction
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• 제15권1호
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• pp.23-39
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• 2023

One of the important problems of concrete placing is the concrete compaction, which can affect the strength, durability and apparent quality of the hardened concrete. Therefore, vibrating operations might be accompanied by much noise and the need for training the involved workers, while inappropriate functioning can result in many problems. One of the most important methods to solve these problems is to utilize self-compacting cementitious composites instead of the normal concrete. Due to their benefits of these new materials, such as high tensile, compressive, and flexural strength, have drawn the researchers' attention to this type of cementitious composite more than ever. In this experimental investigation, six mixing designs were selected as a base to acquire the best mechanical properties. Moreover, forty-eight rectangular composite panels with dimensions of 300 mm × 400 mm and two thickness values of 30 mm and 50 mm were cast and tested to compare the flexural and impact energy absorption. Steel fibers with volume fractions of 0%, 0.5% and 1% and with lengths of 25 mm and 50 mm were imposed in order to prepare the required cement composites. In this research, the composite panels with two thicknesses of 30 mm and 50 mm, classified into 12 different groups, were cast and tested under three-point flexural bending and repeated drop weight impact test, respectively. Also, the examination and comparison of flexural energy absorption with impact energy absorption were one of the other aims of this research. The obtained results showed that the addition of fibers of longer length improved the mechanical properties of specimens. On the other hand, the findings of the flexural and impact test on the self-compacting composite panels indicated a stronger influence of the long-length fibers.

• Computers and Concrete
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• 제5권5호
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• pp.475-490
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• 2008

The paper explores the potential of applicability of Genetic programming approach (GP), adopted in this investigation, to model the combined effects of five independent variables to predict the mini-slump, the plate cohesion meter, the induced bleeding test, the J-fiber penetration value, and the compressive strength at 7 and 28 days of self-compacting slurry infiltrated fiber concrete (SIFCON). The variables investigated were the proportions of limestone powder (LSP) and sand, the dosage rates of superplasticiser (SP) and viscosity modifying agent (VMA), and water-to-binder ratio (W/B). Twenty eight mixtures were made with 10-50% LSP as replacement of cement, 0.02-0.06% VMA by mass of cement, 0.6-1.2% SP and 50-150% sand (% mass of binder) and 0.42-0.48 W/B. The proposed genetic models of the self-compacting SIFCON offer useful modelling approach regarding the mix optimisation in predicting the fluidity, the cohesion, the bleeding, the penetration, and the compressive strength.

• Advances in concrete construction
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• 제7권4호
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• pp.277-288
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• 2019

The formulation of self-compacting concretes (SCC) and the study of their properties at the laboratory level were currently well mastered. The aim of this work is to characterize SCC under hot climatic conditions and their effects on the properties of fresh and hardened SCC. Particularly, the effect of the initial wet curing time on the mechanical behavior such as the compressive strength and the durability of the SCCs (acid and sulfate attack) as well as the microstructure of SCCs mixtures. In this study, we used two types of cement, Portland cement and slag cement, three water/binder (W/B) ratio (0.32, 0.38 and 0.44) and five curing modes. The obtained results shows that the compressive strength is strongly influenced by the curing methods, 7-days of curing in the water and then followed by a maturing in a hot climate was the optimal duration for the development of a better compressive strength, regardless of the type of binder and the W/B ratio.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2002년도 가을 학술발표회 논문집
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• pp.579-584
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• 2002

In this research, the physical properties of self compacting concrete using ground granulated blast furnace slag as a part of cement were investigated. Concrete using ground granulated blast furnace slag was prepared with various ground granulated blast furnace slag replacement(20~80 volume %) for cement and the quantities of coarse aggregate in concrete were 50%, 55% and 60% of ratio of absolute volume of coarse aggregate. The workability, flowing characteristics, air content and compressive strength of concrete using ground granulated blast furnace slag were tested and the results were compared with those of ordinary portland cement concrete. In the experiment, we acquired satisfactory results at the point of flowing characteristics and strengths of concrete using ground granulated blast furnace slag within tile replacement ratio of 50% and the optimum quantity of coarse aggregate in concrete was found to be 50%~55% of ratio of absolute volume of coarse aggregate.