Earticle

초고성능 콘크리트 (UHPC)는 우수한 공학적 성능과 더불어 자기충전성을 갖는 신개념의 재료로 알려져 있다. 그런데, UHPC를 제조함에 있어 다량의 고가 실리카퓸이 사용되어 유동성확보를 위해 다량의 고성능 감수제가 필요한 상황이다. 이는 결국 제조비용의 상승으로 이어져 범용적인 활용을 어렵게 하는 요인이다. 따라서 본 연구에서는 압축강도 180 MPa 수준의 UHPC의 경제적 제조를 위한 SF의 대체재로서 지르코늄 실리카퓸(Zr)의 활용가능성을 검토하고 이들의 사용에 따른 SP제 사용량의 저감효과를 실험적으로 고찰하므로서 경제적 제조방안을 모색하고자 한다. 이를 위해 Zr 치환률 및 SP제 사용량 변화에 따른 UHPC의 레올로지 및 역학적 특성을 고찰하였다. 연구결과 Zr을 치환할 경우 UHPC의 점성 저하에 기인하여 SP제 사용량을 SF 치환대비 60~70% 저감하면서 제반 유동성 및 역학적 성능은 SF 치환 UHPC와 동등한 수준으로 확보할 수 있음을 확인할 수 있었다.

Ultra-High Performance Concrete (UHPC) is a material exhibiting self-compacting ability together with outstanding mechanical performance. Due to the large quantities of silica fume (SF) required in the composition of UHPC, large amount of superplasticizer (SP) is needed to secure the fluidity and results in the increase of the fabrication cost. Accordingly, this study adopts zirconium silica fume (Zr), as a material known to improve the flowability, instead of SF and investigates the corresponding rheological and mechanical performances of UHPC having 180 MPa. For test variables, five different Zr contents from 0.05% to 0.25% and four different SP dosages from 1 to 4% are varied. The results show that plastic viscosity is decreased with increase of Zr and SP contents due to lower blaine fineness than SF. Even if it requires 60 to 70% less SP than UHPC using SF, UHPC using Zr can develop at least flow of 210~230 mm, compressive strength of 180 MPa, flexural strength of 35 MPa, and direct tensile strength of 15 MPa. These results are promising for further application of UHPC by contributing to substantive reduction in the fabrication cost.

Consumption of river sand has been remarkably increased due to lack of fine-natural river sand in current domestic construction site. Taking river sand in any matter human beings please, however, is found to be the major reason of coastal erosion and that of destroying habitats and an egg-laying site of oceanic life. Moreover, both of environmental development limitation and shortage of river sand are pushing further toward the difficulty in collecting an aggregate. As being faced problems with getting an aggregate, researches ―that are suggesting an alternative substitution which can be used instead of a natural aggregate― are now under way. According to the studies, it is required to extent the usage of steel slag. As a part of a basic research focusing on spreading the use of steel slag which is quick frozen with rapid air, this study is aiming for suggesting a ground support from the Physical Properties of Mortar experiment. This experiment is formed that 6 ascending levels of steel slag replacement ratio-0, 20, 40, 60, 80, 100%, and 40 percent of water-cement ratio. Setting two opposite environment, one measured air content and table flow in liquid condition, and another measured compressive strength, tensil strength, and flextural strength in hardening condition. As a result of the experiment, getting higher level tends to show increased fluidity and decreased in air content at the same time. The other measurements-compressive strength, tensil strength, and flextural strength-have also increased as replacement ratio goes up. Therefore, it is considered that if the steel slag substitute concrete aggregate, it will give a boost up the improvement in fluidity and the quality of the aggregate.

Recently skyscrapers with high-strength concrete come to the spotlight internationally and main downtown buildings in the world get ultra higher-storied. However, Korea avoids using high-strength concrete because of the reasons as a lack of its construction experience and study. Therefore, the purpose of the study was to make a close inquiry into each kind of engineering properties with high-strength concrete of 80MPa and to select the optimum combination of high-strength concrete with good applicability and placeability. The study set up its condition of testing combination as W/B(25%), S/a(45%) and W(160㎏/㎥) and enforced experiments, mixing and adding each kind of binders in many ways. Also, the study used the minimal quantity of superplasticizer with in a scope to satisfy slumpflow of its target. As the result, combination of type Ⅱ showed good results in flowability, strength properties and durability.

Currently buildings in Korea get ultra higher-storied by rapidly changed technology of construction and a dense population. However, Korea uses high-price silica fume depending on import in the whole quantity generally to be manifested compressive strength for ultra high-rising buildings and currently has a lot of difficulties in applying high-strength concrete to the field by increase of concrete’s unit price according to using silica fume. Therefore, the study enforced experiments, setting up each kind of water-binder rates and fin aggregate rates to achieve design standard strength and slumpflow of its target and applying each king of additives to analyze engineering properties of high-strength concrete with high-strength binder with which we can replace silica fume. As the result, high-strength binder showed better tendency than the existing silica fume in fluidity and early strength properties.

Recently the study on high flowing which has high workability and self-compacting is being proceeded actively in the university and corporative laboratory. The new kinds of cement as changed by its chemical composition and high range water reducing agent enhancing the workability of concrete having been developed, keeping pace with this tendency. The purpose of this study is aimed for investigating the rheology property and fluidity of cement paste, by changing the substitutional ratio of an admixture, additive dosage of Naphthalene Sulphonate high-range water reducing agent. from result, the fluidity and rheology of paste were different according sorts of powder and additive dosage of agent.

The viscosity of high-flowability paste is very high compared to ordinary concrete for the low water-binder ratio(W/B). Therefore, high-flowability concrete is positively necessary to high-range water reducing agent. High-Flowability paste can make much higher fluidity with no occurrence of segregation, by its higher viscosity and lower yield value than ordinary concrete. The flowability of high-flowability paste must be evaluated not only by convention consistency test such as slump test but also by the base of the rheological properties of the fresh concrete. The purpose of this study is to analyze the physical properties of high-flowability paste according to the replacement ratio of the Polycarboxylate high-range water reducing agent.; high-flowability paste is considered as Bingham plastic fluid with the rheology parameters of the plaste viscosity and yield value.

In this study, we analyzed the The rheological properties of high flowability paste mixing cellulose type viscosity agent. and we suggest that the algorism of a mixing plan in the high flowability concrete and from this, we show the basic report for the right mixing plan. From the results, the yield value and the plastic viscosity is increased in proportion to the added amount of viscosity agent. among the Viscosity Agent, 50us is better than 40us in the plastic viscosity, but is less than in the yield value. this is the fact of the low yield value of the high flowability paste and the flowing Properties with the right Plastic Viscosity. so we concluded that 50us is better than 40us as a viscosity agent of the high flowability concrete.

This study investigates the effect of fiber type on the flowability and mechanical properties of cementless fiber-reinforced composites using a calcium hydroxide-ground granulated blast furnace slag (Ca(OH)2-GGBS) binder system. Four fibers, jute, nylon, polypropylene (PP), and polyvinyl alcohol (PVA), were incorporated at a constant volume fraction of 2% under identical matrix conditions. The binder consisted of GGBS and Ca(OH)2 at a ratio of 0.92:0.08, and both the sand-to-binder ratio and water-to-binder ratio were fixed at 0.30. Slump-flow, compressive strength, direct tensile, and shear tests were conducted to evaluate the fresh and hardened performances of the composites. The results showed that fiber type significantly influenced both flowability and mechanical behavior. PP and nylon mixtures showed relatively high slump-flow values of 695 mm and 691 mm, whereas jute and PVA mixtures showed lower values of 631 mm and 613 mm. The compressive strength ranged from 37.54 to 44.92 MPa, with the nylon mixture showing the highest value. In direct tension, the PVA mixture exhibited the best post-cracking behavior, with a first cracking stress of 3.89 MPa, a tensile strength of 5.45 MPa, and a tensile strain of 4.60%, accompanied by multiple microcracking. In contrast, the jute and PP mixtures showed little or no stress increase after first cracking, while the nylon mixture showed only limited post-cracking tensile response in some specimens. In shear, the PVA mixture showed the highest shear strength of 9.27 MPa, whereas the other mixtures showed similar values ranging from 5.52 to 5.71 MPa. These results indicate that PVA fiber is the most effective for improving the tensile and shear performances of the Ca(OH)2-GGBS-based cementless composites.

The study is propertys analyze such as the paste rheology, yield value and compressive strength etc. with used to the admixture micro powder manufacture high flow mortar, the purpose was the it`s obtain design of mix proportion of the high flow concrete or mix design necessary basic date. The result is admixture balance rate was highed according to the transposition rate to be good working a ball bearing flexibility. However, W/B is raised that it judge the unit volume weigh more than rising the flexibility is the huge affect according to the admixture`s transposition rate or addition rate of high range water reducing admixture. A special quality of mortar was according to the admixture transposition rate drop the early-age strength and it raising strength with keep dropping the W/B. It was reveal that as result of plzzoanic reaction of admixture is low early-age strength and high long-time strength. The conclude, in the more than variety of the mix condition that the research need about the high-fiuidity concrete of theory design of mix proportion or mix design method.

고유동콘크리트 (혹은 자기충전콘크리트)는 콘크리트 타설 시 작업자에 의한 실수를 줄일 수 있어 콘크리트의 품질을 향상시킬 수 있다. 또한 충분한 재료분리 저항성, 충진성 및 높은 유동성으로 인하여 사람에 의한 다짐을 대체할 수 있다. 이러한 고유동콘크리트에 섬유를 혼입하면 고유동콘크리트의 전체적인 특성의 향상 및 거동을 가져다 줄 수 있다. 본 논문에서는 이러한 섬유보강 고유동콘크리트의 유동성 및 특성에 대하여 알아보았다. 16개의 배합설계를 이용하여 유동성, 압축강도, 할렬인장강도 및 휨거동에 대하여 조사하였다. 실험결과 플라이애쉬 치환율 30%까지 슬럼프플로값은 감소하며, 강섬유를 혼입하여도 고유동콘크리트의 강도증진에도 잇점이 없으며, 섬유포함 고유동콘크리트의 휨거동은 무섬유 콘크리트에 비해 상당히 증대됨을 알 수 있었다.

The use of high-flowability concrete (HFC, or self-compacting concrete) will gives several advantages on concrete structures due to the eliminating of some potential human errors during concrete works. Also HFC will reduces the manual compaction efforts of fresh concrete due to higher flowability, filling ability and sufficient segregation resistance. Furthermore, an addition of fibers in HFC may not only improve the overall properties, but may also result in better performance in the HFC. The flowability and mechanical properties of the steel fiber reinforced high-flowability concrete mixtures were studied. Sixteen mixtures were cast without fibers and with fibers. The slump flow, compressive strength, splitting tensile strengths, and flexural capacities of HFC with different fly-ash contents and fiber contents were compared. According to the experimental results, as the increased of fly-ash content up to 30% replacement of cement, the slump flow was decrease, and with the same fly-ash content, the compressive strength of specimens with steel fibers did not show significant differences compared to those of plain concrete. With the addition of fibers, the fracture capacity and the ductility of the self compacting concrete mixtures were increased compared to those of plain concrete.

In additive manufacturing, the flowability of feedstock particles determines the quality of the parts that are affected by different parameters, including the chemistry and morphology of the powders and particle size distribution. In this study, the microstructures and flowabilities of gas-atomized heat-resistant alloys for additive manufacturing applications are investigated. A KHR45A alloy powder with a composition of Fe-30Cr-40Mn-1.8Nb (wt.%) is fabricated using gas atomization process. The microstructure and effect of powder chemistry and morphology on the flow behavior are investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and revolution powder analysis. The results reveal the formation of spherical particles composed of single-phase FCC dendritic structures after gas atomization. SEM observations show variations in the microstructures of the powder particles with different size distributions. Elemental distribution maps, line scans, and high-resolution XPS results indicate the presence of a Si-rich oxide accompanied by Fe, Cr, and Nb metal oxides in the outer layer of the powders. The flowability behavior is found to be induced by the particle size distribution, which can be attributed to the interparticle interactions and friction of particles with different sizes.

Erdosteine, an expectorant, has been known to show a very poor flowability. Furthermore, high dosing amount (300mg/cap) and bulk density make it more difficult to fill in a capsule less than No. 0 size as bulk state. We have studied the possibility of dry granulation process in purpose of getting a better flowability and manufacturing efficiency. A roller compactor was introduced for this purpose and the applicability of laboratory result into commercial scale instrument was also experimented.Roller compacting process was very favorable to obtain the granules with good flowability and improved density profiles. (omitted)

Rare-earth zirconate (Re2Zr2O7, Re = La, Gd, Nd, Y) ceramic materials was synthesized by solid-state reaction methodthrough high-energy ball-milling process (HEBM) and subsequently followed by two different calcination techniques. Theimpacts of the two different calcination techniques on the phase structure, morphology, powder flowability (i.e. particle sizeand distribution, specific surface area, pore size and pore volume) were studied. The effectiveness of the calcination techniquesof the resulting Re2Zr2O7 powders were investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy(FTIR), and Scanning electron microscopy (SEM) techniques. The outcomes demonstrated that both calcination techniquescould produce Re2Zr2O7 powders with an excellent pyrochlore structure. The calcination temperature was reduced by theMicrowave Calcination (MWC) technique when compared with the Conventional Calcination (CVC) technique. The rareearthzirconate powders exhibited different particle size distribution. The resulting particle median diameter was about 2.5-45 μm for CVC and 1.36-2.27 μm for MWC. The powder flowability of Re2Zr2O7 powders was strongly dependent on theparticle size and distribution. Thus MWC technique for the preparation of Re2Zr2O7 powders is the best choice of powderprocessing to achieve desired properties.

In this study, the grinding kinetics and the flowability of balloon flowers (BFs) with various moisture contents (8, 12, and 20%) were determined. Three semiempirical grinding models (Bond, Kick, and Rittinger) were applied to describe the BFs' grinding process. A lower moisture content resulted in a decreased grinding constant value (Bond's index). Based on the kinetics of particles during grinding, a sigmoid model was developed which successfully described changes in the particle sizes of BFs with various moisture contents during the grinding process except for smaller ones (< 0.60 mm) with a high moisture content (20%). The flow function at different particle sizes was not consistently correlated with results regarding the internal friction angle. This might be due to different particle shapes and sizes of BFs. The poorest flowability was observed for BF powder with the smallest particle size.

Various researches on the application of polymer dispersions to the cement mortar and concrete have been carried out in many countries like America, Japan and Germany and so on due to their high performance and good modification effect. PAE of polymer dispersion widely used in situ was employed that the high flowability may be induced in the cement mortar. In order to investigate the modification of cement mortar with high flowability by PAE and fracture mode of adhesive strength properties in tension of that, experimental parameters were set as PAE solid-cement ratio(P/C) and cement: fine aggregate(C:F) and the experiments such as unit weight, flow, consistency change, crack resistance and segregation that inform on the general properties have been done. Adhesion in tension is measured with a view to comprehending the properties and fracture mode in tensile load. Consistency change of cement mortar modified by PAE did grow better as the ratio of PAE solid-cement increased and was much superior to that of resin based flooring such as polyurethane and epoxy which recorded the loss of consistency in 90 min. after mixing. Adhesive strength in tension increased with continuity during curing period and showed the maximum in case of C:F=1:1 and P/C=20%.

이 연구에서는 다중벽 탄소나노튜브(Multi-walled CNT) 혼입량을 Binder 중량 대비 0.1, 0.3, 0.5%로 다르게 하여 CNT 혼입량에 따른 CNT 보강 시멘트 복합체의 굳지 않은 상태에서의 유동특성, 강도 및 강도발현 특성 등을 살펴보았다. 유동특성에 대한 실험결과, CNT 혼입량이 증가함에 따라 굳기 전 상태의 작업성이 저하되는 것으로 나타났으며, 레올로지 실험에서는 CNT 혼입량 증가에 따라 소성점도의 감소와 항복응력의 증가를 확인할 수 있었다. 또한 레올로지 실험에서 얻은 흐름곡선에서는 낮은 전단속도에서의 틱소트로피 현상이 높은 CNT 혼입량에서 더욱 뚜렷하게 나타나는 것을 볼 수 있었다. CNT 혼입량 증가에 따른 강도특성 실험결과에서는 압축강도 및 인장강도 모두 CNT 혼입량이 증가함에 따라 향상되는 것으로 나타났으며, 압축강도에 대한 CNT 보강에 따른 강도향상 효과가 인장강도에 비해 더 크게 나타났다. 한편 재령별 강도 측정 결과에 따르면 CNT 혼입이 초기강도 발현에도 효과적인 것을 확인할 수 있었다.

With several different dosages of multi-walled CNTs which was 0.1, 0.3, and 0.5% of the weight of binder, the fluidity in fresh CNT cement composites, as well as the strength and strength development with age of the hardened composites were investigated in this experimental study. The experimental results from flow test indicated that the increase in the dosage of CNTs badly impacted on the workability of fresh composites, and the results from rheological measurements presented the decrease in plastic viscosity and the increase in yield stress according to the amount of CNTs. In addition, the thixotrophy in the flow curve obtained from the rheology test was observed more noticeably in the composites with higher dosage of CNTs. With the experiments on the strength properties, the improvement of both compressive and tensile strengths with the increase of CNTs dosage could be obtained. Moreover, early strength development by adding CNTs was found when it was compared with plain cementious matrix without CNT.

본 연구에서는 강섬유보강 콘크리트의 시공성 및 품질향상 방안의 일환으로 고유동 자기충전 콘크리트(HSCC)에 형상비 및 길이를 달리한 강섬유(SF)를 혼입한 콘크리트를 제조하여 강섬유보강 일반콘크리트(CC)와 유동 및 강도 특성을 비교 검토하였다. 실험결과 SF를 혼입한 HSCC는 높은 유동성 및 점성의 영향으로 SF 자체의 뭉침현상이 발생하지 않아 강섬유보강 CC의 경우보다 유동성능 및 통과성능이 크게 향상 되었으며, 동일한 압축강도 범위에서 SF를 혼입하지 않은 HSCC의 경우보다 쪼갬 및 휨강도는 SF의 형상비와 관계없이 길이가 길어질수록 증가하는 경향이 나타났다. 이상의 실험결과를 통하여 강섬유를 혼입한 HSCC를 현장 적용할 경우 기존에 사용되고 있는 강섬유보강 CC의 경우보다 시공성 및 품질 향상이 가능할 것으로 판단된다.

In this study, the concrete, in which the steel fiber(SF) with different volume-surface ratios and lengths was intermixed in High flowing Self-Compacting Concrete(HSCC), was produced to compare with steel fiber reinforced concrete as a part of plan to improve the workability and the quality of steel fiber reinforced concrete. As the result of experiment, the flowing and passing characteristics of HSCC intermixed with SF was highly improved as there was no fiber ball phenomenon due to the effect of high flowability and the viscosity, and in the identical range of compressive strength, it showed the tendency that the splitting and flexural strength was increasing as the length was getting longer regardless of volume-surface ratio when compared with HSCC which was intermixed with SF. It is estimated that in case of application of HSCC intermixed with steel fiber to work sites, it would be possible to improve the workability and the quality which would be better than that of steel fiber reinforced concrete which has been used.

본 연구에서는 소요의 유동성능 및 공기량을 확보할 수 있는 병용계 보통강도 고유동 자기충전 콘크리트를 제조하기 위하여 증점제 및 소포제 첨가량를 변화시킨 병용계 고유동 자기충전 콘크리트의 유동 특성을 실험적으로 분석 고찰하였다. 실험결과 증점제를 첨가한 병용계 고유동 자기충전 콘크리트의 Slump flow는 증점제 첨가량이 0.2%(${\times}$W %)일 때 가장 증가하였으며 증점제 첨가량이 높아질 경우 JSCE 기준안(2등급)에서 제시한 V-funnel의 유하시간 규정값을 크게 벗어나는 결과가 나타났다. 또한 증점제, 소포제 및 AE제를 첨가한 배합을 제외한 모든 배합이 목표 공기량 $4.5{\pm}1.5%$를 만족하지 못하였으며, 소포제를 첨가한 병용계 고유동 자기충전 콘크리트 배합은 최초배합 후 시간의 경과에도 불구하고 공기량(A1=1.5%)이 다소 감소하는 결과가 나타났다. 이러한 결과를 통하여 병용계 고유동 자기충전 콘크리트 제조시 소요의 유동성능을 얻기 위한 최적의 혼화제량을 알 수 있었다.

In this research experimentally analyzes the flow characteristics of a combined High flowing Self-Compacting Concrete of which the viscosity agent and defoaming agent addition amount are changed, to make the combined High flowing Self-Compacting Concrete that can secure the required flow performance and air amount. As a result of the experiment, the slump flow of the combined High flowing Self-Compacting Concrete added with viscosity agent increases when the viscosity agent addition amount is 0.2%(${\times}$W %). When viscosity agent addition amount increases, viscosity agent shows that it largely deviates from the regulation value in the flow time of V-funnel, which is presented in the JSCE standards (grade 2). Also, all mixtures, except for mixtures added with viscosity agent, defoaming agent, and AE agent, do not meet a target air amount $4.5{\pm}1.5%$. High flowing Self-Compacting Concrete mixtureadded with defoaming agent shows that although time passes after its first mixture, its air amount reduces a little. Based on the experiment, we can know an optimal polymer amount to obtain the required flow performance

This research has evaluated flowability of ultra flowing self-compacting concrete, which is limitedly used for traditional building structures, in accordance with the first class regulations of Japan Society of Civil Engineering(JSCE) that can be applied to overcrowding-arrangement of bar, as a part of application methods that ultra flowing self-compacting concrete is applied to both precast and prestress bridge structures. The experimental results show that the flowability is acceptable in ternary blended among binary and ternary blended mixings, which satifies the first class regulation of JSCE. It is also concluded to use fly ash to increase viscosity of concrete in the case of segregation resistance because of low viscosity in the mixture of slag from blast furnace and limestone micropowder. Satisfying goals of every mixing after U-box self-compacting experiment, we conclude that ultra flowing self-compacting concrete is applicable to bridges and civil constructions of overcrowding arrangement of bar with evaluation of flowability of ultra flowing self-compacting concrete.