• Proceedings of the Korea Concrete Institute Conference
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• 2010.05a
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• pp.483-484
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• 2010

In this paper, it was intended to understand the effect of the fiber orientation distribution on the tensile behavior of Intra High Performance Cementitious Composites (UHPCC) and to estimate flow-dependent fiber orientation distribution and the corresponding tensile behavior of UHPCC.

• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.1
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• pp.46-54
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• 2013

Two different UHPCCs having different fiber lengths and volume fractions are considered to be applied to bridge decks. The objective of this study is to estimate cracking resistance of the two UHPCCs. The notched beam tests were performed with the UHPCCs, and the relationships between load and CMOD(Crack Mouth Opening Displacement) were obtained from the tests. The tensile stress and crack opening relationships optimally fitting the measured load-CMOD curves were found through the inverse analyses. The UHPCC with 2% volume fraction of 13 mm long fiber has lower fracture energy than the UHPCC with 0.5% and 1.0% volume fractions of 16.3 mm and 19.5 mm long fibers, respectively. It indicates that the latter UHPCC is more effective in uniformly distributing crack formation and reducing crack width.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.4
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• pp.562-570
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• 2020

This study explores manufacturing technology and basic properties of high strength cement composites at 2,000kg/㎥ of specific weight. It is suggested that lightweight-high strength cement composites can be produced by substituting silica sand in ulta-high performance concrete mixture with lightweight materials such as solid bubbles and lightweight fine aggregates. The 28-day compressive strengths of cement composites with solid bubbles were from 116MPa to 141MPa at below 2.0g/㎤ of unit density while the cement composites with lightweight aggregates possessed lower compressive strength and higher unit density. The specific weight calculated from mixture proportions did not have significant difference with unit density of hardened cement composites, indicating that unit density of hardened cement composites can be estimated from the specific weight in mixture proportions.

• Journal of the Korea Concrete Institute
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• v.23 no.4
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• pp.441-448
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• 2011

In this study, experimental tests of chemical and autogenous shrinkage were performed to evaluate the early age shrinkage behaviors of ultra high performance cementitious composites (UHPCC) with various replacement ratios of silica fume (SF), shrinkage reducing agent (SRA), expansive admixture (EA), and superplasticizer (SP). Starting time of self-desiccation, was analyzed by comparing the setting times and the deviated point of chemical and autogenous shrinkage strains. The test results indicated that both SF and SRA augment the early age chemical shrinkage, whereas SP delays the hydration reaction between cement particles and water, and reduces chemical shrinkage. About 49% of autogenous shrinkage was depleted by synergetic effect of SRA and EA. The hardening of UHPCC was catalyzed by containing EA. Self-desiccation of UHPCC occurred prior to the initial setting due to the high volume fraction of fibers and low water-binder ratio (W/B).

• Journal of the Korea Concrete Institute
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• v.23 no.5
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• pp.581-590
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• 2011

Since ultra-high performance cementitious composites (UHPCC) not only represents high early age shrinkage strain due to its low water-to-binder ratio (W/B) and high fineness admixture usage but also reduces the cross section of structure from the higher mechanical properties, it generally has more shrinkage cracks from the restraints of formwork and reinforcing bars. In this study, free and restrained shrinkage experiments were conducted to evaluate the suitability of incorporating both expansive admixture (EA) and shrinkage reducing agent (SRA). The test results indi-cated that approximately 40~44% of free shrinkage strain was decreased. Also, the results showed that 35% and 47% of residual tensile stresses were relieved by synergetic effect of SRA and EA, respectively. Residual tensile stresses from ringtest were relaxed by approximately 61% and 64% of elastic shrinkage stresses due to SRA and EA, respectively, because of the tensile creep effect. Therefore, the creep effect should be considered to precisely estimate the restrained shrinkage behavior of concrete structures. The degree of restraint of UHPCC was approximately in the range of 0.78~0.85. The addition of combined EA and SRA showed minute influence on the degree of restraint. However, the effect decreased when thicker concrete ring was used. Tensile creep strains were measured and compared to the predicted values from 4-parametric prediction model considering time dependent restrained forces.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.6
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• pp.27-32
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• 2021

This study was conducted to improve the workability of cementitious composites using nano-bubble water. The used nano-bubble water contains 7% of nano-sized bubbles with an averaged bubble size of 750 nm. Various different types of cementitious composites including ultar-high performance concrete, lightweight cementitious composites, and high-strength mortar have been tested to identify the changes of material properties. From the use of nano-bubble water, it was confirmed that workability has been improved by 3-22%. On the other hand, other material characteristics such as compressive strength did not have noticeable changes. Therefore, it was proposed that the use of nano-bubble water can enhance workability of cementitious composites without having significant impact on other material properties.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.4
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• pp.49-56
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• 2015

Ultra-High Strength Concrete(UHPC) has ultra-high material performance including high strength and high flowability. On the other hand it is less ductile than high ductile fiber reinforced cementitious composite. This study investigated the effect of combination of steel fiber and micro fiber on the tensile behavior of UHPC. Four types of UHPC containing combination of steel fiber, polyethylene(PE), polyvinyl alcohol(PVA), and basalt fiber were designed. And then uniaxial tension tests were performed to evaluate the tensile behavior of UHPC according to combination of fibers. And density was measured to evaluate whether micro fiber induces unintentional high pore or not. From the test results, it was exhibited that PE fiber with high strength is effective to improve the tensile behavior of UHPC and basalt fiber is effective to increase the cracking and tensile strength of UHPC. Furthermore, it was also verified that micro fiber does not make high pore.

• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.5
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• pp.110-118
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• 2010

This research dealt with the effect of steel-fiber reinforcement on the compressive strength of ultra high performance cementitious composites (UHPCC) and compared with that in normal steel-fiber reinforced concrete(SFRC). With wide range of compressive strength of UHPCC, experiments on the fiber reinforcement effect confirmed that the compressive strength in UHPCC is also improved by adding fibers as in normal SFRC. The experimental results were compared with previous researches about reinforcement effect by adding fibers, which are limited within 100MPa compressive strength. The comparison revealed the linear relationship between $f'_{cf}-f'_c$ and RI regardless of the magnitude of compressive strength, from which a general equation to express the effect of fiber reinforcement, applicable to various SFRC's with wide range of compressive strength including UHPCC.

• Journal of the Korean Recycled Construction Resources Institute
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• v.2 no.3
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• pp.196-201
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• 2014

As political circumstances in oversea countries and Korea varies, the risk of vulnerability from unexpected extreme loading conditions, such as explosions or extreme impacts, also increased. In addition, construction companies in Korea recently have taken chances of overseas expansion to countries where their domestic situations are not in rest. Therefore, the resistance of construction materials for blast or impact loading become taking more consideration from engineering field. This study is a part of the research to develop a high performance fiber reinforced cementitious composite materials with high volume steel fibers and primary purpose of this study is to find an optimum mix proportions of in-fill slurry. In order to accomplish the tasks this study performed experimental investigations on the slurry for consistency, compressive strength, flowability, J-penetration, bleeding and rheology properties as well as mechanical properties, compressive and flexural strength, with respect to different mix proportions.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.1
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• pp.25-32
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• 2016

The purpose of this study is to evaluate the performance on the compressive bonding shear strength of ultra-high strength steel fiber reinforced cementitous composites(UHSCC). As a result of compressive bonding shear strength through Direct shear test, It was found that the specimen($150{\times}150{\times}150mm$) of NC(Normal concrete) + NC showed similar compressive bonding shear strength at whole experimental level. On the other hand, the specimen of UHSCC + UHSCC showed decrease of compressive bonding shear strength from after 30 minutes of the retarded placement than 0 minute. As a result of analyzing failure mode of bonding interface, It was found that the specimen of NC + NC showed mixed failure at whole experimental level. In case of the specimen of UHSCC + UHSCC, it showed interface failure from the specimen that are 30 minutes, 60 minutes and 90 minutes of delay of concrete placing. As a result of analyzing XRD test in terms of the placement interface on the specimen of NC and UHSCC, relatively much amount of $SiO_2$ was detected from the specimen of UHSCC than that of NC. It is judged that the most of main components of coating film shown in the specimen of UHSCC is $SiO_2$. In conclusion, it is judged that UHSCC which is made from after 30 minutes of delay of concrete placing is unable to be used as structural member because of deterioration of bonding performance. From later study, it is judged that the improvement of bonding performance from the part of cold joint occurrence is necessary through the interface preparation method.