• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.5A
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• pp.307-315
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• 2012

Recently, ultra high performance fiber reinforced concrete (UHPFRC) having over 180 MPa compressive strength and 10 MPa tensile strength has been developed in Korea. However, UHPFRC represents different material properties with normal concrete (NC) and conventional high performance concrete (HPC) such as a high early age autogenous shrinkage and a rapid dry on the surface, because it has a low water-binder ratio and high fineness admixtures without coarse aggregate. In this study, therefore, to propose suitable experimental methods and regulations, and to evaluate mechanical properties at a very early age for UHPFRC, setting, shrinkage and tensile tests were performed. From the setting test results, paraffin oil was an appropriate material to prevent drying effect on the surface, because if paraffin oil is applied on the surface, it can efficiently prevent the drying effect and does not disturb or catalyze the hydration of cement. From the ring-test results, it was defined that the shrinkage stress is generated at the time when the graph tendency of temperature and strain of inner steel ring is changed. By comparing with setting test result, the shrinkage stress was firstly occurred as the penetration resistance of 1.5 MPa was obtained, and it was about 0.6 and 2.1 hour faster than those of initial and final sets. So, the starting time of autogenous shrinkage measurement (time-zero) of UHPFRC was determined when the penetration resistance of 1.5 MPa was obtained. Finally, the tensile strength and elastic modulus of UHPFRC were measured from near initial setting time by using a very early age tensile test apparatus, and the prediction models for tensile strength and elastic modulus were proposed.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.6
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• pp.126-136
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• 2018

A steel-plate concrete composite beam is composed of a steel plate, concrete and shear connector to combine inhomogeneous two materials. The steel plate is assembled by welding an existing composite beam. In this study, new steel-plate concrete composite beam, called a SPC Beam, was developed to reduce the shear connector and improve the workability. The SPC Beam was composed of folding steel plates and concrete, without a shear connector. The folding steel plate was assembled using high strength bolt instead of welding. To improve the workability in field construction, a hat-shaped Cap was attached to the junction with a slab. Monotonic load testing under two points was conducted under displacement control mode. The flexural strength of the specimen for positive moment and negative moment was calculated using the plastic stress distribution method. The test results showed that the flexural strength of the new SPC Beam had 80% of the strength of a complete composite beam. In addition, increasing the composite ratio was possible through clearance controls of the cap. In this study, the performance of the SPC Beam was verified through additional experiments and analyses with the cross-sectional shape and cap as variables, because the representative shape in the positive negative moment region is targeted.

• Journal of the Korean Recycled Construction Resources Institute
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• v.2 no.1
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• pp.60-65
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• 2014

Recently, lots of researches on alkali-activated slag (AAS) concrete have been carried out to resolve the environmental issues such as recycling by-products and global warming. AAS concrete would have high strength and high level of durability. On the other hand, it is known that large amount of shrinkage occurred in AAS concrete due to rapid alkaline reaction in the early age, and however, the related studies about autogenous shrinkage of high strength AAS mortar are relatively rare. In this study, fresh mortar properties such as flow and setting time, compressive strength and autogenous shrinkage of AAS mortar with W/B=0.40 to 0.50, were measured. AAS mortar was activated with sodium silicate (Ms=1.0) with 5, 6 and 7 % of $Na_2O$. Test results revealed that AAS morar shows larger autogenous shrinkage than OPC mortar and the lower W/B of AAS mortar, the greater autogenous shrinkage. Therefore, the application of appropriate curing and the use of shrinkage reduction admixture would be needed to reduce autogenous shrinkage of AAS mortar.

• Journal of the Korea Concrete Institute
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• v.25 no.3
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• pp.313-320
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• 2013

In this study, performance of fiber-reinforced polymer-modified mortar was studied for the development of eco-friendly materials for high performance repair and reinforcement. The general cement mortar and eco-friendly UM resin was mixed with a certain percentage for increased durability. To increase the strength of the polymer-modified mortar, PVA fiber, steel fiber and hybrid fiber were added at a constant rate. Hybrid fiber is contains the same percentage of PVA fiber and steel fiber. In order to determine the strength properties of fiber-reinforced polymer-modified mortar, the compressive strength test, the splitting tensile strength test and the flexural strength test were performed. And, in order to determine the durability properties of fiber-reinforced polymer-modified mortar, water absorption test and chemical resistance test were performed. From the experimental results, polymer-modified mortar using UM resin was improved durability. And the tensile strength and flexural strength increased, which were the vulnerability of fiber reinforced polymer-modified mortar. From this study, fiber-reinforced polymer-modified mortar using eco-friendly UM resin can be used to repair and reinforcement for the external exposure of concrete structures to improve the durability.

• Resources Recycling
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• v.21 no.2
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• pp.47-52
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• 2012

According to the diversification of types of concrete structures, the quality of the concrete which is demanded also, is becoming high performance essentially. The high performance of the concrete leads using of admixtures, generally, in order to produce high strength, concrete has been used to silica fume. Silica fume is excellent mechanical properties, but unlikely to be economic. So, recently as a replacement for silica fume, metakaolin is a lot of research underway. In this study, it is used the metakaolin substitute for silica fume. For in order to prevent loss of liquidity when occurs using the admixtures, we used the silica dioxide. Therefore, concrete with the admixtures and silicon dioxide were examined the mechanical properties.

• Journal of the Korean Recycled Construction Resources Institute
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• v.1 no.1
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• pp.35-41
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• 2013

In this study, we investigated the strength development and durability of geopolymer mortar using blast furnace slag only, and admixed with blast-furnace slag and fly ash as cementious materials in oder to develop cementless geopolymer concrete. In order to compare with the geopolymer mortar, the normal mortar using ordinary portland cement was also test. In view of the results, we found out that strength development, the resistance to freezing-thawing of the geopolymer mortar have better than the mortar using ordinary portland cement. Especially, using the combined with blast furnace slag and fly ash develop high strength of above 60 MPa, and improve the resistance of freezing-thawing of approximately 20%, but promote the velocity of carbonation of 2.2~3.5 times.

• Fire Science and Engineering
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• v.24 no.6
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• pp.82-88
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• 2010

Major structural elements such as columns and beams are designed to withstand the vertical and horizontal loads. Futhermore, when the structural elements were engulfed with fire the structural stability should be stand without failure. The beams have been developed in aspects of structural stability but an evaluation of fire performance was not done. So the data of fire resistance performance of beams filled with concrete at web on H-section is not known. The purpose of this paper is to analyse the correlation between temperature analysis and fire test with the beams and to show the fire resistance performance with two methods.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.3
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• pp.269-275
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• 2020

In this study, flexural tests of precast concrete panels according to the thickness of cross-sectional and the with or not of reinforcement were carried out in order to develop and assess of a lightweight precast concrete panel using ultra high performance concrete. For the test, four panels were fabricated, and consisted of one normal concrete panel and three ultra high performance concrete panels. As a test result, it was found that the plain precast panel using ultra high performance concrete had a lower flexural performance than the reinforced normal concrete panel, regardless of the cross-sectional size. The flexural performance of the hollow-sectional precast panel applying ultra high performance concrete, is improved by 150% compared to that of the reinforced normal concrete panel. That is, through additional performance verification and optimization of the cross-sectional design of the panel, the ultra high performance concrete precast panel can be made lighter. Also, the practical use of lightweight precast panels with ultra high performance concrete can be available through evaluation on shear, joint connection and anchoring, etc.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.609-612
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• 2008

Ultra Super Early Strength Cement is a material that satisfies these requirements. early hydration heat however, is significant over regular concrete, thus discretion is advised for thermal cracks in accordance with heat generation when constructing a large-scale structures. In addition, the negative point that it is difficult to achieve required strength in a short period of time following rubbing process while retaining workability, the cement is being used conditionally for engineering material and Ultra Super Early Strength Cement for maintenance material for construction doesn't exist. Magnesia Phosphate Cement, which is currently under studies in overseas uses no extra admixture and has strong points of Ultra Super Early Strength as well as favorable construction-ability and adhesive stability to the prototype concrete. These factors stem recognition that it could be used as maintenance material for construction of diverse applicability. In order to provide necessary data to increase practicality of the magnesia phosphate cement for Ultra Super Early Strength Mortar, the study carried out simulate experiment on member of framework to review field applicability.

• Magazine of the Korea Concrete Institute
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• v.8 no.5
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• pp.163-170
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• 1996

Cellulose fibers, being fairly strong and stiff as well as cheap and plentiful with low energy demand during manufacture, are strong contenders for the reinforcement of cement-based materials. Cellulose fiber-cement composites, generally manufactured by slurry-dewatering procedure, can find applications in the production of flat and corrugated cement sheets and many other thin-sheet cement products. This paper presents the results of an experimental study concerned with the effects of fiber content and moisture conditions on the flexural performance of these composites. An effort was also made to study the effect of pozzolanic admixtures on the flexural performance in different moisture conditions. The test results obtained were analyzed statistically using the analysis of variance in order to derive reliable conclusions. The results generated in this study were indicative of significant effects of fiber content and moisture condition of flexural performance. There is a tendency in flexural strength to increase in increase in fiber content up to 8%: flexural toughness values continue to increase even at higher fiber contents. Moisture content has a significant effect on the flexural performance. There is a tendency in flexural strength to decrease and flexural toughness to increase with increasing moisture content Composites incorporating pozzolans showed an increase in the flexural strength while slightly reducing the flexural toughness and were sensitive to variations in moisture content.