• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.5
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• pp.12-20
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• 2017

This report presents the results of an investigation on the fundamental properties of mortars high fluidity high volume slag cement(HVSC) activated with sodium silicate($Na_2SiO_3$). The ordinary Portland cement(OPC) was replaced by ground granulated blast furnace slag(GGBFS) from 40% to 80% and calcium sulfoaluminate(CSA) was 2.5% or 5.0% mass. The $Na_2SiO_3$ was added at 2% and 4% by total binder(OPC+GGBFS+CSA) weight. A constant water-to-binder ratio(w/b)=0.35 was used for all mixtures. The research carried out the mini slump, V-funnel, setting time, compressive strength and drying shrinkage. The experimental results showed that the contents of superplasticizer, V-funnel, setting time and drying shrinkage increased as the contents of CSA and $Na_2SiO_3$ increase. The compressive strength increases with and an increase in CSA and $Na_2SiO_3$. One of the major reason for these results is the accelerated reactivity of GGBFS with CSA and $Na_2SiO_3$. The maximum performance was CSA 5.0% + $Na_2SiO_3$ 4% specimens.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.12
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• pp.697-704
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• 2017

High-Performance Fiber-Reinforced Cement Composites (HPFRCC) has outstanding durability, and has attracted interest because of its ductility and development of strength, which allows a reduction of the self-weight of a structural member by substantially decreasing the cross section. Therefore, the present study aimed to improve the economic efficiency of HPFRCC by examining experimentally the flexural performance considering various characteristics of the steel fiber. To find an efficient fiber reinforcement method, the flexural performance was evaluated for different shapes, aspect ratios, and volume ratios of the steel fiber. Straight, hooked, and twisted fiber configurations were considered by adopting a fiber length longer than the usual 13 mm. The test results showed that HPFRCC reinforced by 19.5 nun-long straight fibers with a volume fraction of 1.5% shows better flexural performance than that reinforced by 13 mm-long straight fibers with a volume fraction of 2.0%. Consequently, HPFRCC with enhanced economic efficiency can be produced by adopting a reduced amount of steel fiber.

• Journal of the Korea Institute of Building Construction
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• v.22 no.5
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• pp.425-430
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• 2022

Concrete used for the foundation of high-rise buildings is often placed through in an integrated pouring to ensure construction efficiency and quality. However, if concrete is placed integrally, there is a high risk of temperature cracking during the hydration reaction, and it is necessary to determine the optimal mixing design of high-performance, high-durable concrete through the replacement of the admixture. In this study, experiments on salt damage, carbonation, and sulfate were conducted on the specimen manufactured from the optimal high-performance low-heating concrete combination determined in the author's previous study. The resistance of the cement matrix to chlorine ion diffusion coefficient, carbonation coefficient, and sulfate was quantitatively evaluated. In the terms of compression strength, it was measured as 141% compared to the structural design standard of KCI at 91 days. Excellent durability was expressed in carbonation and chlorine ion diffusivity performance evaluation. In particular, the chlorine ion diffusion coefficient, which should be considered the most strictly in the marine environment, was measured at a value of 4.09×E-12m²/y(1.2898×E-10m²/s), and is expected to be used as a material property value in salt damage durability analysis. These results confirmed that the latent hydroponics were due to mixing of the admixture and high resistance was due to the pozzolane reaction.

• Journal of the Korean Society of Marine Environment & Safety
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• v.15 no.2
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• pp.135-142
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• 2009

This study investigates the characteristic properties of strength, flowability, durability and drying shrinkage to control strength and to reduce heat of hydration of high performance concrete using crushed stone fines. According to the experimental results, when crushed stone fines are increased every 10%, $10{\sim}15%$ of compressive strength is decreased and flowability of high performance concrete is effectively improved due to the decrease of modulus of deformation and confined water ratio. When crushed stone fines are replaced every 10%, $4^{\circ}C$ of the highest adiabatic temperature rise is decreased by reducing the unit cement. However, 5% of drying shrinkage is increased in the same condition In the meantime, durability of high performance concrete is excellent, having over 100% of good relative dynamic modulus of elasticity due to fineness of formation mused by the increase of the unit powder content and the improvement of flowability, without regard to the replacement of crushed stone fines. Therefore, It can be said that the usage of crushed stone fines can control the strength of high performance concrete by replacement and reduce heat of hydration.

• Journal of The Korean Society of Agricultural Engineers
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• v.62 no.4
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• pp.23-31
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• 2020

Recently, meteorological disasters have been increasing by climate change, excessive rainfall, and landslide. The purpose is to develop new fabric concrete that can prevent and recover from damages because some of areas are vulnerable to meteorological disaster. Specifically, this technology can minimize time and space constraint when repairing the concrete structure and installing a formwork. The structure of fabric concrete is a mixture of fabric concrete and a high-speed hardened cement, Silica sand, wollastonite mineral fiber, fabric material and waterproof PVC fabric. In this study, the ratio of mechanical properties and durability of the fabric concrete mixture was evaluated by deriving the binder: silica sand mix ratio of the fabric concrete mixture and substituting part of the cement amount with wollastonite mineral fiber. Best binder in performance evaluation: Silica sand mix ratio is 6: 4 and the target mechanical performance and durability are the best when over 15% wollastonite binder is replaced by silicate mineral fiber.

• The Journal of Korean Academy of Prosthodontics
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• v.59 no.1
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• pp.71-78
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• 2021

Implant treatment, which was first attempted in fully edentulous patients, is now widely used in partially edentulous, and a single tooth missing patients. Moreover, implant treatment has become an essential treatment modality in modern dentistry. The material of fabricating implant prostheses has also become more diverse than before, one of which is the use of high-performance polymers. The frequency of using high-performance polymers, which have been used in the medical field, is also increased in the dental field compared to the past. In the first case, a PEKK abutment and a PFG crown (cement-screw-retaining type) were fabricated in the lower left second premolar, and in the second case, a PEKK abutment and a monolithic zirconia crown (cement-screw-retaining type) were fabricated in the missing upper left first molar, and in the third case two PEKK abutments and a splinted PFM crowns (cement-screw-retaining type) were fabricated and connected to the upper right first and second molar implants. Through these procedures the patients obtained esthetically and functionally satisfactory results after 4 years of follow-up.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2013.05a
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• pp.93-95
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• 2013

Recently, with the increase in the construction of ultra-high buildings and long-span structures, there is great demand for high-strength concrete which can reduce the structural weight and thickness of member sections. While developing high-strength concrete to meet performance requirements, certain issues at the design stage must also be considered. The issues include diseconomy from a great amount of per-unit cement, spalling failure by fire at ultra-high building, autogenous shrinkage caused by increased hydration activity of binder from use of a superplasticizer. Therefore, the purpose of this study is examined the strain characteristics of Fiber-reinforced-high-strength concrete(FRHSC), which differ from those of general concrete owing to autogenous shrinkage. Based on the experimental data, we proposed an autogenous shrinkage prediction model.

• Journal of Korean Society of Environmental Engineers
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• v.29 no.8
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• pp.909-914
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• 2007

Fluorine compounds are the essential chemicals for wet processes of semiconductor and LCD production line. Problems of conventional treatments for fluoride wastewater are their high operation costs and low fluoride removal capacity. In this study, cement paste containing various Ca-bearing hydrates such as portlandite, calcium silicate hydrate(CSH), and ettringite was investigated for fluoride removal. The objectives of this study are to assess the feasibility of using cement paste cured mixture of cement and water as an alternative agent for treatment of fluoride wastewater and to investigate fluoride removal capacity of the cement paste. The performance of cement paste was comparable to that of lime in the kinetic test. In column experiment where the effluent fluoride concentrations were below 0.5 mg/L. Then the leached calcium reached the maximum level of 800 mg/L. The nitrate reduced to the level of less than 10 mg/L. Nitrate in the wastewater was exchanged with interlayer sulfate of these cement hydrate LDHs. Phosphate concentration could be reduced to 10 mg/L by forming calcium phosphate. These results indicate that the cement paste generally has advantageous characteristics as an economical and viable substitute for lime to remove fluoride.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.935-940
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• 2008

When reinforced concrete is subjected to high temperature as in fire, there is deterioration in its properties of particular importance are loss in compressive strength, cracking and spalling of concrete, destruction of the bond between the cement paste and the aggregates and the gradual deterioration of the hardend cement paste. Assessment of fire-damaged concrete usually starts with visual observation of color change, cracking and spalling of the surface. In this paper, it was reported the trends of research and practical use on the Explosive Spalling Properties and Performance Based of Structural Design of the High-Strength Concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.05a
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• pp.545-550
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• 2002

Concrete is one of the essential structural materials in the construction. But, concrete consists of many materials and is affected by many factors such as properties of materials, site environmental situations, and skill of constructor. Therefore, concrete mixes depend on experiences of experts. However, it is more and more difficult to determine concrete mixes design by empirical means because more ingredients like mineral and chemical admixtures are included. Artificial Neural Networks(ANN) are a mimic models of human brain to solve a complex nonlinear problem. They are powerful pattern recognizers and classifiers, also their computing abilities have been proven in the fields of prediction, estimation and pattern recognition. Here, among them, the back propagation network and radial basis function network are used. Compositions of high-performance concrete mixes are eight components(water, cement, fine aggregate, coarse aggregate, fly ash, silica fume, superplasticizer and air-entrainer). Compressive strength and slump are measured. The results show that neural networks are proper tools to minimize the uncertainties of the design of concrete mixtures.