• Journal of Korean Society of Coastal and Ocean Engineers
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• v.22 no.4
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• pp.272-278
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• 2010

Some recent researches reported that high temperature rising decreases the carbonation depth of concrete, which is contrary to the previous research results. Carbonation has been known as a reaction between calcium hydroxide and carbon dioxide. But a few researches showed that the other cement hydrates as well as calcium hydroxide react with carbon dioxide. This paper investigates the influence of temperature on carbonation and the variation of $Ca(OH)_2$ and $CaCO_3$ by carbonation. In order to estimate the carbonation depth and the quantities of reactant and product of carbonation reaction, phenolphthalein testing and thermagravimetric analyzer test were conducted. The measurement of carbonation depth with temperature showed that the temperature increase from $20^{\circ}C$ to $30^{\circ}C$C in carbonation environment makes the carbonation depth larger, but the increase from $30^{\circ}C$ to $40^{\circ}C$ has a small influence on the carbonation depth. Comparing calcium hydroxide and calcium carbonate with temperature, the quantity of $CaCO_3$ of specimen carbonated at $30^{\circ}C$ is greater than that of specimen carbonated at $40^{\circ}C$ and the quantity of $Ca(OH)_2$ of specimen carbonated at $30^{\circ}C$ is similar to that of specimen carbonated at $40^{\circ}C$. This observation shows that there is the optimum temperature increasing carbonation depth and the optimum temperature is close to $30^{\circ}C$.

• Journal of the Korean Society for Railway
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• v.20 no.2
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• pp.241-247
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• 2017

Railway bridges with continuously welded rail have a limitation of span length due to track-bridge interaction. In order to overcome this, a sliding slab track system has been developed that comprises with a low-frictional sliding layer between the bridge deck and the track slab to isolate the longitudinal behavior between the bridge and the track. In this study, a real scale track system is prepared to experimentally evaluate the longitudinal frictional behavior. Applied loading rates were 0.2, 1.0, 5.0 and 10mm/min; vertical mass on the track are track slab only, 5,000 and 10,000kg added mass, respectively. Test results showed that the resulting frictional coefficients varied from 0.22 to 0.33. In addition, 10,000 cycle loadings were applied to simulate repetitive sliding to represent 30 years of service life. The frictional coefficient increase was measured and found to be 7% of that of the initial loading stage, which means that the sliding layer is adequate to provide low-frictional behavior for the sliding slab track system. Effects of changes of the frictional coefficient of the sliding layer were analyzed by rail-structure interaction analysis.

• Journal of the Korean Recycled Construction Resources Institute
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• v.11 no.3
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• pp.226-233
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• 2023

In this study, two phases were conducted to investigate the direct injection of gaseous CO₂ into cement mortar. The aim was to advance carbon capture, utilization, and storage (CCUS) technology by harnessing industrial waste CO₂ from the domestic ready-mixed concrete industry. In the first phase, the factors influencing the physical properties of cement mortar when using gaseous CO₂ were identified. This included a review of materials to achieve physical properties comparable to a reference formulation. As a result of this phase, it was confirmed that traditional approaches, such as adjusting the water-to-cement ratio, had limitations in achieving the desired physical properties. Consequently, the second phase focused on the optimization of CO₂-injected mortar. This involved studying the CO₂ application and mixing method for cement mortar. Changes in properties were observed when gaseous CO₂ was injected into the mortar. The optimal injection quantity and time to enhance the compressive strength of mortar were determinded. As a result, this study indicated that an extra mixing time exceeding 120 seconds was necessary, compared to conventional mortar. The optimal CO₂ injection rate was identified as 0.1 to 0.2 % by weight of cement, taking both flowability and compressive strength performance into account. Increasing the CO₂ injection time did not further enhance strength. For this approach to be employed as a CCUS technology, additional studies are required, including a microstructural analysis evaluating the amount of immobilized CO₂.

• Journal of the Korea Concrete Institute
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• v.21 no.3
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• pp.245-253
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• 2009

The importance of chloride ions in the corrosion of steel in concrete has led to the concept for chloride threshold level (CTL). The CTL can be defined as the content of chlorides at the steel depth that is necessary to sustain local passive film breakdown and hence initiate the corrosion process. Despite the importance of the CTL, due to the uncertainty determining the actual limits in various environments for chloride-induced corrosion, conservative values such as 0.4% by weight of cement or 1.2 kg in 1 $m^3$ concrete have been used in predicting the corrosion-free service life of reinforced concrete structures. The paper studies the CTL for blended cement concrete by comparing the resistance of cementitious binder to the onset of chloride-induced corrosion of steel. Mortar specimens were cast with centrally located steel rebar of 10 mm in diameter using cementitious mortars with ordinary Portland cement (OPC) and mixed mortars replaced with 30% pulverized fuel ash (PFA), 60% ground granulated blast furnace slag (GGBS) and 10% silica fume (SF), respectively, at 0.4 of a free W/B ratio. Chlorides were admixed in mixing water ranging 0.0, 0.2, 0.4, 0.6, 0.8, 1.0, 1.5, 2.0, 2.5 and 3.0% by weight of binder(Based on $C1^-$). Specimens were curd 28 days at the room temperature, wrapped in polyethylene film to avoid leaching out of chloride and hydroxyl ions. Then the corrosion rate was measured using the polarization resistance method and the order of CTL for binder was determined. Thus, CTL of OPC, 60%GGBS, 30%PFA and 10%SF were determined by 1.6%, 0.45%, 0.8% and 2.15%, respectively.

• Journal of the Korean GEO-environmental Society
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• v.11 no.1
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• pp.53-59
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• 2010

In seawater deposition condition, the corrosion and chemical attack of grouts are similar to those of concrete structure. Used in domestic MSG (Micro Silica Grouting) mixtured large amounts of silicate materials containing as cement powder is $8,000cm^2/g$ of the specific surface area or more due to the high hydration activity and high-strength, high durability, and features, $C_3A$ content of less than 5% to meet the standards chemical attack of seawater was evaluated as a cement material. Therefore, in this paper, with excellent seawater attack resistant MSG in combination with rapid hardening mineral was used, those of seawater characteristics were evaluated experimentally. Typically, sodium-silicate minerals or rapid hardening cements are used in domestic. About the homogel specimens with combination of MSG and rapid hardening agents for compressive strength, weight and length change characteristics were evaluated experimentally, and so we could present the excellent seawater resistant grouts combination.

• Journal of the Korea Institute of Building Construction
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• v.11 no.6
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• pp.627-633
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• 2011

Evaluation of the amount of chloride ion coming from the sea is very important in assessing the life expectancy of Reinforced Concrete structures. Developed in Japan, the incoming salt collector has been used to this day. Unfortunately, the incoming salt collector has had a bad reputation, which is caused by backward wind. Backward wind causes a reduction of the amount of salt collected in collector's gauze. The collector was developed to eliminate the effect of backward wind. Simulation test in the laboratory and site measurement were performed to determine the amount of incoming salt according to the height. The performance was verified through analytic and experimental methods.

• Journal of the Korea Concrete Institute
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• v.21 no.6
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• pp.713-718
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• 2009

Advanced industries-IT, BT, NT and ET are rapidly developing in 21 century. And the cement industry is becoming the principal factor in air pollution because of the creation of $CO_2$ during manufacturing. Also, the cement industry will be faced with a crisis due to the exhaustion of natural resources. In this study, nano cement by Bottom-up method of a chemical synthesis was developed. The generation of $CO_2$ during the plasticization process of cement manufacturing was avoided. The purpose was to produce building materials that have both high strength and durability as the high value-added growth engine industry of the 21 century. The nano cement was developed using hydrothermal synthesis. This is a method of mixing after ripening, by manufacturing the high density gel and low gel, which does not require special test equipment or pressure conditions to produce. Particle size, SEM, EDX, and porosity tests were conducted. This study investigated the compressive strength of concrete with various compositions. Specimens were tested for compressive strength at 3, 7, 14 and 28 days. The medium-sized (50% by weight) cement particles created by chemical synthesis were less than 168 nm. The compressive strength of the mortar prepared using this cement was 53.9 MPa. But it was judged that succeeding study will be necessary for development of nano building materials with high ability and economical analysis.

• Journal of the Korea Concrete Institute
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• v.27 no.6
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• pp.633-640
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• 2015

Polymer cement slurry (PCS) is made from organic polymer dispersion and cement has good adhesion to steel, waterproofness and acid resistance due to being of polymer films formed in cement slurry. The purpose of this study is to evaluate the bond strength of coated rebar by polymer cement slurry made of EVA and ultra high-early strength cement. The test pieces are prepared with EVA polymer dispersion and ultra high-early strength cement having four types of polymer-cement ratios, four types of coating thicknesses and four curing ages, and tested for the bond strength test. From the test results, in general, bond strength of PCS-coated rebar is better than that of uncoated rebar and epoxy-coated rebar. It is also high bond strength at curing ages of 7-day, and coating thicknesses of $75{\mu}m$ and $100{\mu}m$. The maximum bond strength of PCS-coated rebar with ultra high-early strength cement and EVA at polymer-cement ratio of 80%, and coating thickness of $100{\mu}m$ is about 1.32 and 1.38 times respectively, the strength of uncoated rebar and epoxy-coated rebar. It is apparent that the curing age, coating thickness, type of polymer and cement are very important factors to improve the bond strength of PCS-coated rebar to cement concrete. We can have basic information that PCS-coated rebar with polymer-cement ratio of 80% or 100% and coating thickness of $100{\mu}m$ at curing age of 1-day can replace epoxy-coated rebar.

• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.3
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• pp.65-73
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• 2013

Recently the exterior attaching reinforcement method is being often used by using FRP (Fiber Reinforced Polymer) as a method of strengthening concrete structure. this FRP exterior attaching reinforcement method has several advantages like high intensity, stiffness, good durability and easy installment comparing to its weight. but its structure is airtight covered by reinforcement material whose water permeability is low and water can't be discharged, thus it may provoke a damage to the structure after a long while. the main purposes of this study are to develop GFRP reinforcement material which can discharge the surface water properly and to measure its special functions. for this, we have changed the normal reinforcement material to water permeable structure and measured its water permeance modulus by an indoor test which shows the process of water permeance with the parameter of contained GFRP quantity. also tried to verify the measured value of the water permeance modulus in theory by analyzing the numbers on water permeance process. the test result showed that the biggest quantity of water, 0.5129 g/h $m^2$ was discharged when the fiber contained quantity reached at 75% and the tensile strength was also biggest by 476.6MPa at 75%, so it appeared that COSREM GP panel with 75% fiber contained quantity is the best in ventilation and structure.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.1A
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• pp.183-190
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• 2006

Minimizing the self weight of long-span deck slabs is one of the key factors for the practical and economic design of a composite two-girder bridge. In this paper, the minimum design thickness and rebar details of prestressed concrete deck slabs for composite two-girder bridges with girder span length from 4 m to 12 m are studied based on the safety and serviceability. The bridge deck slab with minimum thickness is designed as a one-way slab considering orthotropic behavior. Then fatigue safety of the deck slab is examined. Serviceability requirements for the deck slab such as deflection and crack width limits are also examined. The result shows that rebars with diameter less than 16 mm is recommended for the improved fatigue behavior, and, for the deck slab with span length longer than 8 m, the deflection limit governs the minimum design thickness. The result also shows that, for the deck slab with span length longer than 4 m, the distribution rebar requirement in the current Korea Highway Bridge Design Code is not sufficient to maintain the structural continuity in bridge axis as expected from the deck slab with span length shorter than 3 m.