• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.513-516
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• 2008

Recently, a demand for reduction of construction cost by reducing construction period is increasing because of the slump of the construction business, the increasing price of raw-materials and the enforcement of after-sale system. As a method of reducing construction period, many construction companies usually apply a method of reducing curing period. But if they use an existing early strength cement or admixture, they spend a heavy cost on materials and there are many problems, such as a heat of hydration and a loss of workability. The purpose of this research is a reduction of construction cost by reducing construction period as a earlier removal time of form. To check up application of concrete using high early strength binder and admixture, comparative tests were carried out with concrete using an existing early strength cement or admixture such as tests of diurnal variation, setting time and compressive strength.

• Resources Recycling
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• v.28 no.6
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• pp.54-63
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• 2019

This study investigated on the compressive strength and the length change test with using the waste glass and graphene oxide for recycling the waste glass as the aggregate. Curing on 3-day and 7-day, the compressive strength was enhanced as the usage of waste glass was increased. Especially, the huge difference in the compressive strength was observed when the amount of substituting on the waste glass was used on 10~50%. With 50% of waste glass condition, the compressive strength was portionally enhanced as the usage of graphene oxide was increased and its value was 42.6 N/㎟ with 0.2% of graphene oxide. In terms of the length change test, the use of high content of waste glass led length change value to increase, but it was dropped down as the portion of waste glass was above 50%. Furthermore, in the case of using 50% of waste glass, the use of high amount of graphene oxide tended to decrease the length change value. That is, graphene oxide may contribute on boosting the cement hydration reaction and blocking the ion's movement.

• Journal of the Korea Institute of Building Construction
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• v.16 no.4
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• pp.289-296
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• 2016

In this study, the self-healing effect of a fiber-reinforced cement composite (FRCC) was examined using a drying-wetting test and an outdoor exposure test. The influence of various curing conditions on the self-healing effect of the FRCC was also investigated. The effect of self-healing was evaluated using a permeability coefficient and by investigating the cracks using a optical microscope. The results confirmed that the FRCC was capable of self-healing under a long wetting time and a low drying temperature. In addition, watertight performance by self-healing was shown to have a significant influence on wetting time. Meanwhile, this self-healing effect was enhanced by hydration as a result of rainfall when the FRCC was put under actual environmental conditions. Moreover, it was determined that cracking self-healing can be improved by using the appropriate admixture materials.

• Journal of the Korean Recycled Construction Resources Institute
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• v.10 no.3
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• pp.343-350
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• 2022

In recent years, nanomaterials, such as nano-silica, carbon nanotubes, and graphene oxide (GO), have been suggested to improve the properties of the interfacial transition zone (ITZ) between aggregates and cement pastes, which has most adversely affected the strength of quasi-brittle concrete. Among the nanomaterials, GO with superior dispersibility has been reported to be effective in improving the properties of ITZ of normal-strength concrete by forming interfacial chemical bonds with Ca²⁺ ions abundant in ITZ. In this study, the effect of GO on the properties of ITZ in the high-strength mortar was elucidated by calculating the change in hydration heat release, ITZ thickness, and the porosity around ISO sand, which was obtained with isothermal calorimetry tests and scanning electron microscope image analysis, respectively.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.697-700
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• 2008

Recently, high strength, flowability, and durability of concrete were required according to increase of large scale and high rise structure. However, cracks occurred easily on the high performance concrete. In this reason, using expansion agent for reducing shrinkage cracks were increased, but it did not consider on durability of high performance concrete. Accordingly, this study1 investigated the resistance of shrinkage and damage form salt by mixing CSA expansion agent on the blast-furnace slag cement and mixed cement for the low heat of hydration by three components. The cases that 8% of expansion agent was mixed and the proportion was OPC were expanded till 43.7 times compared with control concrete. For the resistance to the damage of salt, it was improved when mixing ratio was incresed and the maximum size of coarse aggregate growed bigger. In this study, the resistance to the damage of salt of the cases that 8% of expansion agent was mixed was improved about 16% compared with control concrete.

• Journal of the Korean Ceramic Society
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• v.44 no.9
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• pp.529-535
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• 2007

Calcium oxide has been used as a demolition agent in fracturing rocks and old concrete structures, etc. With the agent, demolition work can be done in safety without a noise, vibration and any other pollution, since high expansive pressure is obtained gradually by only mixing the agents with water and pouring the slurry into boreholes. But application of the non-explosive demolition agent is a time-consuming job, especially in winter. Essentially, this problem is related to the reaction rate of calcium oxide with water. This study examines the influence of additives such as cement and anhydrite on expansion pressure of calcium oxide at different curing temperatures. The expansion pressure of calcium oxide began to increase steadily with the rise of the curing temperature. When mixing calcium oxide alone with water, blown-out shot occurred. But as additives were added to calcium oxide, the reaction of calcium oxide delayed and the expansion pressure showed gradual increment. Especially, anhydrite showed a superior delaying effect than cement on the reaction of calcium oxide.

• Journal of the Korean Recycled Construction Resources Institute
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• v.11 no.3
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• pp.276-281
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• 2023

Water pipes manufactured using existing Portland cement suffer from the problem of rapid deterioration and reduced durability due to the hydration product of cement being vulnerable to acids. Therefore, in this study, water pipes were manufactured using slag and fly ash, which are industrial by-products from various industries, and their characteristics were analyzed. As a result of the experiment, slump in unhardened concrete tended to increase due to the ball bearing action of fly ash, and the amount of air was reduced due to unburned coal, indicating that measures for frost resistance were needed. In addition, the initial strength of the compressive strength was increased through steam curing, and the results were equal to or better than OPC when mixing more than 50 % of slag. The acid resistance results showed that the mass reduction rate was less than 5 %, showing excellent durability performance, and the bending failure load of the water pipe also exceeded the KS standards, so it is judged to be commercializable.

• 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 Academia-Industrial cooperation Society
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• v.18 no.8
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• pp.338-343
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• 2017

In this study, blast furnace slag powder was used in concrete to help reduce carbon dioxide emissions and to recycle industrial waste. Blast furnace slag powder is a byproduct of smelting pig iron and is obtained by rapidly cooling molten high-temperature blast furnace slag. The powder has been used as an admixture for cement and concrete because of its high reactivity. Using fine blast furnace slag powders in concrete can reduce hydration heat, suppress temperature increases, improve long-term strength, improve durability by increasing watertightness, and inhibit corrosion of reinforcing bars by limiting chloride ion penetration. However, it has not been used much due to its low compressive strength at an early age. Therefore, this study evaluates the effects of steam curing for increasing the initial strength development of concrete made using slag powder. The relationship between compressive strength, SEM observations, and XRD measurements was also investigated. The concrete made with 30% powder showed the best performance. The steam curing seems to affect the compressive strength by destroying the coating on the powder and by producing hydrates such as ettringite and Calcium-Silicate-Hydrate gel.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.2
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• pp.78-85
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• 2020

Shotcrete concrete is generally used in the form of ready-mixed concrete products using type I ordinary portland cement(hereinafter referred to as OPC) and about 5% of accelerator mixed separately in the field. In this study, we tested the effect of OPC fineness and SO₃ content on a penetration resistance, compressive strength of binder for shotcrete using calcium aluminate type accerlerator. And we analysed hydrates and pore structure effects on mortar performance. In the future, it is expected to be useful for manufacturing optimized OPC as a binder for shotcrete.