• 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 Institute of Building Construction
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• v.19 no.6
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• pp.503-510
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• 2019

Recently, construction technology of RC structures must be examined for creep in concrete. The factors affecting the creep prediction of concrete and the results of creep in domestic construction field were reviewed. The longer the creep test period and the higher the compressive strength, the higher the creep prediction accuracy. The higher the curing temperature, the higher the initial strength development of the concrete, but the difference in the creep coefficients increased over time. Based on the results of creep evaluation in the domestic construction field and lab. tests, a modified predictive model that complements the ACI-209 model was proposed. In the creep prediction of real members using general to high strength concrete, the test period and temperature should be considered precisely.

• Journal of Energy Engineering
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• v.27 no.2
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• pp.55-60
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• 2018

In this study investigated the Controlled Low Strength Materials using coal ash and steel slag(KR slag) as the main material in the thermal power plant classified as waste resource. Bottom ash and KR slag are mixed at a ratio of 7: 3 to expand the use of industrial by-products through carbonate($CO_2$-fixation) reactions and inhibit the exudation of heavy metals. The results showed that the water content increased as the content of bottom ash increased. It was confirmed that as the powder content increased, the bleeding ratio decreased. Also, as the content of one kind of ordinary portland cement (OPC) decreased, activation of hydration reaction decreased and compressive strength decreased. However, when the mixed composition is appropriately adjusted, the compressive strength of 2.0 MPa required for the controlled low-strength material can be satisfied.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.397-400
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• 2008

MgO powder-mixed concrete, expanded at the lower temperature around $850{\sim}1000$ degree celcius, might have long-term expansibility, which could remunerate for the contraction of concrete with delayed expansion, and through the process, the crack resistance of mass concrete might be improved. Currently used expandable concrete additive has three different types : CSA, CaO and MgO. In this study, therefore, such tests as carbonation, chloride diffusivity, freezing-thawing resistance and sulfate resistance after 56 days' curing were implemented and compared the results with the concrete with no MgO mixed to evaluate the durability of 5% MgO-mixed concrete after longer period of time. The degree of hydration for the MgO-mixed cement paste was analyzed after 1 day, 3 days, 7 days, 28 days, and 56 days using SEM, XRD, DSC.

• Journal of the Korea Concrete Institute
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• v.14 no.2
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• pp.249-256
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• 2002

High performance concrete is prone to large autogenous shrinkage due to its low water to binder ratio (W/B). The autogenous shrinkage of concrete is caused by self-desiccation as a result of water consumption by the hydration of cement. In this study, the autogenous shrinkage of high performance concrete with and without fly ash was Investigated. The properties of fresh concrete, slump loss, air content, and flowability as well as the mechanical properties, compressive strength and modulus of elasticity, were also measured. Test results was shown that the autogenous shrinkage of concrete increased as the W/B decreased. For the same W/B, the autogenous shrinkage of high strength concrete with fly ash was considerably reduced although the development of its compressive strength was delayed at early ages. Furthermore, the autogenous shrinkage and compressive strength of high strength concrete were more rapidly developed than those of normal strength concrete. It was concluded that fly ash could improve the quality of high strength concrete with respect to the workability and autogenous shrinkage.

• Journal of the Society of Disaster Information
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• v.10 no.4
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• pp.566-571
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• 2014

Recently, with concentrated social and engineering interests on durability, diversified subsequent researches have been progressed. The Chloride-induced corrosion, carbonation, freeze-thaw etc, deterioration factors of concrete act to concrete not privately but complexly, Fly ash is most frequently used admixture which is using a reduction method of deterioration. And the fly ash effects on improvement of durability with enhancement of fluidity, decrease of crack with reduction of hydration heat, promotion of long-age strength and have a economic advantage which replaces cement as a binding material. But, fly ash have different qualities and occasionally reduce the durability and strength by adhesion of AE admixture with unburned carbon powder etc. In this study, the experiments will take about various replacement ratio of fly ash concrete, and will analyze, consider the results, after these will verify applicability and validity as admixture and binding material.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.5
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• pp.127-132
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• 2018

The amount of generated Circulating Fluidized Bed Combustion ash (CFBC ash) is annually increasing, but most CFBC ash has been landfilled and discarded due to the limited utilization. The major chemical compositions of CFBC ash are $SiO_2$, CaO and $CaSO_4$, which could form hydration products by reacting with water as self-cementing property such as cement. The purpose of the this study is to derive the optimal mix proportions to improve polymer-modified mortar with the use of CFBC ash which has the self-cementing property. In order to develop polymer-modified mortar, three mix proportions were determined, and fundamental properties for the mixtures were obtained. As a result, the optimal mixture containing 10 percent of silica fume, 1.0 percent of polymer and 3.5 percent of expansive additives were proposed in this study.

• Journal of the Korea Institute of Building Construction
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• v.13 no.2
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• pp.131-138
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• 2013

This study was carried out to investigate the possibility of using basalt powder sludge instead of sand in a normal cement dry mortar as a way to recycle basalt powder sludge, which is a waste product from the manufacturing a process of basalt in Jeju. Basic performance evaluations of the dry mortar material included a compressive strength test, a flexural strength test, and SEM to observe the micro structure. The compressive and flexural strengths were increased to a replacement ratio of 21% of basalt powder sludge, whereby a strength enhancement of about 40% greater than that of normal dry mortar was shown. However, the creation of hydration products affected the replacement ratio of the basalt powder sludge. The possibility of using basalt powder sludge waste was identified in this study, and results showed that the basalt powder sludge waste could be used as a material for a secondary product of concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.601-604
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• 2008

When the concrete is placed, the water, needed for hydration of the cement, is under 30% of W/C including bound and gel water. However, as minimum water content cause bad workability, the W/C have to be higher. Therefore, fresh concrete produce 10${\sim}$20% extra water. As those water remain entrapped air in the concrete, life of the structure is reduced because of the degradation caused by entrapped air. For that reason, if extra water is eliminated, it will be great to improve the durability of the structures. Therefore, this study was performed to verity the fundamental properties through the experiment on the dewatering system using the euro form for eliminating extra water. When the dewatering form was applicated, the compressive strength was increased by 16% than those of normal form. However, the increasing rate of compressive strength got lower as the height is higher. In terms of ultrasonic pulse speed and surface roughness, the dewatering form showed better results than the normal one.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.637-640
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• 2008

Since the first underground LNG tank was constructed in Incheon, continuously many LNG tanks were constructed in Tongyoung and Pyongtaek. The storage capacity of LNG tank increased by 200,000kl and the structure size and the concrete mixing design has changed. The crack of concrete induced by the heat of hydration is a serious problem, particularly in massive concrete structures. In order to control the thermal crack of massive concrete, the low heat portland cement(type Ⅳ) is applied to bottom annular part, bottom central part, lower walls and ring beam. In this study, in order to thermal crack control about the LNG tank wall(lot 8 of #16 Pyongtaek LNG tank) in winter, analysed the concrete temperature, the extention of term, the curing condition and the concrete mixing design. When the concrete mixing design is changed from OPC+FA25% to LHC+FA25%, the thermal crack index is 1.33 and satisfied with construction specifications(over 1.2).