• Proceedings of the Korea Concrete Institute Conference
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• 2009.05a
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• pp.545-546
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• 2009

This study was performed to prove the possibility of utilizing short plastic fibers made for recycled polyethylene terephthalate (RPET) as a structural material. To measure of crack control capacity, restrained drying shrinkage cracking test was performed. In order to verify the capacity of RPET fiber, it was compared with poly propylene (PP) fiber, most widely used short synthetic fiber, for fiber volume fraction of 0%, 0.5%, 0.75%, and 1.0%.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2006.11a
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• pp.5-8
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• 2006

This study investigates the field application, Songdo the # 1st WORLD, on zero-crack construction of the fundamental mass concrete using double bubble sheets and applying low heat mixture. Experimental results of hydration heat analysis showed that crack modulus of concrete incorporating 20% of blast furnace slag cement was 1.0 in 120 hours, representing 50% probability of crack occurrence, thus requiring additional measures. As for a curing method, a specimen insulating two layers of vinyl chloride+double bubble sheets exhibited only $16.5^{\circ}C$ difference between upper and lower sections, and it also showed favorable workability as well as competitive economic side. Therefore it was determined to use it for curing method in this field. For the curing results of practical field, using 2 layers of vinyl chloride+double bubble sheets and applying low heat mixture on the fundamental mass concrete in 3A residential building exhibited less than only $15^{\circ}C$ difference between surface and center section of that in 5 days elapse and less than $20^{\circ}C$ in 9 days. This means that the crack by hydration heat was prevented, and other fields structures also resisted the plastic shrinkage by insulating the vinyl, sinking crack by second temping, even drying shrinkage by the mixture of low unit water. Therefore the crack on the placement has not been found so far, since the construction was started before 6 month.

• Journal of the Korea Concrete Institute
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• v.18 no.1 s.91
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• pp.57-64
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• 2006

The crack presented in concrete structures causes a structural defect, the durability decrease, and external damages etc. Therefore, it is necessary to improve durability through the effort to control the crack. Fluosilicic acid($H_2SiF_6$) is recovered as aqueous solution which absorbs $SiF_4$ produced from the manufacturing of industrial-graded $H_3PO_4$ or HF. Generally, fluosilicates prepared by the reaction between $H_2SiF_6$ and metal salts. Addition of fluosilicates to cement endows odd properties through unique chemical reaction with the fresh and hardened cement. Mix proportions for experiment were modulated at 0.45 of water to cement ratio and $0.0{\sim}2.0%$ of adding ratio of fluosilicate salt based inorganic compound. To evaluate correlation of concrete strength and adding ratio of fluosilicate salt based inorganic compound, the tests were performed about design strength(21, 24, 27 MPa) with 0.5% of adding ratio of fluosilicate salt based inorganic compound. Applications of fluosilicate salt based inorganic compound to reduce cracks resulted from plastic and drying shrinkage, to improve durability are presented in this paper. Durability was evaluated as neutralization, chloride ion penetration depth, freezing thawing resistant tests and weight loss according reinforcement corrosion. It is ascertained that the concrete added fluosilicate salt based inorganic compound showed m ability to reduce the total area and maximum crack width significantly as compared non-added concrete. In addition, the durability of concrete improved because of resistance to crack and watertightness by packing role of fluosilicate salt based inorganic compound obtained and pozzolanic reaction of soluble $SiO_2$ than non-added concrete.

• Journal of the Korea Concrete Institute
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• v.25 no.3
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• pp.347-354
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• 2013

Recently, crushed fine aggregates are being widely used due to the shortage of natural sand. In Korea, the amount of fine particles under 0.08 mm contained in crushed fine aggregates is restricted to be less than 7%, which is similar to the regulations of ASTM but is still very strict compared to the regulations of the other nations. In addition, the crushed aggregates already have in them about 20% of fine particles under 0.08 mm which occurs while they are crushed. The fine particles are not easy to wash out, and also to maximize the use of resources it is deemed necessary to review the possibility of enhancing the limit of the amount of fine particles. Therefore, this study conducted experiments to analyze the characteristics of fine particles under 0.08mm and their influence on the properties of concrete. Experiments using silt and cohesive soil were also done for comparison. In the experiments on fine particles, the methylene blue value was more in the soil dust contained in silt and cohesive soil than in the stone powder contained in crushed fine aggregates. Also, the methylene blue value had a close correlation with packing density and liquid & plastic limit. In the experiments done with concrete, the quantity of high range water reducing agent demanded to obtain the same slump increased as the fine particle substitution rate heightened. However, in the experiment which used stone powder testing the compressive strength and tensile strength of concrete in the same water-cement ratio, there was little change in strength with less than 20% addition of fine particles among the fine aggregates, and no meaningful difference in the amount of drying shrinkage of concrete.

• International Journal of Highway Engineering
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• v.11 no.2
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• pp.99-109
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• 2009

Fine-size exposed aggregate portland cement concrete pavements (FEACP) have surface texture of exposed aggregate by removing upper 2$\sim$3mm mortar of surface of which curing is delayed by using delay-setting agent. FEACPs have advantages of maintaining low-noise and adequate skid-resistance level during the performance period than general portland cement concrete pavements. It is necessary to ensure the durability environmental loading to prevent unexpected distress during the service life of FEACP. In the process of curing, volume change accompanied change in by moisture and temperature could be an important cause of crack in concrete to construct for successful FEACP, The use of chloride containing deicer may accelerate defects of concrete pavement, such as crack and scaling. This study aim to evaluate environmental loading resistance of FEACP, based on the estimation of shrinkage-crack-control-capability by moisture evaporation and scaling by deicer in freeze-thaw reaction.

• Journal of the Korean Recycled Construction Resources Institute
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• v.7 no.3
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• pp.210-215
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• 2019

Concrete members with wide surface area are vulnerable to cracking due to material behavior such as hydration heat and drying shrinkage. Recently many researches have been performed on improvement of strength and cracking resistance through fiber reinforcement, which are mainly focused on enhancement of tensile strength against cracking due to material behavior. In this paper, CFs(Cellulous Fibers) are manufactured for slurry type, and the engineering properties in cement mortar incorporated with CFs are evaluated for flow-ability, compressive, and flexural strength. Through SEM analysis, a pull-off characteristics of CF in matrix are analyzed. With CF addition of $0.5kg/m^3{\sim}1.0kg/m^3$, flexural strength is much improved and enough toughness of pull-off is also observed unlike plastic fiber containing smooth surface.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.1A
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• pp.101-108
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• 2009

The performance of high-early strength pavement concrete for large areas is influenced by the physical and chemical environment during service life. Generally, penetration, diffusion, and absorption of harmful materials that exist outside the concrete cause damage to its structure. Thus, we have to use a mixture for durability to keep the required quality for the planned service life. Moreover, in using high-early-strength cement and accelerators, a high heat of hydration to create the initial strength can cause cracks. Based on evaluations from optimal mix proportions of high-early-strength pavement concrete for large areas, we conducted water permeability, abrasion resistance, freeze-thaw, plastic, drying, and autogenous shrinkage tests. Test result showed that a mix of accelerator and PVA fibers showed excellent performance.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.633-636
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• 2008

Concrete structures are occur many various deteriorations in the course of time and many efforts have progressed to improve on performance of concrete. The purpose of this study is to evaluate the durability of latex modified mortar in order to repair concrete structure which are happened deterioration. In this study, we tested plastic shrinkage, drying shirnkage, repeated freezing and thawing, permeability and resistance of chemical solution. Latex modified mortar and two kinds of sprayed polymer mortar used on durability test. As a result of test, latex modified repair mortar was exhibited durablilty improvement compared to the conventional sprayed polymer mortars. It is judged the fact that latex modified mortar have no problem in site application but additionally many research will be necessary.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.557-560
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• 2008

Fiber reinforcement has been being widely used in concrete to enhance the mechanical properties and to reduce the micro-cracking caused by plastic and drying shrinkage. While researches has been focused on the benefits of fiber reinforcement, the properties of fiber reinforced concrete are strongly dependent on the type, shape and the amount of fibers in concrete. In this study, the resistance of nylon fiber reinforced concrete against the chloride ion penetration was experimentally observed by NT Build 492. The test results showed that the addition of nylon fiber has little effect on the change of the resistivity of concrete to the chloride ion penetration.

• Journal of the Korea Institute of Building Construction
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• v.15 no.3
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• pp.265-271
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• 2015

This study is intended to produce a PC (Precast Concrete) member without a steam curing process in developing the high early strength concrete satisfying the condition of 10MPa in compressive strength at the age of 6 hours, and is intended to ensure economic feasibility by increasing the turnover rate of concrete form. Hence, high early strength cement with high $C_3S$ content and the hardening accelerator of powder type accelerating the hydration of $C_3S$ was used. And the properties of concrete were evaluated according to the hardening accelerator mixing ratio (0, 1.2, 1.6, 2.0). No big difference was found from the tests of both slump and air content. When 1.6 % or higher amounts of the hardening accelerator were mixed, the compressive strength of 10MPa was achieved at the age of 6 hours. From the test results of autogenous (drying) shrinkage and plastic shrinkage, it can be seen that there was a difference according to hydration reaction rate due to the addition of the hardening accelerator. However, it was shown that no problem arose with crack and durability. And it was shown that resistance to freezing-thawing, carbonation, and penetration were excellent.