• Journal of the Korean Recycled Construction Resources Institute
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• v.2 no.1
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• pp.136-143
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• 2006

In this study, recently it is urgently required that demolition waste concrete has to be recycled on the construction because urban development is accelerated and redevelopment project is rapidly expanded, production quantity of construction and demolition waste concrete is being increased. As a results of drying shrinkage test under restrained and unrestrained condition, although workability and mechanical properites of concrete using HQRS were similar to that of concrete using natural sand, there were a great difference in deformation characteristic of dry shrinkage according to replacement ratio of HQRS. And, it makes sure that use of HQRS instead of partial nature sand was effective because drying shrinkage of concrete using 30 volume percentage of HQRS was smaller than that using only natural sand. Therefore, it is the objective of this study to provide the fundamental data about the re-application as an analysis of the drying shrinkage characteristics of concrete using HQRS and it is able to creta a high value-added by using HQRS.

• 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.

• Journal of the Korean Ceramic Society
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• v.42 no.3 s.274
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• pp.198-204
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• 2005

Fluosilicate salts based hydration heat reducer(SWP-HR), used in this study, is composed of fluosilicate salts, soluble silica, aromatic polymer condensate and nitrate salt based inorganic compound with latent heat property. Effects of SWP-HR addition on the hydration heat and anti-crack property of cement mortar were investigated. Adiabatic hydration temperature and drying shrinkage length of SWP-HR added cement mortar had a tendency to decrease compared to those of cement mortar without SWP-HR addition. Also, it was confirmed through crack pattern experiment of plate-form specimen for elucidating crack-reducing characteristic that anti-crack property of SWP-HR added cement mortar was improved.

• Journal of the Korea Concrete Institute
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• v.18 no.5 s.95
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• pp.631-637
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• 2006

In this study, fundamental properties such as fresh and hardened performance of concrete mix(specification : 25-24-18) added fluorine-silicate hybrid based crack reducing agent(FS) were measured. Addition of FS ranged from 0.5% to 2.0% at intervals 0.5% based on cement weight. Adequate dosage(0.5%) of FS derived from basic properties measurements applied and compared resistance for shrinkage crack. The permeability of concrete in the absence(24-S-0.0) and presence(24-S-0.5) of evaluated at a mock-up sized concrete. Concrete added FS improved resistance for shrinkage crack and consequently crack number, length and area decreased to $50{\sim}74.4%$ compared non-added. As well, by the addition of FS, the resistance for permeability and penetration depth to concrete surface region increased 67% and 40%, respectively. Therefore it was confirmed that shrinkage crack resistance and permeability of concrete could be improved by the addition of FS.

• Journal of the Korean Recycled Construction Resources Institute
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• v.2 no.1
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• pp.19-25
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• 2014

The purpose of this study is to establish experimentally the mechanical properties of fiber reinforced concrete using kenaf dosages and propose the usable method of kenaf fiber in the concrete industry as natural fiber materials. Kenaf fiber help make the concrete strength including tensile and flexural stronger, more resistant to plastic and drying shrinkage, less amount of carbon dioxide because of having a rough surface and excellent tensile strength of fiber and improving the concrete's corrosion resistance. It is to select the kenaf dosages of 4 cases (0, 0.3, 0.6 and $0.9kg/m^3$ and perform various tests including slump, air content, plastic and drying shrinkage, flexural and tensile strength for fiber reinforced concrete. The results of this study are as follows : In case of increasing kenaf fiber dosages, show the slump decrease and air content increase, also take effect results for increasing concrete strength including flexural and tensile, decreasing plastic and drying shrinkage. therefore, considered test results and cost, the optimum dosages of kenaf fiber is proposed about $0.6kg/m^3$ and need to study on the site application considering concrete quality and another compared tests.

• Journal of the Korea Institute of Building Construction
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• v.16 no.3
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• pp.201-209
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• 2016

This study is to examine experimentally on the engineering properties of fiber reinforced concrete using kenaf(KN) fiber and another organic fibers for comparing test, and propose the usable method of KN fiber as an natural fiber in the concrete industry. It is to select 4 contents(0, 0.3, 0.6 and $0.9kg/m^3$) of KN fiber and 4 organic fibers (Jute, Cellulose, Polypropylene and Nylon). For this study, it is to perform various tests including slump, air content, plastic and drying shrinkage, flexural and tensile strength, carbonation depth for the fiber reinforced concrete according to contents of KN fiber and 4 organic fibers. The results of this study are as follows : In case of KN fiber contents $0.6kg/m^3$, it shows the effective results from increasing concrete strength including flexural and tensile, from decreasing plastic and drying shrinkage, carbonation depth. Also KN fiber is confirmed having excellent performances by comparing with test results of another organic fibers as same contents $0.6kg/m^3$. Therefore, considering concrete test results, cost and environment, KN fiber is proposed as the optimum contents in the range of $0.6kg/m^3$ and an effective fiber materials, and needs to keep up these study on the site application.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.797-800
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• 2008

To decrease the usage of cement, the pozzolan reaction materials are used as a mineral admixture. Hwang Toh which is broadly deposited in Korea is well known as a environment friendly material and the activated Hwang Toh which has the property of pozzolan reaction is practically used as a mineral admixture of concrete. PET fiber which is made by recycled PET bottle controls micro crack in concrete. But the study about concrete mixed with reinforcing fiber is not enough and the property of Hwang Toh concrete mixed with PET fiber is more complicated case. So this study performed drying shrinkage experiment to analyse mechanical property of Hwang Toh concrete mixed with PET fiber.

• Journal of the Korea Institute of Building Construction
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• v.17 no.5
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• pp.445-451
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• 2017

Because of the supply-demand problem of aggregate, recently, the construction sites using 100% crushed sand are increasing and the use of low quality aggregate such as farmland sand is increasing too. When the low quality aggregate is used, the various quality defect of concrete such as the strength reduction, the increase of shrinkage and bleeding can be occurred. Therefore, in this study, the performance improvement PC admixture was developed to minimize the quality defect of plain concrete of basement parking area, when the low quality aggregate was used at the plain concrete of basement parking area. The slump loss to elapsed time test, the compressive strength test, the bleeding test and the drying shrinkage test were carried out.

• Journal of the Korean Recycled Construction Resources Institute
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• v.2 no.1
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• pp.10-18
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• 2014

This study carried out to evaluate the hydration heat analysis and fundamental characteristics such as air content, slump, compressive strength and dry shrinkage according to concrete with premixed cement, ternary concrete and OPC concrete for using concrete with premixed cement. The results of experiment are founded that concrete with premixed cement have sufficient performances such as workability, compressive strength and dry shrinkage. Also, the results of hydration heat analysis are founded that concrete with premixed cement have more performance than ternary concrete and OPC concrete at a point of view for the quality control such as thermal crack reducing and economic benefit. Therefore, it is desirable that concrete with premixed cement should be used to rise durability performance and convenience of maintenance.

• Journal of the Korean Geotechnical Society
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• v.33 no.11
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• pp.97-104
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• 2017

A bentonite mixing with local soil widely used as liner layer for landfill should have low permeability less than $1{\times}10^{-7}cm/s$. But there are several limitations of bentonite used as liner layer, such as drying shrinkage cracking, ineffective waterproof ability under salt water condition like flocculation under sea water. The purpose of this research is the development of a salt resistance bentonite by mixing sepiolite and guar gum to overcome the weak points of bentonite to get high water resistance capacity and permeability coefficient below $1{\times}10^{-7}cm/s$ under salt water condition. After having performed drying shrinkage cracking test, swelling index test, compaction test, and hydraulic conductivity test we confirmed the optimal mixing ratio of materials and evaluated the performance of materials.