• Proceedings of the Korea Concrete Institute Conference
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• 2002.05a
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• pp.643-648
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• 2002

A research for recycling the demolished-concrete as concrete aggregate has been concerned in all over the world. There, however, are some problems that qualities of recycled aggregates are not only largely different, but also mechanical properties of recycled aggregate concrete decrease a little in comparison with that of natural aggregate concrete. In this study, the resistance of freezing and thawing of concrete using source-concrete recycled aggregate(SRN) and demolished-concrete recycled aggregate(DRA) was investigated. Futhermore a research for improvement of freeze and thaw durability of recycled aggregate concrete was performed. Relative dynamic modulus of elasticity of SRN and DRA recycled aggregate concrete was dropped 60% before 150 of freezing and thawing cycle, and was much lower than that of control concrete. Relative dynamic modulus of elasticity of recycled aggregate concrete was increased to decrease water-cement ratio, but the freeze and thaw durability of recycled aggregate concrete was not enough improved. Futhermore, when metakaolin and silica fume were repalced, the freeze and thaw durability of recycled aggregate concrete containg metakaolin was more improved than that of silica fume.

• The Journal of Engineering Geology
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• v.13 no.3
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• pp.345-358
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• 2003

Recently, the reuse of coarse aggregate derived from demolished concrete was introduced into practice with two environmental aspects: protection of natural sources of aggregate and recycling of construction waste. However, recycled aggregate has been used for the very limited application such as subbase material for pavement and constructional filling material because it was considered as low quality constructional materials. In the present study, in order to examine the possibility that recycled aggregate can be used for concrete mixing, we conducted various experimental tests to identify mineralogical, chemical and mechanical properties of recycled aggregate and to determine the workability and mechanical properties of recycled aggregate concrete (RAC). The cement paste and mortar contained in recycled aggregate significantly affect the basic mechanical properties of aggregate and the workability and mechanical properties of RAC. However, RCA mixed with the proper replacement ratio of recycled aggregate shows the comparable compressive strength and freeze and thaw resistance to those of normal concrete. Therefore, it is considered that recycled aggregate can be widely used for concrete if the cement paste and mortar can be efficiently removed from recycled aggregate and/or if the effective replacement ratios of recycled aggregate are applied for mixing concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 1995.10a
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• pp.256-261
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• 1995

Large-scaling recycling of demolished concrete will concrete will contribute not only to the solution of a growing waste disposal problem, it will also help to consweve natural resoures of sand and gravel and to secure future supply of reasonly priced aggregates for building and other construction purposes within large urban areas. Because recycled aggregate particles consits of substantial amount of relatively soft cement paste component, it is less resistant to mechanical actions. With this view in mind, to obtain a reference data for the development of recycling system and to a basic data the guiedline of recycled aggregate concrete construction and engineering properties of recycled aggregate concrete according to the factors, such as blending ratio of recyced aggregete with the natural aggregate, addition to the factors, such as blending ratio of recycled aggregete with the natural aggregate, addition of flyash, water coment ratio.

• Journal of the Korean Society of Hazard Mitigation
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• v.5 no.1 s.16
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• pp.77-84
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• 2005

Amount of demolished concretes is highly produced as dismantlement of structures to increased owing to usage alteration and deteriorated of concrete structures, but most of them have been used as material for simple reclamation. Therefore, if demolished concrete could be recycled as aggregate for concrete. it will contribute to solve the exhaustion of nature aggregate, in terms of saving resources and protecting environment, especially being want of resources in Korea. In this study it was investigated into experimental results that were carried out demolished concrete recycled aggregate gained from dismantled real structures and source concrete recycled aggregate produced according to respectively 5 steps of replacement ratio for recycling as pavement concrete aggregate.

• Journal of the Korea Concrete Institute
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• v.14 no.3
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• pp.307-314
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• 2002

Utilization of demolished-concrete as recycled aggregate has been researched for the purpose of substituting for insufficient natural aggregate, saving resources and protecting environment. There, however, are some Problems not only the large difference of dualities in recycled aggregates but also a little deterioration of mechanical properties in recycled aggregate concrete in comparison with that of natural aggregate concrete. In this study, the test results of freez and thaw durability of concrete with demolished-concrete recycled aggregate(DRA) arc as follows. Improvement of crushing process is an important assignment because that adhered mortar on source-concrete recycled aggregate(SRA) and DRA highly affects thc qualifies of recycled aggregate. The compressive strength of recycled aggregate concrete was not highly different in comparison with that of control concrete. But the resistance to penetration of Cl in recycled aggregate concrete was shown smaller than that of control concrete because of adhered mortar on recycled aggregate. The resistance to frcezing and thawing of recycled aggregate concrete was highly different due to adhered mortar on recycled aggregate, and durability factor of concrete with NA-SRA and DRA was more decreased than that of control concrete. On the other hand, durability factor of concrete with AA-SRA was larger than that of control concrete. It, therefore, is necessarily required that recycled aggregate including adequate entrained air should be used for satisfying the freez and thaw durability of recycled aggregate concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.05a
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• pp.580-583
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• 2004

Due to the tendency of increase in demolished-concrete produced by alteration and deterioration of concrete structures, recycling of those demolished-concrete is necessary to solve the exhaustion of natural aggregate, in order to save resources and protect environment. In this an experimental study herein, the Chlorine-ion and Carbonation resistance of the recycled aggregate concrete was investigated. Coarse aggregate was replaced with $100\%$ of the recycled aggregate and cement and fine recycled aggregate was replaced with various amount. It was shown that the concrete can obtain resistance of chlorine-ion, when fly ash replaced with up to $30\%$ of cement.

• Journal of the Korea Concrete Institute
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• v.12 no.5
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• pp.3-12
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• 2000

Recently, the amount of disposed construction materials like demolished concrete is growing fast and the shortage of natural concrete aggregates is becoming serious. Therefore, recycling of aggregates extracted from the demolished concrete is getting important and use of the recycled aggregates for concrete has been seriously considered. However, the use of the recycled aggregates even for low performance concretes is very limited because there are few rational standard evaluation criteria for recycled aggregates which should be different from that for natural aggregates. In this study, rational evaluation criteria for the recycled aggregates are proposed for their use as concrete aggregates. The study also shows that the performance for both the recycled aggregates and the recycled concrete manufactured with the recycled aggregates can be evaluated effectively according to water absorption ratio of recycled aggregates.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.217-220
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• 2001

Due to the tendency of increase in demolished-concrete produced by alteration and deterioration of concrete structures, recycling of those demolished-concrete is necessary to solve the exhaustion of natural aggregate, in order to save resources and protect environment, especially being want of resources in Korea. For this purpose, concrete made with the pozzolanic cement and recycled aggregate was tested for compressive and tensile strength. The pozzolanic cement was a mixture of OPC(Ordinary Portland Cement) and pozzolans such as fly ash, other siliceous materials and early rapid hardening cement(ERC). It was found that the compressive strength of the pozzolanic cement was enhanced when 0.75% of ERC was dozed, as compared with OPC mortar. It was also shown that compressive and tensile strength of concrete with recycled aggregate and pozzolanic cement were higher than those of concrete with crushed stones and OPC. It was concluded that the pozzolanic cement influenced on the increase of concrete strengths with recycled aggregate.

• Proceedings of the Korea Concrete Institute Conference
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• 1995.04a
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• pp.177-182
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• 1995

Large-scaling recycling of demolished concrete will contribute not only to the solution of a growing waste disposal problem. it will also help to conserve natural resoures of sand and gravel and to secure future supply of reasonly priced aggregates for builiding and other construction purposes within large urban areas. because recycled aggregate particles consist of substaintial amount of relatively soft cement paste component, it is less resistant to mechanical actions. With this view in mind, to obtain a reference data for the development of recycling system and to a basic data the guideline of recycled aggregate concrete construction and mix design, this study deals with the comparative analysis of the workability and engineering properties of recycled aggregate concrete according to the factors, such as blending ratio of recycled aggregate with the natural aggregate, addition of flyash, water cement ration.

• Structural Engineering and Mechanics
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• v.40 no.3
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• pp.411-429
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• 2011

In the past decades, recycling use of demolished concrete was almost limited to the types of recycled coarse aggregate with a size of about 5-40 mm and recycled fine aggregate with a size of about 0-5 mm for concrete structures, and reuse of demolished concrete lumps (DCLs) with a size much larger than that of recycled aggregate, e.g., 50-300 mm, has been limited to roadbed, backfilling materials, or discarded to landfills. Treatment processes of DCLs are much simpler than those of recycled aggregate, leading to less cost and more energy-saving. In the future, the amount of demolished concrete is estimated to be much higher, so reuse of DCLs for concrete structures will become necessary. The objectives of this paper are to document the process of making reinforced concrete beams with DCLs, and to discuss the flexural and shear behaviors of those reinforced DCL beams through an experimental program, which includes three beams filled with DCLs and one conventional beam for investigating the flexural strengths and deformations, and 12 beams filled with DCLs and two conventional beams for investigating the shear strengths and deformations. The authors hope that the proposed concept offers another sustainable solution to the concrete industry.