• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.723-726
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• 2005

As the importance of recycled materials is being emphasized more in the Korean construction market, the production quality has been improved to a significantly high level. Compared to the high quality, however, there are used very limitedly. Among recycled construction materials, recycled aggregates produced through the retreatment of waste concrete are drawing attention because of lack of natural aggregate and heightened consciousness of resource saving and environmental protection and, as a consequence, they are close to natural aggregates in terms of production technology and quality. Despite the high quality and productivity, however,. the utilization of recycled aggregates is very low. Thus, in order to maximize the utility of recycled aggregates, the present study examined the usability of recycled aggregates using both recycled coarse aggregates and recycled fine aggregates together and derived optimal quantity and mixture ratio in the combined use of the two types of recycled aggregate.

• Structural Engineering and Mechanics
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• v.76 no.4
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• pp.513-528
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• 2020

This paper presents the results of an experimental study on the residual behavior of reinforced recycled aggregate concrete (RRAC) beam-columns after exposure to elevated temperatures. Two parameters were considered in this test: (a) recycled coarse aggregate (RCA) replacement percentages (i.e. 0, 30, 50, 70 and 100%); (b) high temperatures (i.e. 20, 200, 400, 600, and 800℃). A total of 25 RRAC short columns and 32 RRAC beams were conducted and subjected to different high temperatures for 1 h. After cooling down to ambient temperature, the following basic physical and mechanical properties were then tested and discussed: (a) surface change and mass loss ratio; (b) strength of recycled aggregate concrete (RAC) and steel subjected to elevated temperatures; (c) bearing capacity of beam-columns; (d) load-deformation curve. According to the test results, the law of performance degradation of RRAC beam-columns after exposure to high temperatures is analyzed. Finally, introducing the influence coefficient of RCA replacement percentage and high temperatures, respectively, to correct the calculation formulas of bearing capacity of beam-columns in Chinese Standard, and then the residual bearing capacity of RRAC beam-columns subjected elevated temperatures is calculated according to the modified formulas, the calculated results are in good agreement with the experimental results.

• International Journal of Concrete Structures and Materials
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• v.8 no.2
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• pp.165-172
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• 2014

Recycled coarse aggregate (RCA) made from waste concrete is not a suitable structural material as it has high absorption of cement mortar, which adheres on the aggregate surface and on the tiny cracks thereon. Therefore, when using RCA made from waste concrete, much water must be added with the concrete, and slump loss occurs when transporting. Hence, its workability is significantly worse than that of other materials. In this study, surface of RCA was coated with water-soluble polycarboxylate (PC) dispersant so that its characteristics improved. Each possibility was evaluated: whether its slump loss can be controlled, by measuring its workability based on the elapsed time; and whether it can be used as a structural material, by measuring its strength. Moreover, the carbonation due to cement mortar adhesion was measured through a carbonation test. As a result, RCA coated with PC dispersant was found to be better than crushed coarse aggregate and RCA when the physical properties of the fresh concrete and the mechanical, durability of the hardened concrete were tested.

• Journal of the Korean Recycled Construction Resources Institute
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• v.4 no.2
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• pp.157-164
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• 2016

In this research, based on the condition of using desulfurization gypsum(FGD) as a stimulator for high-volume blast furnace slag cement mortar, sieving and heating process methods of removing activated carbon in FGD were compared with the non-processed FGD and recycled and natural fine aggregates were compared for suitable aggregate to be used. According to the result of experiment, sieving with 0.3mm was more efficient than $500^{\circ}C$ heating for processing the FGD, and recycled fine aggregate showed more favorable result than natural fine aggregate at the FGD content was 5 to 10%. On the other hand, the mortar mixture including recycled fine aggregate had a high drying shrinkage, and absorption ratio, and thus specific limitations on applying recycled fine aggregate should be required.

• Advances in concrete construction
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• v.10 no.3
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• pp.237-245
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• 2020

Past research efforts already established geopolymer as an environment-friendly alternative binder system for ordinary Portland cement (OPC) and recycled aggregate is also one of the promising alternative for natural aggregates. In this study, an effort was made to produce eco-friendly mortar mixes using geopolymer as binder and recycled fine aggregate (RFA) partially and study the resistance ability of these mortar mixes against the aggressive environments. To form the geopolymer binder, 70% fly ash, 30% ground granulated blast furnace slag (GGBS) and alkaline solution comprising of sodium silicate solution and 14M sodium hydroxide solution with a ratio of 1.5 were used. The ratio of alkaline liquid to binder (AL/B) was also considered as 0.4 and 0.6. In order to determine the resistance ability against aggressive environmental conditions, acid attack test, sulphate attack test and rapid chloride permeability test were conducted. Change in mass, change in compressive strength of the specimens after the immersion in acid/sulphate solution for a period of 28, 56, 90 and 120 days has been presented and discussed in this study. Results indicated that the incorporation of RFA leads to the reduction in compressive strength. Even though strength reduction was observed, eco-friendly mortar mixes containing geopolymer as binder and RFA as fine aggregate performed better when it was produced with AL/B ratio of 0.6.

• Journal of the Korean Recycled Construction Resources Institute
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• v.4 no.1
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• pp.1-9
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• 2016

While the amount of construction waste has not been changed much in discharge for last 10 years, the recycled resources refined from construction waste have been mainly applied to low-leveled one such as reclamation, back-fill, road base or subbase and so on. Thus this study addresses the applicability of recycled fine aggregate as a replaceable material in precast concrete. To evaluate the possibility, both of dry and wet processes were adopted as well as steam curing, widely used in the field for rapid producing. Most important experimental parameters were driven through preliminary experiments and were evaluated in terms of concrete properties. It is found from aggregate-replacement tests that all of consistency and strengths of concrete were decreased as the ratio of recycled fine aggregate increased, and the amount of decrease can be estimated using proposed equations. Though the recycled fine aggregate showed a decrease of concrete properties more or less, the applicability in large volume as a constituent of precast product was well noted from experimental results.

• Proceedings of the Korea Concrete Institute Conference
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• 1996.04a
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• pp.18-23
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• 1996

Since at least three-quarters of the volume of concrete is occupied by aggregate, it is not surprising that its quality is considerable importance. Not only may the aggregate limit the strength of concrete, as weak aggregate cannot porduce strong concrete, but the properties of aggregate greatly affect the durability and sructural performance of concrete. But, it is ture that aggregate strength is usually not a factor in normal concrete strength because the aggregate particle is several times stronger than the matrix and the transition zone in concrete. This study is to consider the influence the strength of concrete according to the kinds of aggregate, such as crushed river rocks, curshed rocks, high strength recycled aggregate, low strength recycled aggregate at water cement ratio 0.25. It is possible to concern the important of the mechanical role of aggegate for the high strength concrete.

• Computers and Concrete
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• v.10 no.2
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• pp.95-104
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• 2012

This study uses recycled green building materials based on a Taiwan-made recycled mineral admixture (including fly ash, slag, glass sand and rubber powder) as replacements for fine aggregates in concrete and tests the properties of the resulting mixtures. Fine aggregate contents of 5% and 10% were replaced by waste LCD glass sand and waste tire rubber powder, respectively. According to ACI concrete-mixture design, the above materials were mixed into lightweight aggregate concrete at a constant water-to-binder ratio (W/B = 0.4). Hardening (mechanical), non-destructive and durability tests were then performed at curing ages of 7, 28, 56 and 91 days and the engineering properties were studied. The results of these experiments showed that, although they vary with the type of recycling green building material added, the slumps of these admixtures meet design requirements. Lightweight aggregate yields better hardened properties than normal-weight concrete, indicating that green building materials can be successfully applied in lightweight aggregate concrete, enabling an increase in the use of green building materials, the improved utilization of waste resources, and environmental protection. In addition to representing an important part of a "sustainable cycle of development", green building materials represent a beneficial reutilization of waste resources.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.10a
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• pp.233-238
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• 2002

In this paper, the characteristics of fresh and hardened recycled concrete were experimentally compared to investigate the applicability of the recycled fine aggregates with the substitution ratio. Test results show that the workability of the recycled concrete decreases with the increment of substitution ratio of the recycled fine aggregates except for type-D case which has a lower absorption ratio. Also air content was increased with increasing substitution ratio. It was found that the compressive strength and elastic modulus of recycled concrete were decreased with increasing substitution ratio of the recycled fine aggregates. And, the superplasticizer was more effective on the workability recovery of the recycled concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.04a
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• pp.27-32
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• 1999

This study was performed to evaluate properties of recycled concrete for roadway pavement. Recycled concretes was manufactured for the target compressive strength of 280kg/$\textrm{cm}^2$ and 180kg/$\textrm{cm}^2$ with recycled aggregate ratio of 0%, 20%, 40%, 60%, 80%, respectively. Laboratory experiment was conducted for testing properties of fresh concrete and concrete strength at curing 28days and durability by freezing and thawing treatment. The study result presented a maximum replacement ratio of recycled material.