• Proceedings of the Korea Concrete Institute Conference
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• 2010.05a
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• pp.91-92
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• 2010

This paper is experimental study on the confinement effect of concrete using recycled coarse aggregates confined by steel spirals. The experimental results indicated that confinement effect of recycled aggregate concrete was similar to that of natural aggregate concrete ones.

• Journal of the Korean Recycled Construction Resources Institute
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• v.4 no.4
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• pp.404-417
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• 2016

The purpose of this study is to examine the extent to which the deterioration in strength of high strength concrete of 60MPa replaced by a large amount of recycled coarse aggregates (more than 60% to 100% of replacement ratio) could be recovered with steel fiber reinforcement through material compressive strength test and shear failure test on short and middle beams and then to offer useful data for aggregate supply system of a sustainable resource circulation type. This study first examined the results of previous related tests. The results of the material compressive strength tests confirmed that when using a combination of steel fiber reinforcements of volumn ratio 0.75% and high quality recycled coarse aggregates with an water absorption rate within 2.0%, the strength characteristics of high strength concrete of 60MPa level were not only restored to the strength level of concrete made with natural aggregates, but also showed superior ductility. And the shear failure tests on short and middle beams using recycled coarse aggregates more than 60% with shear span to depth ratio (a/d) of 2 and 4 controlled by shear forces mainly confirmed that effects of superior shear strength increase and ductile behavior characteristics were showed by steel fiber reinforcements.

• Journal of the Korean Recycled Construction Resources Institute
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• v.6 no.4
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• pp.229-235
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• 2018

In this study, recycled aggregate and natural aggregate were mixed in advance using an aggregate mixing facility that was developed to improve the quality of recycled aggregate concrete. Then the mixed aggregate was applied and concrete characteristics before and after a mix were considered. Based on the findings extracted, this study aimed to suggest a new direction for quality stabilization and application activation of recycled aggregate. The test results of change rates of mortars and coarse aggregates in fresh concrete mixed by a concrete mixer, before and after mixing aggregates showed that the variations of the mortars and coarse aggregates in the concrete mixed with the aggregates beforehand were decreased than those in the concrete before mixing them. The variation of compressive strength and the mean compressive strength at the ages of 3 and 7 days showed similar results before and after the aggregates were mixed, and the strength at the age of 28 days before and after mixing them showed larger deviation than that at the ages of 3 and 7 days. The use of the mixed aggregates after mixing aggregates beforehand reduced the variation in strength and is believed that it is advantageous for long-age strength development. The above results show that the variations of coarse aggregates and compressive strength in the concrete using the mixed aggregates produced by mixing recycled aggregates and natural aggregates beforehand are reduced so it will be possible to produce the homogeneous concrete by mixing aggregates beforehand.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.1
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• pp.11-17
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• 2013

The use of wasted concrete can settle the environmental pollution and shortage of natural aggregate. However, recycled aggregate includes substantial amount of cement paste, so that these aggregates are more porous, and less resistant to mechanical actions than natural aggregates. Recently, the new manufacturing processes of high quality recycled aggregates were suggested such as heating. In this paper, for the purpose of manufacture of high quality recycled aggregates, the heating processes was considered to the existing process of recycled aggregates. To find the optimum process, the experiment was performed through the statistical design of experiment. The heating temperatures of 4 levels (300, 450, 600 and $750^{\circ}C$) and heating duration time (5, 20, 40, 60minute) were main experimental variables. Through the test results, it was found that the optimum manufacturing condition of coarse recycled aggregate was evaluated to be $600^{\circ}C$ and 40minute.

• Journal of the Korea Institute of Building Construction
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• v.16 no.6
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• pp.479-485
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• 2016

This paper presents an experimental study conducted to investigate the effect of recycled fine aggregate (RFA) on the mechanical properties and chloride diffusion behavior of mortar. The test results revealed that the addition of RFA plays an important role in the mechanical properties and pore structures of the investigated mortar specimens as well as chloride diffusion behavior. The mechanical properties such as compressive strength and flexural strength of recycled fine aggregate mortar (RFAM) were gradually decreased as RFA replacement ratio increase. The pore structure of RFAM was examined by permeability tests. The RFAM showed a increment in the permeability according to replacement ratio increase of RFA. But the chloride diffusion coefficient of RFAM was almost same up to 50% replacement ratio of RFA due to a chloride binding phenomenon of RFAM which may compensate the higher permeability of RFAM.

• Journal of the Korean Recycled Construction Resources Institute
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• v.2 no.1
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• pp.103-112
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• 2006

Along with recent improvement of recycling technique, the quality of the recycled concrete aggregate have become very competitive to the natural concrete aggregate. Therefore, a practical use of the recycled concrete aggregate may be possible for structural members. Majority studies about the recycled concrete aggregate was emphasized a limitation of fundamental study concerned with a strength characteristics and durability of the recycled aggregate concrete, there is use for the structural members. Therefore, for the extension of application of recycled concrete aggregate, this investigation verifies the strength characteristics recycled concrete aggregate of the spun-concrete products with various coarse and fine recycled aggregate replacement ratio(coarse recycled aggregate: 0%, 20%, 40%, 60%, 100%; fine recycled aggregate: 0%, 30%, 60%, 100%) and with addition of cellulose fibers(0%, 0.01%, 0.03%, 0.05%, 0.08%). From the test results, The strength of spun concrete used with recycled aggregate [NR specimen], was measured as 72MPa, was found to be very approximately to the strength of spun concrete used with the natural aggregate(NN specimen), was measured as 74MPa, when only fine aggregate was replaced with the recycled. Therefore, the fine recycled concrete aggregate can be successfully used in the spun high strength concrete product. The compressive strength of all specimens used the specialty cellulose fiber were measured as about 70M Pa, however, the increasement of the specialty cellulose fiber content is showed to decrease compressive strength of spun concrete. Therefore, it is anticipated that the specialty cellulose fiber can be applied to the various spun concrete products.

• Journal of the Korean Recycled Construction Resources Institute
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• v.2 no.2
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• pp.107-114
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• 2014

The objective of this study is to evaluate the strength development of blast furnace slag concrete in response to the use of recycled aggregate as alkali activator. The influence of the amount of recycled aggregate was evaluated depending on different ratios of replacement for each RFA and RCA to NFA and NCA, respectively. The results indicated that as replacement of RFA and RCA increased, their strength exhibited to be increased. This was due to the fact that the latent hydraulic properties of blast furnace slag was activated by the alkali in recycled aggregates. However, in case of 365-days, it showed lower compressive strength than using NA(natural aggregates) which could be explained as the exhaustively use of alkali containing in RA. The specimens using RA showed about 90% of compressive strength comparing with specimens using NA.

• Resources Recycling
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• v.18 no.3
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• pp.27-35
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• 2009

To solve resource exhaustion and waste management problems caused by mass consumption, there are many efforts to change from resource consumption system to recycling system. Specially, interests about management of construction waste have increased, but efficient recycling system of waste concrete is not established yet. In this study, high quality recycled aggregate processing circuit was developed to recycle waste concrete. From the waste concrete which is a hydrated compound with coarse aggregate, fine aggregate, and cement material, high quality recycled coarse aggregate for concrete making was produced by autogenous milling and heat pretreatment method. After then, refinement process was performed to separate fine aggregate and cement material from waste concrete fines by sink float separation and hindered-settling separation. As a result, high quality recycled aggregate was produced from waste concrete by developed processing circuit.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2021.11a
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• pp.150-151
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• 2021

This study aims to achieve an enhancement in the quality of high strength concrete through a reduction in autogenous shrinkage by supplying the moisture needed for hydration through recycled aggregates that retain high amounts of moisture. The result showed that, moisture supply increased with the higher replacement rate, autogenous shrinkage dropped by up to 45 percent.

• Journal of the Korean Recycled Construction Resources Institute
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• v.10 no.4
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• pp.475-481
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• 2022

Recycled aggregates show high water absorption rate compared to natural aggregates due to microcrack developed during production process and adhered cement pastes at the surface of recycled aggregates. This leads to the deterioration of mechanical properties and slow work flow. Currently it is getting hard to satisfy high demand for natural aggregates. Utilizing recycled aggregate more widely may be a substitutable countermeasure for the shortage of natural resources. In this study, two-stage mixing approach(TSMA) suggested by Tam et al. is used to produce recycled aggregate concrete(RAC) with 100 % replacement of coarse natural aggregate and tests for compressive strength, elastic modulus, and chloride ion diffusion coefficient are conducted to find out the effect of TSMA compared to normal mixing method. According to experimental result compressive strength and elastic modulus of RAC with TSMA was superior to those of RAC with normal mixing irrespective of water-cement ratio, and in some cases mechanical properties of RAC with TSMA approached to those of natural aggregate concrete(NAC). However, chloride ion diffusion coefficient of RAC was higher than that of NAC. This illustrates that TSMA is not an appropriate method in reducing chloride ion diffusion coefficient, resulting in inconsequential contribution of TSMA to the durability of RAC.