• Journal of the Korean Recycled Construction Resources Institute
• /
• v.1 no.1
• /
• pp.72-80
• /
• 2005

A recycled aggregate contains impurities that affect negative effects on physical properties of concrete. Therefore, a test method for examining impurities content in recycled aggregate is necessary before use of recycled aggregate. In this study, the test method by visual examination for separating impurities in recycled fine and coarse aggregates was developed. The results of the test are as follow: 1. The current KS F 2576 was necessary for comprehensive revision including types of tested recycled aggregate, definition of terminology, quantity of sample, and test method. 2. Visual examination is appropriate for larger than impurity panicle size of 1.2mm, and the larger panicle size the shorter time was required. 3. For the impurity content test by visual examination, the easiness and accuracy of the test can be obtained from the condition of sample weight of 30 grams with particle size of 2.5mm to 5mm for recycled fine aggregate and the condition of sample weight of 1 kilogram with panicle size of larger than 5mm for recycled coarse aggregate.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.4 no.3
• /
• pp.82-89
• /
• 2009

Recently, the study is progressing actively about manufacture skill of concrete for promoted recycled aggregate and concrete made into recycled aggregate in the construction production field. But, application and study about recycled fine aggregate insufficient compared to recycled coarse aggregate. So, in this study, it presents basic data for development of environmental load reduction fiber reinforcement recycled fine aggregate concrete by comparison and investigation about engineering properties and shrinkage cracking of fiber reinforcement recycled find aggregate concrete for increasing shrinkage cracking reduction and long term stability of environmental load reduction concrete used recycled fine aggregate. In the result of the study, compared to natural fine aggregate, a crack-extent increased by applying recycled fine aggregate, moreover, as a water cement ratio increased, the crack size increased, as well. In addition, it's shown that the specimen mixed with PVA and Nylon, among all kinds of fibers, showed the smallest crack size, so it's verified that the mix of fiber had an effect on decreasing crack-extent.

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

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.9 no.1
• /
• pp.85-91
• /
• 2021

Aggregate waste separator with rotating separating net was designed for applying classification process of construction waste. In order to evaluate the performance of the aggregate waste separator, according to the type of waste, standardized waste samples are prepared using acrylic. The appropriate operating point was evaluated by the classification efficiency and misclassification rate of recycled aggregate according to the control frequency of the blower operating and inlet position of the separating net. The classification efficiency at the operating point of the aggregate waste separator was evaluated through flow analysis assuming recycled aggregate and waste sample as particles. As a result of the performance test, when the distance. between the conveyor belt and the inlet was 0.2m, the classification efficiency was 95%, but the misclassification rate of recycled aggregate was 2% or more, which satisfies the classification efficiency and the misclassification rate of less than 2%. The operating point was shown at a control frequency of 58Hz at a suction distance of 0.254m. As a resu lt of flow analysis, there was no misclassification of recycled aggregate. In order to redu ce constru ction waste in the existing recycled aggregate production process, adsorption system using a rotating separating net that can be operated as an installation type was built.

• Journal of the Korea Concrete Institute
• /
• v.20 no.1
• /
• pp.43-50
• /
• 2008

This paper presents experimental and analytical results on the long-term behavior of the reinforced recycled aggregate concrete beams under sustained loading. In this experimental program, three beams with different conditions of aggregates replacement (natural aggregate 100%, recycled coarse aggregate 100%, recycled fine aggregate 50%) were subjected to the sustained flexural loading that was a half of the nominal flexural capacity over a period of 1 year. The beam were designed with net span of 2,000 mm and rectangular cross-section of 170 mm width and 170 mm effective depth. The beams were instrumented and monitored to observe the change in the long-term behavior due to creep and shrinkage of concrete under sustained loading. The predictions of long-term deflection by ACI code, Branson, Mayer, Neville, EMM and AEMM were compared with the experimental results. From the experimental results, the reinforced concrete beams with recycled aggregates showed the same performance as that of a beam with natural aggregate. The proposed method to predict the long-term deflections of reinforced recycled aggregate concrete beams gives a good estimation for experimental results.

• Journal of Korean Society of Disaster and Security
• /
• v.17 no.1
• /
• pp.27-35
• /
• 2024

This paper presents experimental research results to evaluate the applicability of chemical neutralization reaction and ultrasonic wave to remove cement paste and mortar attached to the surface of recycled aggregate. In order to derive optimal ultrasonic cleaning efficiency and chemical neutralization reaction, experiments were conducted using variables such as ultrasonic frequency and type of chemical solution. As a result, the optimal frequency was found to be 24 kHz, and immersion in a 15% hydrochloric acid solution for 30 minutes of stimulation showed the highest efficiency. In addition, the specific gravity, absorption rate, and wear rate of the quality-improved recycled coarse aggregate were similar to those of general aggregate and were found to satisfy all KS F 2527 standards. Therefore, it is believed that the recycled aggregate whose quality has been improved through the method proposed in this study can be used for concrete.

• Journal of the Korean Geotechnical Society
• /
• v.32 no.11
• /
• pp.21-29
• /
• 2016

In this study, recycled aggregates crushed from waste concrete were sorted into three groups, 10-13 mm, 13-20 mm, and 20-25 mm. They were treated in different ways and then their crushability was evaluated for each treatment. Coffee waste was used for reducing their pH level. The pH of recycled aggregate was almost 11, regardless of aggregate sizes. The pH of coffee waste was nearly 5 and 10, 30, or 50 g of coffee waste was mixed with 1000 ml of distilled water and recycled aggregates. The lowest pH was about 6.2 when 50 g of coffee waste was mixed. Aggregates were treated with microwave or soaked for 1 day in vinegar (pH = 2) for neutralization reaction. Microwave treated and neutralized aggregates showed 3.3% and 6.2% higher crushing values compared to non-treated one, respectively. Neutralized treatment was more effective for crushing. In crushing tests, a sample height of 120 mm was tried, which gave 6.3% higher crushing value. A four stepped loading with each 100 kN gave 7.1% higher crushing value, compared to standard 100 mm height and 400 kN continuous loading.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.22 no.4
• /
• pp.126-132
• /
• 2018

As means to increase the use of concrete with recycled coarse aggregate (RCA), this study aims to evaluate the applicability for flexural strengthening of reinforced concrete beam with high-strength concretes and RCA on which FRP plates, used for repair and strengthening of old and low-durability reinforced concrete structures, is applied. In order to increase the adhesive force of epoxy and FRP plate, FRP plate was installed according to Near-Surface-Mounted (NSM) method. 12 specimens were manufactured using substitution rate of RCA (30%), concrete strengths (40MPa, 60MPa), diameters of deformed bar (D10, D13), and types of FRP plate (AFRP, CFRP) as variables to analyse flexural performance according to FRP plate and substitution rate of recycled aggregate. As a result, in all specimens, specimens strengthened by FRP plate showed a maximum of 17% increase in performance compared to specimens without FRP plate and strengthening performance of CFRP was found to be higher than AFRP. When modulus of rupture was used, the value of cracking moment was similar to that of the reference equation. As bending moment of some specimens strengthened by FRP plate failed to satisfy the criteria of KCI 2012 and ACI 440-2R, additional experiment is deemed as necessary.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.16 no.5
• /
• pp.49-58
• /
• 2012

This study estimates the flexural behavior of reinforced recycled aggregate concrete beams. Three specimens with different types and water absorption of coarse aggregates were constructed and tested. Not only all specimens were designed to be subjected to 4-point concentrated loads, but also the shear span-to-depth ratio of 2.5 was adjusted to all specimens to increase the effect of shear. A nonlinear flexural analysis considering the tension stiffening effect of concrete was performed to predict the moment versus curvature relationships of the specimens. Furthermore, a nonlinear finite element analysis considering the effect of shear was carried out to estimate the behavior of the specimens. It can be found from experimental results that the flexural strength and the crack properties of the specimens with recycled coarse aggregate having a water absorption of 6% were similar to those of the specimen with natural aggregates. The comparison between the experimental and analytical results showed that existing analytical methods can be successfully used to predict the behavior of reinforced recycled aggregate concrete beams.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.8 no.4
• /
• pp.498-505
• /
• 2020

Aggregate occupies about 70-85% of the concrete volume and is an important factor in reducing the drying shrinkage of concrete. However, when constructing high-rise buildings, it acts as a problem due to the high load of natural aggregates. If the load becomes large during the construction of a high-rise building, creep may occur and the ground may be eroded. Material costs increase and there are financial problems. In order to reduce the load on concrete, we are working to reduce the weight of aggregates. However, artificial lightweight aggregates affect the interface between the aggregate and the paste due to its higher absorption rate and lower adhesion strength than natural aggregates, affecting the overall strength of concrete. Therefore, in this study, in order to grasp the interface between natural aggregate and lightweight aggregate by type, we adopted a method of measuring electrical resistance using an EIS measuring device, which is a non-destructive test, and lightweight bone. The change in the state of the interface was tested on the outside of the material through a blast furnace slag coating. As a result of the experiment, it was confirmed that the electric resistance was about 90% lower than that in the air-dried state through the electrolyte immersion, and the electric resistance differs depending on the type of aggregate and the presence or absence of coating. As a result of the experiment, the difference in compressive strength depending on the type of aggregate and the presence or absence of coating was shown, and the difference in impedance value and phase angle for each type of lightweight aggregate was shown.