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

• Proceedings of the Korea Concrete Institute Conference
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• 2003.05a
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• pp.249-254
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• 2003

The thermal coefficient of concrete is measured using dilatometer (AASHTO TP60) and strain gage. Testing parameters such as six different coarse aggregate types, cycles of warming and cooling, specimen shape and measurement types were investigated to evaluate the influencing factors for thermal coefficient of concrete. According to experimental results, the thermal coefficient of concrete made with crushed aggregate showed 9.2 -10.$\mu\varepsilon/^{\circ}C$, , however recycled coarse aggregate classified type II showed a little increasing in comparison with crushed aggregate. The thermal coefficient of concrete made with recycled aggregate was reduced 0.2-0.4$\mu\varepsilon/^{\circ}C$, under temperature cycles. However, specimen shapes were revealed as mainly affecting factors on the thermal coefficient of concrete. Finally the thermal coefficient value determined by the dilatometer device was shown to be similar to the value from PML 60.

• Computers and Concrete
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• v.24 no.1
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• pp.19-35
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• 2019

In this paper, the effect of the type and amount of fibers on the physicomechanical properties of concrete containing fine recycled refractory brick (RRB) and natural aggregate subjected to elevated temperatures was investigated. For this purpose, forta-ferro (FF), polypropylene (PP), and polyvinyl alcohol (PVA) fibers with the volume fractions of 0, 0.25, and 0.5%, as well as steel fibers with the volume fractions of 0, 0.75, and 1.5% were used in the concrete containing RRB fine aggregate replacing natural sand by 0 and 100%. In total, 162 concrete specimens from 18 different mix designs were prepared and tested in the temperature groups of 23, 400, and $800^{\circ}C$. After experiencing heat, the concrete properties including the compressive strength, ultrasonic pulse velocity (UPV), weight loss, and surface appearance were evaluated and compared with the corresponding results of the reference (unheated) specimens. The results show that using RRB fine aggregate replacing natural fine aggregate by 100% led to an increase in the concrete compressive strength in almost all the mixes, and only in the PVA-containing mixes a decrease in strength was observed. Furthermore, UPV values at $800^{\circ}C$ for all the concrete mixes containing RRB fine aggregate were above those of the natural aggregate concrete specimens. Finally, regarding the compressive strength and UPV results, steel fibers demonstrated a better performance relative to other fiber types.

• Journal of the Korea institute for structural maintenance and inspection
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• v.7 no.2
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• pp.159-167
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• 2003

Cracks in reinforced concrete structures reduce overall durability by allowing the penetration of water and aggressive agents, thereby accelerating the deterioration of the reinforcing steel. Highway pavement and bridge decks are especially susceptible to this type of deterioration since these structures exhibit high rates of shrinkage and are frequently exposed to aggressive environmental conditions. The objectives of this investigation included the development of experimental procedures for assessing shrinkage cracking potential of recycled aggregate concrete, the evaluation of mix composition on shrinkage cracking potential, and the development of theoretical models to simulate early-age cracking behavior. Specifically, the influences of shrinkage-reducing admixture(SRA) and recycled aggregate concrete were investigated. The shrinkage-reducing admixture substantially reduces free shrinkage and restrains shrinkage cracking while providing similar mechanical properties. A fracture mechanics modeling approach was developed to predict the behavior of a variety of restrained concrete specimens. This modeling approach was used to successfully explain experimental results from a variety of mixture compositions. The model was used to demonstrate the influence of material and structural properties on the potential for cracking.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.481-484
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• 2008

Recently, the recycling and reusing of construction and demolition waste concrete is urgently required because waste concrete is greatly increased according to the rapid increasing of urban redevelopment project, but the problem solution for demand and supply unbalance of fine aggregate is urgently required because of the restriction of collecting sea fine aggregate. So the utilization of high quality recycled fine aggregate using construction and demolition waste concrete as new fine aggregate for construction industry is urgently. Accordingly, In this study, As recycled fine aggregate manufacturing technology with exceeding in economical efficiency, reduction efficiency of environmental load and quality improvement effect of recycled fine aggregate, it is to develop dry manufacturing system composed specific gravity separator of high-speed rotation impact type and centrifugal Force Powder Collector, etc. And it is to examine mechanism of recycled sand dry manufacturing system.

• International Journal of Concrete Structures and Materials
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• v.9 no.1
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• pp.1-20
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• 2015

This work is devoted to the study of fresh and hardened properties of concrete containing recycled gravel. Four formulations were studied, the concrete of reference and three concretes containing recycled gravel with 30, 65 and 100 % replacement ratios. All materials were formulated on the basis of S4 class of flowability and a target C35 class of compressive strength according to the standard EN 206-1. The paper first presents the mix design method which was based on the optimization of cementitious paste and granular skeleton, then discusses experimental results. The results show that the elastic modulus and the tensile strength decrease while the peak strain in compression increases. Correlation with the water porosity is also established. The validity of analytical expressions proposed by Eurocode 2 is also discussed. The obtained results, together with results from the literature, show that these relationships do not predict adequately the mechanical properties as well as the stress-strain curve of tested materials. New expressions were established to predict the elastic modulus and the peak strain from the compressive strength of natural concrete. It was found that the proposed relationship E-$f_c$ is applicable for any type of concrete while the effect of substitution has to be introduced into the stress-strain (${\varepsilon}_{c1}-f_c$) relationship for recycled aggregate concrete. For the full stress-strain curve, the model of Carreira and Chu seems more adequate.

• Journal of the Korean Recycled Construction Resources Institute
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• v.4 no.2
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• pp.118-124
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• 2016

The purpose of this study is to analyze the rheology characteristics of insulating concrete for each type of insulation performance improvement material and utilize the result as preliminary data for optimal flow designing and pumping analysis. As a result, when lightweight aggregate was mixed, the yield stress decreased significantly, and in case of type 2, the combination of micro form cell admixture (MFA) and calcined diatomite powder (DM) showed the most ideal flow characteristics. In case of type 3, the combination of micro form cell admixture (MFA), calcined diatomite powder (DM) and lightweight aggregate (L) showed the best flow characteristics.

• Resources Recycling
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• v.14 no.4 s.66
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• pp.10-16
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• 2005

In order to recycle the waste concrete from which the reproductive aggregate should be produced in-situ, the applicability of crushers and recycled aggregates, and the compliance with the specification have been evaluated comprehensively. As a result of them, the properties of recycled aggregate particles were inferior to the natural one because of the adherent mortars on the recycled one, and the mobile impact crusher and the eccentric-mounted cone and jaw were superior to the others for the graded aggregates. In the case of anti-frost layer, the recycled one was easily controlled since the dry densities, contrary to natural one, were not largely changed with the moisture contents. It was found that the lean concrete base course is not influenced by absorption as cement dust grows larger, and the 7-day compressive strengths of lean concrete were higher than 10 MPa regardless of the crushing type.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.05a
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• pp.82-85
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• 2006

In this study, the fatigue tests were performed on a series of reinforce concrete beams with type of aggregate to investigate the fatigue behavior. The four point loading system is used in the fatigue tests. In these tests, relations between the repeated loading cycles and mid-span deflections, number of repeated loading cycles when specimen was fractured were observed. On this basis, the mid-span deflections, the crack growth and failure mode of beams were studied. The result of tests, reinforce concrete beams with recycled aggregate were about similar failure mode with natural aggregate concrete beam.

• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.3
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• pp.100-107
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• 2010

This study evaluates the bond behavior of reinforced concrete (RC) beams using recycled coarse aggregates. A total of four specimens were cast and tested. The test parameter was the type of coarse aggregates, that is, natural and recycled coarse aggregates, and the absorption ratio of recycled coarse aggregate. The recycled coarse aggregates with absorption ratios of 3% and 6% were used in this test. The specimens were simply supported and were subjected to a concentrated load. A test method proposed by Ichinose was adopted to estimate effectively the bond properties of specimens. From the experimental results, it was found that there was no difference of bond characteristics according to the absorption ratio of recycled coarse aggregates.