• 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 Korean Recycled Construction Resources Institute
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• v.5 no.2
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• pp.144-151
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• 2017

The mechanical properties such as compressive strength and elastic modulus of recycled aggregate concrete containing fly ash are investigated in this study. The experimental parameters were replacement ratio of recycled coarse aggregate(RCA) and fly ash. Replacement ratio of RCA was 0, 30, 50, and 70% and replacement ratio of fly ash was 0, 15, 30%. The experimental results were extensively discussed about compressive strength and elastic modulus of concrete at ages of 7, 28 and 91 days. Compared with concrete not containing fly ash, the decrease of compressive strength and elastic modulus of concrete containing fly ash with the replacement ratio of 30% was significant. Therefore, the test results represented that the fly ash replacement ratio of less than 30% was favorable in terms of mechanical properties of recycled coarse aggregate concrete.

• Resources Recycling
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• v.19 no.4
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• pp.35-40
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• 2010

Existing porous concrete has problems with reduction of strength due to freezing and thawing and exfoliation of aggregate at joints. In this study, a method for increasing strength and durability of porous concrete by using fine aggregate, silica-fume and high-range water-reducing agent was proposed by laboratory tests. Mixing ratio between silica-fume (10%) and fine aggregate (0%, 7%, 15%) was selected as a major test factor, and laboratory tests for compressive strength, flexural strength, permeability coefficient, porosity, freezing and thawing were conducted. Compressive strength and flexural strength were increased as the mixing ratio of fine aggregate was increased. However, permeability and freezing-thawing resistance were decreased due to reduction of porosity. Therefore, the ratio of fine aggregate should be limited to increase strength and durability of the porous concrete, while the mixing ratio of silica-fume should be over 10%.

• Journal of the Korean Recycled Construction Resources Institute
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• v.2 no.1
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• pp.128-135
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• 2006

Steel slag (divided into electric arc furnace slag and convener slag) is being produced by millions of tons per every year in many industrial countries. About 6.5 million tonnes of steel slag is produced yearly as an industrial by-product in Korea. Generally natural aggregate is relatively stable and does not enter into complex chemical reactions with water. Unfortunately, however. steel slag aggregate contains a small amount of free lime. The hydration of free lime makes steel slag aggregate unstable and liable to expand. In this paper, firstly, several aging methods are used in order to decrease the volume expansion of electric arc furnace slag, that is stabilization. The volume expansion of electric arc furnace slag is formulated from the experiment. From the formula, the residual expansibility is predicted with immersion expansion. Compressive strength of concrete with electric arc furnace slag has relation with the residual expansibility in slag aggregate.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.3
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• pp.302-309
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• 2020

This paper is a basic study for applying the dried recycled sludge of waste sludge generated in construction waste intermediate treatment facility and the crushed recycled glass aggregate of waste glass bottles that cannot be recycled to the recycled cold asphalt mixtures. This paper reviewed the characteristics of recycled cold asphalt mixtures using recycled sludge and recycled glass aggregate. As a result, as contents of recycled sludge and recycled glass aggregate increased, the Marshall stability, indirect tensile strength, and tensile strength ratio of the recycled cold asphalt mixtures decreased, but flow and void ratio of that increased.

• Journal of the Korean Recycled Construction Resources Institute
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• v.7 no.4
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• pp.341-348
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• 2019

In this study, we analyzed the problems of existing construction waste shredding technology to diagnose the problems of low quality recycled aggregates and to develop a new mortar peeling technique to produce high-quality recycled coarse aggregate for concrete. The purpose of this study is to verify the effectiveness of mortar peeling technique by doing simulation prior to on-site application and to check the quality properties of recycled coarse aggregate produced by applying a mortar peeling technique. We manufactured and installed High speed Rotating Grinder on-site and analyzed the correlation between mortar adhesion amount, dry density and water absorption rate of recycled coarse aggregate.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.4
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• pp.379-386
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• 2020

The present study examined the effect of bottom ash aggregate contents on the compressive strength gain and mechanical properties(modulus of elasticity and rupture and splitting tensile strength) of concrete. Main test parameters were water-to-cement ratio and bottom ash aggregate contents for replacement of natural sand. Test results showed that the 28-days compressive strength of concrete and mechanical properties normalized by the compressive strength tended to decrease with the increase in bottom ash fine aggregate content. When compared with fib 2010 model equations, bottom ash aggregate concrete exhibited the following performances: lower rates of compressive strength gain at early ages but greater rates at long-term ages; slightly higher measurements for modulus of elasticity and rupture; and lower measurements for splitting tensile strength.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.4
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• pp.596-603
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• 2020

In this paper, an experimental study was conducted to investigate the applications of bottom ash, which is an industrial by-product obtained from thermal power plants. Bottom ash was used as fine aggregate in this study, and an experiment was conducted to determine the characteristics of the bottom ash aggregate. In addition, 25, 50, 75, and 100% contents of crushed (natural) fine aggregate were replaced with bottom ash aggregate to produce concrete mixture including bottom ash. Thereafter, test results of the unit weight, ultrasonic velocity, compressive strength, and thermal conductivity of bottom ash concrete were obtained. Moreover, the effect of the curing ages of 28 and 91 days on the material characteristics of bottom ash concrete were identified. Test results showed that bottom ash used as fine aggregate had pozzolanic reaction. Finally, based on the extensive experimental results, relationships between thermal conductivity and unit weight, ultrasonic velocity, and compressive strength was suggested.

• Journal of the Korean Recycled Construction Resources Institute
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• v.9 no.2
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• pp.161-166
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• 2021

This study was on leaching test(KSLT) of the aggregate for the products to evaluate the characteristics of contaminants and the possibility of contamination arising from the aggregate. On the basis pH, conductivity, turbidity, TN, TP, COD and heavy metal contents in the aggregate increased as the particle size of the aggregate was smaller. The pH appeared to be 9.9~11.4 which is relatively higher than soil, however, heavy metal has investigated within the 1 region's standard value of soil pollution standards. From the leaching test, there is strong indication that the risk of pollution due to elution of pollutants gets higher with the smaller grain size. Especially conductivity and turbidity are the potential water pollution source and recycled aggregates of 10mm or less could be a potential pollution source since it could elute soluble matters and suspended solid, but there is no proper management standard for them. As a result of evaluating water pollution possibility of the aggregate, the pH displayed in items with a very high possibility of contamination, TN and TP did in item with a low possibility of contamination and on the other hand the heavy metals did in item with a very low possibility of contamination.

• Journal of the Korean Recycled Construction Resources Institute
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• v.12 no.1
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• pp.53-62
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• 2024

In this paper, an experimental study on the strengths and material properties of concrete manufactured by using coal gangue, as a fine aggregate was conducted. Experimental parameters included coal gangue aggregate contents as a replacement of fine aggregate by 50 % and 100 % (by volume) and fly ash contents. The water-binder ratio was fixed at 0.38. In addition, 30 % of the OPC binder was replaced with fly ash in some mixtures. Test of the unit weight, compressive, split tensile, and flexural tensile strength of concrete were performed and test results were analyzed. Unit weight, compressive strength, split tensile strength, and flexural tensile strength decreased as the coal recycled aggregates increased. In addition, TGA and SEM experiments, which are microstructure experiments, were conducted to analyze thermogravimetric analysis and ITZ by section.