• Resources Recycling
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• v.10 no.1
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• pp.16-24
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• 2001

In this study, various mechanical properties of concretes employing waste concrete as aggregate were examined. These concretes were obtained by mixing seven types of aggregate for different ratios. So, the experimental variables are the kinds of aggregates (some different aggregate compositions) and W/C ratio (0.40, 0.45, 0.50). From experimental results, the reliable regression analysis equations between compressive strength and various experimental data for recycled aggregate concrete are presented. Consequently, this study was accomplished to investigate basic engineering properties of recycled aggregate concrete using waste concrete.

• Journal of the Korean Recycled Construction Resources Institute
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• v.2 no.2
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• pp.145-151
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• 2014

This paper evaluated the quality properties of Finex Water Granulated Slag fine aggregate as part of a study to recycle the Finex Water Granulated Slag generated in korea, and examined the availability as fine aggregate for concrete by comparing properties (properties of fresh concrete, mechanical properties of hardened concrete) of concrete using Finex Water Granulated Slag fine aggregate with properties of concrete using river sand as fine aggregate. From the results of this study, it was found that quality properties of concrete using finex water granulated slag as fine aggregate and concrete using river sand as fine aggregate are equivalent level.

• Journal of the Korean Recycled Construction Resources Institute
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• v.6 no.4
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• pp.75-81
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• 2012

In case of crushing rock to produce materials for lean concrete subbase layer in concrete pavement, natural sand is used for the gradation adjustment of aggregates, and the percentage of natural sand used is 30%~40% of the weight ratio of aggregate mix. The supply of natural sand that is used in lean concrete as a fine aggregate is getting harder due to the current of exhaustion of source, and the cost for the purchase of natural sand is included in the cost of roadway construction. This study, therefore, was conducted in order to resolve the exhaustion of materials and economize in construction expenditure by the application of screenings, which is by-product of crushing rock in quarry, as an alternative to natural sand. As a result of a comparative analysis on the application of screenings and natural sand with typical types of rock that is produced in domestic, which was conducted in the first year, It is found out that the use of screenings as a fine aggregate showed better unconfined compression strength. Verification of actual application of screenings was conducted in the second year, after test construction and follow-up investigation. The compressive strength, compaction density, settlement of screenings applied case was higher than that of natural sand. Thus, it is expected that application of screenings to construction in field will contribute to the cost saving, material recycling and the protection of environment.

• International Journal of Highway Engineering
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• v.9 no.4
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• pp.93-104
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• 2007

This study evaluates the mechanical properties of steel fiber reinforced porous concrete for pavement according to content of slag aggregate and fly ash to elicit the presentation of data and the way to enhance its function for the practical field application of porous concrete as a material of pavement. As a result, void ratio and permeability coefficient of porous concrete for pavement increased a little as mixing rate of slag aggregates increased. Void ratio and permeability coefficient increased a lot as mixing rate of fly ash decreased. As fly ash was mixed, national regulation of permeable concrete for pavement(8% and 0.1 cm/sec) was met. Compressive strength and flexural strength decreased as mixing rate of slag aggregates increased, but they increased a lot as mixing rate of fly ash increased. Even when slag aggregates were mixed 50% with 5% fly ash mixed, national regulation of pavement concrete(18MPa and 4.5MPa) was met. In addition, compared to non-mixture, flexural strength increased about 22.8% when 0.75vol.% of steel fiber was added. Regarding sliding resistance, BPN increased as mixing rate of slag aggregates increased. But BPN decreased as fly ash was mixed. Compared to crushed stone aggregates, abrasion resistance and fleers-thaw resistance decreased as mixing rate of slag aggregates increased. When fly ash was mixed, abrasion resistance and freeze-thaw resistance improved remarkably. Compared to non-mixture, 10% mixture of fly ash improved abrasion resistance and freeze-thaw resistance about 5.6% and 14.3 respectively.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.5
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• pp.95-102
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• 2020

For the purpose of developing a PE fiber-reinforced highly ductile cementitious composite having high tensile strain capacity more than 2% under the condition of containing aggregates with large particle size, this study investigated the tensile behavior of composites according to the particle size and distribution of aggregates in the composite. Compared with the mixture containing silica sand of which particle size is less than 0.6 mm, mixtures containing river sand and/or gravel with the maximum particle size of 2.36 mm, 4.75 mm, 5.6 mm, 6.7 mm were considered in the experimental design. The particle size distributions of aggregates were adjusted for the optimized distribution curves obtained from modified A&A model by blending different sizes of aggregates. All the mixtures presented clear strain-hardening behavior in the direct tensile tests. The mixtures with the blended aggregates to meet the optimum curves of aggregate size distributions showed higher tensile strain capacity than the mixture with silica sand. It was also found that the tensile strain capacity was improved as the maximum size of aggregate increased which resulted in wider particle size distribution. The mixtures with the maximum size of 5.6 mm and 6.7 mm presented very high tensile strain capacities of 4.83% and 5.89%, respectively. This study demonstrated that it was possible to use coarse aggregates in manufacturing highly ductile fiber-reinforced cementitous composite by adjusting the particle size distribution.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.12
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• pp.34-41
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• 2020

Ready-mixed concrete is unconsolidated concrete typically transported to construction sites by using mixer trucks. A proper rotation of concrete is necessary to prevent its solidification in mixer trucks during transport: in accordance with the manufacturing method and quality inspection prescribed in KSF4009, this movement is maintained after the manufacturing of concrete in professional production plants and the addition of water, solid materials, and admixtures. Unfortunately, mixer truck parts wear out over long periods of time. In order to improve the wear resistance of the main part of mixer trucks, we used a steel plate with good wear resistance or partially added a reinforcement plate. In this study, we first tested the properties of concrete (as required for the DEM), and then carried out mixing and discharge simulations to define the actual operating conditions of mixer trucks. For each condition, we calculated the amount and location of wear. The reliability of our results was finally verified by comparing them with the measurement values. Overall, this study provided basic data for an optimal design of mixer trucks: one that would reduce the vehicles' weight and production costs.

• Journal of the Korea Concrete Institute
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• v.13 no.1
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• pp.23-29
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• 2001

This study presented the experimental results on the durability properties of recycled aggregate concrete incorporating fly ash. The main experimental variables were the substitution ratio of recycled aggregate and fly ash, where the substitution ratios of recycled aggregate were 0, 30, and 50%, and those of fly ash were 0, 10, 20, and 30%. The tests for evaluating compressive strength, freezing-thawing resistance, and drying shrinkage were conducted for each specimen. As a result, the compressive strength and the durability of the recycled aggregate concrete were compared from those of ordinary concrete. The followings were conclusion; The compressive strengths of recycled aggregate concrete were less than those of ordinary concrete by 5-10%. However, the durability factor of recycled aggregate concrete remained above 90% at the substitution ratio of 30%. The quality of recycled aggregate concrete were improved by substitution at the range of less that 20% of fly ash and 30% of recycled aggregate.

• Journal of the Korean Recycled Construction Resources Institute
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• v.6 no.1
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• pp.95-102
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• 2011

Vicker's hardness and pore size distribution of mortar adhered to the recycled coarse aggregate were tested according to the strength level of original concrete of recycled coarse aggregate to find the change of mortar adhered to the recycled coarse aggregate in cement paste. The strength levels of original concrete of recycled coarse aggregate were 25.5MPa, 41.7MPa and 60.1MPa and the aggregates were used at the state of saturated surface dry condition and oven dry condition. The results of this experimentation indicated that the mean value of Vicker's hardness was increased according to age and strength of original concrete of recycled aggregate. Porosity of $100nm{\sim}10{\mu}m$ size was reduced and porosity of 6nm~100nm size was increased in cement paste.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.389-392
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• 2008

Ultra-high strength concrete becomes one of the main research areas because recently concrete structure is larger. The quality of aggregate (ultra-high strength and uniformity) as well as chemical admixture and mineral additives is a key factor for ultra-high strength concrete development. However, natural aggregate including crushed aggregate is inappropriate for ultra-high strength concrete because ultra-high strength quality cannot be maintained uniformly over whole natural aggregate lot. In this study ceramic aggregate was applied for ultra-high strength concrete in order to assure uniform quality of ultra-high strength aggregate. Ultra-high strength concrete was achieved by applying coated ultra-high strength ceramic aggregate to enhance the bonding strength between aggregate and cement paste. Also for actual application light weight ceramic aggregate(density 2.2 $g/cm^3$) with zero water absorption was tested.

• Resources Recycling
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• v.30 no.5
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• pp.17-24
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• 2021

Natural aggregate regular exploitation has led to environmental and resource depletion issues; consequently, construction waste has become an important raw material in the supply of aggregate smoothly. The recycled aggregate produced in the most of recycled aggregate processing company in Korea has a high adhesion ratio of cement paste and mortar, which affects the water absorption ratio and density. Therefore, the quality of recycled aggregate needs to be improved. In this study, we improved the quality of recycled aggregate through the use of a multistage separation ball mill. This ball mill has a sieve which protects the ball mix and improves the motion. Products produced by using multistage separation ball mill were compared with various quality standard for utilization as recycle aggregate. Finally, we confirmed that the multistage separation ball mill can efficiently separate cement paste and mortar from natural aggregate and that it is suitable for the production of recycled aggregates.