• Journal of the Korean Recycled Construction Resources Institute
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• v.2 no.1
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• pp.113-119
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• 2006

It is now established that more than two types of blended aggregate have beneficial effects on quality and supply of concrete in the long run. However, studies on blended aggregate have not widely been progressive and the evaluation method of its most favorable mixture proportion is still needed. Therefore this study investigated the most favorable mixture proportion through the physical experiment of fresh and hardened state's cement mortar, in response to three types of composite ratio, natural fine aggregate(Ns), crushed fine aggregate(Cs) and recycled fine aggregate(Rs). Test showed that increase of blending ratio of Ns and Cs improved fluidity of mot1ar. For the properties of compressive and flexural strength, mortar blending Ns and Cs properly, exhibited similar value to one using only Cs, while mortar mixing Rs showed lower strength value as less as 6% of control one. Mortar using only Rs exhibited the largest drying shrinkage value. In addition, even thought it is not a clear quantitative analysis, technical-imaging-skill presenting the most favorable mixture proportion 3-dimensionally is proposed in this research, in order to notify the proportion easily.

• Resources Recycling
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• v.15 no.2 s.70
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• pp.24-31
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• 2006

The duality of recycled fine aggregate (RS) which was produced at the waste concrete crushing was investigated. The compressive strength, flexural strength and absorption of mortar utilized with RS were examined. It was evaluated on the application of RS as precast concrete aggregate. The density and absorption of RS were $2.31g/cm^3$ and 8.07% respectively, the quality of RS was satisfied with the criterion of KS F 2573 type 2. The maximum 28days compressive strength of mortar mixed with blended cement MRS1, MRS2 and MRS3 were developed with 15.8, 27.4 and 48.7MPa respectively, in condition to curing temperature $40^{\circ}C$ and water-cement ratio 37.5%. When blended cement MRS1 and MRS2 were used, the maximum flexural strength of mortar was developed at curing temperature $40^{\circ}C$ and water-cement ratio 35.0%. When blended cement MRS3 was used, the maximum flexural strength of mortar was developed at curing temperature $40^{\circ}C$ and water-cement ratio 37.5%. The absorption of mortar mixed with blended cement MRS1, MRS2 and MRS3 were indicated the range of $8.3{\sim}7.3%,\;6.5{\sim}8.5%$ and $3.5{\sim}6%$ respectively. Therefore, when the ratio of blended cement and RS is appropriately centre]led, it would be expected that MRS1, MRS2 and MRS3 will be able to apply the variable low strength, medium strength and high strength precaste concrete.

• Journal of the Korean Recycled Construction Resources Institute
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• v.7 no.3
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• pp.49-55
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• 2012

In this paper, the physical properties of lightweight aggregate such as density and water absorption according to addition ratio and type of flux were investigated. When using $Na_2CO_3$ as flux of lightweight aggregate, burnability was available at low burning temperature and water absorption increased. And as increasing addition ratio of $CaCO_3$, NaOH, $Fe_2O_3$, absorption decreased and $CaCO_3$, NaOH, $Fe_2O_3$ were considered improper to use flux of lightweight aggregate because of high dried density. $Na_2SO_4$ was proper to use flux of lightweight aggregate due to dried density $1.35{\sim}1.50g/cm^3$ and lower absorption. When using glass abrasive sludge as flux of lightweight aggregate, dried density and water absorption were in the range of $1.45{\sim}1.55g/cm^3$ and 9~12% respectively. It was indicated that as increasing addition ratio of blast furnace slag powder, density increased whereas absorption decreased. In use of oxidizing slag as flux, artificial lightweight aggregate which have dried density $1.46g/cm^3$, water absorption 8,5 % can be manufactured at 10 % of addition ratio.

• Journal of the Korean Recycled Construction Resources Institute
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• v.3 no.1
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• pp.15-21
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• 2015

Recently, attempts of replacing some of natural aggregate with mix of low quality aggregate are carried out for stable supply of aggregate. However, low quality aggregate such as recycled aggregate produced during the disposal process of construction wastes and by-product aggregate produced by industrial activities has problem of failing to comply to KS Standards. Therefore, we have compared fundamental properties of concrete by using granite crushed aggregate, recycled aggregate, blast furnace and electric arc furnace slag aggregate for effective utilization of lacking aggregate resources. As the result, slump in case of mixed use of aggregate was increased 0~10% compared to single use. Therefore, it is judged to be economically advantageous as it can expect effects in unit quantity or reduction of SP agent. Compressive strength in case of mixed use of aggregate was increased 0~10% compared to single use as it filled internal crevice of concrete with continuous particle size distribution. Accordingly, if we utilize by satisfying standard particle scope through mix of aggregate with different cause of formation in proper ratio, it was possible to confirm utility of mixed aggregate with demonstration of effects of increases of fluidity and compressive strength of concrete.

• Journal of the Korea Institute of Building Construction
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• v.12 no.5
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• pp.490-502
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• 2012

The use of recycled aggregate, even for low-performance concrete, has been very limited because recycled aggregate, which contains a large amount of old mortar, is very low in quality. To produce a high-quality recycled aggregate, removing the paste that adheres to the recycled aggregate is very important. We have conducted research on a complex abrasion method, which removes the component of cement paste from recycled fine aggregate by using both a low-speed wet abrasion crusher as a mechanical process and neutralization as chemical processes, and well as research on the optimal manufacturing condition of recycled fine aggregates. Subsequently, we evaluated the quality of recycled fine aggregate manufactured using these methods, and tested the specimen made by this aggregate. As a result, it was found that recycled fine aggregates produced by considering the aforementioned optimal abrasion condition with the use of sulfuric acid as reactant showed excellent quality, recording a dry density of 2.4 and an absorption ratio of 2.94. Furthermore, it was discovered that gypsum, which is a reaction product occurring in the process, did not significantly affect the quality of aggregates. Furthermore, the test of mortar using this aggregate, when gypsum was included as a reaction product, showed no obvious retarding effect. However, the test sample containing gypsum recorded a long-term strength of 25.7MPa, whereas the test sample that did not contain gypsum posted a long-term strength of 29.4MPa. Thus, it is thought to be necessary to conduct additional research into the soundness and durability because it showed a clear reduction of strength.

• Journal of the Korean Recycled Construction Resources Institute
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• v.10 no.3
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• pp.327-334
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• 2022

In this study, in order to evaluate the characteristics of mortar and concrete using wood chip cogeneration plant flooring as fine aggregate, mortar characteristics according to wood chip aggregate replacement rate and water-cement ratio as a substitute for crushed sand, and concrete characteristics according to wood chip aggregate replacement rate were compared and evaluated. The cement mortar flow according to the wood chip aggregate replacement rate showed a tendency to increase as the wood chip aggregate replacement rate increased, and the compressive strength and flexural strength increased as the wood chip aggregate replacement rate increased. The slump and air content of concrete increased as the aggregate replacement rate increased, and the compressive strength and tensile splitting strength of concrete tended to increase as the wood chip aggregate replacement rate increased. Accordingly, the possibility of using the flooring by the cogeneration plant as a fine aggregate for concrete was confirmed.

• Journal of the Korea Concrete Institute
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• v.28 no.4
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• pp.435-444
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• 2016

In Korea, approximately 48% of all households live in apartments, which are a form of multi-unit dwellings, and this figure increases up to 58%, when row houses and multiplex houses are included. As such, majority of the population reside in multi-unit dwellings where they are exposed to the problem of floor impact noise that can cause disputes and conflicts. Accordingly, this study was conducted to manufacture a high-weight, high-stiffness foamed concrete in order to develop a technology to reduce the floor impact noise. For the purpose of deriving the optimum mixing ratio for the foamed concrete that best reduces the floor impact noise, the amounts of the foaming agent, lightweight aggregate and binder were varied accordingly. Also, the target characteristics of the concrete to be developed included density of over $0.7t/m^3$, compressive strength of over $2.0N/mm^2$ and thermal conductivity of under 0.19 W/mK. The results of the experiment showed that the fluidity was very excellent at over 190 mm, regardless of the type and input amount of foaming agent and lightweight aggregate. The density and compressive strength measurements showed that the target density and compressive strength were satisfied in the specimen with 50% foam mixing ratio for foamed concrete and in all of the mixtures for the lightweight aggregate foamed concrete. In addition, the thermal conductivity measurements showed that the target thermal conductivity was satisfied in all of the foamed concrete specimens, except for VS50, in the 25% replacement ratio case for Type A aggregate, and all of the mixtures for Type B aggregate.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.1
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• pp.1-9
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• 2014

Recently, natural aggregate was adequate to supply the demand due to increase of building construction. National pollution induced by construction waste caused by the reconstruction and redevelopment was cited as the major social issues in Korea. Therefore, government are required by law to use the recycled aggregate. In order to consider safety, KS F 2573 recommend that recycled aggregate with below design strength 27MPa and replacement ratio of 30%. This study on flexural behaviors of reinforced concrete beam was conducted and the specimens employed in test were planed with high strength concrete (40, 50 and 60MPa) and recycled aggregate replacement ratio (0, 30, 50, 100%). Although the flexural strength of reinforced concrete beam has trendy to decrease with increase of replacement ratio, it is meet to KCI 2007. The comparison results show that reinforced concrete beam using recycled aggregate can apply as flexural member in building construction.

• Journal of the Korean Recycled Construction Resources Institute
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• v.10 no.4
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• pp.359-366
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• 2022

In this paper, the effect of compression levels on the strengths of porous concrete using bottom ash aggregates was analyzed. Coal bottom ash (CBA) was used as aggregate in porous concrete in this study. The aggregate size types used in the CBA concrete mixtures were catagorized into two different ones. One included only a single aggregate particle size and the other included hybrid aggregate particles mixed at a ratio of 8:2 volume proportion. The water-binder ratio was fixed at 0.30, and the compression levels were applied at 0.5, 1.5, and 3.0 MPa valu es to fabricate a porou s concrete specimen. The total porosity, compressive, splitting tensile, and flexural tensile strengths were tested and analyzed. When the compression level increased, the total porosity decreased, meanwhile the compressive, split tensile, and flexural tensile strengths increased. The total porosity of concrete using hybrid aggregate was lower and the strength was larger than those of concrete using single-type aggregate. Finally, the correlation between the total porosity, compressive, split tensile, and flexural tensile strengths of porous concrete were presented. The total porosity and strength characteristics showed an inversely proportional correlation.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.329-332
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• 2008

Recently, land sand is being used more because of the deficiency of river sand. In this paper, in order to manufacture high strength concrete in the range of 70MPa, the effect of sand/aggregate ratio and adding fly-ash. As results, we could come to conclusion that the reduction of sand/aggregate ratio caused the increase of fluidity in the range of $37{\sim}45%$ and the maximum strength was 77MPa obtained at S/a=39%, which could be considered as optimum S/a. Besides, we could also get a conclusion that the larger amount of fly-ash increased the fluidity within 20% of replacement ratio (fly-ash to cement ratio) and the compressive strength at the age of 28days was equal to or larger than that of plane concrete, which represented no replacement by fly-ash, at the same range. from the results, it could be seen that the optimum replacement ratio of fly-ash was in the range of $10{\sim}15%$.