• Journal of the Korea Concrete Institute
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• v.13 no.5
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• pp.438-446
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• 2001

Recently, porous concrete has been used for the purpose of decreasing the load of earth environment. It consists solely of cement, water and uniform-sized coarse aggregate. And its fundamental properties will be considerably affected by the physical properties of aggregate because the aggregate occupies for the most part in its mix proportion. For such a reason, this study was carried out to investigate the influence of the sizes and kinds of aggregate for the fundamental properties of porous concrete. It showed that the fundamental properties of porous concrete were the similar value in all sizes of aggregate except in the case of using the 2.5∼5㎜ aggregate and were varied according to the kinds of aggregate. In particular, compressive strength of porous concrete using 2.5∼5㎜ aggregate was more higher than that using other aggregate, and its void ratio and coefficient of permeability was lower. And the maintenance capacity of permeability of porous concrete was varied by the sizes and the kinds of aggregate. In particular, it was greatly decreased in case of using the 2.5∼5㎜ aggregate. And unlike dynamic modulus of elasticity of ordinary concrete, that of porous concrete was very high value in early ages and was slowly increased after that time.

• 레미콘
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• no.12 s.14
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• pp.4-19
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• 1987

다음은 한국레미콘공업협회가 87.9.26개최한 제3회 레미콘기술세미나에서 충남대 건축공학과 김무한 교원ㆍ남재현 강사가 발표한 내용을 전재했다.

• Journal of the Korean Geotechnical Society
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• v.33 no.12
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• pp.35-44
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• 2017

A large amount of recycled aggregates was produced and crushed from old buildings and pavements. In this study, when these aggregates are re-used in subbase or subgrade materials in near construction sites, their engineering characteristics caused by crushing are investigated in terms of permeability and shear strength. Three different sizes of aggregates (31.5-45.0 mm, 19.0-31.5 mm, 9.5-19.0 mm) and their mixtures, a total of 7 types of aggregates were used in compaction tests (modified D and B methods). After compaction tests, aggregates were sieved and analyzed with four different breakage factors ($B_{15}$, $C_c$, $B_{10}$, $B_r$). The D compaction method gave 2.0-8.0 times more crushable than B compaction method. The breakage factors for the largest size aggregate was 1.4-3.0 times higher than those of the smallest size aggregate. For aggregates with 5.6-9.5 mm sizes, the samples were prepared with $B_{15}$ of 1, 3, 10, 20, 30, 50, 60, and 70 for permeability and direct shear tests. As $B_{15}$ increased, the hydraulic conductivity decreased up to 1/22 for $B_{15}=50$. As $B_{15}$ increased from 1 to 50, the peak friction angle increased from $46.1^{\circ}$ to $54.5^{\circ}$. On the other hand, the friction angle decreased after $B_{15}=60$.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.3
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• pp.317-324
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• 2020

Plastic wastes generated from domestic waste are separated by mixed discharge with foreign substances, and the cost of the separation and screening process increases, so recycling is relatively low. In this study, as a fundamental study for recycling mixed plastic wastes generated from domestic waste into concrete aggregates, changes in concrete properties according to the plastic waste types and the substitution rate were evaluated experimentally. The mixed plastic waste aggregate(MPWA) was found to have a lower density and a higher absorption rate compared to the coarse aggregate with good particle size distribution. On the other hand, the single plastic waste aggregate(SPWA) was composed of particles of uniform size, and both the density and the absorption rate were lower than that of the fin e aggregate. It was found that the MPWA substitution concrete did not cause a material separation phenomenon due to a relatively good particle size distribution even with the largest amount of plastic waste substitution, and the amount of air flow increased little. The compressive strength and flexural strength of the PWA substitution concrete decreased as the amount of substitution of the PWA increased due to the low strength of the PWA, the suppression of the cement hydration reaction due to hydrophobicity, and the low adhesion between the PWA and the cement paste. It was found that the degree of deterioration in compressive strength and flexural strength of concrete substituted with MPWA having good particle size distribution was relatively small.

• International Journal of Highway Engineering
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• v.14 no.1
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• pp.45-53
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• 2012

This study was performed to analyze test results on drying shrinkage for concrete specimens mixed with various constituents in concrete mixes. Test variables are coarse aggregate types(Limestone, Sandstone, Granite, Andesite, Gneiss), fine aggregate types(natural sand, crushed sand) and cement amounts(normal strength, high strength). Epoxy coating of(U&V-H(A,B)) was applied onto the specimen surface to simulate diverse volume surface ratios(22.2, 40, 85.7, 150, 200, 300) with different specimen sizes. The experiments had been executed during 1,014 days at a condition of $20^{\circ}C$ and relative humidity of 60% in environmental chambers. Test results showed that shrinkage strain from the specimen equivalent to real pavement decreased to 39% compared to the standard specimen recommended by KS. Test results also showed that shrinkage strain of the specimen mixed with Limestone was 56~76% of that with Sandstone, thus Limestone mix seems to be suitable to the concrete pavement.

• Economic and Environmental Geology
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• v.50 no.4
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• pp.257-266
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• 2017

Batch experiments were performed to develop the method for the pH reduction of recycled aggregate by using $scCO_2$ (supercritical $CO_2$), maintaining the pH of extraction water below 9.8. Three different aggregate types from a domestic company were used for the $scCO_2$-water-recycled aggregate reaction to investigate the low pH maintenance of aggregate during the reaction. Thirty five gram of recycled aggregate sample was mixed with 70 mL of distilled water in a Teflon beaker, which was fixed in a high pressurized stainless steel cell (150 mL of capacity). The inside of the cell was pressurized to 100 bar and each cell was located in an oven at $50^{\circ}C$ for 50 days and the pH and ion concentrations of water in the cell were measured at a different reaction time interval. The XRD and SEM-EDS analyses for the aggregate before and after the reaction were performed to identify the mineralogical change during the reaction. The extraction experiment for the aggregate was also conducted to investigate the pH change of extracted water by the $scCO_2$ treatment. The pH of the recycled aggregate without the $scCO_2$ treatment maintained over 12, but its pH dramatically decreased to below 7 after 1 hour reaction and maintained below 8 for 50 day reaction. Concentration of $Ca^{2+}$, $Si^{4+}$, $Mg^{2+}$ and $Na^+$ increased in water due to the $scCO_2$-water-recycled aggregate reaction and lots of secondary precipitates such as calcite, amorphous silicate, and hydroxide minerals were found by XRD and SEM-EDS analyses. The pH of extracted water from the recycled aggregates without the $scCO_2$ treatment maintained over 12, but the pH of extracted water with the $scCO_2$ treatment kept below 9 of pH for both of 50 day and 1 day treatment, suggesting that the recycled aggregate with the $scCO_2$ treatment can be reused in real construction sites.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.4
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• pp.537-544
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• 2020

The interfacial transition zone(ITZ) which is the boundary layer between cement composites and aggregates is considered to be the region of gradual transition, heterogeneous, and the weakest part of concrete. For the development of lightweight high strength concrete, it is essential to evaluate the mechanical properties of ITZ between high strength concrete with low water-binder ratio and lightweight aggregates. However, the mechanical properties of ITZ are not well established due to its high porosity and complex structure. Furthermore, the properties of ITZ in concrete using lightweight aggregates are dominated by more various variations (e.g. water-binder ratio, water absorption capacity of aggregate, curing conditions) than normal-weight aggregate concrete. This study aims to elucidate the mechanical properties of ITZ in lightweight high-strength cement composites according to the types of aggregates and the aggregate sizes. Nanoindentation analysis was used to evaluate the elastic modulus of ITZ between high strength cement composites with the water-binder ratio of 0.2 and normal sand, lightweight aggregate with different aggregate siz es of 2mm and 5mm in this study.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.14 no.4
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• pp.357-365
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• 2016

We observed the ${\gamma}-ray$ shielding characteristics and compressive strength of five types of concrete using general aggregates and high-weight aggregates. The aggregates were classified into fine aggregate and coarse aggregate according to the average size. The experimental results obtained an attenuation coefficient of $0.371cm^{-1}$ from a concrete with the oxidizing slag sand (OSS) and oxidizing slag gravel (OSG) for a ${\gamma}-ray$ of $^{137}Cs$, which is improved by 2% compared with a concrete with typical aggregates of sand and gravel. In the unit weight measurement, a concrete prepared by iron ore sand (IOS) and OSG had the highest value of $3,175kg{\cdot}m^{-3}$. Although the unit weight of the concrete with OSS and OSG was $3,052kg{\cdot}m^{-3}$, which was lower than the maximum unit weight condition by $123kg{\cdot}m^{-3}$, its attenuation coefficient was improved by $0.012cm^{-1}$. The results of chemical analysis of aggregates revealed that the magnesium content in oxidizing slag was lower than that in iron ore, while the calcium content was higher. The concrete with oxidizing slag aggregates demonstrated enhanced ${\gamma}-ray$ shielding performance due to a relatively high calcium content compared with the concrete with OSS and OSG in spite of a low unit weight. All sample concretes mixed with high-weight aggregates had higher compressive strength than the concrete with typical sand and gravel. When OSS and IOS were used, the highest compressive strength was 50.2 MPa, which was an improvement by 45% over general concrete, which was achieved after four weeks of curing.

• Journal of the Korean Geotechnical Society
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• v.32 no.11
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• pp.21-29
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• 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 Korean Recycled Construction Resources Institute
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• v.4 no.2
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• pp.101-111
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• 2016

It is possible that aggregates add on to geopolymer based fly ash to mix mortar and concrete like cement. This is necessary to evaluate mineral composition, particle shape, surface, size distribution, density and absorption ratio for fine aggregates due to few detailed research to examine influence of fine aggregates properties on unhardened geopolymer concrete. In this research, used two different fine aggregates, Jumunjin sand(having quartz, mica, feldspar, pyroxene in mineral composition, more than 96% of total size between -0.60 and +0.30mm, angular shape and rough surface) and ISO sand(having almost all quartz in mineral composition, more than 51% size between -1.40 and +0.60mm, simultaneously varied size distribution, spherical shape and smooth surface). After an experimental result of the varied ratio of Si/Al=1.0-4.1 geopolymer paste, mix proportion respectively applied Si/Al=1.5 having the highest compressive strength to mortar and Si/Al=3.5 having the highest consistency to concrete. Geopolymer mortar by mixing with Jumunjin and ISO sand in varied range of 20-50wt.% showed flow size increase between 69.5 and 112.0mm, between 70.5 and 126.0mm respectively. Geopolymer concrete at an addition of 77wt.% of total aggregates ratio showed that average compressive strength was 32MPa and the consistency was favorable to molding. Since ISO sand observing varied size distribution, spherical shape, smooth surface, low absorption ratio resulted in advantageous properties on consistency of geopolymer, geopolymer concrete can be suitable for using the fine aggregates similar to ISO sand.