• Korean Journal of Agricultural Science
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• v.18 no.2
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• pp.140-147
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• 1991

This paper was performed to obtain the data applied to use of synthetic lightweight aggregate concrete affected by alkali silica reaction. The results obtained were summarized as follows : 1. The expansion of each type concrete was increased with increase of curing age, respectively. Also, at the curing age 90 days, the rate of expansion of type A, B, C and D concrete was increased 0.173%, 0.575%, 0.230% and 0.680%, respectively. Specially, the rate of expansion of type D concrete was shown 3.93 times higher than the type A concrete. The cracks width were increased with increase of expansion and at the 0.680% expansion, the maximum width was shown 0.5 mm. 2. The dynamic modulus of elasticity of each type concrete was increased with increase of curing age, respectively. At the curing age 30 days, the highest dynamic modulus of elasticity was showed at each type concrete, respectively. But, it was gradually decreased with increase of curing age at those concrete, respectively. Also, at the curing age A, B, C and D concrete was increased 24.3%, 33.7%, 28.1% and 37.0%, respectively. The rate of loss in type D concrete was shown 1.52 times higher than the type A concrete. 3. The ultrasonic pulse velocity of each type concrete was increased with increase of curing age, respectively. At the curing age 30 days, the highest ultrasonic pulse velocity was showed at each type concrete, respectively. But, it was gradually decreased with increase of curing age at those concrete, respectively. Also, at the curing age 90 days, the percentage loss of ultrasonic pulse velocity of type A, B, C and D concrete was increased 6.4%, 8.7%, 8.5% and 14.2%, respectively. The rate of loss in type D concrete was shown 2.21 times higher than the type A concrete. 4. The relation between dynamic modulus of elasticity and ultrasonic pulse velocity was highly significant. The dynamic modulus of elasticity was increased with increase and decreased with decrease of ultrasonic pulse velocity. Also, the decreasing rate of the dynamic modulus of elasticity was shown 2-7 times higher than the ultrasonic pulse velocity at each age, respectively. 5. The dynamic modulus of elasticity and ultrasonic pulse velocity were decreased with increase of expansion, and the decreasing rates were increased with increase of curing age. The increasing rate of expansion was shown higher than the decreasing rate of dynamic modulus and ultrasonic pulse velocity.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.2A
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• pp.129-136
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• 2011

Recently studies on functional concrete with a photocatalytic material such as $TiO_2$ have actively been carried out in order to remove air pollutants. The absorbtion of $TiO_2$ from those studies is applied by it being directly mixed into concrete or by suspension coated on the surface. When it comes to the effectiveness, the former process is less than that of the latter compared with the $TiO_2$ use. As a result, the direct coating of $TiO_2$ on materials' surface is more used for effectiveness. The Surface spread of it needs to have a more than $400^{\circ}C$ heat treat done to stimulate the activation and adhesion of photocatalysis. Heat treat consequently leads hydration products in concrete to be dehydrated and shrunk and is the cause of cracking. The study produces $TiO_2$ used Sol-gel method which enables it to be coated with a low temperature treat, applies it to pearlite using Lightweight Aggregate Concrete fixed with a low temperature treat and evaluates the spread performance of it. In addition to this, the size of pearlite is divided into two types: One is 2.5 mm to 5.0 mm and the other is more than 5.0 mm for the benefit of finding out the removal characteristics of $CH_3CHO$ whether they are affected by pearlite size, mixing method and ratio with $TiO_2$ and elapsed time. The result of this experiment shows that although $TiO_2$ produced by Sol-gel method is treated with 120 temperature, it maintains a high spread rate on the XRF(X ray Florescence) quantitative analysis which ranks $TiO_2$ 38 percent, $SiO_2$ 29 percent and CaO 18 percent. In the size of perlite from 2.5 mm to 5.0 mm, the removal characteristic of $CH_3CHO$ from a low temperature heated Lightweight concrete appears 20 percent higher when $TiO_2$ with Sol-gel method is spreaded on the 7 percent of surface. In other words, the removal rate is 94 percent compared with the 72 percent where $TiO_2$ is mixed in 10 percent surface. In more than 5.0 mm sized perlite, the removal rate of $CH_3CHO$, when $TiO_2$ is mixed with 10 percent, is 69 percent, which is similar with that of the previous case. It suggests that the size of pearlite has little effects on the removal rate of $CH_3CHO$. In terms of Elapsed time, the removal characteristic seems apparent at the early stage, where the average removal rate for the first 10 hours takes up 84 percent compared with that of 20 hours.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.35 no.3
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• pp.533-544
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• 2015

Unlike the concrete structure built on land, that exposed to the marine environment is greatly degraded in durability due to the exposure to not only the physical action caused by sea wind, tide, and wave, but also the harsh conditions, including the chemical erosion and freeze-thaw which result from $SO_4{^{2-}}$, $Cl^-$ and $Mg^{2+}$ ions in seawater. In the process of the large scaled construction of submerged concrete structures, of course environmental hazardous substance, such as alkaline (pH) and heavy metals, may be leached. Thus, this issue needs to be adequately reviewed and studied. Therefore, this study attempted to develop a CSA (Calcium Sulfo Aluminate) activator using electric arc furnace reducing slags, as well as the eco-friendly concrete for artificial reefs using electric arc furnace oxidizing slag as aggregate for concrete. The strength properties of the eco-friendly concrete exposed to the marine environment were lower than those of the normal concrete by curing 28 days. This suggest that additional studies are needed to improve the early strength of the eco-friendly concrete. With respect to seawater resistance of the eco-friendly concrete, the average strength loss against 1 year of curing days reached 8-9%. the eco-friendly concrete using high volume of ground granulated blast furnace slags and high specific gravity of electronic arc furnace oxidizing slag demonstrated the sufficient usability as a freeze-thaw resistant material. With respect to heavy metal leaching properties of the eco-friendly concrete, heavy metal substances were immobilized by chemical bonding in the curing process through the hydration of concrete. Thus, heavy metal substances were neither identified at or below environmental hazard criteria nor detected, suggesting that the eco-friendly concrete is safe in terms of leaching of hazardous substances.

• International Journal of Highway Engineering
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• v.12 no.1
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• pp.79-86
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• 2010

Cold in-place recycling (CIR) using emulsified asphalt or foamed asphalt has become a more common practice in rehabilitating the existing asphalt pavement due to its cost effectiveness and the conservation of paving materials. As CIR continues to evolve, the engineered emulsified asphalt was developed to improve the field performances such as coating, raveling, retained stability value and curing time. The main objective of this research is to compare the laboratory responses of the engineered emulsified asphalt (CIR-EE) mixtures against the foamed asphalt (CIR-foam) mixtures using the reclaimed asphalt pavement (RAP)materials collected from the CIR project on U.S. 20 Highway in Iowa. Based on the visual observation of laboratory specimens, the engineered emulsified asphalt coated the RAP materials better than the foamed asphalt because the foamed asphalt is to create a mastic mixture structure rather than coating RAP materials. Given the same compaction effort, CIR-EE specimens exhibited lesser density than CIR-foam specimens. Both Marshall stability and indirect tensile strength of CIR-EE specimens were about same as those of CIR-foam specimens. However, Marshall stability and indirect tensile strength of the vacuum-saturated wet specimens of CIR-EE mixtures were higher than those of CIR-foam mixtures. After four hours of curing in the room temperature, the CIR-EE specimens showed less raveling than the CIR-foam specimens. On the basis of test results, it can be concluded that the CIR-EE mixtures is less susceptible to moisture and more raveling resistant than CIR-foam mixtures.

• International Journal of Highway Engineering
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• v.13 no.1
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• pp.79-86
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• 2011

Recently, usage bicycle is encouraged to reduce fuel consumption and air pollution. For this purpose, bike road constructions are actively performed. However, types of pavement used in bike roads have high construction cost and performance comparing the required capacity of bike roads. Thus, an economical pavement type for construction is necessary for the effective development. Roller compacted concrete pavement have good requirements, such as easy construction and low costs, high structural performance of hydration and internal communication aggregation on compaction for bicycle roads. However, the pool landscape surface and resistance to deicer damage cannot be applied to the construction of bicycle roads. Thus, for solving this problem used coating which may have effect of improving the landscape and environmental resistance. To examine this effect were evaluated performance of roller compacted concrete pavement on the coating.

• Journal of the Korea Organic Resources Recycling Association
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• v.12 no.4
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• pp.85-94
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• 2004

Waste wood-plastic composite panels are made on different hot press molding conditions, and tested for apparent density, water absorption, expansion in thickness and flexural strength. From the test results, regardless of molding temperature and molding time, the apparent density of the composite panels is increased with an increase in the molding pressure, while their water absorption is decreased with an increase in the molding pressure. The flexural strength of the composite panels is markedly increased with increasing molding pressure, molding temperature and molding time, and tends to become nearly constant at a molding temperature of $120^{\circ}C$ and a molding time of 15min.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.5
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• pp.66-74
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• 2016

The objective of this study is the investigation of the influence of carbonation on the penetration of chloride ions in reinforced concrete sections for different mix proportions and environmental conditions. A comprehensive numerical model based on the change of the pore structure and the chemical equilibrium was used for this combined action of carbonation and chloride ingress. The empirical formulae of some parameters in this model are estimated according to numerous experimental data. And, a set of data analysis is carried out to simplify the estimation of model variables to reduce the computational cost. A coupled simulation of the transports of carbon dioxide, chloride ions, heat and moisture is carried out. Then, the parametric analysis is given and the numerical results show that the effect of carbonation of the free chloride ingress is significant and depends on the binder types and concrete mix proportion.

• The Journal of Korean Academy of Prosthodontics
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• v.48 no.4
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• pp.308-314
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• 2010

Purpose: The purpose of this study is to analyze the change in re-osseointegration over time and bone reaction at the interface between implant fixture and the surface of the bone, after destroying re-osseointegration by distorting the bone-implant interface artificially. Materials and methods: Experimental implant fixtures (cp titanium, ${\phi}3.75\;mm{\times}4\;mm$) which didn't have surface treatment were produced. Two or three fixtures were implanted on both tibias of twelve female rabbits (New Zealand white, more than 3.5 kg). Then after six weeks, removal torque (RT) was measured and the results were recorded as the first measurement values. The fixtures were submerged again to get reosseointegration between the bone and fixture. To identify the change in re-osseointegration of submerged fixtures over time, six groups had the healing time for four days (group I), one week (group II), two weeks (group III), three weeks (group IV), four weeks (group V) and five weeks (group VI), and then the secondary removal torque was measured for each group. To identify the bone formation under fluorescent light, tetracycline (15 mg/kg, IM) were treated on the rabbits of each group. After the second measurement, the rabbits were sacrificed, and 16 slides were made, two or three for each group. The slides were observed under the fluorescent light with light microscope. To find out the change in the secondary removal torque over the primary removal torque in progress of time, the averages of the increase rate of the primary and secondary torque removal force were calculated. Then, to find out if there were any critical differences between the primary removal torque and the secondary removal torque in each group and among the groups, the results were analyzed statistically by paired t- test, one-way ANOVA, and Duncan's Multiple Range Test. Results: In group I and II, secondary removal torque decreased, especially in group I. In group III, IV, V, and VI, secondary removal torque increased critically. Comparing the differences among the groups, the critical difference was shown between group I, II and group III, IV, V, VI. Mineralization at the interface between the bone and implant fixture was identified from the first week, and bone formation was shown more clearly from the second week. Conclusion: If the implant fixture remains unforced for a certain period of time after the fixture has had iatrogenic mobility, re-osseointegration occurs at the surface of the fixture, and for tibias of rabbits, higher re-osseointegration was obtained within two weeks.

• Journal of the Korea Concrete Institute
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• v.22 no.3
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• pp.287-295
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• 2010

In this study, ordinary Portland cement was used and the air void was minimized by using minute quartz as the filler. In addition, steel fibers were used to mitigate the brittle failure problem associated with high strength concrete. This study is in progress to make an Ultra-high strength powdered concrete (UHSPC) which has compressive strength over 300 MPa. To increase the strength of concrete, we have compared and analyzed the compressive strengths of the concretes with different mix proportions and curing conditions by selecting quartz sand, dolomite, bauxite, ferro silicon which have diameters less than 0.6 mm and can increase the bond strength of the transition zone. Ultra-high strength powdered concrete, which is different from conventional concrete, is highly influenced by the materials in the mix. In the study, the highest compressive strength of the powdered concrete was obtained when it is prepared with ferro silicon, followed in order by Bauxite, Dolomite, and Quartz sand. The amount of ferro silicon, when the highest strength was obtained, was 110%, of the weight of the cement. SEM analysis of the UHSPC showed that significant formation of C-S-H and Tobermorite due to high temperature and pressure curing. Production of Ultrahigh strength powdered concrete which has 28-day compressive strength upto 341MPa has been successfully achieved by the following factors; steel fiber reinforcement, fine particled aggregates, and the filling powder to minimize the void space, and the reactive materials.

• Journal of the Korea Concrete Institute
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• v.19 no.5
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• pp.549-555
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• 2007

Although blast furnace slag has been widely used in concrete as a cementitious admixture or aggregate for many years, the slowly cooled steel slag is not used in concrete but mainly in road. Its use in concrete operates problem such as the lack of volume stability due to high free CaO content, which can be potentially hazardous in concrete. However, the rapidly cooled steel slag by atomization has a low free CaO content, a high density, and a spherical shape, so it is expected to use in concrete so much. This paper is to understand the probability that the rapid cooled steel slag can replace the silica sand used as aggregate in the epoxy mortar. We did the experimental study on the properties of the epoxy mortar having various replacement proportion of rapidly cooled steel slag. This study shown that increasing content of the rapidly cooled steel slag in epoxy mortar lead to increase largely the passing time of nozzle by O-lot, compressive strength and flexural strength. However except the flow is almost same level. So we understand that the rapidly cooled steel slag has positive effect on increasing of properties in epoxy mortar.