• Journal of the Korea Concrete Institute
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• v.16 no.4 s.82
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• pp.529-539
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• 2004

The corrosion of steel rebars has been the major cause of reinforced concrete deterioration. FRP(Fiber-reinforced polymer) rebar has emerged as one of the most promising and affordable solutions to the corrosion problems of steel reinforcement in structural concrete. However, FRP rebar is prone to deteriorate due to other degradation mechanisms than those for steel. The high alkalinity of concrete, for instance, is a possible degradation source. Therefore, the USA, Japan, Canada, UK. etc are using environmental reduction factor. Although difference design guidelines were drawn in many, including USA, Japan, Canada, UK etc, recommendations and coefficients that could take into account the long-term behavior of FRP reinforcement were not well defined. This study focuses on recommendation of environmental reduction factor of FRP rebar. Environment reduction factor were decided using durability test result. FRP rebars were subjected to twelve type of exposure conditions including alkaline solution, acid solution, salt solution and deionized water etc. The water absorption behavior was observed by means of simple gravimetric measurements and durability properties were investigated by performing tensile, compressive and short beam tests. Based on the experimental result, environmental reduction factor of hybrid FRP rebar(A), and (C) and CFRP rebar was decided as 0.85. Also, hybrid FRP rebar(B) and GFRP rebar were decided as 0.7 for the environmental reduction factor

• Journal of the Korea Concrete Institute
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• v.13 no.1
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• pp.54-61
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• 2001

As a part of the movement of natural resources conservation, there have been doing many recycling research works for obsolete aged tire, wasted plastic materials, etc. The purpose of this experimental study is to develop glass concrete by recycling wasted glasses as a cementitious constituent in concrete. First of all, the optimum replacement ratio of powdered waste glasses(PWG) can be determined through pilot compressive strength test on normal and high strength concrete cylinders, which have been made in various mix proportions by changing the replacement ratio of PWG. Then, further tests have been done to figure out mechanical properties of most desirable glass concrete with optimum replacement ratio of PWG, such as static modulus of elasticity, compressive and tensile strengths, flexural strength. On the other hand, the alkali-silica reactions by the mortar-bar method(KS F 2546) have been experimentally doing in various grain sizes of PWG, since the alkali in the cement has a tendency to react with the silica in the PWG. In can be confirmed from the test that glass concrete can have better workability than concrete with silica fume, and they are alike in compressive strength. It is concluded that wasted glasses can be used as pratical additives for economic and environmentally friendly concrete.

• Journal of the Korea Concrete Institute
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• v.16 no.5 s.83
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• pp.645-650
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• 2004

As time passes, bridge structures require extension work on bridge in use from various effects such as social economical, or traffic environment change. When the concrete is poured at the connection of extension work initial curing concrete is influenced by vibration of vehicles that are passing through the old bridge superstructure. Concrete at early curing stage in construction site should be properly protected, enough to have established sufficient integrity to withstand outside vibration, impact etc. Currently there is no standard specification or regulation in our country. In this paper, experimental variables were divided by vibration velocity and time of loading, and concrete compressive strength and bond strength were measured.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.3
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• pp.356-363
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• 2017

Blast furnace slag(BFS) is a by-product generated during the manufacture of pig ion, and is divided into water-cooled slag(WS) and air-cooled slag(AS) by the coking method of BFS. In this study, concrete specimens with ternary binders were produced at the various replacement levels of cement by AS. Various mechanical properties of concrete, such as compressive and split tensile strengths, absorption and water permeable pore, were measured. In addition, the chloride ions penetration resistance and carbonation resistance were tested to evaluate the durability of concrete incorporating AS. The experimental data indicated that the use of AS up to a maximum of 10% replacement level enhanced the concrete performance. However, a higher replacement of AS exhibited poor mechanical properties and concrete durability.

• Fire Science and Engineering
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• v.18 no.3
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• pp.51-56
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• 2004

A fire outbreak in a reinforcement concrete structure looses the organism by the different contraction and expansion of hardened cement pastes and aggregate, and causes cracks by thermal stress, leading to the deterioration of the durability. So concrete reinforcement structure is damaged partial or whole structure system. Therefore diagnosis of deterioration is needed based on mechanism of fire deterioration in general concrete structures. Fundamental information and data on the properties of concrete exposed to high temperature are necessary for accurate diagnosis of deterioration. In this study, it was presented data for the accurate diagnosis and selection of repair and reinforcement system for the deteriorated concrete heated highly, various concrete such as standard design compressive strength, fine aggregate and admixture were exposed to a high temperature environment. And fundamental data were measured engineering properties such as explosive spatting, ultrasonic pulse velocity and compressive strength.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.4A
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• pp.743-752
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• 2006

Confined concrete has enhanced strength and ductility compared with unconfined strength. Cause of these merits of confined concrete, many researches have been performed for confining effects of concrete and been studied in many fields. Although many researches about concrete confined by FRP sheets have been studied recently, it is difficult to apply concrete confined by FRP in real structures because FRP is a brittle material. In this study, the enhanced strength and ductility of concrete which is confined by steel tubes or steel plates were investigated. Fifty one specimens were tested and each specimen has different confining condition. Test results showed enhanced ductility and strength of confined concrete and concrete models were suggested under various confining conditions by regression of experimental data.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.3A
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• pp.547-553
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• 2006

To know the effect of pigments on the material properties of color concrete, mortar and concrete tests were carried out by the using 5 kinds of pigment. The major component of red, yellow and black pigments was iron oxide and coloring component of blue and green pigments was copper phthalocyanine. Properties of mortar and concrete were some of difference according to adding ratio and kind of pigments. In case of using red, yellow and black pigments, setting time of concrete speeded a little and compressive strength was tendency to increase and slump or air content of concrete was same or decreased. On the other hand, in case of using green and blue pigments, compressive strength of concrete decreased largely because of the excessive air entrainment of surfactant and sump or air content of concrete increased highly. When the antifoaming agent was added to the color concrete mixed with green and blue pigments, compressive strength of concrete was improved and similar to that of concrete without pigment.

• Journal of the Korea institute for structural maintenance and inspection
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• v.11 no.6
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• pp.87-94
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• 2007

Reuse of recycled aggregate from demolished concrete structure is beneficial and necessary from the viewpoint of environmental preservation and effective utilization of resources. The most important mechanical properties of recycled aggregate concrete (RAC) are the compressive strength, the tensile and the flexural strengths, the bond strength and the elastic modulus of such concrete. In particular, the stress-strain relation and fracture process of RAC in compression is especially important in theoretical and numerical analysis as well as engineering design of RAC structures. In this paper, to clarify the characteristics of fracture process in RAC, acoustic emission(AE) method is applied to detect micro-cracking in concrete under compression. From AE parameters, it is found that cracking and fracture behaviors in recycled aggregate concrete fairly differ from that of normal and recycled sand concrete.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.7 no.3
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• pp.229-240
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• 1987

Carbonation of concrete is one type of a chemical process. The reaction mechanism is very complex for the case when low-calcium fly ash and blast furnace slag is added. When fly ash and blast furnace slag is used as an admixture in concrete, they improve compressive strength in the long term, permeability and chemical resistance of concrete by a pozzolanic reaction and latent hydraulic property. On the other hand, the pozzolanic reaction of fly ash and latent hydraulic property of the blast furance slag leads to a reduction of the alkalinity of the concrete. It has been pointed out that this will accelerate the carbonation of the concrete and the corrosion of reinforcement steel embedded in the concrete. In order to clarify the effect of fly ash and blast furance slag on the carbonation of concrete, an accelerated carbonation testing of concrete was carried out by varying the conditions of concrete and the initial curing period in water. The test results of accelerated carbonation were compared to the carbonation test results of concrete stored for 15 years in open air, but protected from rain. As a result, the equation for the rate of carbonation based on compressive strength of concrete was proposed.

• Economic and Environmental Geology
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• v.51 no.4
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• pp.371-379
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• 2018

In many countries, recycling coal ashes as backfill materials for subsided lands, abandoned mine tunnels, and road pipeline constructions by making low-strength concretes with minimal amounts of cement is frequently considered for massive treatment of coal ashes. This study investigates the variation of heavy metals in the concrete test pieces prepared for the cases of using only Portland cement as binding material, fly ash as a replacement of the cement, sand as aggregates, and disposed ashes in the ash ponds as a replacement of aggregates. Heavy metal contents were measured based on the aqua regia extraction technique following the Korean Standard for Fair Testing of Soil Contamination and the influences of each materials on the total heavy metal contents were also assessed. Results show that the cement has the highest Cu, Pb, and Zn concentrations than any other materials. Therefore, the test pieces show significant concentration decreases for those metals when the cement was replaced by fly ash. Ponded ash shows low concentrations relative to fly ash in most of the parameters but shows higher Cu and Ni, and lower Pb levels than the sand aggregate. In overall, heavy metal levels of the test pieces are regulated by mixing among the used materials. Test pieces prepared during this study always show concentrations much lower than the Worrisome Level of Soil Contamination (Area 1), which was designated by the Soil Environment Conservation Act of Korea.