• Journal of the Korea Concrete Institute
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• v.12 no.3
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• pp.47-55
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• 2000

Protections from the frost damage at early ages are one of the serious problems to be considered in cold weather concreting. Frost damage at early ages brings about the harmful influences on the concrete structures such as surface cracks and declination of strength development. Therefore, in this paper, protecting periods of frost damage at early ages according to the standard specifications provided in KCI(Korean Concrete Institute) are suggested by appling logistic curve, which evaluates the strength development of concrete with maturity. W/B, kinds of cement and curing temperatures are selected as test parameters. According to the results, the estimation of strength development by logistic curve has a good agreement between calculated values and measured values. As W/B and compressive strength for protecting from frost damages at early ages increase, it is prolonged. It shows that the protecting periods of FAC(Fly Ash Cement) and BSC(Blast-furnace Slag Cement) concrete are longer than those of OPC(Ordinary Portland Cement) concrete. The protecting peridos from frost damage at early age by JASS are somewhat shorter than those by this paper.

• Journal of the Korea Concrete Institute
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• v.16 no.2 s.80
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• pp.277-282
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• 2004

In a hardened concrete, diffusion of oxygen, carbon dioxide, aggressive ions, and moisture from the environment to the concrete takes place through the pore network. It is well known that making dense cement matrix enhances the durability of concrete as well as all the characteristics including strength of concrete. In this paper,9 mix concretes with water to cementitious material ratio (40,45, and $50\%$) and replacement ratio of GGBFS (40 and $60\%$ of cement by weight) were studied on the micro-pore structure by mercury intrusion porosimetry and the accelerated chloride diffusion test by potential difference. From the results the average pore diameter and accelerated chloride diffusivity of concrete were ordered NPC > G4C > G6C. It is concluded that there is a good correlation between the average pore diameter and the chloride diffusivity, and the mineral admixtures has a filling effect, which increases the tortuosity of pore and makes large pores finer, on the pore structure of cement matrix due to the latent hydraulic reaction with hydrates of cement.

• Advances in concrete construction
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• v.8 no.4
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• pp.305-309
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• 2019

Pervious concrete pavements are the need of the day to avoid urban flooding and to facilitate ground water recharge. However, the strength of pervious or porous concrete is considerably less compared to conventional concrete. In this experimental investigation, an effort is made to improve the strength of pervious concrete by adopting fibres and a small amount of fine aggregate. A porous concrete with cement to aggregate ratio of 1:5 and a water-powder ratio of 0.4 is adopted. 30% of the cement is replaced by cementitious material ground granulated blast furnace slag (GGBS) for better strength and workability. Recron fibres at a dosage of 0.5, 1.0 and 1.5% by weight of cement were included to improve the impact strength. Since concrete pavements are subjected to impact loads, the impact strength was also calculated by "Drop ball method" in addition to compressive strength. The effect of fine aggregate and recron fibres on workability, porosity, compressive and impact strength was studied. The investigations have shown that 20% inclusion of fine aggregate and 1.5% recron fibres by weight of cement give better strength with an acceptable range of porosity.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2013.11a
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• pp.68-71
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• 2013

Reactive Powder Concrete (RPC) is an ultra high strength and high ductility cement-based composite material and has shown some promise as a new generation concrete in construction field. It is characterized by a silica fume-cement mixture with very low water-binder (w/b) ratio and very dense microstructure, which is formed using various powders such as cement, silica fume and very fine quartz sand (0.15~0.4mm) instead of ordinary coarse aggregate. However, the unit weight of cement in RPC is as high as 900~1,000 kg/㎥ due to the use of very fine sand instead of coarse aggregate, and a large volume of relatively expensive silica fume as a high reactivity pozzolan is also used, which is not produced in Korea and thus must be imported. Since the density of RPC has a heavy weight at 2.5~3.0 g/㎤. In this study, the modified RPC was made by the combination of ternary pozzolanic materials such as blast furnace slag and fly ash, silica fume in order to economically and practically feasible for Korea's situation. The fire resistance and structural behavior of the modified RPC exposed to high temperature were investigated.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2013.11a
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• pp.194-195
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• 2013

Recently, it is the tendency that the CO₂ gas generated in the manufacturing process is increased every year in case of the portland cement used in the most of constructions and civil engineering field. The method that uses the mineral admixtures as the cement substitute material in order to be more serious and as much as it occupies 7% of the global CO₂ gas outlet amount such as 1 ton produces the cement and it ejects the CO₂ gas of 0.4~1.0 ton, etc conclude this problem is examined. Therefore, PVA fiber was mixed into the inorganic binder recycling the blast furnace slag, which is the industrial byproduct with the purpose studying the Geo polymer which doesn't use the cement at all silica fume, red mud, and etc. In addition, the water curing temperature was differentiated and the strength characteristic of the curing body tried to be examined.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.537-540
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• 2008

Up to now, the RC structures have been recognized as being socially semi-permanent. But in recent years there were reports about the cases of early deterioration of RC structures. Most of all pore structure effects on the durability of concrete as well as mechanical properties of concrete. Therefore, in this study, mixing design was proportioned with the water-binder ratio 0.55 binder compositions corresponding to cement without any supplementary materials(OPC), cement with 50% blast-furnace slag replacement (BFS50), cement with 15% fly ash replacement (FA15), and ternary cement with cement, 15% fly ash, and 35% slag replacement (BFS35+FA15). And this study is to compare pore structure property of concrete by carbonation to investigate the effect of the permeation of deterioration factors such as $CO_2$ and chloride ion under the combined deterioration environments. The results showed that pore volume effects on the diffusibility of chloride ion.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.3
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• pp.39-47
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• 2015

In this study, the properties of strength and drying shrinkage of alkali-activated slag cement (AASC) with magnesium oxide (MgO) contents between 0 and 16 wt% were investigated. The ground granulated furnace blast slag (GGBFS) was activated by potassium hydroxide (KOH) and dosage of activator was 2M and 4M. The MgO was replaced with 2% to 16% of GGBFS by weight. The water-binder ratio (w/b) was 0.5. In the result, the higher MgO content leads to a slightly higher degree of reaction and thus to a higher compressive strength at all ages. The compressive strength and ultra sonic velocity (UPV) increased with increases MgO contents. The drying shrinkage of AASC was decreased as the contents of MgO increases. The results from SEM confirmed that there were densified reaction product of higher MgO content specimens.

• Journal of the Korea Institute of Building Construction
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• v.18 no.4
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• pp.321-327
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• 2018

Blast furnace slag has been actively used as a substitute for cement in the construction field with high value-added through resource recycling research. However, most of the slag cannot find a clear recycling purpose. This is because some slags contain unstable materials and are used for road-use asphalt and embankment, which are low value-added materials. Electric arc furnace reduction slag(ERS) has been reported to contain a large amount of unstable free CaO due to deoxidation and component adjustment. In this study, free CaO of ERS which is generated in Korean steelmakers is quantitatively evaluated by using ethylene glycol method. As a result of free CaO quantitative evaluation of ERS, it was confirmed that there is a big difference according to the location of each field. In addition, ERS generally existed in powder form as undifferentiated characteristics, but it was confirmed that free CaO content was different due to hydration product in aggregate form due to water treatment. In addition, free CaO is an amorphous material and its crystallization characteristics are different due to the influence of temperature when it is cooled. ERS requires a long-term aging period as it contains a lot of free CaO.

• International Journal of Concrete Structures and Materials
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• v.18 no.2E
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• pp.97-102
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• 2006

In this study, the effect of supplementary materials(GGBS, PFA, SF) on sulfuric acid corrosion resistance was assessed by measuring the compressive strength, corroded depth and weight change at 7, 28, 56, 91, 180 and 250 days of immersion in sulfuric acid solution with the pH of 0.5, 1.0, 2.0 and 3.0. Then, it was found that an increase in the duration of immersion and a decrease in the pH, as expected, resulted in a more severe corrosion irrespective of binders: increased corroded depth and weight change, and lowered the compressive strength. 60% GGBS mortar specimen was the most resistant to acid corrosion in terms of the corroded depth, weight change and compressive strength, due to the latent hydraulic characteristics and lower portion of calcium hydroxide. The order of resistance to acid was 60% GGBS>20% PFA>10% SF>OPC. In a microscopic examination, it was found that acid corrosion of cement matrix produced gypsum, as a result of decomposition of hydration products, which may loose the structure of cement matrix, thereby leading to a remarkable decrease of concrete properties.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2012.11a
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• pp.65-66
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• 2012

The cement used in the construction industry of the manufacturing process, large amounts of the greenhouse gas, CO₂ and is currently being studied for cement substitutes that reduce greenhouse gas issue. Therefore, the this study as a replacement for cement industrial by-product of blast furnace slag, red mud, silica fume and alkali-activator, using only inorganic composites without high-temperature calcination process were manufactured. The waste gypsum board micro powder added to compensate for the shrinkage cracks, the compressive strength and flow, and length change characteristics were investigated. Consequently, The setting time was shortened as GB added And liquidity was reduced. GB 2%, 7 days curing the added strength of specimens was the highest. Came out, and change the length of the Plain least.