• Journal of the Korea Institute of Building Construction
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• v.16 no.1
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• pp.35-43
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• 2016

Concrete is a representative heterogeneous material and mechanical properties of concrete are influenced by various factors. Due to the fact that pores in concrete affect determining compressive strength of concrete, studies which deal with distribution and magnitudes of pores are very important. That way, studies using picture imaging have been emerged. Studies on mechanical performance evaluation of structural lightweight foamed concrete and FEM analysis based on picture image are inadequate because lightweight foamed concrete has been researched for only non-structural. Therefore, in this study, cement paste with foaming agent to evaluate mechanical performance is made, FEM analysis with picture image is conducted and young's modulus of experiment and analysis are compared. In this study, dosage of foaming agent is determined 7 level to check pore distribution and water-binder ratio is determined 20% to progress research about structural light weight foamed concrete. Weight of unit volume is minimum at 0.8% of foaming agent dosage. However, weight of unit volume is increased over 0.8% of foaming agent dosage because of interconnection with independent pores. For FEM analysis, cement paste is photographed to use image analyzer(HF-MA C01). Consequently, the fact that Young's Modulus of experiment and FEM analysis are same is drawn by using OOF(Object Oriented Finite elements).

• Journal of the Korean Recycled Construction Resources Institute
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• v.3 no.1
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• pp.1-6
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• 2015

Recently, lots of researches on concrete with high volume mineral admixture such as ground granulated blast furnace slag (GGBFS) have been carried out to reduce $CO_2$. It is known that the precast concrete has an advantage of high strength at early age due to steam curing, even if concrete has high replacement level of mineral admixture. However it demands the investigation of compressive strength properties according to steam curing regimens. In this study, concretes with water-binder ratio of 32, 35% and water content of 135, 150, $165kg/m^3$ were produced to investigate compressive strength properties of high volume (60% by mass) GGBFS cement concrete according to steam curing regimens. Then steam curing was implemented with the maximum temperature of 50, $60^{\circ}C$ and steaming time of 5, 6, 7 hours. From the test results, it was found that steam curing was effective to raise early strength of high volume GGBFS cement concrete, but 28 day compressive strengths of steam cured specimens were lower than those of water cured specimens. Thus, a further study would be needed for the optimum steam curing regimens to satisfy target demolded strength and specified strength for the application of high volume GGBFS cement concrete to precast concrete members.

• Journal of the Korean Recycled Construction Resources Institute
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• v.2 no.1
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• pp.60-65
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• 2014

Recently, lots of researches on alkali-activated slag (AAS) concrete have been carried out to resolve the environmental issues such as recycling by-products and global warming. AAS concrete would have high strength and high level of durability. On the other hand, it is known that large amount of shrinkage occurred in AAS concrete due to rapid alkaline reaction in the early age, and however, the related studies about autogenous shrinkage of high strength AAS mortar are relatively rare. In this study, fresh mortar properties such as flow and setting time, compressive strength and autogenous shrinkage of AAS mortar with W/B=0.40 to 0.50, were measured. AAS mortar was activated with sodium silicate (Ms=1.0) with 5, 6 and 7 % of $Na_2O$. Test results revealed that AAS morar shows larger autogenous shrinkage than OPC mortar and the lower W/B of AAS mortar, the greater autogenous shrinkage. Therefore, the application of appropriate curing and the use of shrinkage reduction admixture would be needed to reduce autogenous shrinkage of AAS mortar.

• Journal of the Society of Disaster Information
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• v.10 no.3
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• pp.432-441
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• 2014

The purpose of this research is to investigate characteristics of lathe scrap for manufacturing fiber reinforced cementitious composites(FRCCs) to use lathe scrap as a alternative materials of steel fiber. It should be noted that the use of the lathe scrap for making FRCCs raised friendly environmental effect as well as economy because the lathe scrap was a by-product of steel manufactures. For this purpose, various steel scraps were collected from processing plants of metal and then their physical properties were evaluated. Also, steel scraps were classified and analyzed according to the KS D 2101 and then of these scraps, lathe scrap as a alternative materials of steel fiber was suggested. In addition, FRCCs containing lathe scraps were made according to their total volume fractions of 0.0, 0.5, 1.0, 1.5, and 2.0% for water-binder ratios of 30%, 40%, respectively, and then characteristics, such as the workability, compressive strength, and flexural strength of those were evaluated. It was observed from the test result that the compressive strengths at 7 and 28 days of FRCCs containing lathe scrap were slightly small but the flexural strengths at 28 days of those increased by 10% compared with plain concrete.

• Journal of the Korean Recycled Construction Resources Institute
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• v.3 no.3
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• pp.261-267
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• 2015

To develop high-strength high-volume ground granulated blast-furnace slag (GGBFS) concrete, this study investigated the characteristics of strength development and durability of concrete with the water-to-binder ratio of 23% and the GGBFS replacement ratio of up to 65%. The results show that the compressive strength of GGBFS blended concrete is lower than that of ordinary Portland cement (OPC) concrete up to 3-day age, but the becomes higher after 7-day age. Together with strength increase, the pore structure becomes tighter, and thus the resistance to chloride ion penetration increases. Therefore, the GGBFS blended concrete has high resistance to freezing and thawing without additional air-entraining, and high resistance to carbonation despite low amount of calcium hydroxide ($Ca(OH)_2$). On the other hand, if silica fume (SF) is blended with GGBFS, the strength becomes lower than that of the concrete blended with GGBFS only, and the resistance to chloride ion penetration deceases. Therefore, it needs further studies on the reaction of SF in high-strength high-volume GGBFS concrete.

• Journal of the Korean Recycled Construction Resources Institute
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• v.3 no.3
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• pp.220-227
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• 2015

Ultra high performance concrete (UHPC) uses large quantities of steel fiber, silica fume, filler and superplasticizer for a low water-to-binder ratio (W/B). Despite of exceptional mechanical performances, UHPC exhibits increased viscosity due to the adoption of silica fume and its fabrication cost is costlier than ordinary concrete because of the use of large quantities of expensive materials. Following, this study evaluates the mechanical properties of 180MPa-UHPC using zirconium silica fume (Zr) instead of silica fume with respect to the quantity and type of superplasticizer (SP) and the size of filler. The results reveal that the Zr-UHPC using W/B of 20%, 100% of Zr, amount of SP-L of 2 to 3% and $4{\mu}m$-filler with steel fiber in 1.5 vol.% can develop better fluidity than the traditional mix composition using silica fume and secure a compressive strength higher than 180 MPa. In addition, the proposed mix composition is shown to enable a reduction of the fabrication cost by 33% compared to traditional UHPC.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.2
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• pp.475-481
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• 2013

Although the lightly burnt MgO at $850{\sim}1000^{\circ}C$ has expansibility, it does not lead to unsound concrete. The expansion of MgO could compensate for shrinkage of concrete for a long-term, because the hydration of MgO occurs at a slow pace. Recently, the study and application of mineral admixture such as fly ash and blast furnace slag have increased for the hydration heat reduction, durability improvement, and reducing $CO_2$ emission in the construction industry. Thus, it is necessary to research on the concrete that contains both a mineral admixture and MgO as an expansion agent. This study investigates fundamental properties of fly ash concrete with lightly burnt MgO through various experiments. The adiabatic temperature test results showed that the fly ash concrete with MgO of the 5% replacement ratio had the slower pace of the temperature rise and the lower final temperature than the fly ash concrete. The influences of MgO on long-term compressive strength varied depending on water-binder ratio, and the long-term length change test results indicated the expansion effects of the FA concrete containing MgO.

• Journal of the Korea Concrete Institute
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• v.18 no.1 s.91
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• pp.21-28
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• 2006

This paper presents both experimental and analytical studies for the development of an ECC(Engineered Cementitious Composites) using ground granulated blast furnace slag(slag). This material has been focused on achieving moderately high composite strength while maintaining high ductility, represented by strain-hardening behavior in uniaxial tension. In the material development, micromechanics was adopted to properly select optimized range of the composition based on steady-state cracking theory and experimental studies on matrix, and interfacial properties. A single fiber pullout test and a wedge splitting test were employed to measure the bond properties of the fiber in a matrix and the fracture toughness of mortar matrix. The addition of the slag resulted in slight increases in the frictional bond strength and the fracture toughness. Subsequent direct tensile tests demonstrate that the fiber reinforced mortar exhibited high ductile uniaxial tension behavior with a maximum strain capacity of 3.6%. Both ductility and tensile strength(~5.3 MPa) of the composite produced with slag were measured to be significantly higher than those of the composite without slag. The slag particles contribute to improving matrix strength and fiber dispersion, which is incorporated with enhanced workability attributed to the oxidized grain surface. This result suggests that, within the limited slag dosage employed in the present study, the contribution of slag particles to the workability overwhelms the side-effect of decreased potential of saturated multiple cracking.

• The Journal of the Korea Contents Association
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• v.15 no.9
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• pp.576-587
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• 2015

This paper presents a quantitative evaluation of water permeability in concrete with cold joint considering mineral admixture and loading conditions. Concrete samples with OPC (Ordinary Portland Cement) and GGBFS(Ground Granulated Blast Furnace Slag) are prepared considering 0.6 of W/C ratio and 40% of replacement. 30% and 60% loading levels for compression and 60% loading level for tension are induced to concrete samples. In compression conditions, the permeability in control case shows $2.41{\times}10^{-11}m/s$ in OPC concrete, and it changes to $2.07{\times}10^{-11}m/s$ (30% of peak) and $2.36{\times}10^{-11}m/s$ (60% of peak). The results in GGBFS concrete shows the same trend, which yields $2.17{\times}10^{-11}m/s$ (control), $1.65{\times}10^{-11}m/s$ (30% of peak), and $1.96{\times}10^{-11}m/s$ (60% of peak), respectively. In tensile conditions, the permeability increases from $2.37{\times}10^{-11}m/s$ (control) to $2.67{\times}10^{-11}m/s$ (60% of peak) while that in GGBFS concrete increases from $2.17{\times}10^{-11}m/s$ (control) to $2.24{\times}10^{-11}m/s$ (60% of peak). Permeability coefficients decreases in 30% of compressive level but increases in 60% level, while results in tensile level increases rapidly. This shows pore structure in concrete is condensed and with loading and permeability increases due to micro-cracking. Permeability evaluation considering the effects of loading conditions, cold joint, and GGBFS is verified to be important since water permeability greatly changes due to their effects.