• Journal of the Korea Institute of Building Construction
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• v.10 no.6
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• pp.61-66
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• 2010

As global warming has had harmful effects on the environment, the construction industry has made efforts to reduce the amount of $CO_2$ generated in the process of cement production. There is an urgent need for an alternative material that can replace cement. To improve the initial strength and economical efficiency pointed out as problems, this research was conducted for Blast Furnace Slag (BFS), an industrial byproduct. Non-sintering cement (NSC) was used by minimizing the amount of high-priced alkali activators. By using Nano-technology, fineness has been maximized, to enhance the initial strength of BFS. This research is based on non-sintered cement replaced by nano-slag using alkali activators, and the fundamental properties and quality of the non-sintered cement were investigated. A variety of activators were used, up to 10 percent of the slag weight. This research aims to present fundamental data through a comparative analysis of flexural strength, compressive strength, time of setting, diabetic temperature, and rising heat.

• Journal of the Korean Recycled Construction Resources Institute
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• v.9 no.3
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• pp.311-321
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• 2021

Many studies have been performed on hybrid fiber reinforced concrete for years, which is to improve some of the weak material properties of concrete. Studies on characteristics of hybrid fiber reinforced concrete using amorphous steel fiber and organic fiber, however, yet remain to be done. The purpose of this research is to evaluate the compressive and tensile behaviors and then propose a material model of high performance hybrid fiber reinforced concrete using amorphous steel fiber and polyamide fiber. For this purpose, the high performance hybrid fiber reinforced concretes were made according to their total volume fraction of 1.0% for target compressive strength of 40MPa and 60MPa, respectively, and then the compressive and tensile behaviors of those were evaluated. Also, based on the experimental results of the high performance hybrid fiber reinforced concrete and mortar, each material model for the compressive and tensile behavior was suggested. It was found that the experimental results and the proposed models corresponded relatively well.

• Journal of the Korean Recycled Construction Resources Institute
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• v.6 no.4
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• pp.275-282
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• 2018

This study examines the ways to address environmental issues by utilizing activated loess to reduce the amount of cements that emit a large amount of carbon dioxide during the process of manufacturing, and by reusing the polysilicon sludge produced as a result of manufacturing polysilicon, one of the components for solar power generation panels. The findings of the experiment showed that the optimal replacement ratio of the polysilicon sludge is 20%, 35% for W/B, and 20% for the ratio of the fine aggregate addition. As it is deemed that utilizing the polysilicon sludge for reinforced concrete may lead to rebar corrosion due to the $CI^-$ contained in the sludge, it can be considered to use for unreinforced concrete or bricks.

• Journal of the Korea Institute of Building Construction
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• v.19 no.5
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• pp.383-389
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• 2019

The supply of natural aggregate for concrete has been difficult, and the amount of construction waste has been continuously increasing. Therefore, the necessity of using recycled aggregate made of construction waste as aggregate is rised. Therefore, many studies on the characteristics of concrete using recycled aggregate have been made and positive studies have been reported mainly in recent studies. A study on the chlorides binding effect of the mortar with recycled coarse aggregate has been reported. However, due to the user's perception of waste, most of the recycled aggregate currently produced is used only for low value-added products. In order to improve the recognition of recycled aggregate and the user's perception of recycled aggregate concrete, long-term monitoring of the structure with 100% recycled aggregate was conducted to confirm the applicability of the recycled aggregate concrete.

• Journal of the Korea Institute of Building Construction
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• v.19 no.3
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• pp.219-228
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• 2019

The aim of the research is to provide a fundamental data of low viscosity typed superplasticizer (SP) on cement-based materials incorporating various supplementary cementitious materials (SCMs). As a relatively new product, low-viscosity typed SP has introduced for high performance concrete with high viscosity due to its high solid volume fraction with various SCMs. However, there are not enough research or reports on the performance of the low viscosity typed SP with cement-based materials incorporting SCMs. hence, in this research, for cement paste and mortar, fluidity and rheological properties were evaluated when the mixtures contained various SCMs such as fly ash, blast furnace slag, and silica fume. From the experiment conducted, it was checked that the low viscosity typed superplasticizer decreased the plastic viscosity of the mixture as well as the yield stress. From the results of this research, it is expected to contribute on introduction of new type SP for high performance concrete or high-viscous cementitious materials.

• Advances in concrete construction
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• v.13 no.1
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• pp.71-81
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• 2022

Aluminosilicate materials as precursors are heterogenous in nature, consisting of inert and partially reactive portion, and have varying proportions depending upon source materials. It is essential to assess the reactivity of precursor prior to synthesize geopolymers. Moreover, reactivity may act as decisive factor for setting molar concentration of NaOH, curing temperature and setting proportion of different precursors. In this experimental work, the reactivities of two precursors, low calcium (fly ash (FA)) and high calcium (ground granulated blast furnace slag (GGBS)), were assessed through the dissolution of aluminosilicate at (i) three molar concentrations (8, 12, and 16 M) of NaOH solution, (ii) 6 to 24 h dissolution time, and (iii) 20-100℃. Based on paratermeters influencing the reactivity, different proportions of ternary binders (two precursors and ordinary cement) were activated by the combined NaOH and Na2SiO3 solutions with two alkaline activators to precursor ratios, to synthesize the geopolymer. Reactivity results revealed that GGBS was 20-30% more reactive than FA at 20℃, at all three molar concentrations, but its reactivity decreased by 32-46% with increasing temperature due to the high calcium content. Setting time of geopolymer paste was reduced by adding GGBS due to its fast reactivity. Both GGBS and cement promoted the formation of all types of gels (i.e., C-S-H, C-A-S-H, and N-A-S-H). As a result, it was found that a specified mixing proportion could be used to improve the compressive strength over 30 MPa at both the ambient and hot curing conditions.

• Computers and Concrete
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• v.29 no.3
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• pp.187-199
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• 2022

The usability of waste materials as raw materials is necessary for sustainable production. This study investigates the effects of different powder materials used to replace cement (0%, 5% and 10%) and standard sand (0%, 20% and 30%) (basalt, limestone, and dolomite) on the compressive strength (f_c), flexural strength (f_r), and ultrasonic pulse velocity (UPV) of mortars exposed to freeze-thaw cycles (56, 86, 126, 186 and 226 cycles). Furthermore, the usability of artificial intelligence models is compared, and the prediction accuracy of the outputs is examined according to the inputs (powder type, replacement ratio, and the number of cycles). The results show that the variability of the outputs was significantly high under the freeze-thaw effect in mortars produced with waste powder instead of those produced with cement and with standard sand. The highest prediction accuracy for all outputs was obtained using the adaptive-network-based fuzzy inference system model. The significantly high prediction accuracy was obtained for the UPV, f_c, and f_r of mortars produced using waste powders instead of standard sand (R² of UPV, f_c and f_f is 0.931, 0.759 and 0.825 respectively), when under the freeze-thaw effect. However, for the mortars produced using waste powders instead of cement, the prediction accuracy of UPV was significantly high (R²=0.889) but the prediction accuracy of f_c and f_r was low (R²f_c=0.612 and R²f_f=0.334).

• Journal of the Korean Recycled Construction Resources Institute
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• v.11 no.1
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• pp.25-31
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• 2023

In this study, the basic properties of CO₂ immobilized desulfurized gypsum (CFBG) and the possibility of being used as a stimulus for slag cement were reviewed, and performance evaluation was conducted through a concrete mixing test. The main components of CFBG were CaO and SO₃, and CaO and SO₃ increased as the drying temperature increased. The moisture content of undried CFBG was 15.7 %, the drying temperature was 1.7 % and the drying temperature was 0.03 % at 105 ℃. Mortar using CFBG tended to have a lower flow value as the drying temperature increased, and the compressive strength was equivalent to that of the FGB use mixture. As a result of the concrete experiment using CFBG SC, both slump and air volume satisfied the target range after 60 minutes, and the compressive strength tended to increase overall compared to the ternary binder mixture.

• Steel and Composite Structures
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• v.46 no.1
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• pp.75-92
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• 2023

The novel composite cold-formed steel (CFS)/engineered cementitious composites (ECC) beams have been recently presented. The new composite section exhibited superior structural performance as a flexural member, benefiting from the lightweight thin-walled CFS sections with improved buckling and torsional properties due to the restraints provided by thinlayered ECC. This paper investigated the shear performance of the new composite CFS/ECC section. Twenty-eight simply supported beams, with a shear span-to-depth ratio of 1.0, were assembled back-to-back and tested under a 3-point loading scheme. Bare CFS, composite CFS/ECC utilising ECC with Polyethylene fibres (PE-ECC), composite CFS/MOR, and CFS/HSC utilising high-strength mortar (MOR) and high-strength concrete (HSC) as replacements for PE-ECC were compared. Different failure modes were observed in tests: shear buckling modes in bare CFS sections, contact shear buckling modes in composite CFS/MOR and CFS/HSC sections, and shear yielding or block shear rupture in composite CFS/ECC sections. As a result, composite CFS/ECC sections showed up to 96.0% improvement in shear capacities over bare CFS, 28.0% improvement over composite CFS/MOR and 13.0% over composite CFS/HSC sections, although MOR and HSC were with higher compressive strength than PE-ECC. Finally, shear strength prediction formulae are proposed for the new composite sections after considering the contributions from the CFS and ECC components.

• 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.