• International Journal of Highway Engineering
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• v.18 no.6
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• pp.137-143
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• 2016

OBJECTIVES : Bituminous materials, such as tack coat, are utilized between pavement layers for improving the bond strength in pavement construction sites. The standards regarding the application of bituminous material are not clearly presented in the Korean construction guideline without RS(C)-4. Hence, the objective of this study is to determine the optimum content of bituminous materials by analyzing interlayer shear strength (ISS) from the direct shear tester, which was developed in this research. The shear strength of tack coat was defined with the sort of bituminous materials. METHODS : The mixtures for the shear test were made using marshall mix design. The specimens were vertically and horizontally separated for the direct shear test. The separated specimens were bonded using bituminous material. The objectives of the experiment are to determine the performance of bond and shear properties resulting from slippage, rutting, shovel, and corrugation of asphalt pavements. A machine based on the Louisiana interlayer shear strength tester (LISST) of NCHRP Report-712 was developed to determine the ISS. The applied types of tack coat were RS(C)-4, AP-3, QRS-4, and BD-coat with contents of $0.3{\ell}/m^2$, $0.45{\ell}/m^2$, $0.6{\ell}/m^2$, and $0.8{\ell}/m^2$, respectively. RESULTS : Table 2 gives the results of the direct shear test using the developed shear machine. The BD-coat type indicated the highest average ISS value compared to the others. Between the surface and binder course, optimum tack coat application rates for AP-3, RS(C)-4, QRS-4, and BD-Coat were $0.6{\ell}/m^2$, $0.3{\ell}/m^2$, $0.6{\ell}/m^2$, and $0.45{\ell}/m^2$, respectively. These optimum contents were determined using the ISS value. CONCLUSIONS : The ISS values of AP-3, RS(C)-4, and QRS-4 showed similar tendencies when ISS increased in the range $0.3{\sim}0.6{\ell}/m^2$, while ISS decreased when the applied rate exceeded $0.6{\ell}/m^2$. Similarly, the highest ISS value of the BD-coat was observed when the applied rate was $0.45{\ell}/m^2$. However, shear strength was similar to the maximum value of ISS when the tack-coat application rate of BD-Coat exceeded $0.45{\ell}/m^2$.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.3
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• pp.294-301
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• 2020

This study evaluated the burnability and hydration reaction of clinker burned with high Al₂O₃ content OPC to apply large amounts of industrial by-products in the cement manufacturing process. Specifically, after preparing a clinker with a high C₃A content by burning the OPC raw material with a high content of Al₂O₃ in a laboratory electric furnace, the burnability of the clinker was evaluated through XRD Rietveld analysis and polarization microscopy, and clinker hydration reactivity was reviewed through the Isothermal conduction calorimetry analysis and the cement compressive strength. As a result, the kiln burning temperature for the production of high Al₂O₃ content clinker lower, and the compressive strength was equal to or higher than OPC. Therefore it was confirmed the possibility to manufacturing energy-saving high Al₂O₃ content clinker using a large amount of industrial by-products.

• The Pure and Applied Mathematics
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• v.11 no.3
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• pp.207-215
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• 2004

Let W(z) be a power series with operator coefficients such that multiplication by W(z) is contractive in extC(z). The overlapping space $\varepsilon$(W) of D(W) in C(z) is a Herglotz space with Herglotz function $\varphi$(z) which satisfies $\varphi$(z) + ${\varphi}^*(z^{-1})$ = 2[1-W$^*(z^{-1})W(z)]$.

• Korean Journal of Materials Research
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• v.16 no.5
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• pp.329-335
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• 2006

In order to improve thermal efficiency of the fossil fuel power plants, we need to develop advanced materials with superior durability in the ultra-super critical state, which requires surface modifications for superior surface properties. In this study, we coated the Incoloy 901 and 12-17Cr steels for turbine buckets and valves with nitriding, boriding, and $Cr_3C_2-NiCr$ HVOF(high velocity oxygen flow) method. Then the samples were heat treated at $650^{\circ}C$ for 100 hours in vacuum. We analyzed the evolution behaviors of nitrides such as $Fe_3N,\;Fe_4N$, and CrN and borides such as FeB and $Fe_2B$ with XRD and SEM/EDS by comparing hardnesses and compositions of the coated layers before and after the heat treatments.

• Interaction and multiscale mechanics
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• v.2 no.3
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• pp.223-233
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• 2009

This paper presents a new nonlocal stress variational principle approach for the transverse free vibration of an Euler-Bernoulli cantilever nanobeam with an initial axial tension at its free end. The effects of a nanoscale at molecular level unavailable in classical mechanics are investigated and discussed. A sixth-order partial differential governing equation for transverse free vibration is derived via variational principle with nonlocal elastic stress field theory. Analytical solutions for natural frequencies and transverse vibration modes are determined by applying a numerical analysis. Examples conclude that nonlocal stress effect tends to significantly increase stiffness and natural frequencies of a nanobeam. The relationship between natural frequency and nanoscale is also presented and its significance on stiffness enhancement with respect to the classical elasticity theory is discussed in detail. The effect of an initial axial tension, which also tends to enhance the nanobeam stiffness, is also concluded. The model and approach show potential extension to studies in carbon nanotube and the new result is useful for future comparison.

• Journal of the Korea Institute of Building Construction
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• v.2 no.3
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• pp.131-138
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• 2002

The objective of the study is to examine the characteristic correlations between reinforcing carbon fiber and interfacial adhesion agent since the interfacial adhesion strength between reinforcing carbon fiber and matrices is believed to be an essential element influencing the physical properties in carbon fiber reinforced cement composite using slurry method. The integrity of interfacial adhesion between reinforcing fiber and cement not only affects the quality of fiber reinforced cement composite but also influences to a large degree the physical properties of the cement composite when producing carbon fiber reinforced cement composite using slurry method. Having analyzed the physical properties 1.e., water content, tensile strength, flexural strength and flexural toughness of carbon fiber reinforced cement composite specimens, C-PAM(cation polyacrylamide) was determined to be an optimum interfacial adhesion agent. The study has also demonstrated that interfacial adhesion strength varies largely on the content and type of the reinforcing fiber. Judging from magnified view of the tensile shear cross-section using VMS(video microscope system), interfacial adhesion strength between reinforcing fiber and matrices is affected by the type of interfacial adhesion agent. According to the result of the experiments, C-PAM was determined to be an ideal interfacial adhesion agent when using carbon fiber in producing carbon fiber reinforced cement composite with the optimum content of carbon fiber being established.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.961-964
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• 2008

There are researches in progress on ensuring the safety of the high impact concrete in case of fire which is a current rising social problem and this research institute also developed PFB technology, the explosion preventing technology. PFB technology is to apply POSCO E&C Fire Board, a fireproof board, with an adhesive agent on the construction site, and this technology passed 3-hour fireproof test and this technology was proven from a previous research that the temperature of main root is maintained under $200^{\circ}C$. Therefore, tests on basic contents was performed in this research before the actual construction, with a full scale of wooden prototype to apply PFB technology to actual construction sites and the tests were done on the workability of fireproof board, the adhesive power, the resistance against imprint of wooden nail, the heat conductivity and etc. As the results of these tests, PFB technology was proven to have an excellent workability at a construction site and to be easy for processing and also, this technology was proven to have a great resisting power against imprint of wooden nail. Therefore, this research has confirmed that PFB technology has no problem to be applied on a construction site.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2019.11a
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• pp.73-74
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• 2019

In order to examine the chemical stabilization through DCG curing of cement paste exposed to high temperature environment, we produced a sample of 40% W/C cement paste and heated it for 180 minutes under the heating temperature of $800^{\circ}C$. The DCG curing time was 6, Three time conditions were divided into 12 and 18 hours. As a result of XRD analysis, Calcite ($CaCO_3$) was found in Theta 29.4, 40, and 46.5o. As the curing time increased, the peak of Calcite also increased, which is due to the increased reaction time with DCG. Therefore, Calcite produced through DCG curing seems to have stabilized chemically by filling the pores generated by heating.

• Journal of the Korean Wood Science and Technology
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• v.39 no.1
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• pp.53-59
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• 2011

A connection was made between a single stretcher and 2 headers with 2 threaded nails (Type-A), and another one between 2 stretchers and 2 headers with 4 threaded nails (Type-B) to use as specimens. Type-C was the stretchers that are connected with 2 threaded nails by half lap joint at end-distance 5D to reinforce Type-B, Type-C1 the stretchers that are connected by half lap joint at end-distance 10D, and Type-C2 with 3 threaded nails at end-distance 10D. Compressive shear strength of Type-C, the supplementation of Type-B, was decreased by 30%, compared with that of Type-B. Those of Type-B and Type-C1 that used longer end-distance than Type-C were about the same, and that of Type-C2 connected with 3 threaded nails was 1.28-times stronger than that of Type-C1. Connection of the retaining wall using existing square timber has a problem between long and short stretchers and 2 headers. So it was investigated in the experiment to replace it. Therefore, if Type-B is replaced with Type-C2 in constructing the retaining wall, the crack and the rupture of timber caused by threaded nail as well as construction period can be reduced, and also it can be expected to increase their own strength.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2014.05a
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• pp.264-265
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• 2014

Currently, CO₂ existed in the air usually reacts concrete, and then CaCO₃ can be appeared. As time goes by, pH of concrete is decreased and corrosion of steel can be happened. This phenomenon is called carbonation. For preventing carbonation of concrete, various methods like using corrosion inhibitor, high compressive strength concrete, and enough covering depth are adopted. But these method are usually passive methods focused on corrosion of steel and have limitation on economic. Thus, as basic study for active method of carbonation, cement pastes with CO₂ reactive material (γ-C₂S, MgO) and GBFS were in accelerated carbonation, and the compressive strengths were measured. On the result, the compressive strength was improved better than non-carbonation. Through measuring the weight change using TG-DTA, as specimens were carbonated, according to decreasing of Ca(OH)₂ and Mg(OH)₂, CaCO₃ and MgCO₃ were increased. Therefore it can be shown that carbonation curing can be realized.