• International Journal of Concrete Structures and Materials
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• v.3 no.2
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• pp.81-90
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• 2009

This paper proposes a semi analytical model to describe the pore structure of concrete by a set of simple equations. The relationship between the porosity and the microstructure of concrete has been considered when constructing the analytical model. The microstructure includes the interface transition zone (ITZ) between aggregates and cement paste. The predicting model of porosity was developed with considering the ITZ for various mixing of mortar and concrete. The proposed model is validated by the rapid experimental programs. Although the proposed model is semi-analytical and relatively simple, this model could be reasonably utilized for the durability design and adapted for predicting the service life of concrete structures.

• Journal of Korean Society of Water and Wastewater
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• v.20 no.3
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• pp.443-450
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• 2006

For understanding sludge concentration profile as a function of time, sludge was sampled at each sampling port. When sludge concentration was 3g/L, the vertical sludge concentration distribution was similar to that of 2g/L of sludge concentration. During the early stage of sludge settling, sludge concentration increased remarkably as the sludge interface height in batch column became lower. The higher sludge concentration became, the worse sludge setteability became. Also, the type of sludge settling was influenced with sludge concentration gradient in batch column. In the same concentration, the greater sludge concentration gradient was, the faster sludge interface settled down. And the changing sludge concentrations in a batch settling or a continuous settling were simulated by using the equation of sludge interface height change model.

• Computers and Concrete
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• v.34 no.2
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• pp.231-245
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• 2024

A 3D discrete element model integrating the rough surface contact concept with the flat-joint model is suggested to examine the mechanical characteristics of the interfacial transition zone (ITZ) in concrete. The essential components of our DEM procedure include the calculation of the actual contact area in an element contact-pair related to the bonded factor using a Gaussian probability distribution of asperity height, as well as the determination of the contact probability-relative displacement form using the least square method for further computing the force-displacement of ITZs. The present formulations are implemented in MUSEN, an open source development environment for discrete element analysis that is optimized for high performance computation. The model's meso-parameters are calibrated by using uniaxial compression and splitting tensile simulations, as well as laboratory tests of concrete from the literature. The present model's DEM predictions accord well with laboratory experimental tests of pull-out concrete specimens published in the literature.

• International Journal of Concrete Structures and Materials
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• v.10 no.1
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• pp.87-97
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• 2016

In this study, a quantitative review was performed on the mechanical performance, permeation resistance of concrete, and durability of surface-modified coarse aggregates (SMCA) produced using low-quality recycled coarse aggregates, the surface of which was modified using a fine inorganic powder. The shear bond strength was first measured experimentally and the interface between the SMCA and the cement matrix was observed with field-emission scanning electron microscopy. The results showed that a reinforcement of the interfacial transition zone (ITZ), a weak part of the concrete, by coating the surface of the original coarse aggregate with surface-modification material, can help suppress the occurrence of microcracks and improve the mechanical performance of the aggregate. Also, the use of low-quality recycled coarse aggregates, the surfaces of which were modified using inorganic materials, resulted in improved strength, permeability, and durability of concrete. These results are thought to be due to the enhanced adhesion between the recycled coarse aggregates and the cement matrix, which resulted from the improved ITZ in the interface between a coarse aggregate and the cement matrix.

• Journal of Welding and Joining
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• v.18 no.2
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• pp.49-56
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• 2000

Recently developed Austenite stainless steel, 309L was used to overlay on 3Cr-1Mo-V-Ti-B steels, using Electroslag welding process, which wide electrodes were adopted. Transition region in welding interlayer relating to disbonding crack was investigated. Also, the effect of welding condition on the width of transition region and coarsening grains of the austenite were studied. 1) With increasing welding speed the width of martensite at transient region was increased, but the amount of delta ferrite in weld metal was reduced, being fine grained. 2) The form of martensite at the transition region was occurred by reversible transformation during cooling since the interdiffusion of Cr and Ni from weld metal and Fe and C from base metals at the transition region, causes to lowering the concentration of Cr and Ni at the transition region, leading to increasing Ms point. 3) With increasing welding speed, the grain of austenite formed at the welding interface was finer. With increasing welding current under the same welding speed, the grain size of the austenite was finer. At high current, original grain size of the austenite is coarse, but the austenite has fine grains because the austenite was transformed to martensite during cooling. 4) In the case of high welding speed, the width of martensite at the welding interface was increased, but the grain size of austenite at the welding interface was finer. This indicates that the inhibition of disbonding crack may be achieved through dispersening fine carbides in the gain boundary.

• Advances in materials Research
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• v.1 no.2
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• pp.147-160
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• 2012

In the present study, diffusion bonding was carried out between AZ31B magnesium and AA2024 aluminium in the temperature range of $405^{\circ}C$ to $475^{\circ}C$ for 15 min to 85 min and 5MPa to 20 MPa uniaxial loads was applied. Interface quality of the joints was assessed by microhardness and shear testing. Also, the bonding interfaces were analyzed by means of optical microscopy, scanning electron microscopy, energy dispersive spectrometer and XRD. The maximum bonding and shear strength was obtained at $440^{\circ}C$, 12 MPa and 70 min. The maximum hardness values were obtained from the area next to the interface in magnesium side of the joint. The hardness values were found to decrease with increasing distance from the interface in magnesium side while it remained constant in aluminium side. It was seen that the diffusion transition zone near the interface consists of various phases of $MgAl_2O_4$, $Mg_2SiO_4$ and $Al_2SiO_5$.

• Journal of Welding and Joining
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• v.18 no.2
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• pp.176-176
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• 2000

Recently developed Austenite stainless steel,309L was to overlay on 3Cr-1Mo-V-Ti-B steels, using Electroslag welding process, which wide electrodes were adopted. Transition region in welding interlayer relating to disbonding crack was investigated. Also. the effect of welding condition on the width of transition region and coarsening grains of the austenite were studied.1) With increasing welding speed the width of martensite at transient region was increased, but the amount of delta ferrite in weld metal was reduced, being fine grained.2) The form of martensite at the transition region was occured by reversible transition region, leading to increasing Ms point.3) With increasing welding speed, the grain of austenite formed at the welding interface was finer. With increasing welding current under the same welding speed, the grain size of the austenite was finer. At high current, original grain size of the austenite is coarse, but the austenite has fine grains because the austenite was transformed to martensite during cooling.4) In the case of high welding speed, the width of martensite at the welding interface was increased, but the grain size of austenite at the welding interface was finer. This indicates that the inhibition of disbonding crack may be achieved through dispersening fine carbides in the grain boudary.(Received August 3, 1999)

• Interaction and multiscale mechanics
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• v.2 no.4
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• pp.353-374
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• 2009

A new seamless multiscale simulation was developed for coupling the continuum model with its molecular dynamics. Kriging-based Finite Element Method (K-FEM) is employed to model the continuum base of the entire domain, while the molecular dynamics (MD) is confined in a localized domain of interest. In the coupling zone, where the MD domain overlaps the continuum model, the overall Hamiltonian is postulated by contributions from the continuum and the molecular overlays, based on a quartic spline scaling parameter. The displacement compatibility in this coupling zone is then enforced by the Lagrange multiplier technique. A multiple-time-step velocity Verlet algorithm is adopted for its time integration. The validation of the present method is reported through numerical tests of one dimensional atomic lattice. The results reveal that at the continuum/MD interface, the commonly reported spurious waves in the literature are effectively eliminated in this study. In addition, the smoothness of the transition from MD to the continuum can be significantly improved by either increasing the size of the coupling zone or expanding the nodal domain of influence associated with K-FEM.

• Journal of The Korean Society of Agricultural Engineers
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• v.50 no.5
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• pp.39-50
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• 2008

This study are decided the mix proportion method of latex modified concrete for agricultural concrete structures from the results of workability and strength test with mix proportion factor. For mix proportion factor, this study are selected the water-cement ratio, unit cement amount and latex content. Also, this study were performed the slump, compressive strength test and microstructure analysis using the scanning electron microscope(SEM). The strength and slump of LMC are dependent with unit cement amount, latex content, and water-cement ratio. Especially, the strength of LMC are not controlled by single mix proportion factor but effected by combined mix proportion factor. Microstructure investigation are showed the LMC are reduced the internal pore volume and enhanced the transition zone between cement paste and aggregate interface. This effect get by consist of latex films in the concrete. Also, this study were recommended the mix proportion method for LMC. These mix proportions method are estimated the mix design for satisfied the target performance which are applied the agricultural concrete structure.

• Journal of the Korea Institute of Building Construction
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• v.23 no.6
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• pp.727-738
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• 2023

In concrete, the interface between the aggregate and cement paste is often the most critical factor in determining strength, representing the weakest zone. Lightweight aggregate, produced through expansion and firing of raw materials, features numerous surface pores and benefits from low density; however, its overall aggregate strength is compromised. Within concrete, diminished aggregate strength can lead to aggregate fracture. When applying lightweight aggregate to concrete, the interface strength becomes critical due to the potential for aggregate fracture. This study involved coating the surface of the aggregate with blast furnace slag fine powder to enhance the interfacial strength of lightweight aggregate. The impedance of test specimens was measured to analyze interface changes resulting from this surface modification. Experimental results revealed a 4% increase in compressive strength following the coating of the lightweight aggregate surface, accompanied by an increase in resistance values within the impedance measurements corresponding with strength enhancement.