• Computers and Concrete
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• v.23 no.4
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• pp.267-272
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• 2019

In order to study the effect of moisture on the compressive strength of low-strength hollow concrete blocks, an experimental study was carried out on 96 samples of locally manufactured hollow concrete blocks collected from three different locations. Uniaxial compression tests were conducted on dry specimens and three types of saturated specimens with moisture contents of 30%, 50% and 80% respectively. The range of moisture content adopted covered the range within which the concrete block samples are saturated in the dry and monsoon seasons. The compressive strength of low-strength hollow concrete blocks decreases with increase in moisture content and the relationship between compressive strength of hollow concrete blocks and their moisture content can be considered to be linear. However, the strength degradation of 30% moist concrete blocks with respect to dry blocks is relatively low and can be considered to be comparable to dry concrete blocks. A formula indicating the relationship between the moisture content and compressive strength of low-strength hollow concrete blocks is also proposed.

• Computers and Concrete
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• v.13 no.4
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• pp.437-456
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• 2014

This work incorporates newly introduced Lattice Discrete Particle Model (LDPM) to assess the failure mechanism and strength of hollow concrete blocks. Alongside, a method for the graphical representation of cracked surfaces in the LDPM is outlined. A slightly modified calibration procedure is also suggested and used to estimate required model parameters for a tested concrete sample. Next, the model is verified for a compressively loaded hollow block made of the very same concrete. Finally, four geometries commonly used in the production of hollow concrete blocks are selected, numerically simulated, and their failure properties are explored under concentric and eccentric compressions.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.12 no.4
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• pp.195-202
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• 2000

Recently, wave dissipating structures with porosity are widely used to improve habor tranquility and to reduce the wave overtopping rate. In this study, hydraulic model tests were performed to examine hydraulic efficiency of slit caissons, igloo blocks, and hollow blocks. The model tests showed that slit caissons were the most effective in dissipating wave energy under moderate wave conditions. Slit caissons and igloo blocks showed no significant difference in reducing wave overtopping rate. Hallow blocks are less effective in reducing wave overtopping rate than slit caissons and igloo blocks lU1der higher wave energy conditions.

• Structural Engineering and Mechanics
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• v.80 no.6
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• pp.689-699
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• 2021

The present study aims to understand the behaviour of low-strength masonry prisms constructed with locally-produced low-strength hollow concrete blocks. Compression tests were conducted on masonry prisms constructed with three different mortar grades of cement-sand ratios of 1:3, 1:4.5 and 1:6 representing strong, moderately strong and weak mortar. Stress-strain curves were generated from the test results for the masonry prisms. The hollow concrete masonry units employed in this study are some of the weakest as compared to other masonry units employed by other researchers. The compressive strengths for masonry prisms with mortar grades 1:3, 1:4.5 and 1:6 are 2.21 MPa, 2.19 MPa and 2.25 MPa respectively. The results indicate that the masonry compressive strength of such low-strength hollow concrete block masonry prisms is not influenced by the mortar strength. Simple relationships to estimate the modulus of elasticity and compressive strength of masonry prisms is also proposed.

• Journal of Information Processing Systems
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• v.19 no.4
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• pp.540-553
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• 2023

The hollow letter CAPTCHA (Completely Automated Public Turing test to tell Computers and Humans Apart) is an optimized version of solid CAPTCHA, specifically designed to weaken characteristic information and increase the difficulty of machine recognition. Although convolutional neural networks can solve CAPTCHA in a single step, a good attack result heavily relies on sufficient training data. To address this challenge, we propose a seed filling algorithm that converts hollow characters to solid ones after contour line restoration and applies three rounds of detection to remove noise background by eliminating noise blocks. Subsequently, we utilize a support vector machine to construct a feature vector for recognition. Security analysis and experiments show the effectiveness of this algorithm during the pre-processing stage, providing favorable conditions for subsequent recognition tasks and enhancing the accuracy of recognition for hollow CAPTCHA.

• Bulletin of the Korean Chemical Society
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• v.30 no.5
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• pp.1118-1120
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• 2009

Micro-size CdS spheres of hollow shape were fabricated through the self-assembly of high density arrow-like nanorods. The synthesis of the CdS hollow spheres were accomplished in an aqueous solution of cadmium nitrate and triblock copolymer (Pluronic P123) at low temperature (80 ${^{\circ}C}$) through the slow release of S2- ions from thioacetamide. Morphology of the fabricated CdS hollow spheres was characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). The results indicate that the arrow-like CdS nanorods are simultaneously grown and attached each other to form the building units that become the spheres with hollow inside as a self-assembled process. The CdS spheres have a diameter of $2{\sim}3 {\mu}m$ and consist of the nanorods with a length of$\sim$800 nm. The nanocrystal building blocks have a hexagonal CdS structure.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.10a
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• pp.3.1-3.1
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• 2011

Nanoengineered materials with advanced architectures are critical building blocks to modulate conventional material properties or amplify interface behavior for enhanced device performance. While several techniques exist for creating one dimensional heterostructures, electrospinning has emerged as a versatile, scalable, and cost-effective method to synthesize ultra-long nanofibers with controlled diameter (a few nanometres to several micrometres) and composition. In addition, different morphologies (e.g., nano-webs, beaded or smooth cylindrical fibers, and nanoribbons) and structures (e.g., core-.shell, hollow, branched, helical and porous structures) can be readily obtained by controlling different processing parameters. Although various nanofibers including polymers, carbon, ceramics and metals have been synthesized using direct electrospinning or through post-spinning processes, limited works were reported on the compound semiconducting nanofibers because of incompatibility of precursors. In this work, we combined electrospinning and galvanic displacement reaction to demonstrate cost-effective high throughput fabrication of ultra-long hollow semiconducting chalcogen and chalcogenide nanofibers. This procedure exploits electrospinning to fabricate ultra-long sacrificial nanofibers with controlled dimensions, morphology, and crystal structures, providing a large material database to tune electrode potentials, thereby imparting control over the composition and shape of the nanostructures that evolved during galvanic displacement reaction.

• Journal of the Korean Geotechnical Society
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• v.38 no.7
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• pp.49-62
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• 2022

The hollow modular concrete block reinforced foundation method is one of the ground reinforcement foundation methods that uses hexagonal honeycomb-shaped concrete blocks with mixed crushed rock to reinforce soft grounds. It then forms an artificial layered ground that increases bearing capacity and reduces settlement. The hollow modular honeycomb-shaped concrete block is a geometrically economical, stable structure that distributes forces in a balanced way. However, the behavioral characteristics of hollow modular concrete block reinforced foundations are not yet fully understood. In this study, a bearing capacity test is performed to analyze the reinforcement effectiveness of the hollow modular concrete block through the laboratory model tests. From the load-settlement curve, punching shear failure occurs under the unfilled sand condition (A-1-N). However, the filled sand condition (A-1-F) shows a linear curve without yielding, confirming the reinforcement effect is three times higher than that of unreinforced ground. The bearing capacity equation is proposed for the parts that have contact pressure under concrete, vertical stress of hollow blocks, and the inner skin friction force from horizontal stress by confining effect based on the schematic diagram of confining effect inside a hollow modular concrete block. As a result of calculating the bearing capacity, the percentage of load distribution for contact force on the area of concrete is about 65%, vertical force on the area of hollow is 16.5% and inner skin friction force of area of the inner wall is about 18.5%. When the surcharge load is applied to the concrete part, the vertical stress occurs on the area of the hollow part by confining effect first. Then, in the filled sand in the hollow where the horizontal direction is constrained, the inner skin friction force occurs by the horizontal stress on the inner wall of the hollow modular concrete block. The inner skin friction force suppresses the punching of the concrete part and reduces contact pressure.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.6
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• pp.185-192
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• 2021

In this study, Full-scale hollow slab Mock-up with VPS(Void Plywood Slab System) was produced. Through Mock-up, the safety of the flat plate hollow slab against short-term sagging and long-term sagging is to be evaluated. The hollow rate of the mock-up specimen to which the hollow core slab was applied was designed to be 24%. When loading through concrete blocks, the most central part of the slab was deflection 8.88mm when loading. However, it shows a safe value compared to the reference value (l_n/240=17.93mm) for short-term deflection. As a result of 3 months of measurement of the mock-up experiment, the deflection at the center of the slab increased by 6.792mm from the initial deflection. In addition, it was found that the reference value by the load used suggested by KBC2016 was satisfied.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.10a
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• pp.4-4
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• 2011

Extensive research efforts are directed toward the development of highly sensitive gas sensors using novel nanostructured materials. Among the different strategies for producing sensor devices based on nanosized building blocks, polymeric fiber templating approach which is combined by chemical and physical synthesis routes was attracted much attention. This unique morphology increases the surface area and reduces the interfacial area between film and substrate. Consequently, the surface activity is markedly enhanced while deleterious interfacial effects between film and substrate are significantly reduced. Both effects are highly advantageous for gas sensing applications. In this presentation, facile synthesis of hollow and porous metal oxide nanostructures and their applications in chemical sensors will be discussed.