• Journal of the Korean Recycled Construction Resources Institute
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• v.5 no.2
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• pp.168-176
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• 2017

This study, as a research for using crushed sand as a fine aggregate of concrete for nuclear structures, we improved the performance of impact crusher in the existing crushed sand production process and adjusted grain size to conform to ASTM C 33 The shape and grain size characteristics of a crushed sand were examined and concrete was prepared according to the substitution ratio of the sand to investigate the properties of fresh concrete and hardened concrete. The experimental results show that most of the concrete characteristics are equivalent to those of concrete using only heavy sand. However, when the substitution rate of steel sand exceeds 50%, the amount of air, compressive strength and tensile strength are somewhat reduced.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.8
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• pp.1041-1047
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• 2011

In this study, two types of die material cast iron was treated for surface hardening by using high power diode laser to improve mechanical properties of die which is using as essential production technology in the parts manufacturing in virtually all the infrastructure industries now. First of all, the heat treatment characteristics of FCD550 material which is spheroidal graphite cast iron, and through the heat treatment of HCI350 material which is flake graphite cast iron, the heat treatment characteristics of the two materials were compared. The hardness of hardened zone increased over 3 times over base material for both specimens, but as for required heat input, HCI350 was higher than FCD550 material depending on the heat conductivity of the materials by the content amount and shape of graphite contained in the material.

• Journal of Conservation Science
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• v.17 s.17
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• pp.57-64
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• 2005

In the course of examining the micro structure of Iron chisel and Iron arrowhead, a relics of the 16th or 17th of Chosun Dynasty unearthed at near Gangsun-tower, Chengpyeong temple. Collected un-eroded samples from the relics were looked into the metallic structure through optical metallography. Non-metallic inclusions were-analysed by SEM and EDS. The micro structure examination and SEM-SDS analysis revealed that Iron chisel and Iron arrowhead had been produced from the sponge iron close to pure iron made by low temperature reducing in a solid and then the surface carbon content was increased by carburizing treatment. It was also found that Iron chisel had been hardened through the repetitive processes of quench hardening and heat treatment, after increasing carbon content to a certain level. Up to now, there have been a number of studies in the domestic academia which were studied mainly on the structure of metallic relics in the period of the Three Kingdoms or before. Although this research was limited in type and number of the relics, it turned out to be interesting in that it revealed the 16th or 17th century way of processing iron, even in fragments. It is thought to be fruitful that iron had been made even in the Chosun Dynasty from the sponge iron.

• Journal of Powder Materials
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• v.26 no.6
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• pp.493-501
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• 2019

In this work, ultra-fine calcium oxide (CaO) powder derived from eggshells is used as the starting material to synthesize mineral trioxide aggregate (MTA). The prepared CaO powder is confirmed to have an average particle size of 500 nm. MTAs are synthesized with three types of fine CaO-based powders, namely, tricalcium silicate (C3S), dicalcium silicate (C2S), and tricalcium aluminate (C3A). The synthesis behavior of C3S, C2S and C3A with ultra-fine CaO powder and the effects of C₃A content and curing time on the properties of MTA are investigated. The characteristics of the synthesized MTA powders are examined by X-ray diffraction (XRD), field emission-scanning electron microscope (FE-SEM), and a universal testing machine (UTM). The microstructure and compressive strength characteristics of the synthesized MTA powders are strongly dependent on the C3A wt.% and curing time. Furthermore, MTA with 5 wt.% C3A is found to increase the compressive strength and shorten the curing time.

• Resources Recycling
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• v.15 no.2 s.70
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• pp.10-17
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• 2006

The purpose of this study was to evaluate the effects of blast-furnace slag on strength development and durability of latex-modified concrete (LMC) and ordinary portland cement concrete as slag contents. Main experimental variables were performed latex contents (0%, 10%, 15%) and slag contents (0%, 30%). The compressive and flexural strengths, chloride-ion rapid permeability and chemical attacks resistance were measured to analyze the characteristic of the developed LMC and BS-LMC(latex-modified concrete added blast-furnace slag) on hardened concrete. The test results showed that compressive and flexural strength of BS-LMC increased as the slag contents increased from 0% to 30% at the long term of curing. It considers blast furnace slag used when latex content was up to 10%. The permeability resistance of BS-LMC(latex 10%, blast 30%) was extremely good at the curing time 90 days. Also. the effects of added blast furnace slag on OPC and LMC were increased on the permeability and chemical attacks resistance.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.59-64
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• 2002

Effects of the aging treatments on the microstructure and strength of heat affected zone(HAZ) in the welds of a age-hardened Al-Mg-Si alloy, 5N01-T5, were investigated. The base metal aging treatments before MIG welding were conducted at 423K to 473K for 28.8ks Post weld heat treatment(PWHT) to recover the HAZ strength was performed at 448K for 28.8ks. Microstructure observations, hardness measurements and tensile tests were conducted to study properties of the MIG weld joints. The position of the softest region in HAZ where the hardness insufficiently recovered after natural aging and PWHT was at a distance of approximately 15mm from the center of the fusion zone. Hardness of the softest regions after natural aging and PWHT decreased with increase in the base metal aging temperature. TEM observation clarified that strengthening ${\beta}$"(Mg$_2$Si) precipitates and coarse ${\beta}$′ precipitates affected the hardnes of HAZ. Incomplete recover of hardness in HAZ after PWHT was caused by the precipitating of non-hardening ${\beta}$′ phase during the weld thermal cycle. In order to examine the effects of weldheat input and welding speed, the laser weld joints were also investigated and compared with the MIG weld ones. Laser welding had the narrower width of the softened regions in HAZ compared with MIG welding. The hardness of the softest regions of the laser welds after PWHT was higher than that of the MIG welds. Quantitative relations between hardness of the softest region and base metal aging temperature were obtained for both welding processes. Accordingly, the equations to estimate the strength of the weld joints after PWHT with varying base metal temperatures were proposed for MIG welding and laser welding.

• Journal of the Korea Concrete Institute
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• v.28 no.1
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• pp.67-74
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• 2016

With several different dosages of multi-walled CNTs which was 0.1, 0.3, and 0.5% of the weight of binder, the fluidity in fresh CNT cement composites, as well as the strength and strength development with age of the hardened composites were investigated in this experimental study. The experimental results from flow test indicated that the increase in the dosage of CNTs badly impacted on the workability of fresh composites, and the results from rheological measurements presented the decrease in plastic viscosity and the increase in yield stress according to the amount of CNTs. In addition, the thixotrophy in the flow curve obtained from the rheology test was observed more noticeably in the composites with higher dosage of CNTs. With the experiments on the strength properties, the improvement of both compressive and tensile strengths with the increase of CNTs dosage could be obtained. Moreover, early strength development by adding CNTs was found when it was compared with plain cementious matrix without CNT.

• Advances in concrete construction
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• v.9 no.2
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• pp.217-225
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• 2020

The recovery of waste proves a solution with two impacts: the environmental impact by the reduction of pollution and the gain of the occupied space by this waste, and the economic impact by the use of these lasts in the building and in the area of public works. The present research consists in recovering a waste marble (thrown powder exposed to the different meteorological phenomena) generated by the quarry marble of Fil-fila, located at the east side of Skikda in the north-east of Algeria, and add it, as sand in the composition of sand concrete. To carry out this research, we analyzed the evolution brought by the substitution of ordinary sand by marble waste sand, with 25%, 50%, 75% and 100% on the properties in the fresh state (density, workability and air content) and in the cured state (compressive strength, tensile strength, surface hardness and sound velocity). For durability we tested water absorption by immersion and chloride penetration. The results obtained are compared with control samples of 0% of substitution rate. In order to have a good filling of the voids in the granular skeleton; we added a quantity of limestone recycled fines from the quarries and for a good workability a super-plasticizing additive. The results showed that the partial substitution modified both the fresh and the hardened characteristics of the tested concretes, the durability parameters also improved.

• International Journal of Concrete Structures and Materials
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• v.8 no.3
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• pp.213-228
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• 2014

Alkali-activated binder (AAB) is recently being considered as a sustainable alternative to portland cement (PC) due to its low carbon dioxide emission and diversion of industrial wastes and by-products such as fly ash and slag from landfills. In order to comprehend the behavior of AAB, detailed knowledge on relations between microstructure and mechanical properties are important. To address the issue, a new approach to characterize hardened pastes of AAB containing fly ash as well as those containing fly ash and slag was adopted using scanning electron microscopy (SEM) and energy dispersive X-ray spectra microanalyses. The volume stoichiometries of the alkali activation reactions were used to estimate the quantities of the sodium aluminosilicate (N-A-S-H) and calcium silicate hydrate (CSH) produced by these reactions. The 3D plots of Si/Al, Na/Al and Ca/Si atom ratios given by the microanalyses were compared with the estimated quantities of CSH(S) to successfully determine the unique chemical compositions of the N-A-S-H and CSH(S) for ten different AAB at three different curing temperatures using a constrained nonlinear least squares optimization formulation by general algebraic modeling system. The results show that the theoretical and experimental quantities of N-A-S-H and CSH(S) were in close agreement with each other. The $R^2$ values were 0.99 for both alkali-activated fly ash and alkali-activated slag binders.

• Journal of the Korea Concrete Institute
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• v.25 no.6
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• pp.675-682
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• 2013

In this study, to enhance the quality of concrete surface by removing the surplus water, permeable liner attached the euroform was applied for manufacturing concrete specimens. Various kinds of concrete mixtures with different water to binder ratios were applied and the strength properties of the hardened concrete surfaces were evaluated at different heights. Experimental results showed that the rebound values by schmidt hammer test and the compressive strengths on the surfaces of concrete specimens were increased as proportion to the amount of mixture water which is dependent on the water to binder ratio of each concrete mixture, and more enhancements were observed on the middle and lower specimen surfaces than the upper region. SEM analysis also showed that much denser hydrate structures were observed on the specimen surfaces by the application of the permeable liner while similar hydrate formations were occurred regardless of surface treatment conditions. From the MIP test results of the concrete surfaces, it was observed that, by the application of permeable liner, the pore volume below $0.01{\mu}m$ was decreased with a maximum of 50% resulting in the densification of pore structures.