• Steel and Composite Structures
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• v.44 no.3
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• pp.389-406
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• 2022

Recycling concrete construction waste is an encouraging step toward green and sustainable building. A lot of research has been done on recycled aggregate concretes (RACs), but not nearly as much has been done on concrete made with recycled aggregate. Recycled aggregate concrete, on the other hand, has been found to have a lower mechanical productivity compared to conventional one. Accurately estimating the mechanical behavior of the concrete samples is a most important scientific topic in civil, structural, and construction engineering. This may prevent the need for excess time and effort and lead to economic considerations because experimental studies are often time-consuming, costly, and troublous. This study presents a comprehensive data-mining-based model for predicting the splitting tensile strength of recycled aggregate concrete modified with glass fiber and silica fume. For this purpose, first, 168 splitting tensile strength tests under different conditions have been performed in the laboratory, then based on the different conditions of each experiment, some variables are considered as input parameters to predict the splitting tensile strength. Then, three hybrid models as GWO-RF, GWO-MLP, and GWO-SVR, were utilized for this purpose. The results showed that all developed GWO-based hybrid predicting models have good agreement with measured experimental results. Significantly, the GWO-RF model has the best accuracy based on the model performance assessment criteria for training and testing data.

• Journal of the Korean Society of Industry Convergence
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• v.27 no.4_2
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• pp.981-989
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• 2024

In recent years, there has been a growing focus on preserving the global environment and utilizing resources efficiently. The significance of energy conservation has led to the development of systems that recycle waste heat from factories and use eco-friendly refrigerants. This study aims to enhance the performance of adsorption-desorption systems using thermoelectric devices, which are known for their ability to convert temperature differences into electrical energy. The research focuses on improving the efficiency of these systems by integrating thermoelectric modules to cool the adsorption side and heat the desorption side, thus enhancing overall system performance. The experiments utilized a typical thermoelectric device and silica gel as the adsorbent. Key experimental parameters included varying the inlet air temperature and relative humidity on the desorption side. The results indicated that increasing the relative humidity of the inlet air on the desorption side significantly enhanced the overall mass transfer coefficient while reducing the completion time of the process. Similarly, higher inlet air temperatures led to an increase in the mass transfer coefficient and a decrease in process completion time. These findings suggest that optimizing the operational conditions of thermoelectric devices can substantially improve the performance of adsorption-desorption systems, offering potential benefits for applications in ventilation systems and other related fields.

• Korean Journal of Materials Research
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• v.25 no.2
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• pp.75-80
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• 2015

The carbon dioxide($CO_2$) released while producing building materials is substantial and has been targeted as a leading contributor to global climate change. One of the most typical method to reducing $CO_2$ for building materials is the addition of slag and fly ash, like pozzolan material, while another method is reducing $CO_2$ production by carbon negative cement development. The MgO-based cement was from the low-temperature calcination of magnesite required less energy and emitted less $CO_2$ than the manufacturing of Portland cements. It is also believed that adding reactive MgO to Portland-pozzolan cements could improve their performance and also increase their capacity to absorb atmospheric $CO_2$. In this study, the basic research for magnesia cement using $MgCO_3$ and magnesium silicate ore (serpentine) as main starting materials, as well as silica fume, fly ash and blast furnace slag for the mineral admixture, were carried out for industrial waste material recycling. In order to increase the hydration activity, $MgCl_2$ was also added. To improve hydration activity, $MgCO_3$ and serpentinite were fired at $700^{\circ}C$ and autoclave treatment was conducted. In the case of $MgCO_3$ as starting material, hydration activity was the highest at firing temperature of $700^{\circ}C$. This $MgCO_3$ was completely transferred to MgO after firing. This occurred after the hydration reaction with water MgO was transferred completely to $Mg(OH)_2$ as a hydration product. In the case of using only $MgCO_3$, the compressive strength was 3.5MPa at 28 days. The addition of silica fume enhanced compressive strength to 5.5 MPa. In the composition of $MgCO_3$-serpentine, the addition of pozzolanic materials such as silica fume increased the compression strength. In particular, the addition of $MgCl_2$ compressive strength was increased to 80 MPa.

• Journal of Korea Foundry Society
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• v.43 no.3
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• pp.107-136
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• 2023

Natural silica sand was commonly used for sand casting of cast steel products, and chromites sand was used to suppress seizure defects due to the lack of thermal properties of silica sand. However there are disadvantages such as deterioration by repeated use, system sand mixing problem, difficulty separating and removing, increased during mold according to high density and to being waste containing chrome. Recently, industrial waste reduction and atmospheric environment improvement have been highlighted as important tasks in the casting industry. In order to solve the problems that occur when using foundry Sand and to improve the environment of casting factories, various artificial sands that can be applied instead of natural silica sand have been developed and introduced. Artificial sands can be classified into artificial sand manufactured by the electric arc atomization or gas flame atomization, artificial sand manufactured by the spray drying & sintering process, artificial sand manufactured by the sintering & crushing process and exhibit different physical properties depending on the type of raw-minerals and manufacturing method. In this study, comparative evaluation tests were conducted on the physical properties of various foundry sands, mold strength, physical durability, thermal durability, and casting test pieces. When comprehensively considering the actual amount of molding sand used according to density, the mold strength according to the shape of sand, the physical and thermal durability of foundry sand, and the heat resistance characteristics of foundry sand, 'Molten artificial sand A1' or 'Molten artificial sand B' is judged to be the most suitable spherical artificial sand for casting of heavy steel castings.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.3C
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• pp.159-165
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• 2010

The problems such as natural resource exhaustion, pollutant emission and waste generation are increasing worldwide with the industrial development. The quantity of the industrial by-product in Korea is 6 million tons a year, and even its basic treatment processes including landfill, incineration and storage have reached their limits. In this study, fly ash and silica fume were applied to shotcrete to develop a method for the reuse of resources and to increase the use of fly ash, which is an industrial waste. An environmental hazard evaluation is a must to actively address the worldwide environmental problems, though. Therefore, an environmental impact assessment was conducted using the chemical content analysis test and heavy metal exudation test, for ten mixtures that were obtained through the pre-mixing and compressive strength tests. The results of the compressive strength test showed that all mixtures satisfied national and international standards. Cr, Cd and Hg were not detected, and Pb was detected only in some cases with fly ash. Cu and As were detected in all mixtures, but all of them satisfied national and international standards.

• Journal of Microbiology and Biotechnology
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• v.21 no.5
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• pp.494-502
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• 2011

Coenzyme $Q_{10}$ ($CoQ_{10}$) is a widely used supplement in heart diseases treatment or antioxidative dietary. The microbial production of $CoQ_{10}$ was enhanced by addition of solanesol and novel precursors recovered from waste tobacco. The novel precursors were separated by silica gel and identified as ${\alpha}$-linolenic acid (LNA) and butylated hydroxytoluene (BHT) based on the effect on $CoQ_{10}$ production and GC-MS. The effects of novel precursors on $CoQ_{10}$ production by Sphingomonas sp. ZUTE03 were further evaluated in a two-phase conversion system. The precursor's combination of solanesol (70 mg/l) with BHT (30 mg/l) showed the best effect on the improvement of $CoQ_{10}$ yield. A maximal $CoQ_{10}$ productivity (9.5 mg $l^{-1}$ $h^{-1}$) was achieved after 8 h conversion, with a molar conversion rate of 92.6% and 92.4% on BHT and solanesol, respectively. The novel precursors, BHT and LNA in crude extracts from waste tobacco leaves, might become potential candidates for application in the industrial production of $CoQ_{10}$ by microbes.

• 한국태양에너지학회:학술대회논문집
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• 2011.04a
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• pp.204-209
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• 2011

According to the environment report of UN, korea was classified as potable water shortage countries. Approximately 71% of the Earth's surface is covered by ocean. However, it is difficult to use for industry of residential purpose without a certain processing. The development of solar and waste-heat used absorption desalination technology have been examined as a viable option for supplying clean energy. In this study, the modelling of the main devices for solar and waste-heat used and adsorption desalination system was introduced. The design is divided into three parts. First, the evaporator for the vaporization of the top water is designed, and then the reactor for the adsorption and release of the steam is designed, followed by the condenser for the condensation of the fresh water is designed. In addition, new features based on the energy balance are also included to design absorption desalination system. In this basicresearch, One-bed(reactor) adsorption desalination plant that employ a low-temperature solar and waste energy was proposed and experimentally studied. The specific water yield is measured experimentally with respect to the time controlling parameters such as heat source temperatures, coolant temperatures, system switching and half-cycle operational times.

• Resources Recycling
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• v.13 no.4
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• pp.3-10
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• 2004

The intension of this study is to produce ordinary portland cement using ash, both bottom ash and fly ash, obtained from municipal solid waste incineration ash (MSWI). We used limestone, waste molding sand, shale, slag from converting furnaces and fly ash as main raw materials and mixed them, setting the lime saturation factor (LSF) within 91.0, the silica modulus (SM) within 2.40, and iron modulus (IM) within 1.80. We conducted tests adding bottom ash alone 1, 2 and 3％ by weight, respectively, and a mixture of bottom ash 0.9％ and fly ash 0.1 ％ by weight. The result of analysis on clinker shows that the more ash is added, the lower the burnability index (B.I.) falls, lowering the mineral evolution of calcium silicate accordingly. From the measurement of compressive strength we have learned that the more ash is used, the lower the strength becomes.

• Nuclear Engineering and Technology
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• v.11 no.3
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• pp.203-212
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• 1979

The thermal decomposition of simulated Magnox highly active waste and of HARVEST feed slurries (SW and SG) which include tile glass forming chemicals has been studied. The waste and the slurries are almost completely calcined by 500-55$0^{\circ}C$. The colour of the solids from the slurries varies little until about 90$0^{\circ}C$ when it darkens considerably. The slurries begin to vitrify at this temperature and are completely vitrified at 1000-105$0^{\circ}C$. On the other hand. the sulphate impurity in SN slurry causes a yellow phase to separate above 75$0^{\circ}C$. The density of the intermediate solids is fairly low until 650$^{\circ}$-$700^{\circ}C$ is reached. This temperature seems to mark the onset of fluxing as tile density rises quickly to 2g/㎤ at 700$^{\circ}$ -80$0^{\circ}C$. The strengh of the solids decreases with temperature up to 50$0^{\circ}C$, and then rises as the solids begin to sinter. Below 50$0^{\circ}C$ the SN solids are the stronger. suggesting that the impurity renders this silica more reactive.

• Advances in concrete construction
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• v.9 no.2
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• pp.139-147
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• 2020

This paper reports the effect of Rice Husk Ash (RHA) in geopolymer concrete on strength, durability and microstructural properties under ambient curing at a room temperature of 25℃ and 65±5% relative humidity. Rice husk was incinerated at 800℃ in a hot air oven. and ground in a ball mill to achieve the required fineness. RHA was partially added in 10, 15, 20, 25, 30 and 35 percentages to fly ash with 10% of GGBS to produce geopolymer concrete. Test results exhibit that the substitution of RHA in geopolymer concrete resulted in reduced strength properties during initial curing. In the initial stage, workability of GPC mixes was affected by RHA particles due to the presence of dormant particles in it. It is evident from the microstructural study that the presence of RHA particles densifies the matrix reducing porosity in concrete. This is due to the presence of RHA in geopolymer concrete, which affects the ratio of silica and alumina, resulting in polycondensation reactions products. This study suggests that incorporation of rice husk ash in geopolymer concrete is the solution for effective utilization of waste materials and prevention of environmental pollution due to the dumping of industrial waste and to produce eco-friendly concrete.