• Elastomers and Composites
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• v.33 no.4
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• pp.290-296
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• 1998

Recycling of waste tire has been limited and very simple, few applications have been observed. This study introduces a new elastic and permeable pavement made of scrap tire. Experimental results showed that key factors affecting the compressive strength were the size of scrap tire, size of aggregate, amounts and property of binder. Also, the water permeability depended on the size of aggregate and scrap tire. The compressive strength and water permeability of the samples were 1.4 and 116 times higher than those of the conventional porous cement concrete, respectively.

• Computers and Concrete
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• v.7 no.5
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• pp.469-482
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• 2010

This paper investigates the concrete permeability through a numerical and statistical approach. Concrete is considered as a random heterogeneous composite of three phases: aggregates, interfacial transition zones (ITZ) and matrix. The paper begins with some classical bound and estimate theories applied to concrete permeability and the influence of ITZ on these bound and estimate values is discussed. Numerical samples for permeability analysis are established through random aggregate structure (RAS) scheme, each numerical sample containing randomly distributed aggregates coated with ITZ and dispersed in a homogeneous matrix. The volumetric fraction of aggregates is fixed and the size distribution of aggregates observes Fuller's curve. Then finite element method is used to solve the steady permeation problem on 2D numerical samples and the overall permeability is deduced from flux-pressure relation. The impact of ITZ on overall permeability is analyzed in terms of ITZ width and contrast ratio between ITZ and matrix permeabilities. Hereafter, 3680 samples are generated for 23 sample sizes and 4 contrast ratios, and statistical analysis is performed on the permeability dispersion in terms of sample size and ITZ characteristics. By sample theory, the size of representative volume element (RVE) for permeability is then quantified considering sample realization number and expected error. Concluding remarks are provided for the impact of ITZ on concrete permeability and its statistical characteristics.

• Journal of the Korean Recycled Construction Resources Institute
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• v.5 no.4
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• pp.458-465
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• 2017

The purpose of the present study was to examine the method of physically processing oyster shells for use as raw material(aggregate) through experimentation. The results of the experiment found that the adequate particle size of the pulverized oyster shells should be smaller than 10mm due to their shape. Also, after considering various particle size distributions and residual rates by particle size, the study found the cutter mill to be the most suitable tool for pulverizing oyster shells. The use of a cutter mill resulted in recovery rates of 97.3%, 98.2%, and 98.9% for inner screens of 8mm, 12mm, and 20mm respectively, revealing how the increase of screen size results in slightly higher recovery rates. The experiment involving the difference between the inner screen of the cutter mill and the speed of the inverter shows that a smaller screen size and a faster inverter speed result in a lower fineness modulus, while a rise in inverter speed for an identical screen made possible the material recovery of a much lower range of particle sizes.

• IE interfaces
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• v.17 no.1
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• pp.71-77
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• 2004

At the present time, container transportation plays a key role in the international logistics and the efforts to increase the productivity of container logistics become essential for Korean trucking companies to survive in the domestic as well as global competition. This study suggests an approach for determining fleet size for container road transportation with dynamic demand. Usually the vehicles operated by the transportation trucking companies in Korea can be classified into three types depending on the ways how their expenses occur; company-owned truck, mandated truck which is owned by outsider who entrust the company with its operation, and rented vehicle (outsourcing). Annually the trucking companies should decide how many company-owned and mandated trucks will be operated considering vehicle types and the transportation demands. With the forecasted monthly data for the volume of containers to be transported a year, a heuristic algorithm using tabu search is developed to determine the number of company-owned trucks, mandated trucks, and rented trucks in order to minimize the expected annual operating cost. The idea of the algorithm is based on both the aggregate production planning (APP) and the pickup-and-delivery problem (PDP). Finally the algorithm is tested for the problem how the trucking company determines the fleet size for transporting containers.

• Journal of the Korea Concrete Institute
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• v.24 no.3
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• pp.333-340
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• 2012

The current study prepared 9 laboratorial concrete mixes and 3 ready-mixed concrete batches to examine the size and shape effects in compression failure of lightweight aggregate concrete (LWC). The concrete mixes were classified into three groups: normal-weight, all-lightweight and sand-lightweight concrete groups. For each concrete mix, the aspect ratio of circular or square specimens was 1.0 and 2.0. The lateral dimension of specimens varied between 50 and 150 mm for each laboratorial concrete mix, whereas it ranged from 50 to 400 mm with an incremental variation of 50 mm for each ready-mixed concrete batch. Test observations revealed that the crack propagation and width of the localized failure zone developed in lightweight concrete specimens were considerably different than those of normal-weight concrete (NWC). In LWC specimens, the cracks mainly passed through the coarse aggregate particles and the crack distribution performance was very poor. As a result, a stronger size effect was developed in LWC than in NWC. Especially, this trend was more notable in specimens with aspect ratio of 2.0 than in specimens with that of 1.0. The prediction model derived by Kim et al. overestimated the size effect of LWC when lateral dimension of specimen is above 150 mm. On the other hand, the modification factors specified in ASTM and CEB-FIP provisions, which are used to compensate for the shape effect of specimen on compressive strength, were still conservative in LWC.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.3
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• pp.317-324
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• 2020

Plastic wastes generated from domestic waste are separated by mixed discharge with foreign substances, and the cost of the separation and screening process increases, so recycling is relatively low. In this study, as a fundamental study for recycling mixed plastic wastes generated from domestic waste into concrete aggregates, changes in concrete properties according to the plastic waste types and the substitution rate were evaluated experimentally. The mixed plastic waste aggregate(MPWA) was found to have a lower density and a higher absorption rate compared to the coarse aggregate with good particle size distribution. On the other hand, the single plastic waste aggregate(SPWA) was composed of particles of uniform size, and both the density and the absorption rate were lower than that of the fin e aggregate. It was found that the MPWA substitution concrete did not cause a material separation phenomenon due to a relatively good particle size distribution even with the largest amount of plastic waste substitution, and the amount of air flow increased little. The compressive strength and flexural strength of the PWA substitution concrete decreased as the amount of substitution of the PWA increased due to the low strength of the PWA, the suppression of the cement hydration reaction due to hydrophobicity, and the low adhesion between the PWA and the cement paste. It was found that the degree of deterioration in compressive strength and flexural strength of concrete substituted with MPWA having good particle size distribution was relatively small.

• Journal of Broadcast Engineering
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• v.20 no.2
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• pp.300-309
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• 2015

In IEEE 802.11n WLANs(Wireless Local Area Networks), to support high throughput, MAC(Media Access Control) layer adopts A-MSDU(Aggregate-MAC Service Data Unit) and A-MPDU(Aggregate-MAC Protocol Data Unit). Generally, as the A-MPDU uses a selective retransmission capability, A-MPDU provides higher throughput than A-MSDU. However, although A-MPDU uses the selective re-transmission capability, if the size of MPDU within A-MPDU is smaller than the size of minimum MPDU starting spacing, A-MPDU can reduce throughput because of the overhead of retransmission owing to the addition of delimiter, that is a dummy MPDU. Therefore, to overcome the above problem, two-level Aggregation method, where the small MPDU within A-MPDU is replaced by not delimiter but A-MSDU, has been introduced. In the two-level Aggregation method, the existing re-transmission scheme retransmits only A-MPDU, but if the size of retransmission data is smaller than the size of the minimum MPDU starting spacing, the proposed retransmission scheme retransmits the aggregated retransmission data and MSDUs. Therefore, we know that the proposed retransmission scheme have better throughput that the existing retransmission scheme.

• Spatial Information Research
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• v.19 no.3
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• pp.95-106
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• 2011

Recently as efficient processing of aggregate queries for fetching desired data from sensors has been recognized as a crucial part, in-network aggregate query processing techniques are studied intensively in wireless sensor networks. Existing representative in-network aggregate query processing techniques propose routing algorithms and data structures for processing aggregate queries. However, these aggregate query processing techniques have problems such as high energy consumption in sensor nodes, low accuracy of query processing results, and long query processing time. In order to solve these problems and to enhance the efficiency of aggregate query processing in wireless sensor networks, this paper proposes Bucket-based Parallel Aggregation(BPA). BPA divides a query region into several cells according to the distribution of sensor nodes and builds a Quad-tree, and then processes aggregate queries in parallel for each cell region according to routing. And it sends data in duplicate by removing redundant data, which, in turn, enhances the accuracy of query processing results. Also, BPA uses a bucket-based data structure in aggregate query processing, and divides and conquers the bucket data structure adaptively according to the number of data in the bucket. In addition, BPA compresses data in order to reduce the size of data in the bucket and performs data transmission filtering when each sensor node sends data. Finally, in this paper, we prove its superiority through various experiments using sensor data.

• Journal of the Korea Concrete Institute
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• v.28 no.3
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• pp.329-340
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• 2016

Increase in demotion and repair works on buildings in the construction market generates a large amount of construction waste. Recycling of construction waste is important for saving of resources, preservation of environment and constant advance of the construction industry. Accordingly, the environmental and economic value of recycled aggregate, which is produced after waste concrete is crushed, is increasingly highlighted. It is generally known that compared to concrete made of ordinary aggregate, concrete made of recycled aggregate has low quality, and the low quality is dependent on the amount of the bonding heterogeneous (cement paste and mortar) as well as the amount of the pores within the bonding heterogeneous. Reports on carbonation mechanism shows that the pores of cement-based materials are filled up by the progress of carbonation. Therefore, this study aims at an estimation of the period for optimum carbonation reforming appropriate for the thickness of the bonding heterogeneous of recycled aggregate, based on carbonation mechanism, with a view to improving the product quality by means of filling up the pores of the bonding heterogeneous of recycled aggregate. This study drew the carbonation depth according to the passage of age by calculating the bonding ratio and bonding thickness of the bonding heterogeneous as against the particle size distribution of recycled aggregate as well as by chemical quantitative analysis according to the age of accelerated carbonation of mock-up samples imitating bonding heterogeneous. Based on the correlation between the age of accelerated carbonation and carbonation depth, this study also proposed the estimated period of carbonation reforming of recycled aggregate appropriate for the thickness of the bonding heterogeneous.

• Journal of the Korea Concrete Institute
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• v.17 no.1 s.85
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• pp.19-25
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• 2005

Recycling of waste materials in the construction Industry is a useful method that can cope with an environment restriction of every country. In this study, synthetic lightweight aggregates are manufactured with recycled plastic and fly ash with 12 percent carbon. Nominal maximum-size aggregates of 9.5 mm were produced with fly ash contents of 0, 35, and $80\%$ by the total mass of the aggregate. An expanded clay lightweight aggregate and a normal-weight aggregate were used as comparison. Gradation, density, and absorption capacity are reported for the aggregates. Five batches of concrete were made with the different coarse aggregate types. Mechanical properties of the concrete were determined including density, compressive strength, elastic modulus, splitting tensile strength, fracture toughness, and fracture energy. Salt-scaling resistance, a concrete durability property, was also examined. Compressive and tensile strengths were lower for the synthetic aggregates; however, comparable fracture properties were obtained. Relatively low compressive modulus of elasticity was found for concretes with the synthetic lightweight aggregate, although high ductility was also obtained. As nv ash content of the synthetic lightweight aggregate increased, all properties of the concrete were improved. Excellent salt-scaling resistance was obtained with the synthetic lightweight aggregate containing 80 percent fly ash.