• Journal of Korean Society of Water and Wastewater
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• v.24 no.5
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• pp.485-493
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• 2010

Chemical coagulation destabilizes colloidal particles so that particles grow to larger flocs. Solid particles are then removed by solid-liquid separation after typical precipitation. Rapid precipitation enhances the separation by reducing the precipitation time with larger and denser particles. Conventionally, polyelectolyte compounds (polymers) function as a flocculant aid by introducing a interparticle binding, which increases the particle size and density. And more recent ballasted flocculation adds a ballasting agent (microsand) to form denser particles with its high-density(sp gr=2.65). The current research was to evaluate the manner in which ballasted flocs are formed under different injection timings of microsand and to recognize the effects on floc formation. $FeCl_3$ as a coagulant, anionic polymer for a flocculation aid and microsand were used for the floc formation. Floc size (diameter) was widely ranged with the highest mean value when microsand was injected between $FeCl_3$ and polymer. Mean floc density was larger when the floc formed smaller. Settling velocity increased with larger floc size, whilst not significantly affected by the timing of microsand injection. The additional slow mixing on floc formation increased floc size to some extent.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.04a
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• pp.147-152
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• 1998

This study is to investigate the application of concrete with crushed sand on site. As a result, it is showed that the combined sand mixed with sea sand is very desirable for obtaining workability and strength of concrete, and the optimal replacement percentage of crushed sand is 50% with sea sand. After all, the crushed sand could be sufficiently used as a fine aggregate for concrete in the aspect of economical efficiency and quality, but the particle shape and microsand passing No.200 sieve should be firstly improved for increasing workability of concrete on site.

• Environmental Engineering Research
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• v.16 no.3
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• pp.165-173
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• 2011

The equilibrium and kinetic adsorption of arsenic on six different adsorbents were investigated with one synthetic and four natural types (two surface and two ground) of water. The adsorbents tested included magnetic ion exchange resins (MIEX), hydrous ion oxide particles (HIOPs), granular ferric hydroxide (GFH), activated alumina (AA), sulfur modified iron (SMI), and iron oxide-coated microsand (IOC-M), which have different physicochemical properties (shape, charge, surface area, size, and metal content). The results showed that adsorption equilibriums were achieved within a contact period of 20 min. The optimal doses of adsorbents determined for a given equilibrium concentration of $C_{eq}=10\;{\mu}g/L$ were 500 mg/L for AA and GFH, 520-1,300 mg/L for MIEX, 1,200 mg/L for HIOPs, 2,500 mg/L for SMI, and 7,500 mg/L for IOC-M at a contact time of 60 min. At these optimal doses, the rate constants of the adsorbents were 3.9, 2.6, 2.5, 1.9, 1.8, and 1.6 1/hr for HIOPs, AA, GFH, MIEX, SMI, and IOC-M, respectively. The presence of silicate significantly reduced the arsenic removal efficiency of HIOPs, AA, and GFH, presumably due to the decrease in chemical binding affinity of arsenic in the presence of silicate. Additional experiments with natural types of water showed that, with the exception of IOC-M, the adsorbents had lower adsorption capacities in ground water than with surface and deionized water, in which the adsorption capacities decreased by approximately 60-95%.

• Journal of the Korea Institute of Building Construction
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• v.3 no.3
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• pp.107-112
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• 2003

This study is to investigate the properties of concrete with crushed sand on site and to propose a quality guideline for its use as artificial sand and concrete. From our experimental result in laboratory and site, we found that demand water of concrete with crushed sand for target slump increased by 18kg/m3 compared to mixed sand and l8kg/m3 compared to sea sand respectively. The compressive strength increased by around 3∼6% when compared to concrete with sea sand. Accordingly, our study showed that the combined sand mixed with sea sand would be desirable to obtain workability and strength of concrete including dry shrinkage and bleeding test. Furthermore, the optimal replacement percentage of crushed sand was 50% with sea sand. As such, crushed sand would be sufficient as fine aggregate for concrete in terms of economic efficiency and quality. Crushed sand, on the other hand can only be used as fine aggregate when VFS(Very Fine Sand) is below 3.5 percentage of weight of sand and particle shape is above 55 percentage. Also, the particle shape and microsand passing NO.200 sieve should continually be improved to increase workability of concrete on site.