• Journal of the Korea Concrete Institute
• /
• v.16 no.2 s.80
• /
• pp.147-154
• /
• 2004

It is the aim of this study to propose the fundamental data for the establishment of the application and qualify standard of the mixed type superplasticizer after investigating and comparing the fluidity of high flowing concrete according to the component ratio of superplasticizer such as naphthalene sulfonated and melamine sulfonated. The results of this study were shown as the followings; 1) The fluidity and adsorption ratio of cement-paste were improved according to the increasing of naphthalene sulfonated component ratio, and apparent viscosity of cement-paste was improved according to the Increasing of melamine sulfonated component ratio. 2) In case of using the granulated blast-furnace slag, the fluidity of cement-paste was considerably good and the adsorption ratio was decreased and in case of using fly-ash, the apparent viscosity and adsorption ratio of cement-paste were improved. 3) The dispersive capacity performance of concrete can be improved by means of the increasing of naphthalene sulfonated component ratio. Also the viscosity and early strength can be improved by means of the increasing of melamine sulfonated component ratio.

• Journal of the Korea Concrete Institute
• /
• v.16 no.2 s.80
• /
• pp.241-248
• /
• 2004

The rheological properties of cement paste system mixed with mineral admixtures (MAs) used to increase the strength and improve durability and fluidity of concrete were investigated. And cement paste systems were designed as one-, two- and three-ingredients blended paste systems. The rheological properties of paste systems were assessed by Rotovisco RT 20 rheometer (Hakke inc.) having a cylindrical serrated spindle. The rheological properties of one-ingredient paste systems were improved with increasing the dosage of superplasticizer. For two-ingredients paste systems, as increasing the replacement ratio of blast furnace slag (BFS) and fly ash (FA), the yield stress and plastic viscosity were decreased compared with non-replacement. In the ordinary portland cement (OPC)-silica fume (SF) paste systems, in accordance with an increase in the replacement ratio of SF, the yield stress and plastic viscosity were increased steeply. For three-ingredients paste systems, both OPC-BFS-SF and OPC-FA-SF paste systems, the rheological properties were improved compared with the only replacement of SF. In the case of both two-and three-ingredients paste systems, the rheological properties using BFS were improved more than FA.

• Asian Journal of Atmospheric Environment
• /
• v.6 no.4
• /
• pp.288-303
• /
• 2012

In this study, real time measurements of particle number size distribution in urban Gwangju, coastal Taean, and industrial Yeosu in Korea were conducted in 2008 to understand the occurrence of ultrafine particle (UFP) (<100 nm) events, the variation of its concentration among different sampling sites, and UFP formation pathways. Also, to investigate seasonal and long-term variation of the UFP number concentration, data were collected for the period of 5 years (2007, 2008, 2010, 2011, and 2012) in urban Gwangju. Photochemical and combustion events were found to be responsible for the formation of UFP in the urban Gwangju site, whereas only photochemical event led to the formation of UFP in the coastal Taean site. The highest UFP concentration was found in industrial Yeosu (the average UFP number fractions were 79, 59 and 58% in Yeosu, Gwangju, and Taean, respectively), suggesting that high amount of gas pollutants (e.g., $NO_2$, $SO_2$, and volatile organic carbon (VOC)) emitted from industries and their photochemical reaction contributed for the elevated UFP concentration in the industrial Yeosu site. The UFP fraction also showed a seasonal variation with the peak value in spring (61.5, 54.5, 50.5, and 40.7% in spring, fall, summer, and winter, respectively) at urban Gwangju. Annual average UFP number concentrations in urban Gwangju were $5.53{\times}10^3\;cm^{-3}$, $4.68{\times}10^3\;cm^{-3}$, $5.32{\times}10^3\;cm^{-3}$, $3.99{\times}10^3\;cm^{-3}$, and $2.16{\times}10^3\;cm^{-3}$ in the year 2007, 2008, 2010, 2011, and 2012, respectively. Comparison of the annual average UFP number concentration with urban sites in other countries showed that the UFP concentrations of the Korean sites were lower than those in other urban cities, probably due to lower source strength in the current site. TEM/EDS analysis for the size-selected UFPs showed that the UFPs were classified into various types having different chemical species. Carbonaceous particles were observed in both combustion (soot and organics) and photochemical events (sulfate and organics). In the photochemical event, an internal mixture of organic species and ammonium sulfate/bisulfate was identified. Also, internal mixtures of aged Na-rich and organic species, aged Ca-rich particles, and doughnut shaped K-containing particles with elemental composition of a strong C with minor O, S, and K-likely to be originated from biomass burning nearby agricultural area, were observed. In addition, fly ash particles were also observed in the combustion event, not in the photochemical event.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.20 no.4
• /
• pp.128-135
• /
• 2016

In the current concrete structure of the highway is still the major problem most of concrete deterioration caused by the freeze-thaw and deicing salt, which is of issues that are not completely resolved. In particular, a single freezing event does not cause much harm, durability of concrete under multi-deterioration environment by repeated freeze-thaw and deicing salt is rapidly degraded and reduce its service life. In this study, the exposure environmental condition according the regional highway points were established. The damage condition and chloride content of the concrete at general and severe environmental exposure condition were also investigated. In addition, the experimental test of chloride ion permeability, scaling resistant and freeze-thaw resistance were carried out to improve the durability of the mechanical placing concrete of subsidiary structure. According to the results of this study, in observation of concrete surface condition, the concrete exposed by severe environmental condition showed broad ranges of damage with high chloride contents. Meanwhile, the water-binder(W/B) ratio and the less water content, and fly ash concrete than the specified existing mix proportion is significantly improved the durability. Also, the optimal mix proportion derived for test is satisfied the strength and air contents, water-binder ratio, and durability criteria of concrete specifications, as well as service life seems greatly improved.

• Economic and Environmental Geology
• /
• v.54 no.2
• /
• pp.285-297
• /
• 2021

Globally, nuclear-decommissioning facilities have been increased in number, and thereby hundreds of thousands of wastes, such as concrete, soil, and metal, have been generated. For this reason, there have been numerous efforts and researches on the development of technology for volume reduction and recycling of solid radioactive wastes, and this study reviewed and examined thoroughly such previous studies. The waste concrete powder is rehydrated by other processes such as grinding and sintering, and the processes rendered aluminate (C3A), C4AF, C3S, and ��-C2S, which are the significant compounds controlling the hydration reaction of concrete and the compressive strength of the solidified matrix. The review of the previous studies confirmed that waste concretes could be used as recycling cement, but there remain problems with the decreasing strength of solidified matrix due to mingling with aggregates. There have been further efforts to improve the performance of recycling concrete via mixing with reactive agents using industrial by-products, such as blast furnace slag and fly ash. As a result, the compressive strength of the solidified matrix was proved to be enhanced. On the contrary, there have been few kinds of researches on manufacturing recycled concretes using soil wastes. Illite and zeolite in soil waste show the high adsorption capacity on radioactive nuclides, and they can be recycled as solidification agents. If the soil wastes are recycled as much as possible, the volume of wastes generated from the decommissioning of nuclear power plants (NPPs) is not only significantly reduced, but collateral benefits also are received because radioactive wastes are safely disposed of by solidification agents made from such soil wastes. Thus, it is required to study the production of non-sintered cement using clay minerals in soil wastes. This paper reviewed related domestic and foreign researches to consider the sustainable recycling of concrete waste from NPPs as recycling cement and utilizing clay minerals in soil waste to produce unsintered cement.