• The Journal of Engineering Geology
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• v.20 no.4
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• pp.359-370
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• 2010

$CO_2$ leakage from a geological formation utilized for $CO_2$ storage could result in failure of the facility and threaten the environment, as well as human safety and health. A reactive transport model of a $CO_2-H_2O$-cement reaction was constructed to understand chemical changes in the case of $CO_2$ leakage through a cement crack in an injection well, which is the most probable leakage pathway during geological storage. The model results showed the dissolution of portlandite and CSH (calcium silicate hydrate) within the cement paste, and the precipitation of secondary CSH and calcite as the $CO_2$ plume migrated along the crack. Calcite occupied most of the crack after 3 year of reaction, which could be maintained until 30 years after crack development. The present results could be applied in the development of technology to prevent $CO_2$ leakage and to enhance the integrity of wells constructed for $CO_2$ geological storage.

• International Journal of Highway Engineering
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• v.3 no.4 s.10
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• pp.117-126
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• 2001

In this research, evaluation of adhesion in tension property of SBR-modified concrete to ordinary portland cement concrete was conducted with uniaxial direct tensile bond test which was proposed by Kuhlmann. A test set-up was fabricated in order to minimize the eccentric force by introducing a joint which might fully rotate. The main experimental variables were cement-latex ratios, surface preparations and moisture levels. The results obtained were as follows: The LMC specimen at 15% latex-cement ratio increased the adhesion in tension by range of 37% compared to that of conventional cement concrete. This might be due to latex film formed between cement paste and aggregate. The effects of surface preparation on bond of latex modified concrete to conventional concrete were significant at the conditions by sand paper and wire brush. A better bond could be achieved by rough surface rather than smooth. The saturated and surface dry (SSD) condition were considered to be the most appropriate moisture level followed by wet, finally by dry. Thus, a proper surface preparation and moisture level are quite necessity in order to obtain better bonding at LMC overlay.

• Journal of the Korean Recycled Construction Resources Institute
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• v.4 no.2
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• pp.90-96
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• 2009

The high rising building construction makes increasing the requirement of high strength concrete. Especially, the workability analysis is related with dispersion of admixture such as SF for improving strength and FA, BS for reducing construction cost and improving durability of Ultra High Strength Concrete which has over 100 MPa of compressive strength is very important. Precisely, decreases dispersion because of lumping situation of each admixture and it causes the workability of admixture is decreased. Therefore, the workability of cement paste is tested for analyze effects of pre-mixed cement for solving those problems with it to this research. The summary of the results are like below. First of all, OBS is increasing workability more than OFS. This result causes that the glassy surface of BS in the OBS is increasing workability and the absorption of admixture of FA in the OFS is decreasing workability. In the case of mixing methods, pre-mixing method is increasing workability more than normal one. This result shows that the normal mixing method is bad dispersion of binders. The other side, the pre-mixing method is good. Furthermore, depending on the mixing time, according to the increasing mixing time such as 30, 60, and 120 seconds, the dispersion of binders and workability turns better.

• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.5
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• pp.153-160
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• 2010

This study aims to obtain technical data for improvement of utilization of Blast Furnace Slag(BFS), recycled aggregate in the future by complementing fundamental problems of BFS such as manifestation of initial strength and excessive alkali quantity as well as weakness of recycled fine aggregate through manufacturing of recycled fine aggregate mortar using BFS. The recycled aggregate includes the cement paste hardened as the surface and the type of the aggregate, which contains plenty of calcium hydroxide($Ca(OH)_2$) as well as the unhydrated cement. Accordingly, the objectives of this study are to inspect the manufacturing the recycled fine aggregate mortar used with blast furnace slag, to consider the effects of the recycled aggregate on the strength development of ground granulated blast furnace slag, and then to acquire the technical data to take into consideration the further usages of the recycled aggregate and blast furnace slag. In eluted ions from recycled aggregate, it showed that there were natrium($Na^+$) and kalium($K^+$), expected to be flown out of unhydrated cement, as well as calcium hydroxide($Ca(OH)_2$). Application of this water to mix cement mortar with ground granulated blast furnace slag was observed to expedite hydration as calcium hydroxide($Ca(OH)_2$) and unhydrated cement component were expressed to give stimuli effects on ground granulated blast furnace slag. The results of the experiment show that the recycled aggregate mixed with blast furnace slag has comparatively higher hydration activity in 7 day than the mortar not mixed with one in 3 day mortar does, causing the calcium hydroxide in the recycled fine aggregate to work on as a stimulus to the hydration of ground granulated blast furnace slag.

• Journal of the Korean Recycled Construction Resources Institute
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• v.10 no.4
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• pp.465-474
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• 2022

Research on the recycling of waste concrete has been conducted mainly focusing on the production of high-quality recycled ag g reg ate, and as a result, standards and specifications for recycled ag g reg ate have been established. However, in the case of waste concrete powder, although a lot of research on its utilization has been conducted in Korea, an innovative technology leading to commercialization has not yet been announced. Recently, research on technology using waste concrete powder as a raw material for clinker or cement has been actively conducted in major overseas advanced countries. This study investigated the overseas cases with regard to high value-added recycling technology and commercialization trend of waste concrete powder for carbon neutrality in cement and concrete industries. A number of studies have reported that it is essential to completely separate the aggregate and hydrated cement paste fraction for recycling of waste concrete powder. Also in major foreig n countries such as EU and USA, commercialization and standardization of using waste concrete powder as a raw material for clinker or a additive for cement are now in progress beyond the R&D stage. Therefore, Research and standardization for recycling of waste concrete powder should be urgently carried out from the perspective of carbon neutrality in Korea.

• Land and Housing Review
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• v.15 no.1
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• pp.147-156
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• 2024

This study aims to reduce CO₂ generated during the manufacturing process by using limestone (CaCO₃), a carbonate mineral used in the production of cement clinker, as a decarbonated raw material that does not contain CO₂. Among various industrial by-products, we attempted to use cement paste attached to waste concrete. In general, limestone for cement must have a CaCO₃ content of at least 80% (CaO, 44% or more) to ensure the quality of cement clinker. However, the CaO content of waste concrete fine powder is about 20% on average, so in order to use it as a cement clinker raw material, the CaO content must be increased to more than 35%. Therefore, by using the difference in hardness of the mineral composition of waste concrete fine powder to selectively crush CaO type minerals with relatively low hardness, classify and sieve, the CaO content can be increased by more than 35%. Accordingly, in this study, we experimentally and statistically reviewed and analyzed the optimal conditions for efficiently separating CaO and SiO₂ and other components by selectively pulverizing minerals containing relatively low CaO through a grinding process. As a result of the optimal grinding conditions experiment, it was found that the optimal conditions were a grinding time of less than 5 minutes, a type of material to be crushed of 30 mm, and an amount of material to be crushed of 1.0 or more. However, it is judged that it is necessary to review pulverized materials of mixed particle sizes rather than pulverized products of single particle size.

• Economic and Environmental Geology
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• v.39 no.6 s.181
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• pp.699-710
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• 2006

Batch scale experiments to investigate the efficiency of the solidification process for metal mine tailing treatment were performed. Portland and MSG (micro silica pouting) cements were used as solidifier and three kinds of mine tailings (located at Gishi, Daeryang, and Aujeon mine) were mixed with cements to paste solidified matrices. Single axis com-pressible strengths of solidified matrices were measured and their heavy metal extraction ratios were calculated to investigate the solidification efficiency of solidified matrices created in experiments. Solidified matrices ($5cm{\times}5cm{\times}5cm$) were molded from the paste of tailing and cements at various conditions such as different tailing/cement ratio, cement/water ratio, and different cement or tailing types. Compressible strengths of solidified matrices after 7, 14, and 28 day cementation were measured and their strengths ranged from 1 to $2kgf/mm^2$, which were higher than Korean limit of compressible strength for the inside wall of the isolated landfill facility ($0.21kgf/mm^2$). Heavy metal extractions from intact tailings and powdered matrices by using the weak acidic solution were performed. As concentration of extraction solution for the powdered solidified matrix (Portland cement + Gishi tailing at 1:1 w.t. ratio) decreased down to 9.7 mg/L, which was one fifth of As extraction concentration for intact Gishi tailings. Pb extraction concentration of the solidified matrix also decreased to lower than one fourth of intact tailing extraction concentration. Heavy metal extraction batch experiments by using various pH conditions of solution were also performed to investigate the solidification efficiency reducing heavy metal extraction rate from the solidified matrix. With pH 1 and 13 of solution, Zn and Pb concentration of solution were over the groundwater tolerance limit, but at pH $1{\sim}13$ of solution, heavy metal concentrations dramatically decreased and were lower than the groundwater tolerance limit. While the solidified matrix was immerged Into very acidic or basic solution (pH 1 and 13), pH of solution changed to $9{\sim}10$ because of the buffering effect of the matrix. It was suggested that the continuous extraction of heavy metals from the solidified matrix is limited even in the extremely high or low pH of contact water. Results of experiments suggested that the solidification process by using Portland and MSG cements has a great possibility to treat heavy metal contaminated mine tailing.

• Advances in concrete construction
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• v.2 no.1
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• pp.13-27
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• 2014

The principal objective of this study is to deepen the characterization studies already led on sand concretes in previous works. Indeed, it consists in studying the effect of the sand type on the main properties of sand concrete: fracture and mechanical properties. We particularly insist on the determination of the fracture characteristics of this material which apparently have not been studied. To carry out this study, four different types of sand have been used: dune sand (DS), river sand (RS), crushed sand (CS) and river-dune sand (RDS). These sands differ in mineralogical nature, grain shape, angularity, particle size, proportion of fine elements, etc. The obtained results show that the particle size distribution of sand has marked its influence in all the studied properties of sand concrete since the sand having the highest diameter and the best particle size distribution has given the best fracture and mechanical properties. The grain shape, the angularity and the nature of sand have also marked their influence: thanks to its angularity and its limestone nature, crushed sand yielded good results compared to river and dune sands which are characterized by rounded shape and siliceous nature. Finally, it should further be noted that the sand concrete presents values of fracture and mechanical properties slightly lower than those of ordinary concrete. Compared to mortar, although the mechanical strength is lower, the fracture parameters are almost comparable. In all cases, the sand grains are debonded from the paste cement during the fracture which means that the crack goes through the paste-aggregate interface.

• Journal of the Korea Institute of Building Construction
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• v.7 no.1 s.23
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• pp.115-121
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• 2007

Ordinary concrete uses aggregate sufficiently soaked with water, and is weighed, mixed with other materials and placed in accord with performances required in the construction field. Recently special concrete with high fluidity and durability is required but it is difficult to use top-quality concrete due to lack of high-quality aggregate, delayed transportation because of traffic jam, etc. In addition, sometimes the use of a remicon is inevitable just for small-sized concrete constructions or it is difficult for a remicon to reach remote construction places such as mountainous areas. To solve these problems, this study attempted to pack concrete materials. In other words, it is to instantize concrete. This study dried aggregate, a material of concrete, and compared the change of absorption phase of the aggregate in water and in paste in order to examine the effect of the dryness of aggregate on its absorption rate and, based on the absorption rate, decided water addition ratio necessary for the reduction of unit quantity caused by the use of dry aggregate in designing concrete mixture, and analyzed the properties of unhardened concrete according to water addition ratio in manufacturing concrete using aggregate in the state of absolute dryness and in the state of surface dryness.

• Journal of the korean academy of Pediatric Dentistry
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• v.41 no.4
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• pp.335-343
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• 2014

Regenerative endodontic treatment has the potential to heal a necrotic pulp, which can affect root development in immature teeth. However, several drawbacks and unfavorable outcomes are associated with regenerative endodontic treatment, of which the most significant is coronal discoloration due to the presence of minocycline in triple antibiotic paste and mineral trioxide aggregate (MTA). To prevent tooth discoloration following pulp treatment, the modified triple antibiotics (ciprofloxacin, metronidazole, clindamycin) were used as canal disinfectants and Retro MTA, a $ZrO_2$-containing calcium aluminate cement, was used to seal the canal. Following access cavity acquisition, the canal was copiously irrigated with 2.5% sodium hypochlorite. A modified triple antibiotic paste was then applied to the canal. Once the tooth was asymptomatic (after between 3 and 8 weeks), Retro MTA was carefully placed over the blood clot or a collagen plug. Follow-up radiographs revealed normal periodontal ligament space and root development. In two cases, successful regenerative endodontic treatment of the infected immature tooth, without discoloration, was achieved with disinfection using modified triple antibiotics and Retro MTA sealing.