• Journal of the Korean Ceramic Society
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• v.34 no.12
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• pp.1261-1267
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• 1997

Four kids of powder admixtures(A, B, C, D) based on anhydrite were manufactured by mixing at a fixed rate of II-anhydrite, fly ash and active silica as an industrial by-product. Fluidity properties of cement paste such as mini-slump, apparent viscosity with elapsed time, as well as setting time of cement pastes of these admixtures substituted up to 11wt% of cement were compared to those of cement paste(SS) substisuted by marketed high-strength powder admixture(S). Among these powder admixtures, the fluidity of cement pastes(PA, PC) substituted by A and C powder admixtures manufactured from II-anhydrite and fly ash had an excellent property than that of cement paste substituted by marketed powder admixture and also a good fluidity-retention effect with elapsed time by adding of superplasticizer. The setting time of cement paste substituted by powder admixtures based on anhydrite slightly retarded than that of cement paste substituted by marketed powder admixture.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.469-472
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• 2006

The use of admixture(PNS type & PC type) played a important role in the development of rapid hardening concrete. This paper presents an experimental study on the effect of a kinds of admixture on hydration characteristics, mini slump, apparent viscosity of fresh cement pastes and workability, compressive strength properties of hardened concrete for rapid hardening. Measurements have showed that their characteristics depends on the type of the admixture. As a result, the excellent quality was obtained, also being widely used for the construction field is expected.

• Journal of the Korea Institute of Building Construction
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• v.17 no.5
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• pp.445-451
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• 2017

Because of the supply-demand problem of aggregate, recently, the construction sites using 100% crushed sand are increasing and the use of low quality aggregate such as farmland sand is increasing too. When the low quality aggregate is used, the various quality defect of concrete such as the strength reduction, the increase of shrinkage and bleeding can be occurred. Therefore, in this study, the performance improvement PC admixture was developed to minimize the quality defect of plain concrete of basement parking area, when the low quality aggregate was used at the plain concrete of basement parking area. The slump loss to elapsed time test, the compressive strength test, the bleeding test and the drying shrinkage test were carried out.

• Journal of the Korean Society of Industry Convergence
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• v.13 no.2
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• pp.99-106
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• 2010

The effects of additive and shrinkage reducing agent on the drying and autogenous shrinkage of high strength concrete are investigated in this study. As results, when the ratio of W/B(low water to binder ratio) increase, the compressive strength is decreased. Comparing with PC(portland cement) concrete, the strength is 2.8%, 3.2% and 3.8% lower respectively than that of PC when concrete mixing ratio is 0.2%, 0.3% and 0.4% in 28 days curing. Drying shrinkage strain of PC concrete showed $-650{\times}10^{-6}$ in 91 days curing. When SR(shrinkage reducing agent) of 0.2%, 0.3% and 0.4% is mixed, the drying shrinkage strains are 21%, 34% and 41% lower than those of PC in 91 days curing. Autogenous shrinkage strain of PC concrete appeared $-480{\times}10^{-6}$ in 56 days curing. When SR of 0.2%, 0.3% and 0.4% is mixed, the autogenous drying shrinkage strain are 12.5%, 19.8% and 33.3% lower than those of PC in 56 days curing. In cases of using the mineral and shrinkage agent or only using a shrinkage reducing agent also appeared same reducing effects for drying shrinkage and autogenous shrinkage.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.05a
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• pp.391-396
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• 2001

Exposed concrete execution is utilized insufficiently due to surface honecomb and undesirable appearance by entrapped air when existing placing method is applied. Therefore, surface glossing and impact properties of cement mortar incorporating fiber glass net blast furnace slag, expansive admixture and Polypropylene fiber are investigated in order to develop precast exposed concrete pannel by dry construction method. The kinds of the forms, placing method and admixture contents are varied. According to test results, surface glossing decrease with elapse of age. Considering the form kinds, surface glossing with acryle + astage shows the best performance. Placing horizontally shows positive results in reducing surface defects such as honecomb. Impacting resistance shows the best performance when glass fiber net applied, due to the enhance in toughness and absorption of impact.

• Proceedings of the Korea Concrete Institute Conference
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• 1994.10a
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• pp.405-414
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• 1994

The High Strength Concrete REsearch Team of the Dong-Ah Construction R&D Institute has achieved the preactical use of the PHC pile manufacture technique at the Dong-Ah Chang-dong PC Plant. Components of the high strength concrete are used high strength cement, admixtures(water reducing high range admixture, micro silion fume, fly ash, gypsum). The design strength required 800kg/$\textrm{cm}^2$ was developed raging from 870kg/$\textrm{cm}^2$ to 1010kg/$\textrm{cm}^2$. The new manufacture procedure of HPC pile which include placing, molding, steam curing is able to apply a current PC pile manufacture procedure easily without using the high pressure steam curing.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.457-460
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• 2008

It was predicted that the most recent technological developments in concrete technology rely on enhanced admixture efficiency rather than on improvement in cement manufacturing. Four major commercially available of organic chemical admixtures are modified lignosulfonates (LS), sulfonated naphthalene-formaldehyde resins (SNF), sulfonated melamine-formaldehyde resins(SMF) and polycarboxylate(PC). In this study, various sulfonated melamine-formaldehyde (SMF) superplasticizers were synthesized via four synthetic steps and reaction conditions such as the mole ratio of melamine to formaldehyde was changed. After application of SMF superplasticizer to cement concrete, the physical properties including workability, slump loss, compressive strength were compared with SNF

• Journal of the Korean Ceramic Society
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• v.46 no.1
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• pp.58-68
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• 2009

In this study, rheological properties of ternary system cement containing ground fly ash(F3, Blaine specific surface area $8,100\;cm^2/g$) were investigated using mini slump, coaxial cylinder viscometer and conduction calorimeter. In the results, the segregation resistance was observed at high W/B and PC area while the replacement ratio of F3 was increasing. The 2:5:3 system was shown in higher fluidity and lower hydration heat than 3:4:3 system. The segregation range of cement pastes occurred over 175 mm in average diameter by mini slump and below $10\;dynesec/cm^2$ of the plastic viscosity or below 50 cP of the yield stress by coaxial cylinder viscometer. It was observed that even if BFS and FA blended together admixture properties would remaine as they were separately. The properties of admixture would not be changed. On the above results, the decreased replacement ratio of OPC and increased replacement ratio of admixtures would be possible.

• Journal of the Korean Ceramic Society
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• v.53 no.1
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• pp.116-121
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• 2016

The amount of 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 methods of reducing $CO_2$ in building materials is the addition of slag and fly ash, like pozzolan material another method is to reduce $CO_2$ production by developing carbon negative cement. MgO-based cement 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 can improve their performance and also increase their capacity to absorb atmospheric $CO_2$. In this study, basic research on magnesia cement using $MgCO_3$ and magnesium silicate ore (serpentine) as the main starting materials, as well as blast furnace slag for the mineral admixture, was carried out for industrial waste material recycling. In order to increase the overall hydration activity, $MgCl_2$ was also added. In the case of the addition of $MgCl_2$as accelerating admixture, there was a promoting effect on the compressive strength. This was found to be due to the production of needle-like dense Mg-Cl hydrates. Mgnesia cement has a high viscosity due to its high specific surface area therefore, when the PC-based dispersing agent was added at a level of more than 1.0%, it had the effect of improving fluidity. In particular, the addition of $MgCl_2$ in magnesia cement using $MgCO_3$and magnesium silicate ore (serpentine) as main starting materials led to a lower expansion ratio and an increase in the freeze-thaw resistance finally, the addition of $MgCl_2$ as accelerating admixture led to good overall durability.

• Journal of the Korea Concrete Institute
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• v.20 no.6
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• pp.721-729
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• 2008

The purpose of this study is to investigate the engineering properties of concrete for the early strength development. As a result of reviewing it by establishing each experimental factor and level, the cement had more excellent quality performance in CHC and HESPC than OPC. This study has shown that the PC series admixture was more excellent in side of elapsed time (aging) and early strength development than PNS series admixture. In addition, there was much difference according to the curing temperature, but the early strength development showed the considerable vulnerability in curing temperature below $12^{\circ}C$. To satisfy the strength requirements of 5 MPa/18 hr this study has shown that it needed the curing temperature over $17^{\circ}C$ to the minimum in OPC, over $14^{\circ}C$ in CHC, and over $11^{\circ}C$ in HESPC. On the other hand, as to the strength properties according to W/C, the less W/C was, the more strength development was excellent. If this study is to be used in construction filed on a basis of this result, this researcher is considered as possible of the economic execution of construction by advancing the early strength and by the reduction of construction cost according to shortening construction duration.