• Proceedings of the Korea Concrete Institute Conference
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• 2005.05b
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• pp.397-400
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• 2005

This study is a result that, in order to improve the early stage strength of fly ash, the calciumsulfoaluminate in which the generation of ettringite was very active in the early stage was substituted by some amount, and then the effect on the early stage was analyzed. when fly ash was substituted by 30$\%$, the strength dropped by maximum 54 $\%$ in the 3rd day of aging, compared to the cement mixture, but when CSA was substituted by 8 $\%$ in the fly ash amount, the strength improved at the 86 percent level of cement, it is suggested as an economical and effective method to improve the early-stage strength that CSA should be mixed by 8$\%$ compared to the fly ash amount used

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.889-892
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• 2006

In this study, we compared and analysed the early strength properties of mortar according to the kinds and replacement ratio of mineral admixture to select the kinds and replacement ratio of mineral admixture of high early strength concrete. For this purpose, mortar mixtures according to the kinds(FA, MK, ZR, BFS, DM) and replacement ratio(0, 2, 4% by volume of sand) of mineral admixture were selected. From our test data, early-age compressive strength decreased in accordance with the increase of replacement ratio of fly-ash(FA) & blast furnace slag powder(BSF) and, in case of addintion admixture, early-age compressive strength of with containing ZR & BFS appeared higher compared with containing other mineral admixture.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.10a
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• pp.219-222
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• 1999

Concrete is to be important quality in placement point and exact test method needed about early judgement method concrete on placement point. But early judgement method of concrete proposed various kind of method because the problems of accuracy and the time required of test exists, it is used within the limits. This study is to propose of early strength judgement by using microwave for accurate estimating early strength of concrete and to develop test machine. Through out this study we find that belows. 1) Strength development of concrete specimen according to the time heated by microwave showed the height strength development in 9 minutes regardless of slump and w/c. 2) As cooling time is long, strength of concrete specimen according to the time heated by microwave showed high strength development and this tendency is like regardless of heating time, w/c and slump. 3) As w/c is high, accelerating strength development according to w/c showed lower strength development and this tendency is like regardless of slump, heating time and cooling time. 4) As slump is big, compressive strength of specimen in standard curing showed lower value and as w/c is big, strength development showed lower

• Journal of the Korea Institute of Building Construction
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• v.7 no.2 s.24
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• pp.59-65
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• 2007

Recently, due to the increase of high-rise buildings construction, many researches for making harden of concrete earlier and remove of forms faster are being performed to reduce construction period. In this study, we compared and analysed the early strength properties of mortar according to the kinds and replacement ratio of mineral admixture to select the kinds and replacement ratio of mineral admixture of high early strength concrete. For this purpose, mortar mixtures according to the kinds(FA, MK, ZR, BFS, DM) and replacement ratio(0, 2, 4% by volume of sand) of mineral admixture were selected. From our test data, early-age compressive strength decreased in accordance with the increase of replacement ratio of fly-ash(FA) & blast furnace slag powder(BSF) and, in case of addition admixture, early-age compressive strength of with containing 4% appeared higher compared with containing 2%.

• Journal of the Korea Institute of Building Construction
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• v.12 no.6
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• pp.566-574
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• 2012

To address the problem of global warming, consumption of cement, the main material of concrete, should be decreased. Unfortunately, when industrial by-products are used in large quantities as admixture, the early age strength of concrete will be decreased, reducing its viability for use in concrete structures. Therefore, in this study, the application of an ionization accelerator and alkaline activator as addition agent of superplasticizer were investigated to secure a similar early age strength to that of normal concrete, thus increasing the viability of low cement concrete. Through the investigation, it was found that specimens that used a combination of Alkaline-activator (Na2Sio3) and ionization accelerator (Amine) had the highest early and long-age compressive strength. From this, we can determine an appropriate range of application of superplasticizer to improve early-age compressive strength of low cement concrete.

• Journal of the Korea Concrete Institute
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• v.12 no.6
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• pp.51-56
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• 2000

Fly ash used as a cement replacement material increases the long term strength and also improves the durability of concrete and mortar. However, the use of fly ash is a little in spite of great benefit. In order to increase the consumption of fly ash, it has to be used as a cement replacement materials in the production of mortar and concrete, and the reduction of early strength development due to the use of fly ash also has to be diminished. In this study, many chemical compounds which accelerate the early strength was investigated. The $Na_2$$SO_4$, $K_2$$SO_4$, Triethanolamine were selected and applied to the production of mortar. It was found that they enhance the early strength development of mortar(1, 3day) and decrease the amount of $Ca(OH)_2$, and also increase the production of ettringite. According to the results of mercury instruction test, the pores ranged from 0.01 $\mu\textrm{m}$ to 5$\mu\textrm{m}$ were decreased and it was also found in the analysis of X ray and SEM that fly ash increases the amount of ettringite at early ages.

• Computers and Concrete
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• v.12 no.1
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• pp.53-64
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• 2013

The curing temperature is known to influence the rate of mechanical properties development of early age concrete. In realistic sites the temperature of concrete is not isothermal $20^{\circ}C$, so the paper measured adiabatic temperature increases of four different concretes to understand heat emission during hydration at early age. The temperature-matching curing schedule in accordance with adiabatic temperature increase is adopted to simulate the situation in real massive concrete. The specimens under temperature-matching curing are subjected to realistic temperature for first few days as well as adiabatic condition. The mechanical properties including compressive strength, splitting strength and modulus of elasticity of concretes cured under both temperature-matching curing and isothermal $20^{\circ}C$ curing are investigated. The results denote that comparing temperature-matching curing with isothermal $20^{\circ}C$ curing, the early age concretes mechanical properties are obviously improved, but the later mechanical properties of concretes with pure Portland and containing silica fume are decreased a little and still increased for concretes containing fly ash and slag. On this basement using an equivalent age approach evaluates mechanical properties of early age concrete in real structures, the model parameters are defined by the compressive strength test, and can predict the compressive strength, splitting strength and elasticity modulus through measuring or calculating by finite element method the concreted temperature at early age, and the method is valid, which is applied in a concrete wall for evaluation of crack risking.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.05a
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• pp.741-744
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• 2003

In this study, the influence of chemical admixture on early strength development of concrete is discussed. According to the results, fluidity with variation of kinds of chemical admixture is lower in the case of acceleration type than in the case of normal type. Setting time of naphthalene acceleration type is shortened by I hour, and that of melamine is nearly same, but that of polycarbonic acid is somewhat retarded in comparison with that of naphthalene normal type. Early compressive strength gains 5MPa in about 18hours regardless of the kinds of chemical admixture. But as time elapses, compressive strength is higher in order of polycarbonic acid, naphthalene and melamine type. The relativity between compressive strength and the rebound value of P-type schmidt hammer is also favorable at early age, and compressive strength of 5MPa is estimated at the rebound value of 22.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2009.05b
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• pp.77-80
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• 2009

The purpose of the study was to examine engineering characteristics due to fine particle cement and gypsum contents to improve early strength of concrete substituted blast furnace slag powder. The results were as follows. Above all, For fluidity, generally all mixtures had lower fluidity than Plain mixture and was not satisfied target scope, but for mixture substituted the gypsum showed a little increasing trend. For air content, generally all mixtures compared to Plain mixture had decreasing tendency. However, all mixtures were satisfied target scope. For compressive strength, long-term strength was better than early strength according to ternary blast furnace slag contents was increased. For complex mixture was better than individual use of gypsum and fine particle cement.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2019.11a
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• pp.145-146
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• 2019

In this study, we evaluated the early strength of red clay soil with the polymer aqueous solution at rammed earth construction. In order to satisfy the demolding strength of the formwork be due to the rammed of red clay soil, the polymer aqueous solution was added to evaluate the compressive strength at the early age according to the consolidation level. As a result, a high compressive strength was exhibited with the formulation to which the polymer aqueous solution was added.