• Proceedings of the Korean Institute of Building Construction Conference
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• 2022.11a
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• pp.187-188
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• 2022

In this study, the compressive strength and carbonation properties of geopolymer paste according to the amount of alkali admixture added were evaluated for the development of geopolymer concrete that recycles industrial waste. A geopolymer paste specimen was prepared using Ca(OH)2 as an admixture, and the prepared specimen was standard cured for 28 days. After curing, the compressive strength of the specimen was measured. As the amount of alkali admixture increased, the compressive strength increased. After curing, carbonation was carried out for 7 days in a CO2 5% environment. As a result of comparative evaluation of the amount of CaCO3 produced according to carbonation, the amount of CaCO3 produced increased as the amount of Ca(OH)2 added increased. However, when the amount of admixture added exceeds 5%, the increase rate decreases, so the optimum addition rate is considered to be 5%.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.965-968
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• 2008

The KS F 2403 method used on domestic sites for checking the compressive strength of a structure, sets the compressive strength of the concrete used in structural specimens as the compressive strength of testing specimens. Under this regulation, the curing method used for testing the specimens must be the standard ponding curing method (20$\pm$2$^{\circ}$C). However, because in-placed concrete is exposed to open air and cured under the seasonal temperature changes, the compressive strength of a real structure is different from the tested compressive strength. (Therefore,) This thesis first identifies the distinct characteristics of the strength development by applying the curing method listed under the KS and used for testing specimens on compressive strength tests; the atmospheric curing method, the sealed curing method, and the structural specimen core strength testing methods used for the in-sites quality checks including reckoning of the compressive strength of the structural specimens and form-demolding period; and the curing method suggested in this research, which sets the internal conditions of the structural specimens as the conditions of the applied curing method. Then, the thesis suggests the specimen curing method that most closely reenacts the compressive strength of the concrete used on the structural specimens

• Proceedings of the Korean Institute of Building Construction Conference
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• 2013.11a
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• pp.58-59
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• 2013

In this study, the standard specimen heated to curing experiments and simulation experiments the absence of porosity distribution and the effect on the compressive strength has been investigated.

• Journal of the Korean Recycled Construction Resources Institute
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• v.2 no.4
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• pp.360-366
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• 2014

In this study, effect of types and replacement ratio of alkali activator on compressive strength of ground granulated blast furnace slag mortar has been reviewed. Types of alkali activator are NaOH, $Ca(OH)_2$, $Na_2SO_4$, and KOH. Replacement ratio of alkali activator is 7.5, 10, 12.5, and 15%, respectively. As results, under high temperature curing condition, 1 day compressive strength development with NaOH and KOH was higher than that of $Ca(OH)_2$ and $Na_2SO_4$. Regardless of types of alkali activator, compressive strength increased with increasing pH. This can be explained by the fact that impermeable film on the surface of slag which is generated when slag contacts water has been destroyed by alkali activator, and this promotes hydration reaction. Also, 1 day age compressive strength of specimen with high temperature curing was higher than that of specimen with standard curing. 28 days age compressive strength of specimen with high temperature curing was less than or equal to that of specimen with standard curing.

• Proceedings of the Korea Concrete Institute Conference
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• 2009.05a
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• pp.273-274
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• 2009

The curing method used on domestic sites for checking the concrete compressive strength of a structure. The curing method used for testing the specimens must be the standard ponding curing method (20${\pm}$%$2^{\circ}$C). However, because in-placed concrete is exposed to open air and cured under the seasonal temperature changes, the compressive strength of a real structure is different from the tested compressive strength. Therefore the curing method suggested in this research, which sets the internal conditions of the structural specimens as the conditions of the applied curing method. this thesis suggests the specimen curing method that most closely re-enacts the compressive strength of the concrete used on the structural specimens

• Proceedings of the Korea Concrete Institute Conference
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• 2000.10a
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• pp.31-45
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• 2000

Because of the high unit cement content in the concrete mix, major concrete temperature rises are observed in the initial stages of hardening in structural members with large cross-sections made of high-strength concrete. While this temperature rise in the initial stages of hardening contributes to the initial development of the concrete strength, it also causes thermal cracking and obstructs medium to long-term increases of the concrete strength. In the study reports below, investigations were made on the effects of the concrete temperature rise in the initial stages of hardening on the medium to long-term development of the strength of structural concrete between the ages of 28 and 91 days. In the study, comparisons were made, for example, between the compressive strength of a control specimen subjected to standard curing at 28 days and the compressive strength of core specimens taken from structural members, and observations were made on the methods of evaluating the concrete strength in structure, defined here as the compressive strength of core specimens at 91 days. The results obtained indicate that, when the maximum temperature of the concrete is the structure does not exceed $60^{\circ}C$, the concrete strength in structure at the age of long-term will generally be greater than the compressive strength of the standard-curing specimens at 28 days, allowing one to evaluate the strength of the structural concrete in terms of the compressive strength of the 28-days standard-curing specimens. When, on the other hand, the maximum temperature of the concrete in the structure exceeds $60^{\circ}C$, the strength in concrete structure may be smaller than the compressive strength of the 28-days standard-curing specimens, creating risks in the evaluation of the concrete strength in structure by latter.

• Journal of the Korea Institute of Building Construction
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• v.9 no.6
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• pp.113-119
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• 2009

This study is to investigate the fundamental and fireproof qualities of high strength concrete corresponding to changes in the curing factors and the PP fiber ratio. The results were as follows. For the fundamental characteristics of concrete, the fluidity was reduced in proportion to the increase in the PP fiber ratio. The compressive strength was somewhat reduced according to an increase in the PP fiber ratio. However, it had the high strength scope of more than 60 MPa at 7 days and of more than 90 MPa at 28 days. On the spalling mechanism followed by changes of the water content ratio, spalling was prevented in all combinations, except the specimen without PP fiber and subjected to 3.0% of moisture contents. When spalling was prevented at that time, the residual compressive strength ratio was 22%~41% and the mass reduction ratio was 5%~7%, which was relatively favorable. As the spalling mechanism corresponds to changes in the curing method, spalling was prevented in concrete with a PP fiber mixing ratio of more than 0.05% in the event of standard curing, and in concrete with a PP fiber mixing ratio of more than 0.10% in the case of steam curing and autoclave curing. In these cases, when spalling was prevented, the residual compressive strength ratio was 23~42% and the mass reduction ratio was 7~11%. In these results, the ease of spalling prevention in high strength concrete was inversely proportional to the water content ratio. Depending on the curing method, spalling was prevented in concrete with over 0.05% PP fiber with standard curing and in concrete with over 0.1% PP fiber with steam curing and autoclave curing.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2023.05a
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• pp.129-130
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• 2023

The compressive strength of concrete is greatly affected by the temperature inside the concrete at the initial age immediately after pouring. In the KCI Concrete Standard Specification, only the temperature correction strength (Tn) according to the curing temperature is applied in the mixing strength calculation formula, and mSn is not considered. The formula based on the Chrino model of the blast furnace slag concrete was calculated, and the strength of the structural concrete and the strength of the water cured specimen in the same mixture were compared with the predicted strength. As a result, the error between the predicted strength and the measured strength was greater in the structural concrete than in the concrete specimen.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.781-784
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• 2008

Recently as application of high-strength concrete on concrete structures has been on the rise, use of non-standard specimen is increasing. Therefore, this study investigated the effect of specimen's size effect, ratio of height/diameter and curing conditions on concrete compressive strength. Results of experiments showed that as size of specimen increased as much as 1 mm, standard design compressive strength of 24MPa fell as much as0.15MPa 40MPa fell as much as 0.1MPa 80MPa fell as much as 0.3MPa, and it indicates that as the level of strength is intensified, the decrement of compressive strength increases. As ratio of height/diameter increased as much as 1.0, compressive strength of 24MPa fell as much as 2.9MPa 40MPa fell as much as 3.7MPa 80MPa fell as much as 9.8MPa, and it means that as strength of concrete is higher, influence of ratio of height/diameter becomes bigger.

• 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