• Proceedings of the Korean Institute of Building Construction Conference
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• 2021.05a
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• pp.131-132
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• 2021

In this study, as part of the study to reduce and integrate heat of hydration of concrete, the performance change of super retarding agent is examined in the mortar area under high temperature conditions. It was confirmed that the setting time delay can be adjusted from several hours to several days depending on the high temperature and the change of super retarding agent mixing rate. With the increase of super retarding agents, the early age strength was delayed while at 28 days the use of super retarding agent results in an increase of strength remakably.

• Journal of the Korean Ceramic Society
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• v.36 no.2
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• pp.130-135
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• 1999

The enhanced slag fineness and the batch water of low water-to-cement ratio(W/C) were employed in order to improve the early strength of blast-furnace slag blended cement at low temperature. A grinding aid was used to grind the blast-furnace slag into the fineness of 6,280$\textrm{cm}^2$/g (Blaine), and this fine slag was then homogeneously mixed with the ordinary Portland cement to produce the blast-furnace slag blended cement containing 40% slag by weight composition. On the other hand, the batch water could be reduced from W/C=0.50 (KS L 5105) to W/C=0.33 through a commercial, naphthalene type superplasticizer. Through the method mentioned above, the early strength of the blast-furnace slag blended cement at low temperature could be enhanced even somewhat higher than the Portland cement strength. And the microsturcture of the cement was studied by both the pore structure analysis and the A.C. impedance measurement.

• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.6
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• pp.184-194
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• 2011

This study is to analyze the internal temperature and relative humidity of concrete at early age, as well as the mechanical behavior. Three different levels of cement unit content were cosidered as an experimental variable. In order to measure internal temperature and relative humidity immediately after concrete placement, this study developed a unique measuring device, which provided reliable results. Different cement content did not significantly affected the strengths including compressive, tensile and flexural strength and after 7 days of curing, strengths did not increase noticeably. Internal temperature reached the maximum about 11 hours later the placement and decreased after removal of forms. The internal temperature varied depending on the location and the exposure condition. In addition, the internal relative humidity was more affected by the exposure condition rather than the cement content.

• Journal of the Korean Ceramic Society
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• v.49 no.6
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• pp.575-580
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• 2012

Geopolymers were synthesized using raw materials produced from two different areas: one was from Indonesia and the other was from Habcheon, Korea. The constituting phases of the Indonesian raw material were quartz and kaolinite, while those of the Habcheon sample were quartz, halloysite and albite. They were both calcined at $750^{\circ}C$ for 6 hours, and solution of NaOH and water glass was added to activate the geopolymeric reaction. The compressive strength of geopolymer synthesized from the Indonesian raw material showed a low value of $151\;kgf/cm^2$ after curing for 28 days. However, it could be greatly increased by adding blast furnace slag powders of $1188\;kgf/cm^2$ and $1969\;kgf/cm^2$ at 20 wt% and 40 wt% additions, respectively. The compressive strength of the geopolymer synthesized from the Habcheon raw material was high, at $557\;kgf/cm^2$, after 28 days, and the very high early-stage (3 days) strength of $556\;kgf/cm^2$ for this sample was remarkable. Commercially available Habcheon metastate raw material, of which composition showed low CaO and $Na_2O$ contents compared to the calcined Habcheon raw material, was also examined. It was found that the compressive strength of the commercial metastate type was nearly identical to that of the calcined Habcheon raw material except for the relatively low value at an early curing stage and at a high curing temperature of $60^{\circ}C$.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.5
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• pp.129-136
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• 2012

Temperature of fresh concrete can be effectively used to predict the strength of concrete being cured and make an informed decision for stripping the molds. A hygrothermograph and thermo-couple sensors that require an extensive wiring have been applied to measure a temperature of concrete at the early stage of the curing process on site. However, these methods have limits to provide the temperature data in real time due to harsh working environment including frequent cutting of wires. Therefore, this study is aiming at developing a device based on wireless sensor network to measure the temperature of concrete being cured in formwork. The result showed that the wireless sensor with probe type thermistor which is developed had the same temperature data compared to the existed wire type thermistor, and we confirmed the temperature history of concrete in real time for 28 days throughout the gateway by wireless network that collects the temperature data measured from specimens in laboratory. Also, the network device for transmission can be easily separated from the probe sensor part and reused consistently. If the wireless sensor network device developed uses in the field, the temperature management of concrete will be systematically conducted from at the early stage of the curing, and especially be effective for cold weather concrete construction. In addition, it will contribute to the establishment of advanced quality control system for concrete and productivity of supervisors on site will be increased in the future.

• Journal of the Korea Institute of Building Construction
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• v.17 no.2
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• pp.149-155
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• 2017

In this research, the surface covered curing method using the double-layered bubble sheet was evaluated. This double-layered bubble sheet has outstanding insulating performance with its low heat conductivity and high economic feasibility with its high durability. However, in the case of wall-typed building construction, the area of exposed rebar is curious on curing performance with the double-layered bubble sheet in spite of the double-layered bubble sheet showed favorable performance for slab. Therefore, in this research, regarding the actually constructed wall-typed apartment building, the most efficient curing method was suggested based on the evaluation of curing performance depending on temperature distribution depending on various location of covered or exposed rebar. As a result, the D method was determined as the most efficient curing method without any concern of early-age frost damage. However, by considering easiness of construction, the B method of covering the pieced double-layered bubble sheet on gap between rebars can be another option of desired result.

• Journal of the Korean Recycled Construction Resources Institute
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• v.4 no.1
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• pp.74-80
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• 2009

This study analysis the fundamental properties of temperature-dependence corresponding the change of curing temperature classified by the replacement ratio of BS, and the results are summarized as following. As the properties of flow, plain satisfied with the target slump, and as the replacement ratio of BS increased, the flow increased, but the air content slightly decreased. The time of set delayed as the replacement ratio of BS increased, but the curing temperature $35^{\circ}C$, even with 80% BS replaced concrete, the time of set was faster than $5^{\circ}C$, $20^{\circ}C$ plain, so the temperature-dependence was much greater. The compressive strength was decreased as the replacement ratio of BS increased, especially as the curing temperature lower, the compressive strength was lower comparatively. Also as the age increased, the plain developed more strength, therefore it show the temperature-dependence is much larger.

• Journal of the Korea Institute of Building Construction
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• v.14 no.1
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• pp.37-44
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• 2014

Recently, many efforts related to the utilization of industrial by-products have been made to reduce carbon dioxide emissions in the construction industry. Of these various efforts, concrete incorporating ground granulated blast furnace slag (BFS) provides many advantages compared to conventional concrete, such as high long-term compressive strength, improved durability and economic benefits because of its latent hydraulic property, and low compressive strength at early curing age. This paper investigates the compressive strength of high-activated ground granulated blast furnace slag blended mortar with slag by-product S type(SBP-S). The results of the experiment revealed that incorporating high-activated ground granulated blast furnace slag would affect the compressive strength of mortar. It was found that increasing the Blaine fineness and replacement ratio of slag by-product S type shows high compressive strength of mortar at early curing age because of its high $SiO_2$ and CaO contents in the slag. It is confirmed that an increase of curing age does not affect the compressive strength of mortar made with slag by-product S type at a high curing temperature. Moreover, it is possible to develop and design concrete manufactured with high-activated ground granulated blast furnace slag as binder considering the acceleration curing conditions and mix proportions.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.05a
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• pp.607-612
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• 2002

In road pavements, it is known that cement concrete pavement has superior durability, safety compared. But in repairing pavement, cement concrete pavement is not usually applied because of the length of time while the road is interrupted when using Ordinary and Rapid-hardening Portland Cement. And Super High Early Strength Cement and Ultra Super High Early Strength Cement are not favorable for ready mixed concrete because of rapid setting time, high slump loss and other restrictions. We developed special cement developing 1 day strength of over 30.0N/mm$^2$ to open the road within 1 day and workable time is maintained over 1 hour so that it can be used as ready mixed concrete. We performed experimental overlay construction with the cement and evaluated the mechanical property and the durability. At curing temperature of 8-l8$^{\circ}C$,the flexural strength was 6.4N/mm$^2$at 1 day, so that the road can be open to traffic within 1 day. In durability test, the hardened concrete showed higher durability than Portland cement concrete.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2008.11a
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• pp.1-5
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• 2008

In this study, batcher plant composition test and mock-up test were carried out to conduct comparison and analysis on flow behavior and strength properties of concrete at early age. As a result, it was found that slump and amount of air in batcher plant composition test reached the target range. As for compressive strength, composition using HESPC showed the most excellent strength development. In mock-up test which was carried out to find out the strength properties, two methods with specimen and core test body both revealed HESPC as the most excellent composition. However, strength estimation with ultrasonic survey presented less reliable data. As a result of the previously conducted indoor composition test and the mock-up test in this study, target performance of concrete at early age was 4day/cycle. It was found that the optimum conditions that meet the required strength, 5MPa/18hr and 14MPa/36hr in mullion and transom are; curing temperature above 15℃, W/B 45%, unit-water 165kg/㎥ and CHC cement.