• Proceedings of the Korea Concrete Institute Conference
• /
• 1990.10a
• /
• pp.151-156
• /
• 1990

This is an experimental study to investigate chante of early strength of polymer concrete due to curing temperature change. Polymer binders that were used in the experiment include 2 types of epoxy system and 4 types of polyester system which are commercially producer in Korea. The study result showed that there was a difference in early strength by curing temperature. At $35^{\circ}C$ which is a higher than normal curing temperature, higher strengths were developed in polymer concretes prepared with KB-Clear and YD-128 of epoxy system, and G-550 and H-660 of polyester system. However, at the same temperature, reduced strengths were obtained for FH-103 and TR-132 of polyester system. Further study under various curing conditions with humidity and temperature change will warrant more generalized result.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2006.11a
• /
• pp.817-820
• /
• 2006

This study investigated on the differentiation of microstructure of blast furnace slag concrete(BBSC) using Mercury Intrusion Porosimetry(MIP). From the test result, it was found that the BBSC did not show shortcomings of high temperature curing. The BBSC gives more fineness microstructure than that of plain concrete when it is cured same curing condition. The curing age making stable structure to poor surroundings was 28, 14, 7 days for blast furnace concrete cured at 5, 20, $30^{\circ}C$, respectively.

• Proceedings of the KSR Conference
• /
• 2008.11b
• /
• pp.1065-1068
• /
• 2008

Concrete is still one most common construction materials even in railway structures. As structures become massive and mega-sized, the importance of early age concrete quality control becomes more significant. Among various factors, relative humidity and temperature are the primary factors governing the early age quality. Temperature raise due to cement hydration causes stress, which can develop to cracking with internal and/or external restraints. Exposure conditions including ambient temperature, humidity and wind also significantly affect the cracking behavior of early age concrete. Among many of studies on the early age concrete behavior, investigation on the variation of temperature and relative humidity internal of concrete is not common. That is in part because the difficulties in measuring the relative humidity and temperature inside the concrete. This study used a digital sensor with an appropriate logger to measure internal temperature and relative humidity. This direct measuring method is expected to provide more reliable and comprehensive data acquisition on the early age behavior of concrete.

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2020.11a
• /
• pp.127-128
• /
• 2020

This research is part of the research for unifying the mass concrete and utilizing the rate of super retarding agent. We analyzed the performance of super retarding agent 20℃ conditions. It was found that there was no deterioration in fluidity and air quality due to the change in the super retarding agent mixing rate. It was found that when super retarding agent was mixed up to 0.5 %, it was delayed for 22.3 hours at 20℃. Therefore in order to ensure the performance required at the site, the super retarding agent mixing rate must be determined by fully considering the situation at the site. In addition it will be analyzed that super retarding agent performance analysis at high temperature will be required in subsequent studies.

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2020.06a
• /
• pp.73-74
• /
• 2020

In this study, the feasibility of the durometer into super retarding concrete was studied by comparing the penetration resistance with the hardness of each durometer using the penetration resistance and the improved Durometer and Durometer A-Type according to the ultra-delay mixture rate. The test results showed that initial setting time by improved Durometer and Durometer A-Type were fixed at 25, 50 HD, respectively, and the 35, 80 HD showed at final setting time. It was also found that the use of the durometer can be available to measure the setting time of the concrete.

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2023.11a
• /
• pp.153-154
• /
• 2023

In this study, analyzed the difference in compressive strength of concrete under cold conditions, using the 28-day standard curing compressive strength as a reference and examining variations based on cement types and curing temperatures. The results showed that the strength difference based on curing temperatures reached up to 9MPa at 0℃. However, as the curing period progressed, the difference in strength due to curing temperature gradually diminished. These findings are anticipated to be valuable for concrete mixing and quality control in cold weather conditions.

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2023.11a
• /
• pp.223-224
• /
• 2023

This study compared the curing temperature of the bubble sheet and the photothermal insulation sheet incorporating carbon-based photothermal materials to reduce concrete curing time as a part of shortening construction period. As a result of the experiment, bubble sheet with photothermal material B is judged to be effective in shortening the curing time under hot environment.

• Journal of the Korea Institute of Building Construction
• /
• v.15 no.1
• /
• pp.25-33
• /
• 2015

In this study, initial crack index was evaluated by FEM analysis to find the crack propagation from hydration heat in precast concrete. As results, as the usage of hardening accelerator increased, initial compressive strength increased and setting time was shortened. Additionally, as amounts of hardening accelerators increased, the central temperature of concrete increased and the time to reach the highest temperature was shortened. It was demonstrated that the hardening accelerators accelerated the hydration reaction of cement, and caused the increase of hydration heat within the short period of time. Furthermore, the crack index for evaluating the heat level was performed by FEM. As results, there was no problem about the cracks, despite of the growth of initial high hydration heat. This is because of the increased tensile strength that is large enough to sustain the thermally induced-stress.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.21 no.6
• /
• pp.811-823
• /
• 2019

Slip form method is applied to many cases of a shaft these days because it is safer, more economical and faster than cast-in-place method. Slip-up height of the method is approximately 2.5 to 4.0 m/day. If the temperature of concrete is outside the range of 10 to 30℃, the effects of changes in strength or elastic characteristics are significant. Therefore, it is difficult for slip-up speed to be higher than 3 m/day during winter construction. In addition, concrete has heat caused by hydration, which causes temperature cracking of hardened concrete. Therefore, temperature control of concrete curing is necessary for the continuous slip-up of slip form. In this study, the rebound hardness, time of ultrasonic waves propagation, heat of hydration, and external temperature are measured by developing heating panels and test devices for the continuous slip-up. Based on this, heating slip form is manufactured; this was applied to "Kimpo sites" and "Sinwol sites". The compared slip-up speed samples were 1.9 m/day or 0.200 m/hr on average at Gimpo sites (08:00~17:30) and 2.0 m/day or 0.210 m/hr at Sinwol sites.

• Journal of the Korea Institute of Building Construction
• /
• v.14 no.1
• /
• pp.110-117
• /
• 2014

The objective of this study is to investigate an effect of curing temperature on autogenous shrinkage of high strength cement mortar with 0.15 of W/B incorporating fly ash and silica fume in terms of equivalent age. The contents of fly ash and silica fume are varied from 10% to 30%. Non linear regression model applying equivalent age was used to estimate the autogenous shrinkage evolution. To obtain apparent activation energy($E_a$), setting time method by Pinto and existing method were calculated and compared respectively. Test results showed that use of silica fume increased autogenous shrinkage while use of fly ash decreased it. It was also found that poor agreements were obtained when $E_a$ by setting time was applied. But, application of existing $E_a$ resulted in a good agreement between calculated autogenous shrinkage and measured one.