• Proceedings of the Korean Institute of Building Construction Conference
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• 2007.04a
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• pp.71-74
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• 2007

This study investigates the fundamental properties of high strength concrete made with various blame values of cement, manufactured by the particle screening method in a pulverizing process. Test showed that concrete using lower blame of cement, such as large particle (L) and both ordinary and large particle (OL), increased the fluidity of fresh concrete. As tine progressive, it was noticeable that the specimens using ordinary cement (OPC) gradually decreased the fluidity, but the other specimens showed the sudden decline until 30 minutes, which is followed by a gradual decrease after 60 minutes. For the setting time, higher blaine of cement accelerated the initial and final setting time, especially concrete using minute size of cement (M) was 10 hours faster than OPC. Compressive strength of L exhibited similar value at 1 days as to that of strength in OPC at 3 days. Importantly, the specimens using M also revealed the similar strength value, regardless of curing temperature between $-5^{\circ}C$ and $20^{\circ}C$, which means that using this minute particle of cement in concrete can secure the strength development even in the lower temperature circumstance. Therefore it is clear that using OPC+M simultaneously at cold weather concreting can resist the early frost and develop the early strength of concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.05a
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• pp.339-344
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• 2001

This study is to investigate properties of high strength.high flowing concrete using blast-furnace slag in temperature conditions of 5, 10, 15 and $20^{\circ}C$. The result of this study can be summarized as follows. 1) The use of blast-furnace slag leads to decrease of air content and increase of fluidity in the fresh concrete. 2) The early compressive strength of high strength.high flowing concrete containing blast-furnace slag is lower than the case with portland cement only. 3) The compressive strength development of incorporating in the concrete is poor at low temperature below about $15^{\circ}C$.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2012.11a
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• pp.93-94
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• 2012

In this study, prediction of later-age compressive strength of ultra-high strength concrete, based on the accelerated strength of concrete cured in 80℃ warm water was investigated. As a result, the nature of ultra-high strength concrete showed a rapid early strength enhancement, compressive strength using warm water method of 80℃ at 2days is same compressive at 28days using standard curing.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.04a
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• pp.95-101
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• 1999

This study was performed to evaluate the characteristics of workability and strength of the concrete containing mineral admixtures such as flyash, blast furnace slag, zeolite powder. As a result, considering their workability and strength, the optimum replacement ratio of them to plain concrete were obtained for each ternary admixture. This increased compressive strength was ascribed to both the closer parkinof fine particles and pozzolan reactivity of powders. This work showed that could be effectively utilized as a blending material without any decrease in the strength of early hydration stage. On the other hand, we found that the compressive strength at early ages ternary ordinary and high strength concrete untill 7 days was small, but that ternary concrete at 28days was highly increased about 31% and 15% extent.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.05a
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• pp.647-650
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• 2001

The purpose of this study was the influence of cold weather ready mixed concrete quality according to needs of customer were investigated by measurements of slump, air content, temperature and compressive strength. As a results, cold weather ready mixed concrete using high standard admixtures, high early strength admixtures and cold weather concrete plant were similarly to slump, air content, temperature and compressive strength.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2010.05a
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• pp.63-65
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• 2010

The purpose of the study was to analyze dry shrinkage of HVFAC (high volume fly ash concrete) with admixture to improve early strength. The results were as follows. In dry shrinkage of HVFAC with admixture to improve early strength, F3 had the lowest amount of dry shrinkage. The next is in order of Plain, F3-f15 and F3-f15r5. The study used index function modelfor analysis on dry shrinkage. Coefficient of determination was more than 0.97 in all mix, which made it possible to have a good estimation.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2008.11a
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• pp.85-88
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• 2008

As super-high-strength concrete uses a large amount of binder, there is an autogenous shrinkage strain larger than dry shrinkage and it degrades the quality of structures. Thus, we need a technology to minimize the shrinkage strain of super-high-strength concrete. Accordingly, the present study prepared super-high-strength concrete with design strength of over 100MPa and, using an embedded gauge, measured the shrinkage strain of free shrinkage specimens for super-high-strength concrete containing expansion agent. According to the results of this study, the expansion rate of concrete increased in the early stage due to the admixture of expansion agent, but the shrinkage rate went down with the lapse of time. The effect of the admixture of expansion agent on compressive strength appeared insignificant. Further research shall be made on different kinds of expansion agents and various mixture ratios for basic analysis to reduce autogenous shrinkage of super-high-strength concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.05a
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• pp.53-58
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• 2003

Many researchers have rigorously studied the nonlinear behavior of stress-strain relationship of concrete using mathematical curves. Most of model equations for stress-strain relationship, however, have been focused on old age concrete, and were not able to adequately represent the behavior of concrete at an early age. A wide understanding on the behavior of concrete from early age to old age is very important in evaluating the durability and service life of concrete structures. In previous study by authors of this paper, a stress-strain model equation for low- and medium-strength concretes was suggested. In this paper, to extend the application region of compressive stress-strain curve to high-strength concrete, an analytical research was performed. An analytical expression of stress-strain curve with strength and age was developed using regression analyses on the experimental results. For the verification of the proposed model equation, it was compared to the experimental data. The result showed that the proposed model equation was not only compatible with the experimental data quite satisfactorily but also describing well the effect of strength and age on stress-strain curve.

• Advances in concrete construction
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• v.15 no.6
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• pp.359-376
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• 2023

Ultra-high-performance concrete (UHPC) has become an attractive cast-in-place repairing material for existing engineering structures. The present study aims to investigate age-dependent high-early-strength UHPC (HESUHPC) material properties (i.e., compressive strength, elastic modulus, flexural strength, and tensile strength) as well as interfacial shear properties of HESUHPC-normal strength concrete (NSC) composites cured at different season temperatures (i.e., summer, autumn, and winter). The typical temperatures were kept for at least seven days in different seasons from weather forecasting to guarantee an approximately consistent curing and testing condition (i.e., temperature and relative humidity) for specimens at different ages. The HESUHPC material properties are tested through standardized testing methods, and the interfacial bond performance is tested through a bi-surface shear testing method. The test results quantify the positive development of HESUHPC material properties at the early age, and the increasing amplitude decreases from summer to winter. Three-day mechanical properties in winter (with the lowest curing temperature) still gain more than 60% of the 28-day mechanical properties, and the impact of season temperatures becomes small at the later age. The HESUHPC shrinkage mainly occurs at the early age, and the final shrinkage value is not significant. The HESUHPC-NSC interface exhibits sound shear performance, the interface in most specimens does not fail, and most interfacial shear strengths are higher than the NSC-NSC composite. The HESUHPC-NSC composites at the shear failure do not exhibit a large relative slip and present a significant brittleness at the failure. The typical failures are characterized by thin-layer NSC debonding near the interface, and NSC pure shear failure. Two load-slip development patterns, and two types of main crack location are identified for the HESUHPC-NSC composites tested in different ages and seasons. In addition, shear capacity of the HESUHPC-NSC composite develops rapidly at the early age, and the increasing amplitude decreases as the season temperature decreases. This study will promote the HESUHPC application in practical engineering as a cast-in-place repairing material subjected to different natural environments.

• 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%.