• Proceedings of the Korean Institute of Building Construction Conference
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• 2013.05a
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• pp.56-58
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• 2013

In order to develop concrete generating compressive strength of 15MPa~30MPa aging for 6~12 hours in the room temperature curing, Hardening accelerator containing Ca²⁺ mixed with rapid hardening portland cement containing C₃S in quantity. The result was that the more addictive contents of Hardening accelerator is, the more greatly early compressive strength was improved. That s because the composition of Ca(OH)₂ was mass-produced at early-ages.

• Journal of the Korea Institute of Building Construction
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• v.14 no.4
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• pp.322-328
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• 2014

In this study, revelation performance of concrete at early age according to types of cement, water reducing ratio of high performance superplasticizer and mixing of accelerator for early hydration was examined aiming for reduction of construction period of framework through securing strength at early age of concrete. It was observed that strength at early age, 5MPa in 12hours, 14MPa in 18hours, is secured by early strength improvement type cement and using promotion admixture for early hydration which are Sodium persulfate, Potassium hydroxide. Therefore cost reduction is expected to be possible in construction site by reducing construction period of frame work.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.05a
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• pp.224-227
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• 2004

The cement can be influenced by the temperature. Especially, when it is cold weather, it causes some problems in such properties as mixing, placing and curing of concrete. According to the Concrete Standard Specification(2003), in case of the average daily outdoor temperature below $4^{\circ}C$, it recommends to use the cold weather concrete. In this research, the on-site quality characteristics of the cold weather concrete using high early strength portland cement(Type III cement) were studied. As a result, the cold weather concrete using high early strength portland cement can obtain its excellent properties and benefit the cost of construction.

• Proceedings of the Korean Society of Agricultural Engineers Conference
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• 2001.10a
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• pp.193-197
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• 2001

The growth in concrete structures repair has prompted major efforts to develop high early strength concrete. The internal or external restraint of thermal shrinkage movements could thus generate tensile stresses in concrete structures if it is used rapid setting repair concrete. Restrained shrinkage and thermal stresses could produce microcracks in concrete which increase its permeability and accelerate its long-term deterioration under weathering and load effects. This study aims at evaluation and increase of the engineering properties of high early strength concrete using regulated set cement.

• KIEAE Journal
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• v.12 no.3
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• pp.115-122
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• 2012

Based on previous research and existing literature, this study examines the development of admixture, which increases the early concrete strength (1 and 3 day) by mixing blast furnace slag cement and concrete stimulant. The research on early strength development of concrete is necessary in dealing with the drawbacks of slow early strength concrete on site and to shorten the construction time. The study confirmed that when a high alkaline mortar mixture is mixed with blast furnace slag, the early strength of admixture exceeds that of ordinary portland cement (OPC). The use of calcium chloride ($CaCl_2$) promotes hydration of cement at low temperature and show similar strength as the blast furnace slag admixture. Although calcium chloride seems economically advantageous, it causes steel corrosion and its use in concrete should be further studied in-depth.

• 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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• 2006.05b
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• pp.609-612
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• 2006

The quality of the concrete compression strength can be determined after the passage of 28 days, but if any defect is found the quality of concrete after that length of time, there can be serious problems in dismantling and repair. Thus, in response to the use of concrete using non sintering cement (NSC), the present study purposed to propose a method of managing the strength of high strength concrete using NSC in comparison with high strength concrete using ordinary Portland cement (OPC) through early strength estimation using microwave, which enables the quick estimation of the strength of high strength concrete using NSC.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.11a
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• pp.527-532
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• 2003

When fresh concrete is exposed to sufficiently low temperature, the free water in the concrete is cooled below its freezing point and transforms into ice, which causes decrease in compressive strength of concrete. Of the many influencing factors on the loss of compressive strength, the age of concrete at the beginning of freezing, water-cement ratio, and cement-type are significantly important. The objective of this study is to examine how the these factors affect the compressive strength of concrete frozen at early ages. The results from the tests showed that as age at the beginning of freezing is delayed and water-cement ratio is low, the loss of compressive strength decreases. In addition, concrete made with high-early-strength cement is less susceptible to frost damage than concrete made with ordinary portland cement.

• 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.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.05a
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• pp.737-740
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• 2003

In this study, the influence of cement factor on the early strength gain and the other properties of concrete is discussed. According to the result, the setting time is faster in order of alumina cement(AC), high-early-strength cement(HSC) and ordinary Portland cement(OPC), and when OPC are replaced with HSC and AC, the final setting time is faster than when only OPC is used. At 10% replacement of AC, the instant setting happens. As the particle of cement is minute, setting time is shortened. As the properties of hardened concrete, the time when compressive strength of 5㎫, which the form can be removed, is gained is about 18 and 16 hours in the case of OPC and HSC respectively, and in the case of AC, it is about 5 hours. It also shows 16 hours at the replacing ratio of HSC of 50%, and 26 and 72 hours at the replacing ratio of AC of 5 and 10% respectively. And it shows 21, 16 and 12 hours with variation of fineness of cement, so early strength gain is fast with an increase of fineness. The coefficient of correlation between compressive strength and the rebound value is over 0.97, is very favorable. Therefore, if the rebound value of P type Schmidt hammer is more than 25, it is thought that the side forms can be removed.