• Journal of the Korean Society of Hazard Mitigation
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• v.10 no.2
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• pp.47-53
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• 2010

Very-early strength latex-modified concrete (VES-LMC) was developed with a focus on workability, strength development and long-term durability that would allow for opening a bridge to traffic only 3 hours after concrete placement, which would be useful when repairing concrete bridge deck overlays. However, even though usage of latex in VES-LMC improves the durability, it has a disadvantage that it produces lots of entrained air. Therefore, specific plan is necessary since it is weak for freezing and thawing in air-void structure. In the present study ultra-fine fly ash (UFFA) was used. Test results are follows ; Air content of VES-LMC UFFA (VES-LMC using UFFA) concrete was decreased since major pozzolan reaction was happened in one day. It was also found that total air content of concrete was decreased with pozzolan reaction since air content in 28 days was the same with one day air content. The addition of calcium hydroxide increased entrained air which is smaller than size of 200 ${\mu}m$. It was effective to improve the air-void structure of VES-LMC since spacing factor can be confirmed as smaller than size of 200 ${\mu}m$ using more than 15% of UFFA.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.3
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• pp.1040-1046
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• 2010

The main disadvantage of rapid setting concrete is the occurrence of cracking because of fast hydration reaction due to high thermal expansion and shrinkage. However, if the fly ash is used in concrete, it is possible to prevent cracking since the hydration heat can be decreased. Although Very-Early Strength-Latex Modified Concrete(VES-LMC) is an excellent material, occurrence of cracking has been reported because of high hydration heat. In the present study, new method which can apply the fly ash to the VES-LMC was developed. Research for the new method to improve the safety for the cracking was conducted. Safety was confirmed by reducing the shrinkage and hydration heat in the condition of overcoming the low early-age strength. Detailed conclusions are follows. Early-age compressive strength was decreased a little with increase of UFFA content. However, 28-d compressive strength was statistically insignificant regardless of UFFA contents. If the UFFA is replaced 15% to 20% of unit cement weight in concrete, maximum shrinkage can be reduced up to 43% to 47%. Usage of UFFA in VES-LMC guarantees the safety for cracking since it is very effective to control of early-age shrinkage.

• International Journal of Highway Engineering
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• v.10 no.4
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• pp.189-198
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• 2008

Generally, UFF A(Ultra Fine Fly Ash) has merit that advances a greater concrete workability and activates a greater pozzolanic reaction than common fly ash due to its ultra fine particle size. These properties enhance concrete durability by reducing permeability and increasing resistance of alkali silica reaction(ASR) and sulfate attack, etc. Due to these reasons, UFFA can be used in a rapid setting concrete. The purpose of this study is to develop and evaluate the rapid setting concrete with UFF A as a repair material for early-opening-to-traffic. In previous studies, if only UFFA is added to the rapid setting concrete mixture, pozzolanic reaction doesn't happen actively. Therefore, in this study, the chemical and physical tests were performed for rapid setting concrete with UFFA including calcium hydroxide and the activity of pozzolanic reaction was evaluated. Finally, the effectiveness of this mixture on enhancing concrete durability was investigated. As results, adding UFF A decreased the water/cement ratio of concrete, and compensated the reduced portion of the early strength of concrete. Also, rapid setting concrete with UFFA including calcium hydroxide activated a greater pozzolanic reaction than normal-UFF A concrete. As calcium hydroxide increases, electrical indication of concrete's ability to resist chloride ion penetration is promoted significantly.