• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2009.11a
• /
• pp.73-76
• /
• 2009

In ultra-high-strength concrete, chemical shrinkage is larger than drying shrinkage due to using a large amount of cement and admixtures, and this is a factor deteriorating the quality of structures. Thus, we need a new technology for minimizing the shrinkage strain of ultra-high-strength concrete. So, this study have prepared super-high-strength concrete with specified mixing design strength of over 100MPa and have evaluated a method of reducing chemical shrinkage by using expander and shrinkage-reducing agent. According to the results of this study, with regard to the change in length by chemical shrinkage, an expansion effect was observed until the age of seven days. The expansion effect was higher than previous research that used only expander or shrinkage reducing agent. In addition, ultra-high-strength concrete showed a shrinkage rate that slowed down with time, and the effect of the addition of expander material on compressive strength was insignificant. That is shown that required more database to be accumulated through experimental research for the shrinkage strain of members.

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2009.05b
• /
• pp.57-60
• /
• 2009

In ultra-high-strength concrete, autogenous shrinkage is larger than dry shrinkage due to the consume of a large amount of cement and cementitous material, and this is a factor deteriorating the quality of structures. Thus, we need a new technology for minimizing the shrinkage strain for ultra-high-strength concrete. So, this paper have prepared super-high-strength concrete with specified mixing design strength of over 150MPa and have evaluated a method of reducing autogenous shrinkage by utilizing expander and shrinkage-reducing agent. According to the results of this study, with regard to the change in length by autogenous shrinkage, an expansion effect was observed until the age of seven days. The expansion effect was higher when the contents of the expander material were higher. In addition, ultra-high-strength concrete showed a shrinkage rate that slowed down with time, and the effect of the addition of expander material on compressive strength was insignificant. That is shown that required more database to be accumulated through experimental research for the shrinkage strain of members.

• Journal of the Korean Society of Industry Convergence
• /
• v.13 no.2
• /
• pp.99-106
• /
• 2010

The effects of additive and shrinkage reducing agent on the drying and autogenous shrinkage of high strength concrete are investigated in this study. As results, when the ratio of W/B(low water to binder ratio) increase, the compressive strength is decreased. Comparing with PC(portland cement) concrete, the strength is 2.8%, 3.2% and 3.8% lower respectively than that of PC when concrete mixing ratio is 0.2%, 0.3% and 0.4% in 28 days curing. Drying shrinkage strain of PC concrete showed $-650{\times}10^{-6}$ in 91 days curing. When SR(shrinkage reducing agent) of 0.2%, 0.3% and 0.4% is mixed, the drying shrinkage strains are 21%, 34% and 41% lower than those of PC in 91 days curing. Autogenous shrinkage strain of PC concrete appeared $-480{\times}10^{-6}$ in 56 days curing. When SR of 0.2%, 0.3% and 0.4% is mixed, the autogenous drying shrinkage strain are 12.5%, 19.8% and 33.3% lower than those of PC in 56 days curing. In cases of using the mineral and shrinkage agent or only using a shrinkage reducing agent also appeared same reducing effects for drying shrinkage and autogenous shrinkage.

• Journal of the Korea Institute of Building Construction
• /
• v.11 no.6
• /
• pp.538-546
• /
• 2011

This paper is to experimentally investigate the strength and autogenous shrinkage of high strength mortar with the 20 % of water?binder ratio(W/B). In this study, the water substituting liquid(WSL) was used including gasoline, light oil, lamp oil, edible oil, HFE, ethanol, methanol and acetone in order to explore changes in strength and autogenous shrinkage depending on WSL type and replacement. For fresh properties, the replacement of WSL did not affect the fluidity of mortar mixtures considerably, except for ethanol and methanol. However, the replacement of WSL resulted in a slight decrease in flexural and compressive strength. For autogenous shrinkage, the replacement of WSL led to reduce autogenous shrinkage, and especially, the replacement of edible oil led to reduce autogenous shrinkage significantly due to saponification between edible oil and cement.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2006.05b
• /
• pp.429-432
• /
• 2006

The shrinkage mechanism of high strength concrete is different from that of normal concrete. The shrinkage of normal concrete is subjected to evaporate moisture in concrete, but most shrinkage in high strength concrete is caused by chemical reaction. To analyze shrinkage of concrete exactly, it is necessary to divide drying shrinkage with autogenous shrinkage in terms of degree of hydration, especially in concrete with low W/C ratio. The proposed method can provide a rational basis for prediction of shrinkage in high strength concrete structure.

• Magazine of the Korean Society of Agricultural Engineers
• /
• v.43 no.5
• /
• pp.124-131
• /
• 2001

The shrinkage properties of high early strength concrete were investigated. One of the method to control microcrack and crack development due to restrained shrinkage is to reinforce concrete with randomly distributed fibers. Regulated-set cement and two different types of fiber were adopted. The experiments for heat of hydration, drying and autogenous shrinkage were conducted. The desirable resistance of high early strength fiber reinforced concrete to restrained shrinkage microcracking was achieved. These results indicate that use of fiber in high early strength concrete plays an important role in control of crack development due to restrained shrinkage.

• Journal of the Korea Institute of Building Construction
• /
• v.10 no.4
• /
• pp.113-122
• /
• 2010

In this study, 150MPa ultra-high-strength concrete was manufactured, and its performance was reviewed. As technically meaningful autogenous shrinkage reportedly occurs at a W/B ratio of 40% or less, although it occurs in all concrete regardless of the W/B ratio, the effects of the use of expansive admixture and shrinkage reducer, or of the friction and restraint of forms that may result in the effective reduction of autogenous shrinkage, were reviewed. As a result, considering the flow and strength characteristics, it was found that the slump flow time was shorter with expansive admixture, and shortest with shrinkage reducer. All specimens with $30kg/m^3$ expansive admixture showed high strength at early material age. Their strength decreased due to the expansion cracks when there was excessive use of expansive admixture, and the use of shrinkage reducer did not influence the change in the strength according to the material age. The expansive admixture had a shrinkage reduction effect of 80%, while the shrinkage reducer had a shrinkage reduction effect of 30%, indicating that the expansive admixture had a stronger effect. It seems that mixing the two will have a synergistic effect. The shrinkage reduction rate was highest when the W/B ratio was 20%. The form suppressed the expansion and shrinkage at the early period, and the demolding time did not significantly influence the shrinkage. The results of the study showed that the excessive addition of expansive admixture leads to expansion cracks, and the expansive admixture and shrinkage reducer have the highest shrinkage reduction effect when they are mixed.

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

• Journal of the Korean Society of Industry Convergence
• /
• v.16 no.1
• /
• pp.1-8
• /
• 2013

In case that W/B is 20%, 30%, 40% respectively, the effects of additive and shrinkage reducing agent on the autogenous shrinkage for high strengthen concrete through the substitution of FA and SF analysis were obtained as following conclusions. When the ratio of FA increased, the compressive strength of high strengthen concrete is decreased in the early times. As the ratio of SF increase, the compressive strength also increased. Comparing with PC(Portland Cement) for 7 days curing, the strength is 13.8% of FA10 + SR0.5 and 19.2% of FA15 + SR0.5 decreased when W/B is 20%, and 6.1% of SF7.5 + SR0.5, 4.8% of SF15 + SR0.5, the strength are increased. In case that W/B is 30%, 13.1% of FA10 + SR0.5 19.1% of FA15 + SR0.5 the strength is decreased and 4.1% of SF 7.5 + SR0.5, 7.2% of SF15 + SR0.5 the strength are increased. In case of W/B 40%, 4.3% of FA10 + SR0.5, and 8.7% of FA15 + SR0.5, the strength is decreased and 3.3% of SF7.5 + SR0.5, 6.3% SF15 + SR0.5 the strength is increased. When the ratio of SR is 0.5%, autogenous shrinkage strain of OPC concrete appeared $-417{\times}10-6$ in 56days curing, the shrinkage strain is decreased 23.7%. The reducing effects of autogenous shrinkage when the mineral and shrinkage agent are used are the same as ones when only shrinkage agent used.

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2005.11a
• /
• pp.67-70
• /
• 2005

Ultra high strength concrete, nowadays, has been widely applied to construction of high-rise building. To improve ductility and mechanical properties, steel fiber is employed in UHSC. This study investigates practical application of expansive additives(EA) and shrinkage reducing agent(SRA), in order to secure volumetric stability and improved mechanical properties, such as autogenous shrinkage and dry shrinkage of steel-fiber-reinforced-ultra-high-strength-comet-mortar(FHSM). According to the test, individual addition of steel fiber does not affect shrinkage reduction, as expected. However FHSM, with combined addition of 5$\%$ of EA and 1$\%$ of SRA decreased 60$\%$ of autogenous shrinkage. It is considered that Proper combination of EA and SRA can secure the shrinkage resistance of FHSM.