• Proceedings of the Korea Concrete Institute Conference
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• 2002.10a
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• pp.385-390
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• 2002

Autogenous shrinkage of concrete has been defined as decrease in volume due to hydration cement, not due to other causes such as evaporation, temperature change and external load and so on. For ordinary concretes, autogenous shrinkage is so little compared to the other deformations that it has been dignored. It has recently been proved, however, that autogenous shrinkage considerably increase with decrease in water to cement ratio. And it has been reported that cracking can be caused by autogenous shrinkage, when high- strength concretes were used. In this study, we propose an analytical system to represent autogenous shrinkage in cement paste in order to control crack due to autogenous shrinkage. The system is composed with the hydration model and pore structure model. Contrary to the usual assumption of uniform properties in the hydration progress, the hydration model to refine Tomosawa's represents the situation that inner and outer products are made in cement paste. The pore structure model is based upon the physical phenomenon of ion diffusion in cement paste and chemical phenomenon of hydration in cement particle. The proposed model can predict the pore volume ratio and the pore structure in cement paste under variable environmental conditions satisfactorily The autogenous shrinkage prdiction system with regard to pore structure development and hydration at early ages for different mix-proportions shows a reasonable agreement with the experimental data.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05b
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• pp.533-536
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• 2005

Drying shrinkage and strength of the redispersible SBR and PAE powder-modified mortars were experimentally investigated. Results of the study that the drying shrinkage rapidly increased until 7 days of age and it was then saturated to the value of about $1\~2\times10^{4}$ after 14 days. It turned out that the polymer-cement ratio exerted more influence on the drying shrinkage than the content of powder shrinkage-reducing agent did. Flexural (compressive) strength of the mortar increased (decreased) as the polymer-cement ratio increased and it was 7$\~$11 (23$\~$39) MPa at 7 days of age. The average (maximum) increasing (decreasing) rate turned out to be about 10 (30) $\%$. As in the drying shrinkage case, the polymer-cement ratio exerted more influence on both flexural and compressive strengths than the content of powder shrinkage agent did.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.1135-1140
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• 2001

The purpose of this study is to investigate the shrinkage properties of high strength concrete according to the S/A ratio at early age. The main parameters are as follows : S/A ratio is 30, 35, 38, 41, 45%, W/B ratio 24.9%, SF/B ratio 8%. FA/B 15%. The size of specimen is l0$\times$10$\times$40cm and the shrinkage is measured by the embedded gage at each end of the specimens. From the test, it was found that the slump-flow of concrete was high, and also autogenous shrinkage increased and drying shrinkage decreased as S/A ratio increased.

• Journal of the Korea Institute of Building Construction
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• v.6 no.1 s.19
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• pp.73-77
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• 2006

Drying Shrinkage has much complexity as it has relations with both internal elements of concrete and external factors. Therefore, experiments on Concrete Drying Shrinkage are carried out in this study under simplified circumstances applying temperature & Humidity test chamber which enables constant temperature and humidify. Comparative analyses have been made respectively according to the consequences aiming at modelling for prediction of Concrete Drying Shrinkage and making out measures to reduce it. As a result Strain Rate of Drying Shrinkage of concrete was measured to increase by average $10{\times}10^{-5}$ in proportion to additional 4% increase in fine aggregate ratio, when water/cement ratio constant. Strain Rate of Drying Shrinkage in pit sand concrete increased 20% higher than measured when in river sand under the condition of 90-day material age. 6. Strain Rate of Drying Shrinkage in sea sand concrete increased $10%{\sim}15%$ higher than measured when in river sand. The results of prediction of Rate of Drying Shrinkage by Response Surface Analysis are as fellows. The coefficient of correlation of Drying Shrinkage in concrete was over 90%.

• Journal of the Korea institute for structural maintenance and inspection
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• v.9 no.1
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• pp.181-188
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• 2005

Generally, high performance concrete has characteristics such as low water-cementitous material ratio, lots of unit binder powder, thus the drying shrinkage and autogenous shrinkage are tend to be increased. The purpose of this study is to investigate the effect of the glyclos based shrinkage reducing agent on the drying shrinkage and autogenous shrinkage of high performance concrete with 30% of water-cemetitious material ratio as a study to develop the technology to reduce the concrete shrinkage. Test results show that the drying and autogenous shrinkage of high performance concrete are reduced by about 20~35% at the mixing ratio of shrinkage reducing agent of 0.5%, and 1.0%, compared with plain concrete. Therefore, it analyze that the using of shrinkage reducing agent is effective to reduce the drying shrinkage and autogenous shrinkage of high performance concrete.

• Journal of the Korea Institute of Building Construction
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• v.10 no.4
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• pp.113-122
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• 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 Korea Concrete Institute Conference
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• 2006.05b
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• pp.13-16
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• 2006

This paper investigates the shrinkage behavior of Ultra High Strength(UHSC) having three water-to-cementitious material ratio, 0.20, 0.16, 0.12. All of mixtures have same design compressive strength. Free shrinkage test for autogenous and drying shrinkage using $100{\times}100{\times}400$ prismatic specimen was conducted. On all mixture, Effects of fly ash and blast-furnace slag on each shrinkage test results were also investigated. The largest portion of autogenous shrinkage was observed in UHSC12 (w/b=0.12) and the measured strain was as high as 80% of the total drying shrinkage strain. The autogenous shrinkage of UHSC decreased as the amount of fly ash increased as demonstrated in the literature. However, the results of the effect of blast-furnace slag on autogenous shrinkage were somewhat different from previous researches.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.11a
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• pp.473-476
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• 2003

This study discusses the use of anti-shrinkage agent as the method to reduce autogenous and drying shrinkage. According to results, as for the fundamental properties of high performance concrete, fluidity and strength decrease with an increase of the adding ratio of anti-shrinkage agent, but air content increases. Compared with plain concrete, autogenous and drying shrinkage are reduced by 12~52% and 4~22% respectively upto the adding rario of anti-shrinkage agent of 2.0%. When expansive additive is added by 5.0%, they are also reduced by 38~95% and 15~50% respectively. Therefore, as expansive additive of 5.0% and anti-shrinkage agent of 1.0% are added to high performance concrete of around W/B 30%, it is considered that fluidity and strength are hardly influenced, and in addition, crack by shrinkage can be prevented effectively.

• Journal of the Korea Institute of Building Construction
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• v.7 no.3
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• pp.123-130
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• 2007

This study investigated the fundamental properties and shrinkage properties of high performance concrete with water/binder ratio of 0, 30 and with combination of expansive additive and shrinkage reducing agent. According to the results, the fluidity of high performance concrete showed lower the using method in combination with expansive additive and shrinkage reducing agent than the separately using method of that, so the amount of superplasticizer increased when the adding ratio of expansive additive and shrinkage reducing agent increased. However the air content of concrete increased when used in combination with expansive additive and shrinkage reducing agent, so the amount of AE agent decreased. The compressive strength showed the highest at 5% of expansive additive, and decreased with an increase of the amount of shrinkage reducing agent. Furthermore, in order to reduce the shrinkage of high performance concrete, it was found that the using method in combination with expansive additive and shrinkage reducing agent was more effective than separately using method of that. Autogenous shrinkage was predicted using JCI model. Because JCI model is unable to consider the effect of EA and SRA, correction factor should be added to enhance the accuracy.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.308-311
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• 2004

Nowadays, plastic industry has needed to produce parts that require high precision and quality. To make a high precision and quality part, before injection molding, plastic material is investigated about their properties such as shrinkage, warpage, etc. In this study, experiments were conducted with PA6(polyamid) to figure out shrinkage behavior according to three type aspect ratio of samples. The injection speed that affects on shear rate, molecular orientation within plastic part was determined as main variable of experiment. As a result of experimental study, part shrinkage had a tendency to be decreased by increasing injection speed and aspect ratio of samples.