• Proceedings of the Korean Institute of Building Construction Conference
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• 2023.05a
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• pp.259-260
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• 2023

This study attempted to derive an appropriate application range by reviewing the integration performance of joints according to the application range of SRA concrete. As a result, it was confirmed that the integration performance was improved even if SRA concrete was placed only by 75mm, which is 0.5 times the thickness of the member.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.10a
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• pp.763-768
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• 2002

In this study, methyl methacrylate (MMA) - modified polymer mortar(MMPM) was developed and its setting shrinkage and working life properties were surveyed. In order to study the setting shrinkage, setting shrinkage test for the 24 batches were also conducted with taking the MMA monomer content to the UP resin and the mixed content of shrinkage reducing agent(SRA) as variables. Furthermore, in order to study the working life measured gel time, working time, setting time of MMPM and binder. Experimental resurts show that the workability remarkably improved as the mixed MMA content increased. The working life was proportional to MEKPO content and was shorted. also, showed high interrelationship of binder gel time and MMPM working life. Setting shrinkage markedly reduced as the content of MMA and the SRA increased.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.05a
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• pp.128-131
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• 2004

This paper is to investigate the mock up test results of mass concrete for transfer girder using setting time difference with super retarding agent(SRA) to reduce hydration heat. According to test results, the temperature history of plain concrete without placing lift had a steep rising curvature, and plain concrete had a big temperature difference between surface and middle section of mass concrete, which may result in occurrence of temperature crack. However, considering placing method B, because setting time of middle section concrete was retarded with an increase in SRA contents, higher hydration heat temperature was observed at surface section concrete compared with that at middle section concrete at early age, which can lower the possibility of hydration heat crack. In case of placing method C, although peak temperature of hydration heat was much lower, at early age, high crack occurrence possibility of the hydration heat attributable to the big temperature difference between middle section and bottom section of concrete was expected at bottom section concrete. Therefore, the structure above the ground like transfer girder is not applicable to consider the placing method C.

• Journal of the Korea Concrete Institute
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• v.24 no.4
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• pp.491-498
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• 2012

This study examines setting shrinkage, coefficient of thermal expansion, and elastic modulus of unsaturated polyester( UP)-methyl methacrylate(MMA) polymer concrete, which is generally used for repair of portland cement concrete pavement and manufacturing of precast products. In this study, a series of laboratory test were conducted with variables such as UP-MMA ratio, shrinkage reducing agent (SRA) content, and test temperature. The results showed that the setting shrinkage ranged from 29.2 to $82.6{\times}10^{-4}$, which was significantly affected by test temperature. Moreover, the findings revealed that the coefficient of thermal expansion, elastic modulus and ultimate strain of UP-MMA based polymer concrete ranged from 21.6 to $31.2{\times}10^{-6}/^{\circ}C$, 2.8 to $3.3{\times}10^4$ MPa, and 0.00381 to 0.00418, respectively. The results of this study will be used as important data for design and application of UP-MMA based polymer concrete.

• Journal of the Korea Concrete Institute
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• v.23 no.5
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• pp.581-590
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• 2011

Since ultra-high performance cementitious composites (UHPCC) not only represents high early age shrinkage strain due to its low water-to-binder ratio (W/B) and high fineness admixture usage but also reduces the cross section of structure from the higher mechanical properties, it generally has more shrinkage cracks from the restraints of formwork and reinforcing bars. In this study, free and restrained shrinkage experiments were conducted to evaluate the suitability of incorporating both expansive admixture (EA) and shrinkage reducing agent (SRA). The test results indi-cated that approximately 40~44% of free shrinkage strain was decreased. Also, the results showed that 35% and 47% of residual tensile stresses were relieved by synergetic effect of SRA and EA, respectively. Residual tensile stresses from ringtest were relaxed by approximately 61% and 64% of elastic shrinkage stresses due to SRA and EA, respectively, because of the tensile creep effect. Therefore, the creep effect should be considered to precisely estimate the restrained shrinkage behavior of concrete structures. The degree of restraint of UHPCC was approximately in the range of 0.78~0.85. The addition of combined EA and SRA showed minute influence on the degree of restraint. However, the effect decreased when thicker concrete ring was used. Tensile creep strains were measured and compared to the predicted values from 4-parametric prediction model considering time dependent restrained forces.

• Journal of the Korea Concrete Institute
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• v.23 no.4
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• pp.441-448
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• 2011

In this study, experimental tests of chemical and autogenous shrinkage were performed to evaluate the early age shrinkage behaviors of ultra high performance cementitious composites (UHPCC) with various replacement ratios of silica fume (SF), shrinkage reducing agent (SRA), expansive admixture (EA), and superplasticizer (SP). Starting time of self-desiccation, was analyzed by comparing the setting times and the deviated point of chemical and autogenous shrinkage strains. The test results indicated that both SF and SRA augment the early age chemical shrinkage, whereas SP delays the hydration reaction between cement particles and water, and reduces chemical shrinkage. About 49% of autogenous shrinkage was depleted by synergetic effect of SRA and EA. The hardening of UHPCC was catalyzed by containing EA. Self-desiccation of UHPCC occurred prior to the initial setting due to the high volume fraction of fibers and low water-binder ratio (W/B).

• Proceedings of the Korean Institute of Building Construction Conference
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• 2023.11a
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• pp.23-24
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• 2023

This study attempted to derive an appropriate application range by reviewing the integration performance of joints according to the application range of SRA concrete. As a result, it was confirmed that the integration performance was improved even if SRA concrete was placed only by 75mm, which is 0.5 times the thickness of the member.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.3
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• pp.452-459
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• 2017

In recent years, to reduce self-weight of structural elements, the use of SCP (Steel Concrete Plate) instead of prestressed concrete is increasing. Because SCP has a complicated sectional shape and includes a large number of studs, the use of high-fluidity concrete is required. Therefore, in this study, to prevent the restrained shrinkage behavior by the stud, the effects of using an expansive agent (EA) and shrinkage reducing agent (SRA) were investigated, and the optimal mixture proportions to maximize the filling capacity were determined based on the fine aggregate ratio. The test results indicated that the combined use of EA and SRA exhibited the smallest shrinkage. The ratio of the crushed sand and washed sea sand was determined to be 5:5, and the proper fine aggregate ratio was found to be 55.6%, because when the ratio was too high, a decrease in strength and an increase in shrinkage strain were expected. The high-fluidity concrete effectively filled the large-sized SCP module.

• Journal of the Korea Institute of Building Construction
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• v.23 no.6
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• pp.673-682
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• 2023

This study investigates the delay in setting characteristics of mortar influenced by variations in super retarding agent(SRA) content, curing temperature, and strength levels. Utilizing a settimeter, the research introduces an objective approach to accurately determine the setting time of concrete with SRA under diverse environmental and material mixing conditions at construction sites. The findings indicate that the settimeter, in conjunction with a nonlinear regression model, can effectively estimate the setting time of super retarding mortar. Optimal management of the initial setting is recommended at approximately 45ST and the final setting around 80ST. This methodology enables more effective quality control in the setting times of super retarding concrete.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2005.05a
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• pp.21-24
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• 2005

In this paper, field application of mass concrete using setting time difference of super retarding agent is reported to reduce hydration heat of concrete placed at newly constructed apartment house in Daejeon. Horizontal placing lift is applied. According to test results,: slump and air content meets the requirement of target values. For compressive strength, it exceeds the nominal strength ordered by the costumer. For temperature history, maximum temperature of center at top section shows $25.6^{\circ}C$, and at bottom section, $35.4^{\circ}C$. According to naked eye's investigation, no hydration heat crack is observed at the surface of concrete.