• 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 Concrete Institute
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• v.26 no.3
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• pp.343-350
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• 2014

A probabilistic construction stage analysis using the Monte Carlo Simulation was performed to address the effects of uncertainty regarding the material properties, environmental factors, and applied forces. In the previous research, creep and shrinkage were assumed to be completely independent random variables. However, because of the common influencing factors in the material models for the creep and shrinkage estimation, strong correlation between creep and shrinkage can be presumed. In this paper, an Monte Carlo Simulation using CEB-FIB creep and shrinkage equations were performed to actually evaluate the correlation coefficient between two phenomena, and then another Monte Carlo Simulation to evaluate the statistical properties of axial strain affected by partially correlated random variables including the material properties, environmental factors, and applied forces. The results of Monte Carlo Simulation were compared with measured strains of a column on a first story in a 58-story building. Comparison indicated that the variation due to the uncertainty related with the material properties were most severe. And measured strains was within the range of mean+standard deviation.

• Journal of the Korea Concrete Institute
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• v.15 no.6
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• pp.785-793
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• 2003

This study is intended to analyze the effectiveness of expansive additive, shrinkage reducing agent and combination of the two to reduce the autogenous and drying shrinkage of high performance concrete using mineral admixture such as fly ash, blast furnace slag powder and silica fume. According to results, when expansive additive and shrinkage reducing agent are mixed within an appropriate mixing ratio, fluidity and air content are not influenced, and the enhancement of compressive strength is favorable at the age of 91 and 180days. At the mixing ratio of expansive additive of 5% and 10%, the autogenous and drying shrinkage is reduced by 32∼68% and 25∼49% respectively in comparison with plain concrete. And they are reduced by 18∼34% and 16∼26% respectively at the mixing ratio of shrinkage reducing agent of 0.5% and 1.0%, compared with plain concrete. The mixture of EA-SR combined with expansive additive and shrinkage reducing agent is most effective for reduction of shrinkage. Therefore, it is considered that the using method in combination with expansive additive and shrinkage reducing agent is effective to reduce the shrinkage of high performance concrete using mineral admixture such as fly ash, blast slag powder and silica fume.

• International Journal of Highway Engineering
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• v.11 no.4
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• pp.87-94
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• 2009

Volume of concrete slab changes by variations of temperature and moisture after its placement. Shrinkage due to evaporation causes tensile stress in the slab when contraction of the slab is restrained by its self weight, friction with subbase, and etc. Actual tensile stress caused by the shrinkage was less than theoretically predicted stress according to previous studies. It was the stress reduction due to visco-elastic property of the early-age concrete slab partially restrained. In this study, strains of restrained circumferential, unrestrained circumferential, and unrestrained square pillar concrete specimens were measured to investigate stress reduction of the specimens with age of concrete. Elastic modulus of the concrete was measured at the age of 1, 3, 7, 14, 28 days and penetration test was performed. The stress reduction was calculated by input the test results into theoretical equations suggested by previous researchers. The stress reduction of the restrained concrete specimens will be applied to design of concrete pavements based on results of the study.

• Journal of the Korean Recycled Construction Resources Institute
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• v.6 no.4
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• pp.331-335
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• 2018

The purpose of this study is to investigate the feasibility of CFBC artificial fine aggregate as a substitute for natural aggregate used in dry mortar. The basic performance of the flow, compressive strength and dry shrinkage of the dry mortar was evaluated. Four types of test dry mortar specimens using natural aggregate without expansion admixture, a specimen with modified CaO expansion admixture and natural aggregate, a specimen with modified CaO expansion admixture and CFBC artificial fine aggregate, and a specimen using CFBC artificial fine aggregate without modified CaO expansion admixture were evaluated respectively. As a result of evaluation of drying shrinkage performance at 20th day of age, the dry shrinkage performance of the specimen using modified CaO expansion admixture was found to be the highest at $250{\times}10^{-6}$. On the other hand, the specimen containing the modified CaO expansion admixture with CFBC artificial aggregate exhibited a shrinkage of $410{\times}10^{-6}$, and the drying shrinkage of specimen using natural fine aggregate without expansion admixture was $450{\times}10^{-6}$. When the modified CaO expansion material was used, and exhibited performance equal to or higher than that of the shrinkage-drying property.

• International Journal of Highway Engineering
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• v.11 no.4
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• pp.59-68
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• 2009

Torsional behavior of concrete pavement slabs due to temperature and moisture effects is constrained by self weight and friction etc, and causes stress as the result. The stress due to humidity variation in the slab is difficult to calculate while that due to temperature variation can easily be calculated by a commercial structural analysis program. Thus, the slab behavior can be predicted more accurately if the humidity effect is converted to equivalent temperature and is used as an input of structural analysis. In this study, a concrete pavement slab was constructed and strains of the slab due to environmental loadings were measured for long-term period. Thermal strains were subtracted from the measured strains by using thermal expansion coefficient of the concrete measured in a laboratory. Shrinkage strains, the remained strains, was supposed as additional thermal strains to calculate imaginary temperature with equivalent effect of the shrinkage by dividing the shrinkage with the thermal expansion coefficient. An existing shrinkage model was modified by considering the self weight and friction to be used in another model which can convert differential shrinkage between top and bottom of the slab to equivalent temperature difference. Addition research efforts on tensile stress reduction according to steady increase in the compressive strains are warranted for more accurate stress calculation.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.6
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• pp.62-69
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• 2023

Re-damage is frequently occurring for various reasons, including material factors, external factors, and factors caused by poor construction in concrete cross-section restoration work, so it is necessary to identify the cause and improve it. Cement-based materials are the most commonly used maintenance materials for concrete structures, and in particular, additional cross-sectional restoration work may be carried out due to re-damage such as cracks and excitement due to dry contraction of the repair material. In this study, a basic study was conducted to identify the characteristics of concrete while diversifying the maximum dimensions and assembly rate of thick aggregates to examine the effects of using thick aggregates in repair materials. As a result, the slump of concrete increased as the maximum size of thick aggregates increased, and the amount of air content was measured 1.88 to 2.35 times higher in the mixing using aggregates with a maximum aggregate size of 5 mm or more compared to the mixing group with a maximum aggregate size of 10 mm or more. It was found that compressive strength was greatly affected by the performance rate of thick aggregates. The compressive strength was measured the highest in the mixture using thick aggregates with the highest performance rate of 20 mm, and the compressive strength of the mixture with the lowest performance rate was more than 45%. As a result of the dry shrinkage measurement, the dry shrinkage was the lowest as the performance rate of the thick aggregate increased according to the change in the maximum dimensions and assembly rate of the thick aggregate, and the lowest performance rate was the largest in the mix. Through this study, it was confirmed that adjusting the particle size by diversifying the maximum dimensions and assembly rate of thick aggregates used in concrete structure repair materials can improve strength and workability and reduce dry shrinkage.

• Journal of the Korean Society of Hazard Mitigation
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• v.7 no.3
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• pp.19-31
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• 2007

Humidity and strain were estimated for understanding the relation between humidity change by self-desiccation and shrinkage in high-performance concrete with low water binder ratio and containing fly ash and blast furnace slag. Internal humidity change and shrinkage strain were about 10%, 10%, 7%, 11%, 11% and $320{\times}10^{-6}$, $270{\times}10^{-6}$, $231{\times}10^{-6}$, $371{\times}10^{-6}$, $350{\times}10^{-6}$ respectively on OPC30, O30F10, O30F20, O30G40, O30G50 and from the results, fly ash made humidity change and strain decrease but slag increase comparing with ordinary portland cement. Considering only relation internal humidity and shrinkage by self-desiccation, humidity change and shrinkage represented the strong linear relation regardless of mineral admixture. For specifying the relation on internal humidity change and autogenous shrinkage strain, shrinkage model was established which is driven by capillary pressure in pore water and surface energy in hydrates on the assumption of a single network and extended meniscus in pore system of concrete. This model and experimental results had a similar tendency so it would be concluded that the internal humidity change by self-desiccation in HPC originated in small pores less than 20nm, therefore controlling plan on autogenous shrinkage might be focused on surface tension of water and degree of saturation in small pore.

• Journal of Korean Society of Steel Construction
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• v.16 no.6 s.73
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• pp.807-818
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• 2004

Experimental tests and theoretical methods of the analysis of the concrete shrinkage behaviors of steel-concrete composite girders are described herein. Steel-concrete composite test specimens were fabricated in the laboratory, and long-term behaviors such as deflections, curvatures, and strains were measured for one year. Test results were compared to the analytical results obtained by using the age-adjusted effective modulus method (AEMM). In addition, composite girders have been analyzed to investigate the effects of several parameters on the concrete shrinkage behaviors. From the long-term test results, it could be used to validate AEMM for the evaluation of the shrinkage behavior of composite girders. Because the shrinkage of the reinforced concrete slab in composite girders may lead to large tensile stresses in the concrete section, the transverse cracking of the slab could occur both in the positive and negative regions. Therefore, if the cracking of concrete would be ignored,it might lead to an overestimation of the stresses of the steel section of composite girders. Based on this research, it is proposed that the effect of transverse concrete cracking on the shrinkage behavior of steel-concrete composite bridges be considered.

• Journal of the Korea Institute of Building Construction
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• v.16 no.6
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• pp.561-569
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• 2016

Concrete is cheap, easy to deal with, and the quality is satisfactory. Also, it is one of the easiest materials to get because chemical composition of cement is similar to chemical composition of surface. On the other hand, it is so vulnerable to transform because of weak binding capacity and low binding energy that it produces cracks. Cracks decline durability, usability, safety of structures and damage exterior. In order to decline drying shrinkage crack, this study used shrinkage reducing typed Superplasticizer, which is combination of and water-reducing agent for convenience, different with existing study using AE agent, water-reducing agent, shrinkage reducing agent,. Considering SRS field application possibility, this study planned to mix concrete and mortar generally used in ready-mixed concrete company and did basic experiment depending on a change of SRS content ratio and admixture. Based on the experiment result. It is judged that SRS admixture 2% is proper ratio when Given the intensity and length change. Also mass combination will conduct follow-up studies.