• Proceedings of the Korean Institute of Building Construction Conference
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• 2014.05a
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• pp.82-83
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• 2014

Concrete with self-healing admixture can reduce the crack width by using a compound for chemical reaction with incoming water and carbon dioxide through the crack. Also, concrete with self-healing admixtures can reduce early-age shrinkage crack by using a inorganic expansive agent. In this research, we perform the basic workability test and compressive test. Also, We measure the drying shrinkage of concrete specimen. Finally, we make mock-up (3m X 3m X 0.23m) and monitor the crack width and length for 3 months.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2018.05a
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• pp.275-276
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• 2018

Ultra high performance concrete(UHPC) represents high early age autogenous shrinkage strain due to its low water-to-binder ratio(W/B) and high fineness admixture usage. It has been reported that fiber can control restrained tensile stress and crack. The purpose of the present study is, therefore, to investigate the autogenous shrinkage as well as mechanical properties including compressive strength, flexural strength and modulus of elasticity on the UHPC with fiber type and pre-mix of binder.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.10a
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• pp.391-396
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• 2002

The so called setting is defined as the onset of rigidity in fresh concrete. In the analysis of the early-age concrete behavior, we consider fresh concrete as a structural element immediately after mixing. But for the activation of real structural behavior of fresh concrete, it takes some time after the beginning of hydration reaction. So, the very early age deformations due to hydration heat and shrinkage which occur before the setting do not produce restraint stresses. In this paper, we propose a setting characteristic model based on the so called percolation theory. From the analysis using the model, the influence of curing temperature is investigated and analytical results are compared with experimental results. From the comparison, the validity of proposed model is verified. This model is also applied to evaluate stress development in a temperature-stress test machine (TSTM) specimen and then the effect of setting time on the stress development is discussed.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.05a
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• pp.427-432
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• 2003

An analytical method to predict the flexural behavior of composite girder is presented in which the early-age properties of concrete are specified including maturing of elastic modulus, creep and shrinkage. The time dependent constitutive relation accounting for the early-age concrete properties is derived in an incremental format by expanding the total form of stress-strain relation by the first order Taylor series with respect to the reference time. The sectional analysis calculates the axial and curvature strains based on the force and moment equilibriums. The deflection curve of the box girder approximated by the quadratic polynomial function is calculated by applying to the proper boundary conditions in the consecutive segments. Numerical applications are made for the 3-span double composite steel box girders which is a composite bridge girder filled with concrete at the bottom of the steel box in the negative moment region. The one dimensional finite element analysis results are compared with those of the three dimensional finite element analysis and the analytical method based on the sectional analysis. Close agreement is observed among the three methods.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2009.05b
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• pp.73-76
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• 2009

Autogenous shrinkage of high-strength mass concrete is affected high temperature history. So to evaluate autogenous shrinkage of high-strength mass concrete accurately, thermal expansion in it should be removed. In this study, compensated autogenous shrinkage was calculated after gathering thermal expansion coefficient at early age experimentally. As a result of the study. Autogenous shrinkage of mass specimen (300 ${\times}$ 300 ${\times}$ 300mm) was remarkably higher than it of standard specimen (100 ${\times}$ 100 ${\times}$ 400mm). So it was found that compensation on thermal expansion should in evaluating autogenous shrinkage of high-strength mass concrete. And this study shows results on opc and similar own contraction, if used retarder.

• Journal of the Korea Concrete Institute
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• v.14 no.6
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• pp.813-822
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• 2002

The purpose of the present study is first to refine the mathematical material models for moisture and temperature distributions in early-age concrete and then to incorporate those models into finite element procedure. The three dimensional finite element program developed in the present study can determine the degree of hydration, temperature and moisture distribution in hardening concrete. It is assumed that temperature and humidity fields are fully uncoupled and only the degree of hydration is coupled with two state variables. Mathematical formulation of degree of hydration Is based on the combination of three rate functions of reaction. The effect of moisture condition as well as temperature on the rate of reaction is considered in the degree of hydration model. In moisture transfer, diffusion coefficient is strongly dependent on the moisture content in pore system. Many existing models describe this phenomenon according to the composition of mixture, especially water to cement ratio, but do not consider the age dependency. Microstructure is changing with the hydration and thus transport coefficients at early ages are significantly higher because the pore structure in the cement matrix is more open. The moisture capacity and sink are derived from age-dependent desorption isotherm. Prediction of a moisture sink due to the hydration process, i.e. self-desiccation, is related to autogenous shrinkage, which may cause early-age cracking in high strength and high performance concrete. The realistic models and finite element program developed in this study provide fairly good results on the temperature and moisture distribution for early-age concrete and correlate very well with actual test data.

• Journal of the Korea Institute of Building Construction
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• v.19 no.1
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• pp.59-66
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• 2019

In this study, the effects of blast furnance slag cement and frost-resistant accelerator on shrinkage properties and shrinkage properties of mortar were examined. As a result, the addition of the frost-resistant accelerator to both OPC and BB has a small effect on the flash properties of mortar and the compressive strength increases from the early ages. In addition, when a frost-resistant accelerator is used in excess of the standard usage amount, it is necessary to examine the relationship of the expansion behavior at the early age, especially, between the compressive strength development and the expansion property. And it was confirmed that the addition of the frost-resistant accelerator tended to increase the shrinkage of mortar using the OPC and BB. With the addition of the frost-resistant accelerator, the amount of pores with a diameter of under the 30nm, especially, the amount of pores with a diameter of 20 to 30nm and the amount of pores with an ink-bottle decrease, and the shrinkage increases. And it is considered that a change in the amount this range of pores has a large effect on the shrinkage property.

• 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 institute for structural maintenance and inspection
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• v.18 no.5
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• pp.19-26
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• 2014

Concrete guide rail and median barrier are an attached RC member, however they are vulnerable to cracking due to slip form construction and large surface of member. In this study, causes and pattern of cracking are analyzed through assessment and NDT (Non-Destructive Technique) evaluation for concrete guide rail and median barrier on highway structure. For this work, analysis on drying shrinkage and hydration heat are performed considering installation period, and plastic shrinkage is also analyzed considering their environmental conditions. From the evaluation, plastic settlement around steel location, drying/ plastic shrinkage, and aggregate segregation are inferred to be the main causes of cracking in the structures. The crack causes and patterns are schematized and techniques of crack-control are suggested. Furthermore concrete guide rail/ median barrier in the bridge on the sea are vulnerable to cracking at early age so that special attentions should be paid at the stages of material selection and construction.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.821-824
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• 2008

In this study, it is willing to present that fundamental data for proposing quantitatively shrinkage cracking evaluation method such as plat-ring type restrained test method. It is possible to decide that specimen diameter is s 150mm with evaluating restrained shrinkage crack properties of concrete according to change of ring diameter in specimen. Also, effectiveness of test method according to mixing of PVA fiber is evaluated as part of a repeatability verification experiment of plat-ring type restrained test method using ring which diameter is 150mm. As a result, it is possible to measure the crack due to the plastic shrinkage which was occurred within 48hours at early age with plat-ring type restrained test method. Hereafter, it is considered that the study concerning environmental condition and mixing factor in plat-ring type restrained test method is need.